Threat of foreign arthropod-borne pathogens to livestock in the United States

Transboundary Tick and Tick-Borne Pathogen Threats to Cattle

Transboundary incursions of ticks and tick-borne pathogens are ever present concerns for US cattle industries. Global trade in livestock and wildlife, historic and emerging transboundary issues with endemic tick populations and pathogens, and migratory bird flyways are pathways of concern. Transboundary challenges are presented for the Asian long-horned tick and Theileria orientalis Ikeda, for 2 cattle fever tick species [Rhipicephalus (Boophilus) annulatus and R (B) microplus] and Babesia bigemina and B bovis, and for the tropical bont tick and Ehrlichia ruminantium.

Livestock and environmental characterization of Colombian municipalities: study of vesicular stomatitis

Amid the surge in data volume generated across various fields of knowledge, there is an increasing necessity for advanced analytical methodologies to effectively process and utilize this information. Particularly in the field of animal health, this approach is pivotal for enhancing disease understanding, surveillance, and management. The main objective of the study was to conduct a comprehensive livestock and environmental characterization of Colombian municipalities and examine their relationship with the distribution of vesicular stomatitis (VS). Utilizing satellite imagery to delineate climatic and land use profiles, along with data from the Colombian Agricultural Institute (ICA) concerning animal populations and their movements, the research employed Principal Component Analysis (PCA) to explore the correlation between environmental and livestock-related variables. Additionally, municipalities were grouped through a Hierarchical Clustering process. The assessment of risk associated with VS was carried out using a Generalized Linear Model. This process resulted in the formation of four distinct clusters: three primarily characterized by climatic attributes and one predominantly defined by livestock characteristics. Cluster 1, identified as "Andino" due to its climatic and environmental features, exhibited the highest odds ratio for VS occurrence. The adopted methodology not only provides a deeper understanding of the local population and its context, but also offers valuable insights for enhancing disease surveillance and control programs.

Identification and distribution of Rhipicephalus microplus in selected high-cattle density districts in Uganda: signaling future demand for novel tick control approaches

BACKGROUND

Rhipicephalus (Boophilus) microplus (Canestrini, 1888), the Asian blue tick, is a highly invasive and adaptable ectoparasite. This tick species has successfully established itself in most regions of the world, with movement of cattle being a major driver for its spread. In the recent past, R. microplus ticks have been reported in three districts of Uganda. Information on its spread and distribution are vital in deepening our understanding of the ecological scenarios that lead to tick persistence and in the formulation of control strategies. This is especially important in the cattle-dense districts.

METHODS

We randomly collected tick specimens from 1,461cattle spread across seven cattle dense districts located in the Central, Karamoja and West Nile regions of Uganda from January to September 2020. The ticks were identified using standard morpho-taxonomic keys and the R. microplus tick species identities were confirmed by sequencing of the ITS2 region, 12S rRNA and 16S rRNA genes and phylogenetic analyses.

RESULTS

Adult ticks (n = 13,019) were collected from 1,461 cattle. Seventeen tick species were identified based on morpho-taxonomic keys and the majority (47.4%; n=6184) of these were R. appendiculatus. In total, 257 R. microplus ticks were found infesting cattle in 18 study sites in the districts of Amudat, Kaabong, Napak (Karamoja region) and Arua (West Nile region). The identity of R. microplus was confirmed using molecular technics. No R. microplus tick was recorded in the districts of Lyantonde and Nakaseke (Central region). Arua district accounted for 82.1% (n=211) of the R. microplus ticks recorded followed by Napak district at 16.3% (n=42), while Amudat and Kaabong districts accounted for 1.5% (n=4). Rhipicephalus microplus and R. decoloratus co-existed in 6 of the 13 study sites in Arua district, while in another 6 study sites, no R. decoloratus was recorded. In the Karamoja region districts R. decoloratus co-existed with R.microplus. Of the total 618 ticks belonging to four species of the subgenus Boophilus recorded in this study, R. decoloratus accounted for 50.04% (n=334), followed by R. microplus at 41.58% (n=257), R. geigyi at 2.75% (n=17) and R. annulatus at 1.61% (n=10). In the districts of Amudat, Kaabong and Napak, R. decoloratus was more dominant (76.1%; n=179) of the three Rhipicephalus (Boophilus) tick species recorded, followed by R. microplus (19.5%; n=46) and R. geigyi (4.2%; n=10). Contrariwise, R. microplus was more dominant (84%; n=211) in Arua district followed by R. decoloratus (10.7%; n=27), R. annulatus (3.9%; n=10) and R. geigyi (1.1%; n=3). Phylogenetic analyses of the ITS2 region, 12S rRNA and 16S rRNA genes revealed subgrouping of the obtained sequences with the previously published R. microplus sequences from other parts of the world.

