Potential impacts of climate change on geographical distribution of three primary vectors of African Trypanosomiasis in Tanzania's Maasai Steppe: G. m. morsitans, G. pallidipes and G. swynnertoni

In the Maasai Steppe, public health and economy are threatened by African Trypanosomiasis, a debilitating and fatal disease to livestock (African Animal Trypanosomiasis -AAT) and humans (Human African Trypanosomiasis—HAT), if not treated. The tsetse fly is the primary vector for both HAT and AAT and climate is an important predictor of their occurrence and the parasites they carry. While understanding tsetse fly distribution is essential for informing vector and disease control strategies, existing distribution maps are old and were based on coarse spatial resolution data, consequently, inaccurately representing vector and disease dynamics necessary to design and implement fit-for-purpose mitigation strategies. Also, the assertion that climate change is altering tsetse fly distribution in Tanzania lacks empirical evidence. Despite tsetse flies posing public health risks and economic hardship, no study has modelled their distributions at a scale needed for local planning. This study used MaxEnt species distribution modelling (SDM) and ecological niche modeling tools to predict potential distribution of three tsetse fly species in Tanzania’s Maasai Steppe from current climate information, and project their distributions to midcentury climatic conditions under representative concentration pathways (RCP) 4.5 scenarios. Current climate results predicted that G. m. morsitans, G. pallidipes and G swynnertoni cover 19,225 km², 7,113 km² and 32,335 km² and future prediction indicated that by the year 2050, the habitable area may decrease by up to 23.13%, 12.9% and 22.8% of current habitable area, respectively. This information can serve as a useful predictor of potential HAT and AAT hotspots and inform surveillance strategies. Distribution maps generated by this study can be useful in guiding tsetse fly control managers, and health, livestock and wildlife officers when setting surveys and surveillance programs. The maps can also inform protected area managers of potential encroachment into the protected areas (PAs) due to shrinkage of tsetse fly habitats outside PAs.

Spatial variation of African Trypanosomiasis burden depends on distribution of biotopes necessary for tsetse flies to thrive. Therefore, mapping the occurrence of the tsetse fly species is a useful predictor of African Trypanosomiasis transmission risk areas. Climate is a major determining factor for occurrence and survival of tsetse flies, the vector responsible for both HAT and AAT. Since resources for prevention and control of tsetse fly species and the disease they transmit are generally scarce in endemic settings, understanding potential impacts of climate change on tsetse fly species distribution in space and time is essential for informing coherent strategies for vector and disease control at a local scale.

In silico analysis of tkt1 from avian pathogenic Escherichia coli and its virulence evaluation in chickens

Extraintestinal pathogenic Escherichia coli (ExPEC) contain tktA and tktB which code for transketolases involved in the pentose phosphate pathway. Recent studies demonstrated that a third gene coding for transketolase 1 (tkt1) was located in a pathogenicity island of avian and human ExPEC belonging to phylogenetic group B2. In the present study, in silico analysis of tkt1 revealed 68% and 69% identity with tktA and tktB, respectively, of ExPEC and 68% identity with tktA and tktB of E. coli MG1655. The translated tkt1 shared 69% and 68% identity with TktA and TktB proteins, respectively, of ExPEC and E. coli MG1655. Phylogenetically, it is shown that the three genes (tktA, tktB and tkt1) cluster in three different clades. Further analysis suggests that tkt1 has been acquired though horizontal gene transfer from plant-associated bacteria within the family Enterobacteriaceae. Virulence studies were performed in order to evaluate whether tkt1 played a role in avian pathogenic E. coli CH2 virulence in chickens. The evaluation revealed that mutant virulence was slightly lower based on LD50 when compared to the wild type during infection of chickens, but there were no significant differences when the two strains were compared based on the number of deaths and lesion scores.

Investigations of the occurrence of Avibacterium paragallinarum infections in Uganda

Investigations were conducted to determine the occurrence of Avibacterium paragallinarum in poultry in Uganda. A total of 710 each of bacteriologic and serum samples were taken from chickens and turkeys for demonstration of A. paragallinarum and antibodies. Samples for isolation of A. paragallinarum were also subjected to direct polymerase chain reaction (PCR) for demonstration of the organism's presence. Antibodies to A. paragallinarum were demonstrated in the sera using the hemagglutination inhibition test. A total of five isolates were recovered from two out of five commercial layer chicken farms investigated where suspected cases of infectious coryza were reported, and all of them belonged to Page's serovar C. PCR detected more positive samples (11/68) than did culture (5/68). Isolates were not recovered from free-range poultry nor were there any positive samples by PCR. The overall seroprevalence was 40.5% and the seroprevalence to serovars A, B, and C were 18%, 0.5%, and 22%, respectively. Antibodies to all Page's serovars A, B, and C were demonstrated in free-range chickens but only serovar C antibodies were demonstrated in commercial chickens. No antibodies were demonstrated in turkeys. This is the first time infectious coryza has been confirmed in Uganda and the causative agent, A. paragallinarum, isolated. A high seroprevalence observed in free-range chickens seems to indicate a subclinical infection under extensive village management conditions.

