Prevalence and risk factors of bovine tuberculosis in dairy cattle in Eritrea

Background

The prevalence of bovine tuberculosis (BTB) in dairy cattle in the three major milk producing regions of Eritrea was assessed by subjecting 15,354 dairy cattle, 50 % of Eritrea’s dairy cattle population, to the single intradermal comparative tuberculin test (SICTT). Skin test results were interpreted according to guidelines of the World Organization for Animal Health (OIE) with >4 mm as cutoff in skin thickness increase. In addition, we studied the relation between ‘physiological’ variables related to pregnancy and lactation, and the variable ‘region’ on the probability to be skin test positive.

Results

The BTB prevalences at animal and herd levels were: 21.5 % and 40.9 % in Maekel, 7.3 % and 10 % in Debub, and 0.2 % and 1.6 % in the Anseba region, respectively. Overall, in the regions included, prevalence was 11.3 % (confidence interval (CI) 95 % CI, 11.29 – 11.31 %) and 17.3 % (95 % CI, 17.27–17.33 %), at animal and herd level, respectively. Considering positive herds only, the animal BTB prevalence was 36.8 %, 30.1 %, and 1.8 %, in Maekel, Debub and Anseba, respectively, and the overall animal prevalence within these herds was 32 %. In adult dairy cattle the probability of positive reactivity in the SICTT test was highest in pregnant animals as compared to the other categories.

Conclusion

This study reports persistent prevalence of BTB as defined by positive SICTT in the dairy sector of Eritrea, especially in the regions of Maekel and Debub that are located in the central highlands of the country. To our understanding this is the first report that has encompassed all the major dairy farms in Eritrea and it will be instrumental in advocating future BTB control programs in the dairy sector.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0705-9) contains supplementary material, which is available to authorized users.

First Report of Watermelon chlorotic stunt virus Infecting Watermelon in Saudi Arabia

In the Saudi Arabian deserts, watermelon [Citrullus lanatus (Thunb.)] is cultivated in the lowlands and wadis (washes) where water accumulates following rainfall, and where heat, salt, and drought stress are common constraints on production. During the spring of 2014, watermelon leaves exhibited yellowing and severe chlorotic mottling symptoms. The foliar symptoms were reminiscent of Watermelon chlorotic stunt virus (WmCSV), a bipartite begomovirus previously reported in several neighboring countries (1,3). Ten samples were collected from three farms in the Leith region, where 100% of the watermelon plants were symptomatic. Total nucleic acids were extracted from the symptomatic watermelon plants and were subjected to PCR using WmCSV DNA-A specific primers designed based on a complete genome sequence (GenBank Accession No. AJ012081), WmCSVF-3'-CGTGCTGTTGCCCCCACTGT-5' and WmCSVR-3'-CCTGCATATCTCGTGCCAGAATC-5' to obtain an expected size fragment of 1,111 bp located between the nucleotide (nt) coordinates 400-1510. The amplicons (one per sample) were cloned, and the DNA sequence was determined for each and used to search the NCBI database. The top hits for sequences obtained from all 10 samples were to WmSCV sequences, with shared nt identity values of 97 to 98%. To clone the full-length begomoviral DNA-A and DNA-B components, nucleic acids were subjected to rolling circle amplification (RCA) (2). The RCA products were cloned into the pGEM7 plasmid vector using the unique restriction sites, identified as HindIII for DNA-A, and as EcoRI for DNA-B, respectively. Ten DNA-A clones and two DNA-B component clones were sequenced. The DNA-A components ranged in size from 2,751 (KM066100) to 2,752 bp (KJ939448), whereas the DNA-B components were 2,757 bp in size (KJ939447). Analysis of the viral sequences from the DNA-A clones indicated they had the characteristics of a typical genome of a begomovirus DNA-A component that consist of a hairpin stem-loop structure in the intergenic region, two tandem copies of the iteron (TGGAGAC) located between the nt coordinates 2675 and 2680, 2682 and 2688 predicted to be involved in Rep binding, and six predicted genes encoding proteins with high sequence identity to those encoded by other WmCSV isolates. The 10 DNA-A component sequences were aligned with sequences for previously described WmCSV isolates available in GenBank using Muscle, followed by pairwise comparisons using SDT software (4). The analysis revealed that the cloned DNA-A components shared 99 to 100% nt sequence identity with each other, and 97 to 98% nt identity with WmCSV isolates reported from Yemen (AJ012081), Jordan (EU561237), Iran (AJ245652), and Sudan (AJ245650). Further, the WmCSV DNA-B from Saudi Arabia shared the highest nt identity with sequences from Yemen (AJ012082) at 96%, Iran (AJ245653) at 95%, and only 94% with DNA-B from both Sudan (AJ245651) and Jordan (EU561236). To our knowledge, this is the first report of WmCSV in Saudi Arabia. WmCSV poses a serious threat to the production of this highly valued crop in Saudi Arabia and considerably reduces crop yield (1). References: (1) I. D. Bedford et al. Eur. J. Plant Pathol. 100:243, 1994. (2) A. Idris et al. Plant Dis. 97:910, 2007. (3) A. Kheyr-Pour et al. Phytopathology 90:629, 2000. (4) B. Muhire et al. Arch. Virol. 158:1411, 2013.

Identification of Weed Hosts of Tomato yellow leaf curl virus in Cyprus

An extensive study was conducted during 2007 and 2008 in three major tomato production areas of Cyprus, where Tomato yellow leaf curl virus (TYLCV) is commonly found, to assess the incidence and prevalence of naturally infected weed species that could serve as TYLCV reservoirs. Approximately 4,000 of the most common dicotyledonous plants belonging to 122 species from 25 families were collected, identified, and tested for TYLCV presence using serological and molecular methods. The tests included a previously reported conventional polymerase chain reaction (PCR) assay and a real-time TaqMan PCR assay developed and optimized in this study. Real-time PCR was found to be the most sensitive technique, and enabled the detection of TYLCV in 461 samples of 49 different species belonging to the families Amaranthaceae, Chenopodiaceae, Compositae, Convolvulaceae, Cruciferae, Euphorbiaceae, Geraniaceae, Leguminosae, Malvaceae, Orobanchaceae, Plantaginaceae, Primulaceae, Solanaceae, Umbelliferae, and Urticaceae. The results further indicated that the host range of TYLCV in Cyprus is far more extensive than previously documented and, therefore, new management strategies are required. These should focus on the control of alternative virus hosts during the growing season and in crop-free periods.

Characterization of Rhynchosia yellow mosaic Yucatan virus, a new recombinant begomovirus associated with two fabaceous weeds in Yucatan, Mexico

Rhynchosia minima (L.) DC. (Fabaceae) plants exhibiting bright golden mosaic symptoms were previously associated with begomovirus infection in Yucatan, México [1]. To characterize the begomovirus infecting these plants, the complete bipartite genome was cloned and sequenced. Sequence comparisons indicated that the virus was distinct from all other begomoviruses known to date, including those previously identified from symptomatic R. minima, and the name Rhynchosia yellow mosaic Yucatan virus (RhYMYuV) is proposed. Pairwise comparisons indicated that RhYMYuV DNA-A [2,597 nt, (EU021216)] and DNA-B [2,542 nt, (FJ792608)] components shared the highest nt sequence identity with Cabbage leaf curl virus (CaLCuV), 87% for component A and 71% for component B. Phylogenetic analysis indicated that both components of RhYMYuV are most closely related to other New World begomoviruses, having as closest relatives immediate outliers to the major Squash leaf curl virus (SLCV) clade. Recombination analysis of the RhYMYuV genome indicated that the DNA-A component has arisen through intermolecular recombination. R. minima plants inoculated with the monomeric clones developed a bright yellow mosaic similar to symptoms observed in naturally infected plants, confirming that the clones were infectious. Nicotiana benthamiana plants biolistically inoculated with monomeric clones developed curling and chlorosis in the newly emerging leaves. RhYMYuV was also detected in symptomatic Desmodium sect. Scorpiurus Benth. (Fabaceae) that were collected near the RhYMYuV-infected plants.

First Report of "Candidatus Liberibacter psyllaurous" or "Ca. Liberibacter solanacearum" Associated with Severe Foliar Chlorosis, Curling, and Necrosis and Tuber Discoloration of Potato Plants in Honduras

From 2006 to 2009, all commercial potato fields in Azacualpa F.M. Honduras were heavily infested with the potato psyllid Bactericera cockerelli (Sulc.). Plants exhibited interveinal chlorosis, vein-greening, downward curling, stunting, above ground tuber formation, and brownish flecks in some tubers. Disease incidence ranged from 50 to 95%. Leaf samples and psyllids were collected from seven fields in two potato-growing regions of Honduras. Total DNA was purified from the leaves of 30 symptomatic and three asymptomatic plants. DNA was extracted from 20 adult and 10 immature (4th to 5th instar) psyllids according to Frohlich et al (1). PCR primers, PSY680F 5'-GTTCGGAATAACTGGGCGTA-3' and PSY1R 5'-CCCATAAGGGCCATGAGGACT-3', were used to amplify a 680-bp fragment of the 16S rDNA for the recently described "Candidatus Liberibacter physallaurous" (2) and "Ca. L. solanacearum" (3). PSY1R/PSY680F primer design was based on the association of a previously undescribed liberibacter with vein-greening symptoms in greenhouse tomato plants in Arizona from 2006 to 2007 (GenBank Accession No. GQ926918) that lead to the hypothesis that a similar bacterium could be associated with symptomatic potato plants in Honduras. PCR amplification, cloning, and sequencing of the resultant 16S rDNA amplicons indicated that 17 of 30 potato plants, 8 of 20 adult and 7 of 10 third to fourth instar psyllids, respectively, were positive for liberibacter based on 99 to 100% shared nucleotide sequence (nt) identity with the analogous sequence from liberibacter (EU812558 [2]). To substantiate these results, a second molecular marker was targeted using the 1611F and 480R primers (~980 bp) that amplify the 16S-23S-ITSrDNA of liberibacter (2) for selected liberibacter-positive samples (above). Amplicons of the expected size were obtained from 12 of 17 potato and 7 of 10 immature psyllids. No PCR product of the expected size was obtained from asymptomatic potato samples or the PCR negative (water) control. The resultant PCR amplicons were cloned and 12 to 15 clones per amplicon were sequenced. The sequences were aligned and the percentage pair wise nt identity was calculated by Clustal W revealing that the 16S rDNA and 16S-23S-ITS sequences, respectively, shared 99 to 100% nt identity with each other. BLAST analysis against the NCBI database indicated that the 16S rRNA sequences from potato plants (GQ926922) and immature psyllids (GQ926923), and the 16S-ITS-23S sequence from potato plants (GQ926924) and immature psyllids (GQ926925), shared 98.5 to 100% nt identity with 'Ca. Liberibacter' reported from potato (EU812556; [2,4]) and tomato (EU812558, EU812559, EU935005; [2,3]). Evidence for the widespread presence of liberibacter and the potato psyllid in potato fields in Honduras, together with foliar and tuber symptoms that are reminiscent of those recently described in potato plants in the United States affected with 'zebra chip' disease (4), suggest that a similar or identical disease of the potato also occurs in Honduras. This emergent disease poses a serious threat to potato production in Honduras and elsewhere in Central America. References: (1) D. R. Frohlich et al., Mol. Ecol. 8:1683, 1999. (2) A. K. Hansen et al. Appl. Environ. Microbiol. 78:5862, 2008. (3) L. W. Liefting et al. Plant Dis. 93:208, 2009. (4) J. E. Munyaneza et al. J. Econ. Entomol. 100:656, 2007.