CONCLUSION

Rhipicephalus microplus ticks were found infesting cattle in four districts of Uganda. The inability to find R. decoloratus, an indigenous tick, from six sites in the district of Arua is suggestive of its replacement by R. microplus. Rhipicephalus microplus negatively affects livestock production, and therefore, there is a need to determine its distribution and to deepen the understanding of the ecological factors that lead to its spread and persistence in an area.

Tick Control in a Connected World: Challenges, Solutions, and Public Policy from a United States Border Perspective

Ticks are able to transmit the highest number of pathogen species of any blood-feeding arthropod and represent a growing threat to public health and agricultural systems worldwide. While there are numerous and varied causes and effects of changes to tick-borne disease (re)emergence, three primary challenges to tick control were identified in this review from a U.S. borders perspective. (1) Climate change is implicated in current and future alterations to geographic ranges and population densities of tick species, pathogens they can transmit, and their host and reservoir species, as highlighted by Ixodes scapularis and its expansion across southern Canada. (2) Modern technological advances have created an increasingly interconnected world, contributing to an increase in invasive tick species introductions through the increased speed and frequency of trade and travel. The introduction of the invasive Haemaphysalis longicornis in the eastern U.S. exemplifies the challenges with control in a highly interconnected world. (3) Lastly, while not a new challenge, differences in disease surveillance, control, and management strategies in bordering countries remains a critical challenge in managing ticks and tick-borne diseases. International inter-agency collaborations along the U.S.-Mexico border have been critical in control and mitigation of cattle fever ticks (Rhipicephalus spp.) and highlight the need for continued collaboration and research into integrated tick management strategies. These case studies were used to identify challenges and opportunities for tick control and mitigation efforts through a One Health framework.

Bovine babesiosis in India: Estimation of prevalence by systematic review and meta analysis

Bovine babesiosis is a serious threat to the livestock sector especially in tropical countries like India. Understanding the epidemiology of the disease in the country is essentially important in strategizing the available methods to effectively control the disease. Keeping this as the background, the present study was undertaken to estimate the pooled prevalence of bovine babesiosis in India. The relevant literature pertaining to bovine babesiosis was identified and a total of 49 studies published between 1983 and 2018 were included in the final systematic review and meta-analysis. Meta-analysis was conducted using meta-package of R software and prevalence estimates were calculated. Bovine babesiosis was reported from 21 states of India with pooled prevalence estimate of 6% (95% CI = 4%-9%) using random effect model. Zone wise analysis revealed highest pooled prevalence in the west zone and north zone (8%) followed by east zone (7%), central zone (6%), south zone (4%) and northeast zone (4%). The results of meta-analysis indicated high variability between studies. In addition, the pooled seroprevalence was high (29%) compared to prevalence of active infection (5%) of bovine babesiosis in India. Further, the pooled prevalence estimate of B. bigemina infection in India was more (7%) compared to B. bovis infection (1%). The estimation of prevalence of active infection and seroprevalence separately will helps to understand the actual disease prevalence in the country. The study indicated the wide prevalence of bovine babesiosis in India which urges for immediate mitigation strategies.

Adaptive radiation and speciation in Rhipicephalus ticks: A medley of novel hosts, nested predator-prey food webs, off-host periods and dispersal along temperature variation gradients