Virulence characterization ofAvibacterium paragallinarumisolates from Uganda

Avibacterium paragallinarum isolates from Uganda were characterized for their virulence by comparison of their pathogenicity and their resistance to serum. Pathogenicity was evaluated using commercial Hisex Brown layer chickens, local indigenous chickens, local turkeys and local guineafowls inoculated with 108 colony-forming units of Av. paragallinarum and comparing their overall mean disease scores over a period of 20 days. Persistence of the bacteria in the host and water was also investigated for a 60-day period by culture and polymerase chain reaction as well as use of sentinel chickens. Serum resistance was measured by comparison of the growth kinetics and survival indices at 3 and 6 h. There was no difference in the virulence of the isolates. Commercial layer chickens and local indigenous chickens were equally susceptible to challenge, while turkeys and guineafowls only showed transient mild signs and did not transmit infection. Turkeys and guineafowls did not acquire the infection when placed in contact with infected chickens. The isolates were resistant in normal chicken serum at both 3 and 6 h of incubation but were resistant at 3 h and sensitive at 6 h in turkey and guineafowl sera. The resistance of the isolates to serum correlated with their pathogenicity in the different hosts. No carrier status was demonstrated in this study using polymerase chain reaction and culture. The present study demonstrates that Ugandan Av. paragallinarum isolates are pathogenic to chickens with only transient signs in turkeys and guineafowls, and that serum resistance could be a subject for further investigation as a predictor of virulence of these bacteria. The role of turkeys and guineafowls in transmission of Av. paragallinarum was not demonstrated in the present investigation.

Differences in resistance toSalmonella entericaserovar Gallinarum infection among indigenous local chicken ecotypes in Tanzania

A study was conducted to evaluate the disease resistance potential in 105 chickens of six indigenous local chicken ecotypes in Tanzania by orally challenging 1-week-old chicks with 2.5 x 10(8) colony-forming units of virulent S. Gallinarum. For 14 days post infection, clinical signs, necropsy findings, antibody titres, packed cell volume, leukocyte population count, and viable bacterial cell counts in the liver and spleen were recorded. Clinical signs were recorded daily but other parameters were recorded on the day of infection, then on days 3, 6, 10 and 14 after infection. Clinical signs of fowl typhoid were evident in chickens from day 3 post infection and disappeared by day 9 post infection. Pathological lesions on sacrificed birds included enlargement of the liver and spleen with foci of necrosis on the liver, spleen and myocardium. The mean viable bacterial cell counts in the liver and spleen varied between ecotypes, although the differences were not statistically significant. There were significant differences in the leukocyte population in the peripheral blood, with one ecotype (Morogoro-medium) showing a consistent and significantly higher heterophil count compared with other ecotypes. It was concluded that there is a selectable resistance potential to S. Gallinarum among the local chicken ecotypes in Tanzania that may be attributable to non-specific host immune responses. Further studies are suggested.

Escherichia coli 0157: H7 reservoir, transmission, diagnosis and the African situation: a review

OBJECTIVES

To provide an overview of the current understanding of verotoxigenic Escherichia coli 0157:H7 (VTEC) and to describe clinical picture, reservoir, transmission and diagnosis and African situations of VTEC.

DATA SOURCE

A literature review was performed of major published series between 1980 and 2001 inclusive, using the PUB MED and MEDLINE search. Some earlier published series were also reviewed in instances where they directly led to the understanding of current review.

STUDY SELECTION

Data from laboratory studies on cultural and isolation, serological and molecular techniques are summarised in this review.

RESULTS

Verotoxigenic Escherichia coli 0157:H7 (VTEC) is an important cause of uncomplicated diarrhoea, bloody diarrhoea (BD) and haemolytic uremic syndrome (HUS) in developed countries. The incidence and importance of 0157: H7 (VTEC) infections in most developing countries are not known; however, 0157: H7 (VTEC) cases have been isolated from many sporadic cases of diarrhoea, BD and HUS, while several cases have also been associated with diarrhoeal disease outbreaks in Africa.

CONCLUSION

The morbidity and mortality associated with several recent outbreaks of VTEC disease have highlighted the threat these organisms pose to public health. For this reason, there is an increasing demand for improved diagnostic procedures for detection of VTEC in clinical specimen and in particular, in foods such as meat and dairy products in developing countries.