First Report of "Candidatus Liberibacter psyllaurous" (synonym "Ca. L. solanacearum") Associated with 'Tomato Vein-Greening' and 'Tomato Psyllid Yellows' Diseases in Commercial Greenhouses in Arizona

During the winter of 2006-2007, plants in commercial tomato greenhouses (GH-1 and GH-2; total 320 acres [129.5 ha]) in Arizona were infested with the potato psyllid Bactericera cockerelli (Sulc) and more than 60% and ~20% of the plants, respectively, exhibited leaf curling, chlorosis, and shortened internodes. In addition, some plants in GH-1 developed an unusual 'vein-greening' phenotype. Nucleic acids were isolated from 10 symptomatic and three asymptomatic plants from each greenhouse. PCR primers designed to amplify a phytoplasma-like 16S rDNA (850 bp) yielded the expected size product from GH-1 samples, whereas samples from GH-2 and the asymptomatic samples from both greenhouses did not. Several 16S rDNA PCR products (3 of 60) when cloned and sequenced, surprisingly shared 97% homology with 'Candidatus Liberibacter asiaticus' (GenBank No. GQ926917). PCR primers PSY680F 5'-GTTCGGAATAACTGGGCGTA-3' and PSY1R 5'-CCCATAAGGGCCATGAGGACT-3', based on the resultant 16S rDNA sequences, were used to amplify a 680-bp fragment from plant DNA extracts and psyllid lysates (1). A robust PCR product (~680 bp) was obtained from 10 of 10 GH-1 plant extracts (GQ926918) and from a GH-1-derived psyllid colony (28 of 35 adults) (GQ926919) and the tomato plants on which they were reared. In contrast, no 680-bp product was obtained from GH-1 asymptomatic plants (0 of 3), GH-2 plants (0 of 10 symptomatic; 0 of 3 asymptomatic), GH-2-derived psyllid colonies (0 of 35 adults), or psyllid colony tomato plants (data not shown). At least three 680-bp amplicons for each sample type were cloned and 8 to 10 inserts were sequenced for each. BLAST analysis revealed that all 680-bp sequences shared 99 to 100% nt identity with the analogous 16SrDNA from "Ca. Liberibacter psyllaurous" (2) and synonym "Ca. L. solanacearum" (3). A second molecular marker was obtained with the 1611F and 480R primers (2) to amplify the 16SrDNA-23S-ITS (980 bp) from >3 plant extracts and psyllid lysates that tested positive for liberibacter. Clustal W alignment of the 16S-23S-ITS sequences from GH-1 original tomato plants and psyllid colony plants (GQ926920) and psyllids (GQ926921) indicated they were 100% identical to each other and BLAST analysis indicated 99 to 100% shared identity with "Ca. L. psyllaurous" (EU812558) (synonym "Ca. L. solanacearum"). Transmission electron microscopy examination of GH-1 and GH-2 psyllids revealed rod and pleomorphic-shaped bacteria (0.5 to 2.0+ μm) at the brain-salivary gland interface in psyllids from the GH-1 liberibacter-positive colony. No such bacteria were observed in GH-2 liberibacter-negative psyllids. These results support an etiological role of a new liberibacter spp. in the development of the 'vein-greening' symptom phenotype. In contrast, the GH-2 'yellows' phenotype is reminiscent of 'psyllid toxicity' in tomato colonized by B. cockerelli (4). To our knowledge, this is the first report of distinct psyllid-associated diseases in greenhouse tomato in Arizona, one associated with a new 'Ca. Liberibacter' spp., manifest as 'vein-greening' disease, and the other associated with psyllid feeding, in which liberibacter is undetectable in plants and psyllids, and is manifest as the 'tomato psyllid yellows' disease. References: (1) D. R. Frohlich et al. Mol. Ecol. 8:1683, 1999. (2) A. K. Hansen et al. Appl. Environ. Microbiol. 74:5862, 2008. (3) L. W. Liefting et al. Plant Dis. 93:208, 2009. (4) H. J. Pack. Utah Agric. Exp. Stn. Bull. 209, 1929.

Geminivirus-mediated gene silencing from Cotton leaf crumple virus is enhanced by low temperature in cotton

A silencing vector for cotton (Gossypium hirsutum) was developed from the geminivirus Cotton leaf crumple virus (CLCrV). The CLCrV coat protein gene was replaced by up to 500 bp of DNA homologous to one of two endogenous genes, the magnesium chelatase subunit I gene (ChlI) or the phytoene desaturase gene (PDS). Cotyledons of cotton cultivar 'Deltapine 5415' bombarded with the modified viral vectors manifested chlorosis due to silencing of either ChlI or PDS in approximately 70% of inoculated plants after 2 to 3 weeks. Use of the green fluorescence protein gene showed that replication of viral DNA was restricted to vascular tissue and that the viral vector could transmit to leaves, roots, and the ovule integument from which fibers originate. Temperature had profound effects on vector DNA accumulation and the spread of endogenous gene silencing. Consistent with reports that silencing against viruses increases at higher temperatures, plants grown at a 30 degrees C/26 degrees C day/night cycle had a greater than 10-fold reduction in viral DNA accumulation compared to plants grown at 22 degrees C/18 degrees C. However, endogenous gene silencing decreased at 30 degrees C/26 degrees C. There was an approximately 7 d delay in the onset of gene silencing at 22 degrees C/18 degrees C, but silencing was extensive and persisted throughout the life of the plant. The extent of silencing in new growth could be increased or decreased by changing temperature regimes at various times following the onset of silencing. Our experiments establish the use of the CLCrV silencing vector to study gene function in cotton and show that temperature can have a major impact on the extent of geminivirus-induced gene silencing.

Melon chlorotic leaf curl virus: characterization and differential reassortment with closest relatives reveal adaptive virulence in the squash leaf curl virus clade and host shifting by the host-restricted bean calico mosaic virus

The genome components of the Melon chlorotic leaf curl virus (MCLCuV) were cloned from symptomatic cantaloupe leaves collected in Guatemala during 2002. The MCLCuV DNA-A and DNA-B components shared their closest nucleotide identities among begomoviruses, at approximately 90 and 81%, respectively, with a papaya isolate of MCLCuV from Costa Rica. The closest relatives at the species level were other members of the Squash leaf curl virus (SLCV) clade, which is endemic in the southwestern United States and Mexico. Biolistic inoculation of cantaloupe seedlings with the MCLCuV DNA-A and -B components resulted in the development of characteristic disease symptoms, providing definitive evidence of causality. MCLCuV experimentally infected species within the Cucurbitaceae, Fabaceae, and Solanaceae. The potential for interspecific reassortment was examined for MCLCuV and its closest relatives, including the bean-restricted Bean calico mosaic virus (BCaMV), and three other cucurbit-infecting species, Cucurbit leaf crumple virus (CuLCrV), SLCV, and SMLCV. The cucurbit viruses have distinct but overlapping host ranges. All possible reassortants were established using heterologous combinations of the DNA-A or DNA-B components. Surprisingly, only certain reassortants arising from MCLCuV and BCaMV, or MCLCuV and CuLCrV, were viable in bean, even though it is a host of all of the "wild-type" (parent) viruses. The bean-restricted BCaMV was differentially assisted in systemically infecting the cucurbit test species by the components of the four cucurbit-adapted begomoviruses. In certain heterologous combinations, the BCaMV DNA-A or -B component was able to infect one or more cucurbit species. Generally, the reassortants were less virulent in the test hosts than the respective wild-type (parent) viruses, strongly implicating adaptive modulation of virulence. This is the first illustration of reassortment resulting in the host range expansion of a host-restricted begomovirus.

Two Distinct Isolates of Tomato yellow leaf curl virus Threaten Tomato Production in Arizona and Sonora, Mexico

Severe yellow leaf curl and plant stunting symptoms were observed in tomato plants from two home gardens in central Arizona (Phoenix area) and a tomato field in Sonora, Mexico during the fall of 2006. Disease symptoms were reminiscent of those reported in Florida during 1994 (4) and more recently in tomato fields in the Pacific Coast state of Sinaloa, Mexico found to be infected with the exotic Tomato yellow leaf curl virus (TYLCV) (2). Total DNA was extracted from two symptomatic tomato plants from Arizona and Sonora and used as a template in PCR. PCR products of the core region of the begomovirus coat protein gene (Cp) were cloned (n = 3) and the DNA sequence was determined. BLAST analysis of the 579 bases with sequences available in the NCBI GenBank database indicated the closest match was to an isolate of the monopartite begomovirus TYLCV from Israel, which was known to have been introduced into the Caribbean region, including Puerto Rico, the southeastern United States, and Mexico from 1990 to 1996 (1,4). The full-length TYLCV genome (approximately 2,800 bases) was amplified for a field isolate from each location by rolling circle amplification (RCA) using TempliPhi (Amersham Biosciences, Piscataway, NJ). RCA products were cloned into the plasmid vector pGEM7 (Promega, Madison, WI) that had been previously digested with SacI endonuclease. The complete TYLCV genome sequence was determined for six clones from each RCA product. Nucleotide analysis indicated that the complete TYLCV genome sequences from Sonora and Arizona, respectively, shared 97.6 and 97.7% nt identity. The comparative sequence analysis indicated that TYLCV-Sonora (TYLCV-Son) (GenBank Accession No. EF210555) was 99.1% nt identical to TYLCV reported recently from Culiacan, Mexico (GenBank Accession No. DQ631892). In contrast, TYLCV-AZ (GenBank Accession No. EF210554) shared 99.3% identity with an isolate from Texas, TYLCV-TX (GenBank Accession No. EF110890) (3). Interestingly, the TX and AZ TYLCV isolates contained a unique 29-nt deletion in the intergenic region (IR) between the TATA-box and the nonanucleotide, initiating at nt coordinate 2696. Except for the deletion in the IR region of the AZ and TX isolates, these viruses shared 97.6 to 99.1% nt identity to other TYLCV isolates reported in the Western Hemisphere. The genome sequence for TYLCV-Son shares high nt identity with TYLCV isolates identified in the Yucatan Peninsula and Pacific Coast of Mexico (2), the Caribbean region, and the southeastern United States, suggesting that a single TYLCV species was introduced and has spread throughout North America and the Caribbean (4). The absence of other TYLCV isolates in the Western Hemisphere with the novel 29-nt deletion noted for the TX and AZ isolates suggests that the latter two isolates originated from the same U.S. source. In Mexico, TYLCV was first introduced in the east coast and Yucatan region approximately in 1996. From there, this isolate has spread to the western part of the country (Sinaloa and Sonora) from 2004 to 2006 (2). Similarly, in the United States, TYLCV was introduced and spread in the eastern U.S. states beginning in 1994 (4), where it had been confined until it was discovered in Texas (3) and now Arizona during 2006. References: (1) J. Bird et al. Plant Dis. 85:1028, 2001. (2) J. K. Brown and A. M. Idris. Plant Dis. 90:1360, 2006. (3) T. Isakeit et al. Plant Dis. 91:466, 2007. (4) J. E. Polston et al. Plant Dis. 78:831, 1994.

Widespread Outbreak of Cucurbit yellow stunting disorder virus in Melon, Squash, and Watermelon Crops in the Sonoran Desert of Arizona and Sonora, Mexico

Bright yellow, interveinal chlorosis was observed for the first time on leaves of the older and mid-growth of cucurbit plants in southern Arizona and Sonora (Mexico) during September and October of 2006. Some cultivars exhibited substantial yield losses of 30 to 80%. In Arizona, symptoms were in Cucumis melo (muskmelon and honeydew melon) fields in the Yuma Valley and Hyder. In Sonora, honeydew and muskmelon, Cucurbita pepo (acorn, spaghetti, and summer [yellow and zucchini] squash), and Citrullus lanatus (watermelon) were symptomatic in Hermosillo, whereas, in Caborca, honeydew and cantaloupe developed similar symptoms. Interveinal chlorosis was observed in 60 to 100% of the plants in each field. Crops planted mid-to-late season were 100% infected, whereas, the early-season fields experienced approximately 60 to 80% incidence. All symptomatic fields in the Sonoran Desert and vicinity were infested by the whitefly Bemisia tabaci (Genn.), which was identified as the 'B biotype' on the basis of mitochondria COI sequence analysis (data not shown). Whitefly population levels were variable and ranged from 5 to 200 per plant. Total RNA was isolated from leaf samples collected from symptomatic plants using Tri Reagent (Molecular Research Center, Cincinnati, OH). Purified RNA was used in reverse transcriptase-PCR with primers specific to the Cucurbit yellow stunting disorder virus (CYSDV) coat protein (CP) gene (RNA2-deoxyribonucleotide coordinates 4927-4950 and 5657-5679) for the suspected whitefly-transmitted bipartite CYSDV (4). PCR yielded the CYSDV CP fragment, at 753 bp (GenBank Accession Nos. EF21058 and EF21059), which was cloned into pGEM T-Easy and sequenced in both directions using universal primers. The CYSDV CP nucleotide sequences (n = 16) obtained from acorn squash, honeydew melon, muskmelon, yellow squash, and watermelon had 99 to 100% identity. The Arizona (AZ) and Sonora (SON) CYSDV CP sequences shared 99 to 100% identity with previously described CYSDV isolates from the Eastern Hemisphere (GenBank Accession Nos. DQ903105 and DQ903108) and also with two isolates of CYSDV collected during 2004 from Zacapa Valley, Guatemala (GenBank Accession Nos. EF21060 and EF21061) (J. K. Brown, unpublished data). CYSDV is a member of the genus Crinivirus, family Closteroviridae. CYSDV was first identified in cucumber and melon crops in the Middle East approximately 15 years ago and 10 years ago in Spain (1). Most recently, this virus was introduced into Texas (2), Guatemala (J. K. Brown, unpublished data), and Arizona and California (3). CYSDV has therefore emerged as an important and potentially worldwide threat to the production of cultivated cucurbits (3). The threat appears to be significant in light of the introduction or establishment of the exotic B. tabaci biotypes B and Q vectors, which also originated in the Middle Eastern-North African-Mediterranean region. To our knowledge, this is the first report of CYSDV infecting field-grown C. pepo (four types) and watermelon, reported previously only as experimental laboratory hosts, and of CYSDV in two types of melon (C. melo) in Mexico. References: (1) A. Celix et al. Phytopathology 86:1370, 1996. (2) J. Kao et al. Plant Dis. 84:101, 2000. (3) Y.-W. Kuo et al. Plant Dis. 91:330, 2007. (4) L. Rubio et al. J. Gen. Virol. 82:929, 2001.