Rhipicephalus are a species-diverse genus of ticks, mainly distributed in the Afrotropics with some species in the Palearctic and Oriental regions. Current taxonomic consensus comprise nine informal species groups/lineages based on immature morphology. This work integrates biogeographic, ecological and molecular lines of evidence to better understand Rhipicephalus evolution. Phylogenetic analysis based on four genes (12S, 16S, 28S-D2 and COI) recovered five distinct clades with nine descendant clades that are generally congruent with current taxonomy, with some exceptions. Historical biogeography is inferred from molecular divergence times, ancestral distribution areas, host-use and climate niches of four phylogenetically significant bioclimatic variables (isothermality, annual, seasonal and diurnal temperature range). Novel hosts enabled host-linked dispersal events into new environments, and ticks exploited new hosts through nested predator-prey connections in food webs. Diversification was further induced by climate niche partitioning along gradients in temperature range during off-host periods. Ancestral climate niche estimates corroborated dispersal events by indicating hypothetical ancestors moved into environments with different annual and seasonal temperature ranges along latitudinal gradients. Host size for immature and adult life stages was important for dispersal and subsequent diversification rates. Clades that utilise large, mobile hosts (ungulates and carnivores) early in development have wider geographic ranges but slower diversification rates, and those utilising small, less mobile hosts (rodents, lagomorphs and afroinsectivores) early in development have smaller ranges but higher diversification rates. These findings suggest diversification is driven by a complex set of factors linked to both host-associations (host size, ranges and mobility) and climate niche partitioning along annual and seasonal temperature range gradients that vary with latitude. Moreover, competitive interactions can reinforce these processes and drive speciation. Off-host periods facilitate adaptive radiation by enabling host switches along nested predator-prey connections in food webs, but at the cost of environmental exposure that partitions niches among dispersing progenitors, disrupting geneflow and driving diversification. As such, the evolution and ecological niches of Rhipicephalus are characterised by trade-offs between on- and off-host periods, and these trade-offs interact with nested predator-prey connections in food webs, host-use at different life stages, as well as gradients in annual and seasonal temperature ranges to drive adaptive radiation and speciation.

Stray Mexico origin cattle captured crossing into Southern Texas carry Babesia bovis and other tick-borne pathogens

Cattle fever ticks, Rhipicephalus microplus and R. annulatus have been eradicated from the United States and inspectors from the U.S. Department of Agriculture (USDA), Animal Plant Health Inspection Service (APHIS), Cattle Fever Tick Eradication Program (CFTEP) monitor the quarantine zone along the Texas border to prevent the introduction of livestock carrying cattle fever ticks from Mexico. Stray livestock apprehended by CFTEP in the zone are checked for ticks and tested for infectious disease-causing pathogens but are not evaluated for evidence of infection with tick-borne pathogens. We tested blood samples collected from stray cattle by CFTEP inspectors for evidence of infection with tick-borne pathogens. As a comparison group representing U.S. resident cattle, we tested blood samples that had been sent to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for unrelated testing. Both sets of blood samples were evaluated using the same specific and broad-spectrum PCR assays. For the border cattle the overall prevalence of infection with one or more tick-borne pathogen was 58.5 % (79/135) with many co-infections, including 30 cattle positive for Babesia bovis and/or Babesia bigemina (22.2 %) and 77 cattle positive for Anaplasma marginale (57 %), three of these animals were also positive for Borrelia theileri. No resident cattle represented by the TVMDL samples were infected with either of the Babesia spp., or with Borrelia theileri, but three were positive for Theileria orientalis and 7.3 % (7/96) were positive for A. marginale. These data show that cattle originating in Mexico have a higher prevalence of infection with tick-borne pathogens relative to resident U.S. cattle and specifically, a proportion are infected with bovine Babesia, which is absent from U.S. cattle populations. Consequently, these stray cattle may be a reservoir of tick-borne pathogens and if populations of Boophilus ticks become reestablished in areas where they had previously been eradicated, could pose a significant risk to the U.S. Cattle industry.

Enduring Challenge of Invasive Ticks: Introduction of Amblyomma oblongoguttatum (Acari: Ixodidae) into the United States on a Human Traveler Returning from Central America

Introduction of exotic tick vectors of bacteria, protozoa, viruses, and filarial parasites into the United States has accelerated in recent years, primarily because of globalization, increased frequency of travel, and a rise in legal and illegal animal trades. We herein report introduction of a live specimen of Amblyomma oblongoguttatum on a human into the United States from Central America, and we review 4 previous similar incidents. This tick species occurs widely in the neotropics, from western and southern Mexico, southwards through Central America, to the northern half of South America. It is a potential vector of bacterial agents of spotted fever group rickettsioses, raising concern that if A. oblongoguttatum ticks become established in this country, they might also be able to carry pathogens of human and veterinary concern. Given the potential for exotic ticks as vectors of numerous pathogens, proper surveillance, interception, and identification of these ticks are vital to protecting human and veterinary health. Rigorous governmental inspections of imported livestock and pet animals at ports of entry and educating human travelers and medical practitioners about the risks should be part of an overall national tick program.