Phenotypes including immunocompetence in scavenging local chicken ecotypes in Tanzania

A study was conducted to determine the variations in physical characters and immunocompetence among scavenging local chicken ecotypes in Tanzania. Eighty-four adult scavenging local chickens from four eco-climatic regions of Tanzania were studied. Measurements of adult body weight, body length, shank length and egg weight and observations of plumage colour and pattern, earlobe colour, skin colour and the shape of the comb were conducted. The antibody response to sheep red blood cells, serum haemolytic complement and the cutaneous response to phytohaemagglutinin-P were assessed. Five ecotypes were identified and named Mbeya, Morogoro-medium, Ching'wekwe, Kuchi and Singamagazi. Singamagazi and Kuchi were significantly heavier, with longer shanks and heavier eggs than the other ecotypes. The average adult body weight for males ranged from 1621 g (Mbeya) to 2915 g (Singamagazi). Average female weights ranged from 1108 g (Morogoro-medium) to 2020 g (Singamagazi). Mean egg weights ranged from 37.65 g (Ching'wekwe) to 45.61 (Singamagazi). The Kuchi had mostly rose and walnut combs, while the other ecotypes were mostly single combed. In each ecotype there were chickens with a high or low antibody response to red blood cells, but there was a significant difference between the ecotypes.

Heterozygosity excess at the cattle DRB locus revealed by large scale genotyping of two closely linked microsatellites

A method for MHC DRB typing in cattle based on two closely linked and highly polymorphic microsatellites is described. The two microsatellites DRBP1ms and DRB3ms are located in intron 2 of the corresponding DRB gene. The very strong linkage disequilibrium between the two loci made it possible to establish DRB microsatellite haplotypes. The typing results with this method on reference samples followed closely that obtained with RFLP and direct sequence analysis of DRB3 exon 2. The method is well suited for large scale genotyping and was successfully applied for typing more than 600 unrelated animals representing 23 breeds. The data were used to test whether the observed DRB allele frequency distributions were consistent with that expected for selectively neutral alleles in populations at mutation-drift equilibrium. A significant heterozygosity excess was detected and there was an obvious trend across breeds towards a more even allele frequency distribution than expected. The deviation may be due to balancing selection acting on the DRB locus or by recent population bottlenecks.

Breed-associated resistance to tick infestation in Bos indicus and their crosses with Bos taurus

The relative resistance to tick infestation of zebu (Bos indicus) in comparison to crossbred (B. indicus x B. taurus) cattle was investigated. B. indicus breeds, all belonging to Tanganyika shorthorn zebu were Meru, Mbullu and Iringa red. Crossbreds were Meru x Friesian and Iringa red x Friesian. Parameters to distinguish between 'tick resistant' and 'tick susceptible' cattle were tick counts on naturally exposed animals, serum complement levels and delayed skin hypersensitivity response to phytohaemagglutinin. Results have shown that pure zebu cattle are less infested with ticks when compared to zebu-taurine crosses under identical field conditions. Zebu cattle also had significantly higher serum complement level than crossbred cattle. While serum complement and tick burden were negatively associated (r = -0.27, P < 0.001), the cutaneous response to phytohaemagglutinin did not vary with tick infestation. The influence of cattle breed on tick infestation and serum complement level is demonstrated.

The PCR typing of MHC-DRB genes in the sheep using primers for an intronic microsatellite: application to nematode parasite resistance

The strong association between polymorphisms in an intronic microsatellite and the coding sequences for (BoLA)-DRB3 genes, previously described for demonstrating alleles of class II major histocompatibility complex (MHC) in the cow, was examined in sheep to see if similar polymorphisms could be demonstrated in the DRB region of the MHC. The bovine primes LA53 and LA54, previously used to amplify the bovine DRB3 microsatellites, were used with DNA from Australian sheep, eight DRB alleles were identified by length polymorphisms of polymerase chain reaction (PCR) products amplified from the DRB microsatellite region. Incomplete amplification of both alleles was sometimes found for sheep DNA samples using bovine primers, so a modified primer (LA53b) was used, and found to amplify the microsatellite next to intron 2 of the MHC more reliably than the LA53 primer. Two additional primers (LA31 and LA32), used in amplification of the exon 2 region of bovine DRB3, were used in the sheep, and the PCR products were analysed by single-stranded conformation polymorphism (SSCP). These primers successfully amplified the variable region of the ovine DRB region coded by exon 2, and the SSCP technique demonstrated polymorphisms with sheep DNA. Family studies demonstrated the segregation of alleles, by amplification both of intronic microsatellites and of the exon 2 variable region. Close correspondence was found between the two regions for several alleles, suggesting that the intronic microsatellites were closely linked to DRB-variable region alleles. Three families of Merino sheep with different antibody responses to intestinal nematode parasites were examined. The sire group with the highest antibody levels possessed two microsatellite alleles of closely similar length (alleles 3 and 4) inherited from the sire and present in high frequency in the lambs. In contrast, the other two sires did not possess these two alleles and the alleles were in low frequency in their progeny. Further studies are required in unrelated sheep to confirm whether these two alleles are associated with resistance to nematode parasites.