Tomato yellow leaf curl virus in Tomato in Texas, Originating from Transplant Facilities

Tomato yellow leaf curl virus (TYLCV), a monopartite virus in the genus Begomovirus (family, Geminiviridae) from the Middle East, is one of the most damaging whitefly-transmitted viruses of tomato (Lycopersicon esculentum) worldwide. TYLCV was first identified in the United States in 1997 in Florida (4), and most recently, in the Pacific Coast states of Mexico where fresh market tomatoes are grown for the U.S. market (1). During September 2006, tomatoes grown from transplants in Waller County, TX exhibited shortened internodes, stunting and puckering of leaflets, green vein banding, and diffuse chlorosis. The disease incidence in two fields (4 ha total) was 95% and yield was substantially reduced. Many of the transplants were symptomatic at planting. The transplants originated from two facilities in Hidalgo County, TX. Both facilities had experienced heavy infestations of the whitefly, Bemisia tabaci (Genn.), during transplant production. At the same time, transplants produced in Uvalde and Bexar counties, TX, where whitefly infestations were also prevalent, had similar virus symptoms. Total DNA was extracted from the leaves of symptomatic tomato plants from 10 samples from these four counties and amplified by PCR (2). DNA samples from Waller, Hidalgo, and Uvalde counties were cloned, and a partial fragment of the viral coat protein gene (core Cp) was sequenced. BLAST analysis of the core Cp sequences of each sample confirmed the presence of TYLCV. No other begomovirus was detected, and all attempts to amplify a bipartite begomovirus by PCR using degenerate DNA-B specific primers (3) were unsuccessful. The full-length TYLCV DNA was amplified from three samples using the rolling circle amplification method as described (1), cloned, and the sequences were determined. The three sequences shared 99.6 to 100% nt identity and so only one sequence was deposited in the NCBI GenBank database (Accession No. EF110890) (1). Analysis of the complete genome nucleotide sequence corroborated TYLCV identity predicted by core Cp analysis that was 98.1% identical with TYLCV from Egypt (GenBank Accession No. AY594174) and Spain (GenBank Accession No. AJ489258), 97.6% with TYLCV from Mexico (GenBank Accession No. DQ631892), and 96.5% with TYLCV-Is (GenBank Accession No. X15656). Additionally, a Southern blot with TYLCV as the probe detected replicating (double-stranded) TYLCV DNA in all samples consisting of three plants from Uvalde County and 21 plants from Bexar County. To our knowledge, this is the first report of TYLCV in Texas that occurred in two transplant production areas approximately 400 km apart. Transplants produced in Uvalde and Bexar counties were planted there, while Hidalgo County transplants were shipped outside of the usual range of the whitefly. Hidalgo County has a subtropical climate, which can allow overwintering of TYLCV and the whitefly vector, allowing the establishment and spread of this virus in the future. References: (1) J. K. Brown and A. M. Idris. Plant Dis. 90:1360, 2006. (2) J. K. Brown et al. Arch. Virol. 146:1581, 2001. (3) A. M. Idris and J. K. Brown. Phytopathology 88:648, 1998. (4) J. E. Polston et al. Plant Dis. 83:984, 1999.

Introduction of the Exotic Monopartite Tomato yellow leaf curl virus into West Coast Mexico

Leaf curl symptoms that are reminiscent of begomovirus (genus Begomovirus, family Geminiviridae) infection were observed widespread in the tomato crop during the early fall 2005 through the spring 2006 growing seasons in Sinaloa State, Mexico. Symptoms were widespread in three major valleys (Culiacan, Guasave, and Los Mochis) that are largely dedicated to fresh-market tomato production for the U.S. market from October to June. Symptoms included stunting of leaves, shortened internodes, distortion of leaf margins, and green vein banding. Fruit set was reduced significantly (as much as 90%) on the portion of the plant that developed above the point of symptom expression. Tomato fields were heavily infested with the B biotype of the whitefly Bemisia tabaci (Genn.) vector and no other insect vectors were noted in the fields. Total DNA was extracted from six symptomatic tomato plants (two from each valley) and used as template to amplify, clone, and sequence the core region of the begomovirus CP. BLAST analysis of begomovirus sequences available in the NCBI GenBank database indicated the closest match was the Old World monopartite begomovirus Tomato yellow leaf curl virus (TYLCV) from Israel (Accession No. X15656) at 97.8% shared nucleotide (nt) identity. The full-length genome was amplified for each of six isolates using TempliPhi (Amersham Biosciences, Piscataway, NJ) and cloned into the pGEM7 vector (Promega, Madison, WI). The complete DNA genome sequence was determined for eight clones by primer walking. Cloned TempliPhi products sequenced represented two to three isolates from each valley. Results indicated that the isolates (n = 8) were 98.9 to 100% identical (Accession No. DQ631892) to each other, and they shared 98% identity with TYLCV isolates reported from the Caribbean Region and Florida. This highly virulent begomovirus of tomato, originating in Israel, was first reported in Mexico from 1996 to 1997 when it was identified in tomato plants in the Yucatan Peninsula (1) (>1,500 miles from Sinaloa). The latter report followed the introduction of TYLCV in tomato seedlings from Florida into several eastern U.S. states (3,4) and then into Puerto Rico (2). The introduction of TYLCV into Sinaloa where tomato production is highly concentrated is significant because the region supplies the majority (as much as 93%) of fresh-market tomatoes to the western United States from October to June (>$750 million dollars). Of equal importance is the immediate proximity of the pandemic to California where more than 90% of the processing tomatoes in the United States are grown. References: (1) J. T. Ascencio-Ibáñez et al. Plant Dis. 83:1178, 1999. (2) J. Bird et al. Plant Dis. 85:1028, 2001. (3) M. T. Momol et al. Plant Dis 83:487, 1999. (4) J. E. Polston and P. K. Anderson, Plant Dis. 81:1358, 1997.

Introduction of the New World Squash leaf curl virus to Squash (Cucurbita pepo) in Egypt: A Potential Threat to Important Food Crops

Squash plants showing leaf curling, yellow mottling, and reduced fruit set were observed in fields in Giza, Egypt in spring 2005. These particular symptoms had not been observed previously in zucchini squash plants in Egypt, but were reminiscent of those caused by begomoviruses (Geminiviridae) that are known to occur in the region, including Watermelon chlorotic stunt virus. Squash plants were heavily infested with the whitefly Bemisia tabaci (Genn.), the only known vector of begomoviruses. Total nucleic acids were isolated from symptomatic squash leaves using the cetyltrimethylammoniumbromide method, and extracts were subjected to polymerase chain reaction (PCR) analysis using two sets of PCR primers. One primer set (prAV2644 and prAC1154) was designed to amplify a fragment that contains the entire viral coat protein (Cp), while the second primer set (prBV1855 and prBC656) was designed to amplify the common region (CR) of DNA-B of begomoviruses (1). The expected size fragments were cloned and the sequence was determined for five clones each. Unexpectedly, the Cp and the CR-B fragments shared their highest nucleotide sequence (nt) identity among well-characterized begomoviruses to the bipartite Squash leaf curl virus (SLCV) native to the western United States. A third primer set (prAC344 and prAV1134) (1) was subsequently used to amplify the remainder of the putative SLCV DNA-A. The fragment was cloned and the DNA sequence was determined. Assembly of the overlapping DNA-A fragments resulted in a complete DNA-A component sequence of 2,636 nt, which is identical to the expected size of the SLCV DNA-A component (GenBank Accession No. DQ285019). Comparison with the latter sequence indicated that the Egyptian squash isolate shared 98% nt identity with SLCV. The sequence for the DNA-B fragment (1,162 nt) shared 94% nt identity with SLCV and was deposited in GenBank as Accession No. DQ285020. The high-shared nt identity with SLCV (2) from the United States suggests that this isolate, herein SLCV-EG, has been introduced into Egypt. The relatively low DNA-B nt sequence identity was a not a surprise since this component is normally less conserved even between strains of a single begomoviral species. Introduction of SLCV is not only potentially significant to the domestic production of crop species in the Cucurbitaceae but also for legume crops. SLCV has a broad host range that also includes members of the Fabaceae, which includes species that contribute significant sources of protein for much of Egypt's population. The virus thus far is thought to be present only in Lower Egypt, however, it could feasibly threaten legume and cucurbit crops if it spreads to Upper Egypt. To our knowledge, this is the first begomovirus of New World origin to become established in the Old World. References: (1) A. M. Idris and J. K. Brown. Phytopathology 88:648, 1998. (2) S. G. Lazarowitz. Virology 180:70, 1991.

Genetic and Phenotypic Variation of the Pepper golden mosaic virus Complex

ABSTRACT Three isolates of the bipartite begomovirus Pepper golden mosaic virus (PepGMV) were characterized for genomic and biological properties. The complete nucleotide sequences of the DNA-A and DNA-B components were determined from infectious clones of PepGMV-Serrano (PepGMV-Ser), PepGMV-Mosaic (PepGMV-Mo), and PepGMV-Distortion (PepGMV-D). Nucleotide sequence identity among PepGMV components ranged from 91 to 96% for DNA-A and from 84 to 99% for DNA-B, with each PepGMV component most closely related to the corresponding component of Cabbage leaf curl virus (CaLCV). However, phylogenetic relationships among begomovirus components were incongruent because DNA-A of PepGMV and CaLCV share an inferred evolutionary history distinct from that of DNA-B. The cloned components of PepGMV-Ser, -Mo, and -D were infectious by biolistic inoculation to pepper but differed in symptom expression: PepGMV-Ser exhibited a bright golden mosaic, PepGMV-Mo produced a yellow-green mosaic, and PepGMV-D caused only a mild mosaic and foliar distortion followed by a "recovery" phenotype in which leaves developing after initial symptom expression appeared normal. Differences in symptoms also were observed on tomato, tobacco, and Datura stramonium. Progeny virus derived from clones of PepGMV-Ser and -Mo were transmitted from pepper to pepper by the B biotype of Bemisia tabaci; progeny virus derived from PepGMV-D clones was not transmissible by the B biotype. Reassortant genomes derived from heterologous DNA components of the three isolates were infectious in all possible pairwise combinations, with symptom phenotype in pepper determined by the DNA-B component. Collectively, these results indicate that the three virus isolates examined may be considered distinct strains of PepGMV that have the capacity to exchange genetic material.

Sequence analysis and classification of apparent recombinant begomoviruses infecting tomato in the nile and mediterranean basins

ABSTRACT Numerous whitefly-transmitted viral diseases of tomato have emerged in countries around the Nile and Mediterranean Basins the last 20 years. These diseases are caused by monopartite geminiviruses (family Gemini viridae) belonging to the genus Begomovirus that probably resulted from numerous recombination events. The molecular biodiversity of these viruses was investigated to better appreciate the role and importance of recombination and to better clarify the phylogenetic relationships and classification of these viruses. The analysis partitioned the tomato-infecting begomoviruses from this region into two major clades, Tomato yellow leaf curl virus and Tomato yellow leaf curl Sardinia virus. Phylogenetic and pairwise analyses together with an evaluation for gene conversion were performed from which taxonomic classification and virus biodiversity conclusions were drawn. Six recombination hotspots and three homogeneous zones within the genome were identified among the tomatoinfecting isolates and species examined here, suggesting that the recombination events identified were not random occurrences.

Cotton leaf curl Gezira virus-satellite DNAs represent a divergent, geographically isolated Nile Basin lineage: predictive identification of a satDNA REP-binding motif

Cotton leaf curl Gezira virus (CLCuGV), a species of the genus Begomovirus (family Geminiviridae), was recently cloned from cotton, okra, and Sida alba plants exhibiting leaf-curling and vein-thickening symptoms in Sudan. Here, we describe a previously unknown lineage of single-stranded DNA satellite (satDNA) molecules, which are associated with CLCuGV, and are required for development of characteristic disease symptoms. Co-inoculation of cotton and Nicotiana benthamiana plants with satDNAs cloned from cotton, okra, and S. alba, together with CLCuGV as the 'helper virus' resulted in the development of characteristic leaf-curling and vein-thickening symptoms in both hosts. An anatomical study of symptomatic, virus-infected cotton leaves revealed that spongy parenchyma cells had developed instead of collenchyma cells at the sites of vein thickening. Phylogenetically, the CLCuGV-associated satDNAs from Sudan, together with their closest relatives from Egypt, form a new satDNA lineage comprising only satDNAs from the Upper and Lower Nile Basins. Analysis of satellites and their helper virus sequences identified a predicted REP-binding site consisting of the directly repeated sequence, 'CGGTACTCA', and an inverted repeated sequence, 'TGAGTACCG', which occur in the context of a 17-nucleotide motif. The conserved REP-binding motif identified herein, together with strict geographic isolation, and apparent host-restriction, may be the collective hallmark of these new satDNA-begomovirus lineages, extant in the Nile Basin.