Environmental Risk Assessment for rVSVΔG-ZEBOV-GP, a Genetically Modified Live Vaccine for Ebola Virus Disease

rVSVΔG-ZEBOV-GP is a live, attenuated, recombinant vesicular stomatitis virus (rVSV)-based vaccine for the prevention of Ebola virus disease caused by Zaire ebolavirus. As a replication-competent genetically modified organism, rVSVΔG-ZEBOV-GP underwent various environmental evaluations prior to approval, the most in-depth being the environmental risk assessment (ERA) required by the European Medicines Agency. This ERA, as well as the underlying methodology used to arrive at a sound conclusion about the environmental risks of rVSVΔG-ZEBOV-GP, are described in this review. Clinical data from vaccinated adults demonstrated only infrequent, low-level shedding and transient, low-level viremia, indicating a low person-to-person infection risk. Animal data suggest that it is highly unlikely that vaccinated individuals would infect animals with recombinant virus vaccine or that rVSVΔG-ZEBOV-GP would spread within animal populations. Preclinical studies in various hematophagous insect vectors showed that these species were unable to transmit rVSVΔG-ZEBOV-GP. Pathogenicity risk in humans and animals was found to be low, based on clinical and preclinical data. The overall risk for non-vaccinated individuals and the environment is thus negligible and can be minimized further through defined mitigation strategies. This ERA and the experience gained are relevant to developing other rVSV-based vaccines, including candidates under investigation for prevention of COVID-19.

In search of the Rhipicephalus (Boophilus) microplus in the western-central regions of the Eastern Cape Province, South Africa

The southern cattle tick, Rhipicephalus (Boophilus) microplus, is an economically important tick that parasitises cattle and is found on other host species if they graze with cattle. The R. (B.) microplus is a highly adapted tick species prevalent in tropical and subtropical regions of the world. In Africa, it has expanded its range and was reported to supersede the native tick, R. (B.) decoloratus. The objective of the study was to determine the distribution of R. (B.) microplus under different ecological zones in the western-central regions of Eastern Cape Province. Engorged adult blue ticks were collected monthly from 360 randomly selected cattle and free living ticks from six replicate drags of the vegetation over a period of 1 year at Bedford Dry Grassland (BDG), Kowie Thicket (KT) and Bhisho Thornveld (BT). A special attention was paid to the lower perineum, neck, dewlap and ventral body parts which are the preferred sites for blue ticks during sampling. In this study, 9 species of ticks which grouped under 5 genera were identified. The identified species of ticks were Amblyomma hebraeum, Haemaphysalis elliptica, Hyalomma rufipes, Ixodes pilosus, R. (B.) decoloratus, R. appendiculatus, R. evertsi evertsi, R. follis and R. simus. Only adult R. (B.) decoloratus (n = 8090) ticks were collected from cattle between April 2016 and March 2017. A total of 4382 females and 3708 males of R. (B.) decoloratus were recovered during the survey. Of the ticks (n = 2885) collected from the vegetation, R. (B.) decoloratus was the most abundant species with a relative prevalence of 58.16%, followed by R. appendiculatus (18.37%) and R. evertsi evertsi (16.90%). Least abundant ticks were H. rufipes (2.98%), A. hebraeum (2.46%), H. elliptica (0.38%), R. follis (0.34%), I. pilosus (0.24%) and R. simus (0.17%). The distribution of R. (B.) decoloratus ticks differ significantly (P < 0.05) among the vegetation types. Significantly more (P < 0.05) engorged R. (B.) decoloratus were collected in KT during summer season (1.39 ± 0.063 females and 1.30 ± 0.063 males) compared to other vegetation types. The R. (B.) decoloratus larvae were significantly higher (P < 0.05) in BT (20.56±1.154) and KT (18.50±1.154) vegetation types during the spring season. R. (B.) microplus was not found in the present study, signifying that it is not yet established in western-central regions of the Eastern Cape Province and as such, continuous monitoring would be advisable.