A polymorphism in randomly amplified DNA that differentiates the Y chromosomes of Bos indicus and Bos taurus

A small number of west African Bos taurus cattle breeds, including the N'Dama, constitute a valuable genetic resource by virtue of their ability to remain productive under trypanosomiasis challenge. However, introgression of Bos indicus genes into the trypanotolerant breeds, particularly by introduction of zebu bulls, is a threat to this resource. This work describes the characterization and cloning of a bovine randomly amplified polymorphic DNA (RAPD) that is generated in polymorphic DNA (RAPD) that is generated in polymerase chain reaction (PCR) with the 10 base primer ILO1065 from Bos indicus male templates, but not from B. taurus male templates or female templates of either type. Male-specific sequences with homology to the RAPD also occur in B. taurus breeds. This suggests that the polymorphism may be due to base substitution(s) in an ILO1065 priming site, or insertion/deletion events either affecting priming sites or occurring between sites on the cattle Y chromosome. We have shown that cattle, whether of B. indicus or B. taurus phenotype, which possess a typically B. indicus metaphase Y chromosome on the basis of QFQ banding, have a B. indicus ILO1065-generated genotype. The ILO1065-primed RAPD can be used in a simple dot blot assay as a probe of RAPD-PCR products, to provide a convenient, reliable and effective means of detecting introgression of zebu genes in B. taurus cattle populations.

Characterization of Zebu cattle breeds in Tanzania using random amplified polymorphic DNA markers

A total of 141 short primers, of arbitrary nucleotide sequence, were used singly in polymerase chain reactions to amplify DNA fingerprints in pools of DNA representing three Zebu cattle breeds. Two primers, which discriminated between the breed-specific DNA pools were used further to amplify individual pool components in order to establish band frequencies of the amplified fingerprints. One of the primers (ILO 1127) amplified a RAPD fingerprint in 61% of TSZ animals but less than 6% in the other breeds, while another primer (ILO 1065) revealed a DNA sequence common to 89% of the Boran animals and less than 30% in the other two breeds. Bandsharing and mean average percentage difference calculated within and between the three breeds using RAPD fingerprint data showed a higher degree of homogeneity within than across the breeds and indicated measurable divergence between the three breeds. It is concluded that RAPD polymorphisms are useful as genetic markers for cattle breed differentiation.

Humoral factors of natural resistance of Bos indicus cattle selected for antibody titre to Brucella abortus

The concentration of lysozyme, total immunoglobulin and bactericidal activity were measured in sera of Bos indicus cattle, retrospectively screened for specific antibodies to Brucella abortus and classified as being positive reactors or negative reactors. In addition, the effect of complement in the sera was studied to demonstrate complement dependence of antibody-mediated bacterial killing. It was observed that, under the test conditions, serum bactericidal activity and concentration of total immunoglobulin were associated with high specific antibody levels (P less than 0.001). Furthermore, there was a slight decrease in the lytic activity of lysozyme in the sera of animals with high antibody titres.

Serum, disc and egg ELISA for the serodiagnosis of Salmonella gallinarum and S. enteritidis infections in chickens

An ELISA was evaluated for the serodiagnosis of fowl typhoid and paratyphoid due to Salmonella enteritidis in chickens. The hot phenol: water lipopolysaccharide (LPS) extract of Salmonella was used as the antigen. Chicken serum, eggs and discs impregnated with chicken blood were tested for the presence of antibodies against Salmonella factor 'O' 9 antigen. The substrate and chromogen used were hydrogen peroxide and orthophenylenediamine respectively. Serological results from the experimentally and naturally infected chickens showed close agreement between the conventional Serum Tube Agglutination Test (SAT) and serum ELISA while serum ELISA results were in close agreement with the egg and disc ELISA results. It was noted that ELISA was highly sensitive, convenient and versatile. It is concluded that ELISA, especially disc ELISA, ought to replace SAT for seroscreening chickens against S. gallinarum and other Salmonella Group D infections.

Production, immunoanalysis and selection of monoclonal antibodies for studies of polymorphism of bovine MHC class I antigens

Two monoclonal antibodies (MoAbs) were raised against bovine lymphocyte antigens of the major histocompatibility complex (MHC) for studies of the polymorphism of MHC class I antigens of African cattle. Immunoanalysis of lymphoid tissues and molecular weight data were used to characterize the epitopes seen by the MoAbs. Competitive binding assays indicated specificity of the MoAbs for two distinct epitopes. Application of the MoAbs for MHC typing of a cattle population showed that the epitopes were co-expressed on the target MHC antigen but occurred independently on non-target MHC antigens. It is concluded that, to obtain MoAbs for studies of MHC polymorphism, it is important to conduct large-scale analysis using immunoassays and population studies.