Evidence for interspecific-recombination for three monopartite begomoviral genomes associated with the tomato leaf curl disease from central Sudan

Two distinct viral genotypes were identified in the same tomato plant collected from Gezira, Sudan and are provisionally designated Tomato leaf curl Sudan virus (ToLCSDV-Gez) and Tomato yellow leaf curl virus-Sudan (TYLCV-SD). A third genotype was identified in tomato samples collected in Shambat, Sudan (ToLCSDV-Sha). The ToLCSDV-Gez and ToLCSDV-Sha isolates were approximately 90% identical, TYLCV-SD from Gezira shared approximately 93% identity with TYLCV-Mld. Recombination analyses identified two fragments in the ToLCSDV-Gez and TYLCV-SD genomes, providing evidence that these two genomes had undergone intermolecular recombination. A half unit size (737 nt) single-stranded satellite DNA was associated with ToLCSDV-Gez and TYLCV-SD.

Cotton leaf crumple virus Is a Distinct Western Hemisphere Begomovirus Species with Complex Evolutionary Relationships Indicative of Recombination and Reassortment

ABSTRACT The bipartite DNA genome of Cotton leaf crumple virus (CLCrV), a whitefly-transmitted begomovirus from the Sonoran Desert, was cloned and completely sequenced. The cloned CLCrV genome was infectious when biolistically delivered to cotton or bean seedlings and progeny virus was whitefly-transmissible. Koch's postulates were completed by the reproduction of characteristic leaf crumple symptoms in cotton seedlings infected with cloned CLCrV DNA, thereby verifying the etiology of leaf crumple disease, which has been known in the southwestern United States since the 1950s. Sequence comparisons confirmed that CLCrV has a genome organization typical of yet sufficiently divergent from all other bipartite begomoviruses to justify recognition as a distinct species. Phylogenetic analyses indicated that CLCrV has a complex evolutionary history probably involving both recombination and reassortment. The relatively low nucleotide sequence identity (77%) of the common region shared by the CLCrV DNA-A and DNA-B components and the distinct phylogenetic relationships of each component are consistent with component reassortment. Sequence analyses indicated that the CLCrV DNA-A component was likely derived by recombination among ancestors of two divergent clades (e.g., the Squash leaf curl virus [SLCV] clade and the Abutilon mosaic virus clade) of Western Hemisphere begomoviruses. The CLCrV DNA-B component also may have originated by recombination among an ancestor of the SLCV clade and another distantly related but unknown Western Hemisphere begomovirus.

Two Newly Described Begomoviruses of Macroptilium lathyroides and Common Bean

ABSTRACT Macroptilium lathyroides, a perennial weed in the Caribbean region and Central America, is a host of Macroptilium yellow mosaic Florida virus (MaYMFV) and Macroptilium mosaic Puerto Rico virus (MaMPRV). The genomes of MaYMFV and MaMPRV were cloned from M. lathyroides and/or field-infected bean and the DNA sequences were determined. Cloned A and B components for both viruses were infectious when inoculated to M. lathyroides and common bean. Comparison of the DNA sequences for cloned A and B components with well-studied begomovirus indicated that MaMPRV (bean and M. lathyroides) and MaYMFV (M. lathyroides) are unique, previously undescribed begomo-viruses from the Western Hemisphere. Phylogenetic analysis of viral A components indicated that the closest relative of MaYMFV are members of the Bean golden yellow mosaic virus (BGYMV) group, at 76 to 78% nucleotide identity, whereas the closest relative for the A component of MaMPRV was Rhynchosia golden mosaic virus at 78% nucleotide identity. In contrast, BGYMV is the closest relative for the B component of both MaYMFV and MaMPRV, with which they share approximately 68.0 and approximately 72% identity, respectively. The incongruent taxonomic placement for the bipartite components for MaMPRV indicates that they did not evolve entirely along a common path. MaYMFV and MaMPRV caused distinctive symptoms in bean and M. lathyroides and were transmissible by the whitefly vector and by grafting; however, only MaYMFV was mechanically transmissible. The experimental host range for the two viruses was similar and included species within the families Fabaceae and Malvaceae, but only MaYMFV infected Malva parviflora and soybean. These results collectively indicate that MaMPRV and MaYMFV are new, previously undescribed species of the BGYMV group, a clade previously known to contain only strains and isolates of BGYMV from the Caribbean region that infect Phaseolus spp. Both MaYMFV and MaMPRV may pose an economic threat to bean production in the region.

Emergence of a New Cucurbit-Infecting Begomovirus Species Capable of Forming Viable Reassortants with Related Viruses in the Squash leaf curl virus Cluster

ABSTRACT Cucurbit leaf curl virus (CuLCV), a whitefly-transmitted geminivirus previously partially characterized from the southwestern United States and northern Mexico, was identified as a distinct bipartite begomovirus species. This virus has near sequence identity with the previously partially characterized Cucurbit leaf crumple virus from California. Experimental and natural host range studies indicated that CuLCV has a relatively broad host range within the family Cucurbitaceae and also infects bean and tobacco. The genome of an Arizona isolate, designated CuLCV-AZ, was cloned and completely sequenced. Cloned CuLCV-AZ DNA A and B components were infectious by biolistic inoculation to pumpkin and progeny virus was transmissible by the whitefly vector, Bemisia tabaci, thereby completing Koch's postulates. CuLCV-AZ DNA A shared highest nucleotide sequence identity with Squash leaf curl virus-R (SLCV-R), SLCV-E, and Bean calico mosaic virus (BCaMV) at 84, 83, and 80%, respectively. The CuLCV DNA B component shared highest nucleotide sequence identity with BCaMV, SLCV-R, and SLCV-E at 71, 70, and 68%, respectively. The cis-acting begomovirus replication specificity element, GGTGTCCTGGTG, in the CuLCV-AZ origin of replication is identical to that of SLCV-R, SLCV-E, and BCaMV, suggesting that reassortants among components of CuLCV-AZ and these begomoviruses may be possible. Reassortment experiments in pumpkin demonstrated that both reassortants of CuLCV-AZ and SLCV-E A and B components were viable. However, for CuLCV-AZ and SLCV-R, only one reassortant (SLCV-R DNA A/CuLCV-AZ DNA B) was viable on pumpkin, even though the cognate component pairs of both viruses infect pumpkin. These results demonstrate that reassortment among sympatric begomovirus species infecting cucurbits are possible, and that, if generated in nature, could result in begomoviruses bearing distinct biological properties.

Molecular Characterization of Rhynchosia mosaic virus-Puerto Rico Associated with Symptomatic Rhynchosia minima and Cajanus cajan in Puerto Rico

A begomovirus (family Geminiviridae) has long been suspected to be associated with Rhynchosia mosaic (RhM) disease of Rhynchosia minima (L.) DC., a weed that is widespread in Puerto Rico (PR). The suspect virus has been transmitted by the Sida biotype of Bemisia tabaci (Genn.) and has been designated RhM virus-PR (RhMV-PR) (1) (synonym, Rhynchosia mosaic virus [RMV]). RhM symptoms in R. minima included yellow foliar mosaic and stunting. The virus has a broad experimental host range and infects species in the Fabaceae, including R. minima, pigeon pea (Cajanus cajan (L.) Millsp.), and Clitoria falcata L. (1). However, until now RhMV has not been identified from naturally infected pigeon pea or Clitoria falcata. R. minima and C. cajan plants exhibiting yellow foliar mosaic and stunting symptoms were collected in Puerto Rico. Using the B biotype of B. tabaci as the vector, their whitefly transmissibility from the respective source plant to R. minima and C. cajan test plants was confirmed, and symptoms in inoculated host were indistinguishable for both isolates. Using polymerase chain reaction (PCR) and primers (2), three amplicons were obtained and cloned for each isolate. PCR products (1.1 and 2.1 kbp) were assembled (~200 nucleotide [nt] overlap) to yield an apparent full-length DNA A component (~2.6 kbp) containing the diagnostically informative viral coat protein gene (CP) and common region (CR-A). PCR primers were used to amplify the DNA B component segment (0.7 kbp) containing the CR-B (2). The DNA sequence for the core CP (533 nt) and full CP (750 nt) were compared with analogous sequences for well-studied begomoviruses, and CR-A and CR-B (153 nt) were compared for RhMV isolates. All isolates noted were obtained from GenBank. The core CP for isolates from R. minima (AF442117) and C. cajan (AY062025) shared 97.9% nucleotide identity (100% AA similarity) and the CR-A (AF442118) and CR-B (AF442119) sequences for R. minima and C. cajan isolates were ~96% identical, indicating the A and B components are of the same begomovirus. Comparison of the core CP sequence for an independent isolate from C. cajan from PR (AY028308) (4) with those for R. minima and C. cajan isolates indicated 95.5% (99.4% AA) and 96.2% (99.4% AA) nucleotide identity, respectively, indicating association of RhMV with both C. cajan samples. The recently archived core CP (533 nt) (AY028308) is actually of RhMV-PR, rather than a distinct begomovirus species, as indicated (4). Interestingly, the core CP of R. minima (AF442117) and C. cajan (AY062025) isolates were 91.7% (98.9% AA) and 92.3% (98.9% AA) identical, respectively, with a PR isolate from Clitoria falcata (AF070924), also confirming that RhMV-PR naturally infects Clitoria falcata. Analysis of the full CP for the R. minima and C. cajan isolates revealed that their closest relatives were Macroptilium mosaic virus (MaMV-PR) (AF176092) and Bean golden mosaic virus (BGMV-PR) (M10070) at 89 and 84% nucleotide identity, respectively. Applying the 90% CP rule (3) to RhMV CP sequences, RhMV is a distinct begomovirus species. At least three begomoviruses, BGMV-PR, MaMV-PR, and RhMV-PR, naturally infect leguminous species in Puerto Rico. References: (1) J. Bird. Phytopathology 52:286, 1962. (2) A. M. Idris and J. K. Brown. Phytopathology 88:648, 1998. (3) M. A. Mayo and C. R. Pringle. J. Gen. Virol. 79:649, 1998. (4) R. L. Rodriguez et al. Plant Dis. 85:1119, 2001.

Three Previously Unidentified Begomoviral Genotypes from Tomato Exhibiting Leaf Curl Disease Symptoms from Central Sudan

Field tomato plants exhibiting upward curling of leaflets, chlorosis, and stunting symptoms described for tomato leaf curl disease in Sudan (2) were collected in 1996 from Gezira (GZ) and Shambat (SH), Sudan. Disease symptoms were reproduced following experimental transmission of the causal agent(s) by the whitefly Bemisia tabaci from field tomato to virus-free tomato seedlings in a glasshouse at Gezira Research Station, Wad Medani, Sudan. Total nucleic acids were extracted from symptomatic tomato test plants. An ≈1.3-kbp fragment, diagnostic for begomovirus, was obtained from extracts by polymerase chain reaction using degenerate primers that amplify the coat protein gene (CP) and the respective flanking sequences for most begomoviuses (1). A second pair of degenerate primers was used to amplify a 2.3-kbp begomoviral fragment that overlaps both ends of the (CP) amplicon by >200 nt (1). At least 10 amplicons for each were cloned, and their sequences were determined, revealing three unique, tomato-infecting begomoviruses genotypes, two from GZ and one from SH. No B component was detected using degenerate primers that direct the amplification of a diagnostic fragment of the B component (1.4 kbp) for most bipartite begomoviruses. The organization of the three, apparently full-length viral genomes, was typical of other monopartite begomoviruses. A GenBank search revealed that the three viruses were previously undescribed. The GZ and SH tomato isolates are herein provisionally named ToLCV-GZ1 (GenBank Accession No. AY044137), ToLCV-GZ2 (GenBank Accession No. AY044138), and ToLCV-SH (GenBank Accession No. AY044139), respectively. All three tomato-infecting begomoviruses have identical stem-loop structures containing the conserved nonanucleotide motif characteristic of all members of the family Geminiviridae; however, the predicted Rep binding element located in the common region is unique for each virus. Phylogenetic analysis of the three viral sequences placed them in a large clade containing all other Old World begomoviruses. Distance comparisons among these and other well-studied begomoviruses indicated that ToLCV-GZ1 and ToLCV-SH shared an overall 90% nucleotide sequence identity, with ˜83% nucleotide sequence identity to ToLCV-GZ2. ToLCV-GZ1 and ToLCV-SH were 83% identical, with their closest relative, Tomato yellow leaf curl virus (TYLCV), while ToLCV-GZ2 shared 93% identity with TYLCV. The genomes of all three Sudan viruses contained regions of homologous nucleotide sequences, suggesting intermolecular exchange among these viruses. Exclusion of the homologous sequences (>800 nt) from the phylogenetic analysis indicated even lower shared nucleotide identities (<90%, the arbitrary cut-off for distinct species), which may warrant their classification as separate species. These three newly described begomoviruses are indigenous to central Sudan, and comprise a unique Old World lineage distinct from previously described begomoviruses associated with leaf curl disease of tomato in Africa and the Mediterranean Region. References: (1) A. M. Idris and J. K. Brown. Phytopathology 83:548, 1998. (2) A. M. Yassin. Trop. Pest Manage. 29:253, 1983.