Evaluating the Addition of CO2 to Black Light Traps for Sampling Culicoides (Diptera: Ceratopogonidae) in Alberta

We examined the effect of augmenting black light trap with CO2 at two release rates for monitoring and surveillance of Culicoides at northern latitudes. Species composition was highly correlated among black light (BL) traps with no CO2 (BL0 traps) and traps augmented with 300 and 1000 ml/min CO2 (BL300 and BL1000 traps, respectively); however, traps augmented with CO2 captured one to three more rare species than BL0 traps and can detect rare species that might be missed if BL0 traps were used. Addition of CO2 increased the number of individuals captured from 1.4 to 38.5-fold for BL300 traps and from 1.5 to 153.5-fold for BL1000 traps. This advantage may be lost in areas with low abundance as might be expected at the limits of species. The daily probability of detecting a species was greater for traps augmented with CO2, but this can be compensated for by operating BL0 traps for sufficient time. The association between numbers captured by BL0 and BL300 and BL1000 traps also suggests that BL0 traps may provide useful measures of relative abundance for Culicoides sonorensis, Culicoides davisi, and Culicoides riethi, again providing the BL0 traps are left to operate for some period. Measurements of diel activity were influenced by trap type only for a single species and were primarily determined by solar radiation, temperature, and windspeed. Overall, the use of BL0 only traps for widescale surveys is supported, especially given their convenience.

Vesicular Stomatitis Virus Transmission: A Comparison of Incriminated Vectors

Vesicular stomatitis (VS) is a viral disease of veterinary importance, enzootic in tropical and subtropical regions of the Americas. In the U.S., VS produces devastating economic losses, particularly in the southwestern states where the outbreaks display an occurrence pattern of 10-year intervals. To date, the mechanisms of the geographic spread and maintenance cycles during epizootics remain unclear. This is due, in part, to the fact that VS epidemiology has a complex of variables to consider, including a broad range of vertebrate hosts, multiple routes of transmission, and an extensive diversity of suspected vector species acting as both mechanical and biological vectors. Infection and viral progression within vector species are highly influenced by virus serotype, as well as environmental factors, including temperature and seasonality; however, the mechanisms of viral transmission, including non-conventional pathways, are yet to be fully studied. Here, we review VS epidemiology and transmission mechanisms, with comparisons of transmission evidence for the four most incriminated hematophagous dipteran taxa: Aedes mosquitoes, Lutzomyia sand flies, Simulium black flies, and Culicoides biting midges.

ATP Binding Cassette Transporter Mediates Both Heme and Pesticide Detoxification in Tick Midgut Cells

In ticks, the digestion of blood occurs intracellularly and proteolytic digestion of hemoglobin takes place in a dedicated type of lysosome, the digest vesicle, followed by transfer of the heme moiety of hemoglobin to a specialized organelle that accumulates large heme aggregates, called hemosomes. In the present work, we studied the uptake of fluorescent metalloporphyrins, used as heme analogs, and amitraz, one of the most regularly used acaricides to control cattle tick infestations, by Rhipicephalus (Boophilus) microplus midgut cells. Both compounds were taken up by midgut cells in vitro and accumulated inside the hemosomes. Transport of both molecules was sensitive to cyclosporine A (CsA), a well-known inhibitor of ATP binding cassette (ABC) transporters. Rhodamine 123, a fluorescent probe that is also a recognized ABC substrate, was similarly directed to the hemosome in a CsA-sensitive manner. Using an antibody against conserved domain of PgP-1-type ABC transporter, we were able to immunolocalize PgP-1 in the digest vesicle membranes. Comparison between two R. microplus strains that were resistant and susceptible to amitraz revealed that the resistant strain detoxified both amitraz and Sn-Pp IX more efficiently than the susceptible strain, a process that was also sensitive to CsA. A transcript containing an ABC transporter signature exhibited 2.5-fold increased expression in the amitraz-resistant strain when compared with the susceptible strain. RNAi-induced down-regulation of this ABC transporter led to the accumulation of metalloporphyrin in the digestive vacuole, interrupting heme traffic to the hemosome. This evidence further confirms that this transcript codes for a heme transporter. This is the first report of heme transport in a blood-feeding organism. While the primary physiological function of the hemosome is to detoxify heme and attenuate its toxicity, we suggest that the use of this acaricide detoxification pathway by ticks may represent a new molecular mechanism of resistance to pesticides.