Introduction of the Exotic Tomato yellow leaf curl virus-Israel in Tomato to Puerto Rico

Thirty-five-day-old tomato plants (cultivar Florasette) exhibited yellow leaf curling, stunting, and extremely reduced fruit set in spring 2001, in Guanica, Puerto Rico (PR). Twenty percent disease incidence was observed in this field and, 8 weeks later, 75% of the plants showed symptoms. These symptoms were distinct from those caused by other tomato-infecting begomoviruses reported previously from PR, namely Merremia mosaic virus, Tomato mottle virus (ToMoV), and Potato yellow mosaic virus (1). A colony of the B biotype of Bemisia tabaci (Genn.) was used to transmit the suspect virus from symptomatic plants collected in the field and established in the greenhouse in Rio Piedras, PR. The suspect virus was transmitted readily to tomato cultivar Roma (10 of 10 plants), and symptoms were like those observed in the field. Symptoms also were reminiscent of those described for several Old World begomoviruses, referred to as Tomato yellow leaf curl virus (TYLCV). Total nucleic acids were isolated from three symptomatic field samples and three greenhouse-inoculated tomato plants showing typical disease symptoms. Extracts were analyzed by polymerase chain reaction (PCR) with primers AV2466 and AC1145 to amplify a begomoviral fragment (approximately 1.1 bp) that contains a portion of the intergenic region and the viral coat protein gene (CP) (2). Amplicons were cloned, and their nucleotide sequences were determined. A comparison of CP with other well-studied begomoviral nucleotide sequences revealed that the CP sequences for field isolates 1 to 6 shared 99.7 to 100% identity with each other and 99.9 to 100% identity with TYLCV from Israel (TYLCV-IL; accession no. X76319) as well as TYLCV-IL isolates discovered in the Dominican Republic (DO; accession no. AF024715) and, subsequently, in Florida. TYLCV-specific PCR primers (forward) 5'-GAATTCCGCCTTTAA-TTTG-3' and (reverse) 5'-GAATTCCCACTATCTTTCTC-3' were used to amplify the complete viral genome form a PR field isolate. An expected-sized amplicon of approximately 2.8 kb was obtained, and the nucleotide sequence of two cloned amplicons was determined. Genome organization revealed a predicted precoat open reading frame of 351 bp, which is characteristic of other Old World begomoviruses, including TYLCV-IL. Nucleotide comparisons indicated that the PR isolate shared 99% nucleotide sequence identity with TYLCV-IL (first reported from Israel) and introduced TYLCV-IL isolates in DO and Florida, thereby confirming the introduction of TYLCV-IL into PR. TYLCV-IL was first identified several years ago in the Western Hemisphere, and the virus has been reported in five offshore locations and three continental U.S. states since its initial introduction into the DO in the early 1990s. Considering the extreme virulence of TYLCV-IL compared with most New World tomato-infecting begomoviruses, this introduction, which likely occurred from a nearby Caribbean country or Florida, has the potential to destroy the fresh-market tomato industry in PR, which supplies tomatoes to the continental United States during the winter months. There is compelling evidence for the routine movement of tomato seedlings from the continental United States to this location in PR throughout the last 10 years, including the previous introduction of ToMoV (1). These incidences and others indicate the need for those in infected areas to take precautions to avoid further spread of this highly damaging virus in and adjacent to the Caribbean region. References: (1) A. M. Idris et al. Phytopathology 88:S42, 1998. (2) A. M. Idris and J. K. Brown, Phytopathology 88:648, 1998.

Melon chlorotic leaf curl virus, a New Begomovirus Associated with Bemisia tabaci Infestations in Guatemala

In 2000, geminivirus-like symptoms were widespread in muskmelon (Cucumis melo L.) fields (70 to 80% incidence) in Zacapa Valley, Guatemala. Muskmelon fields were infested with the whitefly Bemisia tabaci (Genn.), and plants exhibited patchy foliar chlorosis, leaf curling, and reduced fruit set, which is reminiscent of symptoms caused by certain whitefly-transmitted geminiviruses. Quarantine restrictions prevented experimental transmission experiments from being carried out with the whitefly vector or biolistic inoculation. Leaves collected from six symptomatic plants were assessed for the presence of begomovirus DNA by polymerase chain reaction (PCR) with the use of degenerate primers that amplify the core region of the coat protein (CP) gene of most begomoviruses (1). PCR products of the expected size (approximately 576 bp) were obtained from all three melon samples. The core CP amplicons were cloned, and their nucleotide sequences were compared. Nucleotide sequences of core CP fragments shared 99.7% identity, suggesting the presence of a single begomovirus in all assayed symptomatic melon plants. Two additional pairs of degenerate primers were used to obtain contiguous viral fragments containing the CP gene, the common region of the A component (CR-A; approximately 2,100 bp), and a fragment containing the CR of the B component (CR-B; approximately 1,100 bp), respectively (2). At least three amplicons obtained with each primer pair were cloned and their nucleotide sequence was determined. Virus-specific PCR primers were then designed within the CP open reading frame and used to obtain fragments that overlapped with the 2,100-bp fragment to yield an apparent full-length A component of 2,662 nucleotides (accession no. AF325497). CR-A and CR-B (accession no. AF325498) sequences (161 nucleotides) shared 98.1% identity and contained an identical directly repeated, replication-associated protein (REP) binding site: GGTGT CCT GGTGT. Nucleotide sequence alignment, with CLUSTAL W, of the melon virus A-component with that of other well-studied begomoviruses revealed that its closest relatives were members of the Squash leaf curl virus (SLCV) group. The melon virus from Guatemala shared its greatest sequence identity, 83.1%, with SLCV extended (SLCV-E) (accession no. M38183), indicating that it is a new, previously unidentified begomovirus species, herein referred to as Melon chlorotic leaf curl virus (MCLCV). The next closest relatives of MCLCV were SLCV restricted (SLCV-R; 78.6%) (S. G. Lazarowitz, unpublished) Cucurbit leaf curl virus-Arizona (CuLCV-AZ; accession no. AF256199; 74.1%) (3), Cabbage leaf curl virus (CaLCV; 72.0%), Bean calico mosaic virus (BCMoV; 71.7%), and Texas pepper virus-Tamaulipas (71.4%). Additionally, the theoretical REP binding element, GGTGT, is 100% identical among MCLCV and BCMoV, CaLCV, CuLCV-AZ, SLCV-E, and SLCV-R. On the basis of shared nucleotide sequence identities with other begomoviruses described to date and the presence of B. tabaci in melon fields, it is likely that MCLCV also is whitefly-transmitted. Collectively, CP and CR sequences suggest that MCLCV is a new species of the SLCV lineage that contains other bipartite begomoviruses indigenous to Central America, Mexico, and the U.S. Sunbelt states. References: (1) S. D. Wyatt and J. K. Brown. Phytopathology 86:1288, 1996. (2) A. M. Idris and J. K Brown. Phytopathology 88:648, 1998. (3) J. K. Brown et al. Plant Dis. 84:809, 2000.

The core region of the coat protein gene is highly useful for establishing the provisional identification and classification of begomoviruses

Polymerase chain reaction (PCR) was applied to detect and establish provisional identity of begomoviruses through amplification of a approximately 575 bp fragment of the begomoviral coat protein gene (CP), referred to as the 'core' region of the CP gene (core CP). The core CP fragment contains conserved and unique regions, and was hypothesized to constitute a sequence useful for begomovirus classification. Virus relationships were predicted by distance and parsimony analyses using the A component (bipartite viruses) or full genome (monopartite viruses), CP gene, core CP, or the 200 5'-nucleotides (nt) of the CP. Reconstructed trees and sequence divergence estimates yielded very similar conclusions for all sequence sets, while the CP 5'-200 nt was the best strain discriminator. Alignment of the core CP region for 52 field isolates with reference begomovirus sequences permitted provisional virus identification based on tree position and extent of sequence divergence. Geographic origin of field isolates was predictable based on phylogenetic separation of field isolates examined here. A 'closest match' or genus-level identification could be obtained for previously undescribed begomoviruses using the BLAST program to search a reference core CP database located at our website and/or in GenBank. Here, we describe an informative molecular marker that permits provisional begomovirus identification and classification using a begomoviral sequence that is smaller than the presently accepted, but less accessible CP sequence.

Apoptosis and expression of Bax and Bcl-2 in snuff- and non-snuff associated oral squamous cell carcinomas

BACKGROUND

Oral squamous cell carcinoma (OSCC) is etiologically linked to tobacco and alcohol consumption. A higher frequency of p53 gene mutations was reported in snuff (toombak)-associated OSCC from the Sudan versus those from non-users (Ibrahim et al., 1999, 10).

MATERIALS AND METHODS

OSCC from Sudanese toombak users (n = 13) and non-users from the Sudan (n = 6) and Norway (n = 24) were analysed for bax, bcl-2 and Ki-67 immunohistochemically. Apoptosis was evaluated by the TUNEL method. The OSCC from the Sudan had previously been studied for p53 gene mutations.

RESULTS

We found a higher apoptotic rate and a higher bax expression in OSCC from Norway compared with those from the Sudan (p < 0.05) irrespective of toombak use. No significant differences were detected in apoptosis, bax, bcl-2 and Ki-67 in OSCC from the Sudan in relation to toombak use or p53 gene status.

CONCLUSION

In OSCC, apoptosis was associated with bax expression and was unaffected by p53 gene status or toombak use in OSCC from the Sudan.

Cucurbit leaf curl virus, a New Whitefly Transmitted Geminivirus in Arizona, Texas, and Mexico

In 1998 to 1999, geminivirus-like symptoms were observed in whitefly-infested pumpkin, honeydew melon, and muskmelon in Arizona and Texas and in Coahuilla, Mexico (MX), respectively. Plants exhibited leaf curl and/or mottling, reminiscent of symptoms caused by Squash leaf curl virus (SLCV-WAZ) described from Arizona in 1981 (2). The isolate from Arizona pumpkin fields was experimentally transmitted to pumpkin seedlings by the "B type" of Bemisia tabaci (Genn.), and symptoms were indistinguishable from those observed in infected fields. Samples from AZ, MX, and TX were assessed for begomovirus presence by polymerase chain reaction (PCR) using degenerate primers that amplify a contiguous fragment containing the viral coat protein (Cp) gene and common region (CR) of the A component (CR-A) (~2,100 bp) and a fragment containing the CR of the B component (CR-B) (~1,100 bp). One to four isolates from each location were examined by PCR using both primer pairs, and at least three amplicons per isolate were cloned and their sequences determined. Alignment of viral Cp nucleotide (nt) sequences revealed that AZ [AF256199], MX, and TX field isolates shared 98.7 to 100% sequence identity, but were only 84.5 to 85.6% identical to the Cp gene of SLCV-extended (SLCV-E) [M38183] and SLCV-restricted (SLCV-R) (S. G. Lazarowitz, unpublished), respectively, suggesting a new, previously undescribed begomoviral species (3). Further, the Cp nt sequence of the three field isolates was 6 nt shorter than SLCV-E, SLCV-WAZ [AF256203], and SLCV-R Cp sequences. The CR-A [AF256200] and CR-B [AF256201] sequences (179 nt, each) of field isolates, including the theoretical Rep binding element, GGTGT, were 100% identical. Although the Rep binding site is identical among field isolates, SLCV-E, SLCV-R, and SLCV-WAZ, the field isolate CR sequence shared only 64.2, 67.5, and 66.9% overall identity with CR-A SLCV-E, SLCV-R [M63155], and SLCV-WAZ [AF256202], respectively. Prior to 1998 to 1999, SLCV-WAZ was the only New World begomovirus of cucurbits known to infect both melon (Cucumis) and pumpkin (Cucurbita) (1). Therefore, SLCV was initially suspected as the causal agent. However, here we provide evidence for a new, previously undescribed bipartite begomovirus of cucurbits in AZ, MX, and TX that is herein provisionally designated Cucurbit leaf curl virus (CuLCV). Prediction of its closest begomovirus relatives by Cp nt sequence and Rep binding site comparisons suggest that CuLCV is a new member of the SLCV lineage, also containing Bean calico mosaic virus, Cabbage leaf curl virus, SLCV-E, and Texas pepper virus-TAM. References: (1) J. K. Brown and M. R. Nelson. Phytopathology 74:1136, 1984. (2) J. K. Brown and M. R. Nelson. Ann. Appl. Biol. 115:243, 1986. (3) M. A. Mayo and C. R. Pringle. J. Gen. Virol. 97:649, 1998.