Vaccines against bovine babesiosis: where we are now and possible roads ahead

SUMMARY Bovine babesiosis caused by the tick-transmitted haemoprotozoans Babesia bovis, Babesia bigemina and Babesia divergens commonly results in substantial cattle morbidity and mortality in vast world areas. Although existing live vaccines confer protection, they have considerable disadvantages. Therefore, particularly in countries where large numbers of cattle are at risk, important research is directed towards improved vaccination strategies. Here a comprehensive overview of currently used live vaccines and of the status quo of experimental vaccine trials is presented. In addition, pertinent research fields potentially contributing to the development of novel non-live and/or live vaccines are discussed, including parasite antigens involved in host cell invasion and in pathogen-tick interactions, as well as the protective immunity against infection. The mining of available parasite genomes is continuously enlarging the array of potential vaccine candidates and, additionally, the recent development of a transfection tool for Babesia can significantly contribute to vaccine design. However, the complication and high cost of vaccination trials hinder Babesia vaccine research, and have so far seriously limited the systematic examination of antigen candidates and prevented an in-depth testing of formulations using different immunomodulators and antigen delivery systems.

Targeted surface expression of an exogenous antigen in stably transfected Babesia bovis

Babesia bovis is a tick-borne intraerythocytic protozoan responsible for acute disease in cattle which can be controlled by vaccination with attenuated B. bovis strains. Emerging B. bovis transfection technologies may increase the usefulness of these live vaccines. One use of transfected B. bovis parasites may be as a vaccine delivery platform. Previous transfection methods for B. bovis were limited by single expression sites and intracellular expression of transfected antigens. This study describes a novel transfection system in which two exogenous genes are expressed: one for selection and the other for a selected antigen designed to be delivered to the surface of the parasites. The strategy for duplicating the number of transfected genes was based on the use of the putative bidirectional promoter of the B. bovis 1.4 Kb ef-1α intergenic region. The ability of this region to regulate two independent expression sites was demonstrated using a luciferase assay on transiently transfected B. bovis parasites and then incorporated into a stable transfection plasmid to control independent expression of the selectable marker GFP-BSD and another gene of interest. A chimeric gene was synthetized using sequences from the protective B-cell epitopes of Rhipicephalus microplus tick antigen Bm86 along with sequences from the surface exposed B. bovis major surface antigen-1. This chimeric gene was then cloned into the additional expression site of the transfection plasmid. Transfection of the B. bovis Mo7 strain with this plasmid resulted in stable insertion into the ef-1α locus and simultaneous expression of both exogenous genes. Expression of the Bm86 epitopes on the surface of transfected merozoites was demonstrated using immunofluorescence analyses. The ability to independently express multiple genes by the inclusion of a bidirectional promoter and the achievement of surface expression of foreign epitopes advances the potential of transfected B. bovis as a future vaccine delivery platform.

Invasive potential of cattle fever ticks in the southern United States

Abstract'

Widespread movement of invasive cattle fever ticks (Rhipicephalus microplus) in southern Texas leads to shared local infestations on cattle and deer

Background

Rhipicephalus (Boophilus) microplus is a highly-invasive tick that transmits the cattle parasites (Babesia bovis and B. bigemina) that cause cattle fever. R. microplus and Babesia are endemic in Mexico and ticks persist in the United States inside a narrow tick eradication quarantine area (TEQA) along the Rio Grande. This containment area is threatened by unregulated movements of illegal cattle and wildlife like white-tailed deer (WTD; Odocoileus virginianus).

Methods

Using 11 microsatellite loci we genotyped 1,247 R. microplus from 63 Texas collections, including outbreak infestations from outside the TEQA. We used population genetic analyses to test hypotheses about ecological persistence, tick movement, and impacts of the eradication program in southern Texas. We tested acaricide resistance with larval packet tests (LPTs) on 47 collections.