Identification of a New, Monopartite Begomovirus Associated with Leaf Curl Disease of Cotton in Gezira, Sudan

Cotton leaf curl disease (CLCuD) was first reported in Sudan in 1931. Disease symptoms in cotton were characterized by vein thickening and leaf curling, and the suspect causal agent was shown to be transmitted by the whitefly Bemisia tabaci (Genn.) among cotton, okra, and several weed species (2). Although begomovirus etiology was suspected based on symptomatology and vector transmission, no evidence was available that confirmed or disputed this hypothesis. During 1994 to 1996, four cotton samples exhibiting typical CLCuD symptoms were collected from different fields in the Gezira region in Central Sudan and examined for presence of begomovirus DNA. Total nucleic acids were isolated from cotton plants and subjected to polymerase chain reaction (PCR) using degenerate primers (pAV 2644 and pAC 1154) to amplify begomovirus coat protein (Cp) gene and its flanking sequences (1). An amplicon of the expected size (1,300 bp) was obtained by PCR from each sample, and their nucleotide (nt) sequences were determined. Virus-specific primers designed around the Cp sequence were used to amplify an apparent full-length DNA component. Amplicons were cloned and their sequences were determined, yielding a begomoviral component of approximately 2,761 nt (AF260241). Despite exhaustive attempts to amplify a putative viral B-component using degenerate primers based on the intergenic region sequence of the putative "A-component," or sequences that are highly conserved for other begomoviruses, no B component was detected. The four cotton isolates shared 99.9 to 100% nt sequence identity, and the number and arrangement of predicted open reading frames were similar to those known for other monopartite begomoviruses. Phylogenetic analysis of the putative CLCuV genome with other begomoviruses indicated that its closest relative was Althea rosea enation virus (AREV) from Egypt (AF014881) with which it shares 79% sequence identity, indicating that CLCuV is a unique begomovirus species with a probable origin in the Eastern Hemisphere. CLCuV shared 66% identity with its second closest relative, Cotton leaf curl virus-Pakistan (CLCuV-PK) (AJ002448). These data provide the first direct evidence for the association of a monopartite begomovirus with the leaf curl disease of cotton in Gezira, Sudan, that is distinct from all other begomoviral species described to date. Herein, we provisionally designate this unique begomoviral species as Cotton leaf curl virus from Sudan (CLCuV-SD). References: (1) A. M. Idris and J. K. Brown. Phytopathology 88:648, 1998. (2) A. M. Nour and J. J. Nour. Emp. Cott. Gr. Rev. 41:27, 1964.

Tomato curly stunt virus, a New Begomovirus of Tomato Within the Tomato yellow leaf curl virus-IS Cluster in South Africa

Tomato yellow leaf curl virus (TYLCV) causes a serious disease of tomato in many countries throughout the world. Preliminary reports suggested that TYLC disease was present in 1997 in South Africa. In 1998 140 ha of tomato fields in the Onderberg area were assessed for possible presence of TYLCV. Symptoms like those caused by TYLCV isolates in Israel were observed in most fields, and disease incidence ranged from <1 to 50%. Yield losses in individual plants ranged from negligible to 100% and appeared related to the age of the plants at time of infection. Two isolates of the suspect virus were experimentally transmitted from symptomatic tomato to virus-free, glasshouse-grown tomato seedlings by colony. Field and colony whiteflies were identified as the Bemisia tabaci based on mt COI sequence analysis (1). Attempts to transmit the suspect begomovirus by sap inoculation between tomato plants were unsuccessful. Polymerase chain reaction (PCR) amplification with degenerate PCR primers (2) that permit detection of the coat protein gene (AV1) and the common region (CR) of other begomoviruses yielded an amplicon of the expected size (2,100 bp), suggesting begomovirus association with diseased tomato plants. Nucleotide (nt) sequence analysis of AV1 for both tomato isolate AF261885 indicated that they were indistinguishable and shared less than 78% sequence identity with other well-studied begomoviruses, indicating a distinct, previously undescribed begomovirus species. AV1 sequence comparisons also revealed that its closest relatives were members of the TYLCV cluster, which includes South African cassava mosaic virus (77.4%) (AF11785), East African cassava mosaic virus (77.3%) (AJ006459), and TYLCV-IS (76.2%) (X15656). The theoretical Rep binding element in the CR, TCGGT, was identical to TYLCV-IS and Cotton leaf curl virus-Pakistan (AJ002448) (AJ002449). Here, we provisionally designate this new tomato-infecting begomoviral species, Tomato curly stunt virus from South Africa (ToCSV-SA). References: (1) D. R. Frohlich et al. Mol. Ecol. 8:1683, 1999. (2) A. M. Idris and J. K. Brown. Phytopathology 88:648, 1998.

Chino del tomate virus:Relationships to Other Begomoviruses and Identification of A-Component Variants that Affect Symptom Expression

Phylogenetic and distance analyses place Chino del tomate virus (CdTV) in the New World clade of begomoviruses and indicate that CdTV and Tomato leaf crumple virus (TLCrV) are closely related strains of the same virus. One cloned CdTV A component (pCdTV-H6), when inoculated to tomato with the B component (pCdTV-B52), produced mild symptoms and low DNA titers. Another cloned CdTV A component (pCdTV-H8), when coinoculated to tomato with the B component, produced moderate leaf curling and veinal chlorosis similar to that of TLCrV. Coinoculation of both CdTV A components and the B component to tomato produced wild-type chino del tomate (CdT) disease symptoms consisting of severe leaf curling, veinal and interveinal chlorosis, and stunting. The two CdTV A components were nearly identical, except at nucleotide positions 1,722 and 2,324. The polymorphism at nucleotide 1,722 resulted in a change at Rep amino acid 261. The second polymorphism at nucleotide 2,324 resulted in changes at Rep amino acid 60 and AC4 amino acid 10. Two chimeric A components constructed by reciprocal exchange of a fragment bearing the polymorphic site at nucleotide 1,722 were evaluated for symptom phenotype. One chimeric A component (pCdTV-H86) produced wild-type CdT symptoms when coinoculated to tomato with the B component. The reciprocal chimeric A component (pCdTV-H68), when coin-oculated to tomato with the B component, also produced severe leaf curling, veinal chlorosis, and stunting. However, pCdTV-H68 induced less obvious interveinal chlorosis than wild-type or pCdTV-H86. Examination of A component genotypes recovered from tomato coinoculated with pCdTV-H6 and pCdTV-H8 indicated that recombination occurred to produce a genotype identical to pCdTV-H86. These results indicate that subtle genotypic variation has significant effects on symptom expression and may explain phenotypic differences observed among isolates and cloned DNAs of CdTV and TLCrV.

First Report of a Bean-Infecting Begomovirus from Macroptilium lathyroides in Puerto Rico That Is Distinct from Bean Golden Mosaic Virus

Bean golden mosaic begomovirus (BGMV) was long suspected to cause bright yellow mosaic symptoms in Macroptilium lathyroides (L.), a weed common to Puerto Rico. M. lathyroides plants exhibiting bright yellow mosaic symptoms were collected from Puerto Rico during 1994 to 1999, and the biotic and molecular characteristics of the suspect begomovirus were determined. Symptoms in M. lathyroides, indistinguishable from those observed in field-infected plants, were reproducible by whitefly transmission (Bemisia tabaci type B) and biolistic inoculation of leaf extracts (1). In bean, Phaseolus vulgaris (L.) 'Topcrop,' the M. lathyroides virus caused green-yellow mosaic foliar symptoms and stunting, reminiscent of symptoms caused by BGMV from Puerto Rico (BGMV-PR). However, biolistic- or whitefly-mediated inoculation of M. lathyroides with BGMV-PR resulted in no discernible infection. Sequence analysis (2) of the coat protein (CP) gene (AF176092) and common region of the A (CR-A) (AF176093) and B (CR-B) (AF176094) components of the virus from M. lathyroides indicated that these sequences shared only 77.3 to 79.3% and 62.4 to 68.8% identity, respectively, with BGMV from the Dominican Republic, Honduras, Guatemala, Jamaica (JAM), and PR. Alignment of the M. lathyroides virus CP sequence with other well-studied begomoviruses indicate its closest relative is BGMV-PR (82%) and that it shares less than 73% identity with partial CP sequences of Macroptilium golden mosaic virus-JAM (AF089839, AF089840). The directly repeated CR sequences of the M. lathyroides virus, putatively involved in AC1 binding, are TGGTGACTGGTG and are distinct from TGGAGACTGGAG, the analogous direct repeat in BGMV-PR. We provisionally designate the new, previously undescribed begomovirus species from M. lathyroides, Macroptilium mosaic virus (MaMV). Results indicate MaMV-PR and BGMV are distinct, bean-infecting begomoviruses from the Caribbean and that MaMV-PR may pose a new threat to bean production, particularly where the type B vector is established. References: (1) J. K. Brown and R. Ryan. Phytopathology 81:1217, 1991; (2) A. M. Idris and J. K. Brown. Phytopathology 88:648, 1998.

Mutations of the p53 gene in oral squamous-cell carcinomas from Sudanese dippers of nitrosamine-rich toombak and non-snuff-dippers from the Sudan and Scandinavia

Using PCR-SSCP/DNA sequencing methods, we analyzed 14 oral squamous-cell carcinomas (OSCCs) and 8 pre-malignant oral lesions from different Sudanese patients for prevalence of mutations in exons 5 to 9 of the p53 gene in relation to toombak-dipping status. OSCCs (14 from Sudan, 28 from Scandinavia), and 3 pre-malignant oral lesions from Sudanese non-dippers were used as controls. A statistically significant increased incidence in mutations of the p53 gene was found in OSCCs from toombak dippers (93%; 13/14), as compared with those from non-dippers in Sudan (57%; 8/14) and in Scandinavia (61%; 17/28) respectively. In OSCCs from dippers, mutations were found in exons 5 to 9, while in those from non-dippers they were found in exons 5, 7, 8, 9, and no mutations were found in exon 8 in any of the OSCCs from Sudan. Certain types of mutations, however, were similar with respect to exposure to toombak. OSCCs from dippers showed 15 transversions, 9 transitions, 3 insertions and one deletion, compared with 7 transversions, 2 transitions and one deletion found in OSCCs from Sudanese non-dippers, and 9 transversions, 17 transitions and 2 insertions found in those from non-dippers in Scandinavia. No mutations were found in any of the non-malignant oral lesions in relation to dipping or non-dipping status. These findings suggest that (i) the use of toombak plays a significant role in induction of increased p53 gene mutations, (ii) mutations observed were similar to those induced by tobacco-specific N-nitrosamines (TSNAs) in experimental animal models and those already reported in toombak dippers, (iii) types of mutations associated with TSNAs were similar in the exposed and the control groups, (iv) a novel mutation in exon 6 was found in the OSCCs from toombak dippers, (v) the p53 exons 5 (codon 130), 6 (codons 190, 216) and 7 (codons 229, 249, 252) mutations are probable hot spots for toombak-related OSCCs. Further studies are necessary to validate the increased incidence and exon locations of the p53-gene mutations as a biomarker of malignant transformation in populations in which the oral use of tobacco is habitual.

Biotic, molecular, and phylogenetic characterization of bean calico mosaic virus, a distinct begomovirus species with affiliation in the squash leaf curl virus cluster

ABSTRACT Bean calico mosaic virus (BCMoV), a whitefly-transmitted geminivirus from Sonora, Mexico, was purified, and the genome components were cloned and sequenced. Purified viral fractions and cloned genome components were infectious by biolistic inoculation to bean, completing Koch's postulates for both. The B biotype of the whitefly Bemisia tabaci efficiently transmitted both native virus and progeny virus derived from cloned DNA inoculum. Host ranges of native virus and of progeny virus derived from cloned DNA were identical based upon whitefly and biolistic mediated transmission, respectively. BCMoV has a relatively wide experimental host range among begomoviruses known to infect bean, encompassing genera and species within the Fabaceae, Malvaceae, and Solanaceae. BCMoV has a bipartite genome, as do other New World begomoviruses. BCMoV DNA-A shared highest nucleotide sequence identities with squash leaf curl virus-E strain (SLCV-E) and cabbage leaf curl virus (CaLCV) at 80.1 and 80.7%, respectively. BCMoV DNA-B shared highest nucleotide sequence identity with SLCV-E at 70.7%. The common region (CR) sequences of BCMoV and SLCV-E are 73 to 76% identical; however, modular cis-acting elements within the CR involved in replication origin function and recognition are 100% conserved. Phy-logenetic analysis indicated that BCMoV DNA-A shares a most recent common ancestor with the DNA-A of two viruses that also occur in the Sonoran Desert, SLCV-E and Texas pepper virus (TPV-TAM), and CaLCV from Florida. In contrast, a phylogenetic analysis indicated that BCMoV DNA-B shares a most recent common ancestor with SLCV-E; whereas DNA-B of CaLCV clustered in a separate clade with pepper hausteco virus. Collectively, biological and molecular characteristics indicate that BCMoV is a distinct begomovirus species with the northernmost distribution of any begomovirus isolated from bean in the Americas. Furthermore, the phylogenetic relationships of begomovirus cognate components are not necessarily identical, suggesting that DNA-A and DNA-B of some begomoviruses may have different evolutionary histories.

First Report of Chino del Tomate and Pepper Hausteco Geminivurses in Greenhouse-Grown Tomato in Sonora, Mexico

Tomato plants grown in commercial greenhouses in Sonora, Mexico, developed either yellow mosaic, leaf curling, and stunting (phenotype 1; 20 to 35%) or chlorosis and a feathery appearance of leaves (phenotype 2; 15 to 25%) in December 1997 and again in October 1998. Polymerase chain reaction (PCR) with diagnostic primers (prAV324 and prAC889) that amplify an approximately 576-bp fragment of the coat protein (CP) gene of whitefly-transmitted geminiviruses indicated the presence of a begomovirus. Biolistic inoculation of tomato seedlings with RNase-treated extracts of three symptomatic tomato samples, each, resulted in reproduction of disease symptoms. With PCR primers prAV2644 and prAC1154 (1), the entire CP (approximately 776 bp) and its flanking sequences were amplified from extracts of symptomatic tomato, and amplicons were cloned and sequenced. Comparisons of a minimum of three CP gene sequences from each phenotype revealed the presence of at least two begomoviruses. The phenotype 1-associated CP gene shared 92.6, 86.2, and 85.3% identity with the CP sequence of chino del tomate (CdTV) [AF106936], tomato mottle, and abutilon mosaic geminiviruses, respectively. The CP sequence associated with phenotype 2 was 94.6, 77.1, and 77.1% identical to pepper hausteco (PHV) [X70418], bean golden mosaic-Guatemala (BGMV-GU), and Texas pepper (TPV) gem-iniviruses, respectively. Previously, CdTV was reported from tomato in Chiapas, Morelos, Sinaloa, and Tamaulipas, Mexico, while PHV has been identified in Guanajuato, Quintana Roo, Sinaloa, and Tamaulipas, Mexico, and in Texas (2). This is the first report of CdTV-like (>92% identity) and PHV-like (>94% identity) geminiviruses associated with greenhouse-grown tomatoes in Sonora, Mexico. References: (1) A. M. Idris and J. K. Brown. Phytopathology 88:648, 1998; (2) I. Torres-Pacheco et al. Phytopathology 86:1186, 1996.

First Report of Sinaloa Tomato Leaf Curl Geminivirus in Costa Rica

In October 1998, geminivirus-like symptoms were widespread in tomato plantings near Turrialba, Costa Rica. Isolates from several fields were experimentally transmitted to tomato seedlings with whiteflies from a Bemisia tabaci (Genn.) colony maintained at CATIE, which resulted in interveinal chlorosis and leaf curling symptoms indistinguishable from those observed in the field. Total DNA was extracted from leaves of 16 of these experimentally inoculated plants and assayed by polymerase chain reaction (PCR) for the presence of begomovirus DNA with the degenerate primers AV324 and AC889 (2) to amplify the core region of the coat protein gene (core Cp). PCR yielded the expected size core Cp fragment (576 bp) from 16 of 16 samples. The core Cp fragments of six samples were cloned and sequenced. A comparison of the core Cp sequences with reference begomovirus sequences indicated all Costa Rican isolates were >95% identical to Sinaloa tomato leaf curl geminivirus reported in 1994 from Sinaloa, Mexico (STLCV-SINALOA). Virus identity was confirmed by multiple sequence alignments of the viral coat protein gene (Cp) and the common region (CR) sequences of A and B components (CR-A and CR-B), respectively, with analogous reference begomovirus sequences. Cp and CRs were obtained by PCR, and amplicons were cloned and sequenced as described (1). The Cp open reading frame (ORF; 756 nucleotides) (AF110515) identified within the A component amplicon shared 92.9% sequence identity with STLCV-SINALOA Cp (AF040635). The CR sequences of the A (AF1150516) and B (AF110517) components (163 nucleotides) shared 98.2% sequence identity with each other, suggesting that they were amplified from the cognate A and B components of the same virus. Further, the CR-A and CR-B components contained the same putative Rep binding site, TGGGGT-AA-TGGGGT, which was also identical to that of STLCV-SINALOA. The mean percent divergences between viral Cp and CR amplicons (n = 6+) ranged from 98 to 100%. Collectively, STLCV-like symptoms in tomato, >92% identity between viral Cp sequences, and identical CR iterons indicate that the Costa Rican tomato virus is STLCV, or a closely related strain. This is the first report of an STLCV-like begomovirus in tomato in Costa Rica (STLCV-CR). References: (1) A. M. Idris and J. K. Brown. Phytopathology 88:648, 1998. (2) S. D. Wyatt and J. K. Brown. Phytopathology 86:1288, 1996.

Characterization of tobacco geminiviruses in the Old and New World

Biological differences and molecular variability between six phenotypically distinct tobacco-infecting geminivirus isolates from southern Africa (Zimbabwe) and Mexico were investigated. Host range studies conducted with tobacco virus isolates ZIM H from Zimbabwe and MEX 15 and MEX 32 from Mexico indicated all had narrow host ranges restricted to the Solanaceae. Alignment of coat protein gene (CP) and common region (CR) sequences obtained by PCR, and phylogenetic analysis of the CP sequences indicated Zimbabwean isolates were distantly related to those from Mexico and that geographically proximal isolates shared their closest affinities with Old and New World geminiviruses, respectively. Zimbabwean isolates formed a distinct cluster of closely related variants (> 98% sequence identity) of the same species, while MEX 15 segregated independently from MEX 32, the former constituting a distinct species among New World geminiviruses, and the latter being a variant, Texas pepper virus-Chiapas isolate (TPV-CPS) with 95% sequence identity to TPV-TAM. Results collectively indicated a geographic basis for phylogenetic relationships rather than a specific affiliation with tobacco as a natural host. MEX 15 is provisionally described as a new begomovirus, tobacco apical stunt virus, TbASV, whose closest CP relative is cabbage leaf curl virus, and ZIM isolates are provisionally designated as tobacco leaf curl virus, TbLCV-ZIM, a new Eastern Hemisphere begomovirus, which has as its closest relative, chayote mosaic virus from Nigeria.

The Swedish snus and the Sudanese toombak: are they different?

In Sweden, snuff (locally known as snus), was introduced since the year 1637. Presently, Sweden has the highest per capita consumption and sale figures of snuff in the world, and the habit is becoming increasingly popular. Snus is manufactured into a dry form used in the nasal cavity and a moist form used in the oral cavity. Snus manufactured for oral use is a moist ground tobacco of Dark Kentucky or Virginia species mixed with an aqueous solution of water and other blending ingredients. This form of snuff is found in two types: (1) loose and (2) portion-bag-packed. These are the most widely used. The loose moist form (1-2 g a quid) is the most popular type consumed by 73% of the males, followed by the portion-bag-packed form (0.5-1 g a quid), consumed by 13% of the males, while 14% of the males are mixed users. The majority of snus users place the quid in the vestibular area of the upper lip, and the prevalence among persons 15 years of age or older in 15.9% among males and 0.2% among females. The pH of snus has declined from a previous range of 8-9 to a range of 7.8-8.5, moisture content ranges 35-60% and nicotine content is in the order of 5-11 mg/g dry wt tobacco-specific N-nitrosamines (TSNAs) in micrograms (N'-nitrosonornicotine: NNN 5-9; 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone: NNK 1-2; N'-nitrosoanatabine: NAT 2-5). In the Sudan, snuff, locally known as toombak, was introduced approximately 400 years ago. It is always processed into a loose moist form, and its use is widespread in the country. Tobacco used for manufacture of toombak is of the species Nicotiana rustica, and the fermented ground powder is mixed with an aqueous solution of sodium bicarbonate. The resultant product is moist, with a strong aroma, highly addictive and its use is widespread particularly among males. Its pH range is 8-11, moisture content ranges 6-60% and nicotine content is from 8 to 102 mg/g dry wt, and TSNAs contents in micrograms (NNN 420-1 550; NNK 620-7 870; NAT 20-290). Snus and toombak dippers develop a clinically and histologically characteristic lesion at the site of dipping. Probably due to control of the TSNAs in snus, this type of snuff is associated with a lower risk of cancer of the oral cavity (relative risk: RR 5-6-fold), whereas the risk for cancer of the oral cavity among toombak users was high (RR 7.3-73.0-fold). In conclusion, the two snuff products significantly differ in many aspects. Most notable differences are tobacco species, fermentation and ageing, nicotine and TSNAs content, pH, expression of the p53 tumour suppressor gene, and keratin types 13, 14, and 19. It was, therefore, the object of the present study to highlight the oral health hazards of toombak, and to compare it with snus regarding the aforementioned differences.

Expression of keratin 13, 14 and 19 in oral squamous cell carcinomas from Sudanese snuff dippers: lack of association with human papillomavirus infection

In stratified squamous epithelia, altered expression of keratins (Ks) is one possible marker of malignant potential. In the epithelium of the uterine cervix, presence of human papillomaviruses (HPVs) is increasingly regarded as a marker of risk for cervical cancer. However, a similar role in oral cancer and precancer remains controversial. To address these questions, formalin-fixed, paraffin-embedded oral carcinomas from Sudanese snuff dippers (n=14) and oral carcinomas from Sudanese (n=14), Swedish (n=19) and Norwegian (n=41) non-snuff dippers were examined by immunohistochemistry for expression of K types 13, 14 and 19 using monoclonal antibodies. HPV infection was searched for in all the carcinomas by in situ hybridization (ISH) using the cocktail HPV OmniProbe and the ViraType probe. Carcinomas from Sudanese (snuff dippers/non-snuff dippers) were also examined for HPV infection by polymerase chain reaction (PCR) using the general HPV primers GP5+/GP6+. For the oral carcinomas from snuff dippers, moderate to intense expression of K13 (71%; 10/14), K14 (86%; 12/14) and K19 (93%; 13/14) was found. For the oral carcinomas from non-snuff dippers, weak to moderate expression of K13 (64%; 47/74), K14 (43%; 32/74) and K19 (45%; 33/74) was found. HPV DNA was not detected in any of the carcinomas from three countries when examined by ISH. The Sudanese (from snuff dippers/non-snuff dippers) oral carcinomas were also negative for HPV DNA with the PCR. The present study shows that (i) there is a high level of expression of K13, K14 and K19 in oral carcinomas from snuff dippers compared to those from non-snuff dippers, (ii) this high level of expression may arise from dysregulation of keratinocyte proliferation and maturation caused by damaging effects of snuff, (iii) the HPV genome is not found in Sudanese (snuff dippers/non-snuff dippers), Swedish or Norwegian oral carcinomas, and (iv) this may suggest that these viruses do not play a prominent role in the aetiology of oral carcinomas from these countries.

Toombak use and cigarette smoking in the Sudan: estimates of prevalence in the Nile state

BACKGROUND

Survey data on the prevalence of use of oral snuff (toombak) and cigarette consumption according to various demographic factors are needed in the Sudan.

METHODS

A house to house cross-sectional survey of a random population sample of 4,535 households was performed. Of the 23,367 household members identified, 21,648 (92.6%) eligible individuals were questioned about tobacco use.