Results

LPTs revealed acaricide resistance in 15/47 collections (32%); 11 were outside the TEQA and three were resistant to multiple acaricides. Some collections highly resistant to permethrin were found on cattle and WTD. Analysis of genetic differentiation over time at seven properties revealed local gene pools with very low levels of differentiation (F_ST 0.00-0.05), indicating persistence over timespans of up to 29 months. However, in one neighborhood differentiation varied greatly over a 12-month period (F_ST 0.03-0.13), suggesting recurring immigration from distinct sources as another persistence mechanism. Ticks collected from cattle and WTD at the same location are not differentiated (F_ST = 0), implicating ticks from WTD as a source of ticks on cattle (and vice versa) and emphasizing the importance of WTD to tick control strategies. We identified four major genetic groups (K = 4) using Bayesian population assignment, suggesting multiple introductions to Texas.

Conclusions

Two dispersal mechanisms give rise to new tick infestations: 1) frequent short-distance dispersal from the TEQA; and 2) rare long-distance, human-mediated dispersal from populations outside our study area, probably Mexico. The threat of cattle fever tick transport into Texas is increased by acaricide resistance and the ability of R. microplus to utilize WTD as an alternate host. Population genetic analyses may provide a powerful tool for tracking invasions in other parts of the world where these ticks are established.

Diseases at the livestock-wildlife interface: status, challenges, and opportunities in the United States

In the last half century, significant attention has been given to animal diseases; however, our understanding of disease processes and how to manage them at the livestock-wildlife interface remains limited. In this study, we conduct a systematic review of the scientific literature to evaluate the status of diseases at the livestock-wildlife interface in the United States. Specifically, the goals of the literature review were three fold: first to evaluate domestic animal diseases currently found in the United States where wildlife may play a role; second to identify critical issues faced in managing these diseases at the livestock-wildlife interface; and third to identify potential technical and policy strategies for addressing these issues. We found that of the 86 avian, ruminant, swine, poultry, and lagomorph diseases that are reportable to the World Organization for Animal Health (OIE), 53 are present in the United States; 42 (79%) of these have a putative wildlife component associated with the transmission, maintenance, or life cycle of the pathogen; and 21 (40%) are known to be zoonotic. At least six of these reportable diseases-bovine tuberculosis, paratuberculosis, brucellosis, avian influenza, rabies, and cattle fever tick (vector control)-have a wildlife reservoir that is a recognized impediment to eradication in domestic populations. The complex nature of these systems highlights the need to understand the role of wildlife in the epidemiology, transmission, and maintenance of infectious diseases of livestock. Successful management or eradication of these diseases will require the development of cross-discipline and institutional collaborations. Despite social and policy challenges, there remain opportunities to develop new collaborations and new technologies to mitigate the risks posed at the livestock-wildlife interface.

Eradication and control of livestock ticks: biological, economic and social perspectives

Comparisons of successful and failed attempts to eradicate livestock ticks reveal that the social context of farming and management of the campaigns have greater influence than techniques of treatment. The biology of ticks is considered principally where it has contributed to control of ticks as practiced on farms. The timing of treatments by life cycle and season can be exploited to reduce numbers of treatments per year. Pastures can be managed to starve and desiccate vulnerable larvae questing on vegetation. Immunity to ticks acquired by hosts can be enhanced by livestock breeding. The aggregated distribution of ticks on hosts with poor immunity can be used to select animals for removal from the herd. Models of tick population dynamics required for predicting outcomes of control methods need better understanding of drivers of distribution, aggregation, stability, and density-dependent mortality. Changing social circumstances, especially of land-use, has an influence on exposure to tick-borne pathogens that can be exploited for disease control.

Integrated Strategy for Sustainable Cattle Fever Tick Eradication in USA is Required to Mitigate the Impact of Global Change