RESULTS

Among children and adolescents (4-17 years) prevalence of tobacco use was quite low (2%, range 1-2%), but there was an abrupt increase up to 25% in late adolescence. Among the adult population aged 18 years and older the prevalences of toombak use (34%) and cigarette smoking (12%) among males were significantly higher than among females (2.5 and 0.9%, respectively). The prevalence of toombak use among the male population aged 18 years and older was significantly higher in the rural than in the urban areas (35% vs 24%), while cigarette smoking had a higher prevalence in urban areas (18% vs 12%). The highest rates of toombak use were found in rural areas among the male population ages 30 years and older (mean 46.6%, range 45-47%).

CONCLUSIONS

In view of the high prevalence of tobacco use, especially of toombak, among the population surveyed, there is an urgent need to educate the public on the health consequences of these habits.

Sinaloa Tomato Leaf Curl Geminivirus: Biological and Molecular Evidence for a New Subgroup III Virus

ABSTRACT The biological and molecular properties of Sinaloa tomato leaf curl virus (STLCV) were investigated in line with the hypothesis that STLCV is a previously uncharacterized, whitefly-transmitted geminivirus from North America. STLCV causes yellow leaf curl symptoms in tomato and yellow-green foliar mottle in pepper. Five species belonging to two plant families were STLCV experimental hosts. STLCV had a persistent relationship with its whitefly vector, Bemisia tabaci. Polymerase chain reaction fragments of STLCV common region (CR) sequences of the A or B genomic components and the viral coat protein gene (AV1) were molecularly cloned and sequenced. The STLCV A- and B-component CR sequences (174 nucleotides each) shared 97.9% identity and contained identical cis elements putatively involved in transcriptional regulation and an origin of replication (the AC cleavage site within the loop of the hairpin structure and two direct repeat sequences thought to constitute the Rep binding motif), which collectively are diagnostic for subgroup III geminiviruses. The STLCV CR sequence shared 23.1 to 77.6% identity with CR sequences of representative geminiviridae, indicating the STLCV CR sequence is unique. Molecular phylogenetic analysis of CR or AV1 sequences of STLCV and the respective sequences of 31 familial members supported the placement of STLCV as a unique bipartite, subgroup III virus most closely related to other viruses from the Western Hemisphere. STLCV is provisionally described as a new species within the genus Begomovirus, family Geminiviridae.

Characterization of an amorphous deposit in the lamina propria in oral snuff users in the Sudan as collagen

Histological and ultrastructural features of 25 oral snuff dipper's lesions with distinctive subepithelial hyaline deposits were investigated. Periodic acid-Schiff reaction with and without diastase digestion demonstrated the presence of glycogen and other carbohydrates, but histochemical stains for normal collagen, elastin and fibrin showed a weak variable reactivity of the deposit. Although in 7/25 cases the deposit was in close proximity to labial salivary glands and on occasions ducts were found within the deposit, the presence of mucin was not a consistent feature. Congo red staining and immunohistochemical investigation with an anti-amyloid antibody did not support the previous contention that such deposits were amyloid in nature. Immunohistochemically, collagen antibodies also provided negative results, but ultrastructural features of three biopsies studied suggest that the bulk of this deposit is made up of collagen, as typical cross-striated fibrils were found. The pathogenesis of this deposit could therefore be interpreted as over-production and/or reduced turnover of collagen by resident fibroblasts, which is further altered by the ingredients of toombak. The deposit does not appear to be a secretory product.

Expression of keratin 13, 14 and 19 in oral hyperplastic and dysplastic lesions from Sudanese and Swedish snuff-dippers: association with human papillomavirus infection

Changes in the expression of keratins (Ks), indicating disturbed tissue differentiation, is one possible marker of malignant potential in stratified squamous epithelia. The presence of human papillomaviruses (HPVs) in the epithelium of the uterine cervix is increasingly regarded as a marker of risk for cervical cancer: However, a similar role in oral cancer and precancer remains controversial. To address these questions, potentially malignant oral mucosal lesions from Sudanese (9 hyperplasias/40 dysplasias) and Swedish (15 hyperplasias) snuff-dippers were examined by immunohistochemistry for expression of K types 13, 14 and 19 using monoclonal antibodies directed against each. HPV infection was searched for by in situ hybridization (ISH) using the cocktail HPV OmniProbe and the ViraType probe. For the Sudanese lesions, moderate to intense expression of both K13 (basal, basal/intermediate, basal/intermediate/superficial and intermediate/superficial cell layers) and K14 (basal, basal/intermediate cell layers) was found in 49/49 (100%). For the Swedish lesions, weak to moderate expression of K13 (basal, basal/intermediate cell layers) was found in 12/15 (80%) and 10/15 (67%), respectively. In the Sudanese lesions, expression of K13 showed a distinct pattern through the oral mucosa and its verrucous projections, with an increase towards the superficial cell layers of dysplastic, but not hyperplastic epithelium. K19 was expressed in the basal cell layer in 16/49 (33%) of the Sudanese lesions, while all the Swedish lesions were negative. HPV was found in only 2 Sudanese cases, both of which harboured both type 6 and type 11: both these cases demonstrated mild epithelial dysplasia, The present study shows that a) there is a high prevalence of expression of both K13 and K14 in oral lesions from Sudanese toombak dippers indicating dysregulation of keratinocyte maturation b) one-third of the Sudanese oral lesions expressed K19, regarded as a basal keratin representing epithelial dedifferentiation, which may prove to be a valuable risk marker in follow-up studies c) HPV genome is found infrequently in oral lesions from Sudanese toombak-dippers, suggesting that these viruses may not play a prominent role in the early stages of carcinogenesis in these subjects. These markers were less often expressed in the Swedish lesions, consistent with their much lower rate of malignant transformation.

Immunohistochemical detection of p53 in non-malignant and malignant oral lesions associated with snuff dipping in the Sudan and Sweden

Immunohistochemistry was used to examine the expression of p53 in pre-malignant oral lesions and oral squamous-cell carcinomas (SCCs) from Swedish and Sudanese snuff-dippers, as well as in pre-malignant oral lesions and oral SCCs from non-snuff-dippers from the Sudan, Sweden and Norway. Of the 14 SCCs from Sudanese snuff-dippers, 21% (3/14) expressed p53. Of the 14, 60 and 41 SCCs from non-snuff-dippers from the Sudan, Sweden and Norway, 64% (9/14), 65% (39/60) and 68% (28/41) expressed p53, respectively. A statistically significant difference in expression of p53 was found in SCCs from Sudanese snuff-dippers compared to those from non-snuff-dippers from all/or any of the 3 countries. None of the suspected pre-malignant oral lesions from Sudanese snuff dippers or non-snuff-dippers expressed p53. Only 2 out of the 15 oral fibro-epithelial hyperplastic lesions from Swedish snuff-dippers expressed p53. Some of the oral epithelial dysplastic lesions, as well as the carcinoma in situ lesions from Norwegian non-snuff-dippers, expressed p53, while the oral fibro-epithelial hyperplastic lesions did not. The low relative frequency of p53 expression found in oral SCCs from snuff-dippers compared to those from non-snuff-dippers might suggest differences in mechanisms of oncogenic action induced by snuff. Alternatively, the pathogenesis of malignant oral lesions from snuff-dippers may follow a p53-independent pathway. In view of the unusually high levels of the tobacco-specific nitrosamines (TSNA) found in the type of snuff used in the Sudan, investigations of p53 mutations or oncogenes are needed.

Toombak-associated oral mucosal lesions in Sudanese show a low prevalence of epithelial dysplasia

Clinical (n = 281) and histopathological (n = 141) characteristics of toombak-associated oral mucosal lesions detected in an epidemiological study in northern Sudan in 1992/93 are described. The lesional site in the majority of toombak users was the anterior lower labial groove and the lower labial mucosa. 4 degrees (1-4) of clinical severity of lesions, similar to those used to characterise Swedish snuff-dipper's lesion, were applied. An association between the severity of mucosal lesions and a longer lifetime duration (> 10 years) of toombak use was found, but the severity was not related to the daily frequency of the habit. Parakeratosis, pale surface staining of the epithelium and basal cell hyperplasia were commonly observed, but epithelial dysplasia was infrequent (10/141). The most significant observation was a PAS-positive amorphous deposit between the lamina propria and the submucosa, found in 25/141 biopsies. The clinical and histopathological features of toombak lesions are closely similar to Swedish moist snuff-dipper's lesions and this may reflect the high alkalinity of these products, resulting in an alkaline burn on the oral mucosa following chronic exposure. The low prevalence of epithelial dysplasia implies a low risk of malignant transformation. Nevertheless, the high concentrations of tobacco-specific nitrosamines present in toombak, and the high prevalence of oral cancer in Sudan, mandate biopsy and careful histopathological analysis of any such lesions detected in habitues.

Toombak dipping and cancer of the oral cavity in the Sudan: a case-control study

To investigate the possible causal association between squamous-cell carcinomas of the oral cavity and use of toombak, we retrospectively compared the history of use of this substance in 375 patients with squamous-cell carcinomas of the lip, buccal cavity and floor of mouth, and 271 patients with squamous carcinomas of the tongue, palate and maxillary sinus, with 204 patients exhibiting non-squamous oral and non-oral malignant neoplasms and 2,820 individuals who had no malignancy, selected from the general population. The study revealed that the high prevalence of oral cancer in the Sudan is largely due to chronic use of toombak. The adjusted ORs associated with toombak dipping for the first case group, cancer of the lip, buccal cavity and floor of mouth in comparison with the hospital and population control groups, were 7.3 and 3.9 (95% confidence limits, 4.3-12.4 and 2.9-5.3) respectively and among long-term users the adjusted ORs were 11.0 and 4.3 (95% confidence limits, 4.8-25.1 and 2.9-6.3) respectively. The elevated risk found when investigating intra-oral cancers of sites in direct contact with toombak quid compared to those with little or no contact, confirms the hypothesis that direct contact with tissues is an important factor in tobacco carcinogenesis in the mouth. The increased risk associated with the use of toombak is of particular concern in view of its wide consumption in the Sudan.

Descriptive epidemiology of oral neoplasms in Sudan 1970-1985 and the role of toombak

Data from 1,916 cases of oral neoplasms occurring in the Sudan in a 16-year period, from January 1970 to December 1985, were retrieved and analysed. The study revealed a relatively high frequency of oral neoplasms in comparison with neighbouring countries. In this study, squamous-cell carcinoma was the most common oral malignancy (66.5%), followed by tumours of the salivary gland (14.7%), neoplasms of nonodontogenic and non-epithelial origin (9.6%) and odontogenic neoplasms (8.6%). Men had a higher frequency than women. The older age group of both genders showed a relatively high frequency of squamous-cell carcinoma. Among northern Sudanese there was a high rate of squamous-cell carcinoma, while southern Sudanese showed a high rate of odontogenic and salivary-gland neoplasms. The use of toombak has been stated to play a major role in the aetiology of oral squamous-cell carcinoma in the Sudan, and is suspected to be associated with neoplasms of the salivary glands.

Toombak: a major risk factor for cancer of the oral cavity in Sudan

BACKGROUND

Snuff dipping as practiced in North America and Western Europe is causally associated with cancer of the oral cavity and pharynx. In the Sudan, natives use local Nicotiana rustica, a tobacco species with high levels of nicotine and nornicotine, to prepare their own snuff which they call toombak. The finely ground tobacco leaves are mixed with sodium bicarbonate, water is added, and a paste is made. The resulting "saffa" is placed in the oral vestibule where it remains up to several hours. In general, a saffa is replaced 10-30 times per day.

METHODS

A cross-sectional survey was initiated for establishing the extent of toombak dipping in the Northern Sudan. Using earlier published methods, toombak and the saliva of toombak dippers were analyzed for the major carcinogens, the nicotine- and nornicotine-derived tobacco-specific N-nitrosamines.

RESULTS

Survey data on the use of toombak in the Nile Province in the Northern Sudan encompass 2,000 households with 5,500 adults. About 40% of the males dip toombak, including 9% who are also cigarette smokers. The toombak habit is especially prevalent (> 45%) among males ages 40 years or older. Among women, toombak use is popular only in the older age groups, where up to 10% engage in the habit, whereas cigarette smoking is uncommon (< 1.5%). So far, only one descriptive study has dealt with toombak dipping and oral cancer. Among 62 patients with oral cancer 50 were toombak users; the majority of these had tumors at the site of contact with the tobacco, or in adjacent areas. Chemical analytical studies revealed that toombak contains at least 100-fold higher concentrations of the tobacco-specific N-nitrosamines (TSNA) than US and Swedish commercial snuff brands. The TSNA are by far the most powerful and most abundant carcinogens in snuff. Their concentrations in the saliva of toombak dippers are about the same as those in a solution that had been assayed in rats by twice daily swabbing of the oral cavity and had induced tumors of the cheek and palate.

CONCLUSION

The need for in-depth epidemiological studies and further laboratory research to prove that toombak chewing causes cancer is discussed. The data at hand point to the urgent need for educational programs and preventive measures against the use of toombak.