The ticks Rhipicephalus (Boophilus) annulatus and R. (B.) microplus, commonly known as cattle and southern cattle tick, respectively, impede the development and sustainability of livestock industries throughout tropical and other world regions. They affect animal productivity and wellbeing directly through their obligate blood-feeding habit and indirectly by serving as vectors of the infectious agents causing bovine babesiosis and anaplasmosis. The monumental scientific discovery of certain arthropod species as vectors of infectious agents is associated with the history of research on bovine babesiosis and R. annulatus. Together, R. microplus and R. annulatus are referred to as cattle fever ticks (CFT). Bovine babesiosis became a regulated foreign animal disease in the United States of America (U.S.) through efforts of the Cattle Fever Tick Eradication Program (CFTEP) established in 1906. The U.S. was declared free of CFT in 1943, with the exception of a permanent quarantine zone in south Texas along the border with Mexico. This achievement contributed greatly to the development and productivity of animal agriculture in the U.S. The permanent quarantine zone buffers CFT incursions from Mexico where both ticks and babesiosis are endemic. Until recently, the elimination of CFT outbreaks relied solely on the use of coumaphos, an organophosphate acaricide, in dipping vats or as a spray to treat livestock, or the vacation of pastures. However, ecological, societal, and economical changes are shifting the paradigm of systematically treating livestock to eradicate CFT. Keeping the U.S. CFT-free is a critical animal health issue affecting the economic stability of livestock and wildlife enterprises. Here, we describe vulnerabilities associated with global change forces challenging the CFTEP. The concept of integrated CFT eradication is discussed in reference to global change.

Multiple transcripts encode glucose 6-phosphate dehydrogenase in the southern cattle tick, Rhipicephalus (Boophilus) microplus

Glucose 6-phosphate dehydrogenase (G6PDH) is an enzyme that plays a critical role in the production of NADPH. Here we describe the identification of four transcripts (G6PDH-A, -B, -C, and -D) that putatively encode the enzyme in the southern cattle tick, Rhipicephalus (Boophilus) microplus. The genomic DNA that is spliced to produce G6PDH-A and -B is 8,600-9,000 bases in length and comprises 12 exons. Comparison of the R. microplus G6PDH gene structure with those available from insects and mammals revealed that the tick gene is most like that of humans. Detection of the four transcripts was evaluated by quantitative RT-PCR using template from larvae, unfed adult females and males, salivary gland tissues from 2- to 3-day-fed adult females and males, and salivary gland tissue of 4- to 5-day-fed adult females. The G6PDH-A and -C transcripts were present in all templates, and both displayed induced expression in salivary gland tissue of fed, adult females but not matched males. The G6PDH-D transcript was detected only in unfed adults and in larvae, a stage in which it was most abundant relative to the other three transcripts. The G6PDH-B transcript, while detectable in all templates, was of low copy number suggesting it is a rare transcript. Induced expression of G6PDH-A and G6PDH-C in fed females may play a role in the tolerance of oxidative stress that is induced upon feeding, and the transcript abundance in fed females may be a function of bloodmeal volume and the time adult females spend on the host relative to adult males.

One Health approach to identify research needs in bovine and human babesioses: workshop report

BACKGROUND

Babesia are emerging health threats to humans and animals in the United States. A collaborative effort of multiple disciplines to attain optimal health for people, animals and our environment, otherwise known as the One Health concept, was taken during a research workshop held in April 2009 to identify gaps in scientific knowledge regarding babesioses. The impetus for this analysis was the increased risk for outbreaks of bovine babesiosis, also known as Texas cattle fever, associated with the re-infestation of the U.S. by cattle fever ticks.

RESULTS

The involvement of wildlife in the ecology of cattle fever ticks jeopardizes the ability of state and federal agencies to keep the national herd free of Texas cattle fever. Similarly, there has been a progressive increase in the number of cases of human babesiosis over the past 25 years due to an increase in the white-tailed deer population. Human babesiosis due to cattle-associated Babesia divergens and Babesia divergens-like organisms have begun to appear in residents of the United States. Research needs for human and bovine babesioses were identified and are presented herein.

CONCLUSIONS

The translation of this research is expected to provide veterinary and public health systems with the tools to mitigate the impact of bovine and human babesioses. However, economic, political, and social commitments are urgently required, including increased national funding for animal and human Babesia research, to prevent the re-establishment of cattle fever ticks and the increasing problem of human babesiosis in the United States.

Species abundance and seasonal activity of mosquitoes on cattle facilities in southern Alberta, Canada

Seventeen mosquito species were collected at eight cattle facilities in southern Alberta, Canada, during 2002-2004. Five species, Culiseta inornata (Williston), Aedes dorsalis (Meigen), Culex tarsalis (Coquillett), Aedes vexans (Meigen), and Aedes campestris Dyar & Knab accounted for 93.6% of the mosquitoes collected. Culiseta inornata, Ae. dorsalis, and Ae. campestris were trapped earliest in the year. Cs. inornata was active latest in the year and had the longest period of activity. Ae. dorsalis finished activity in late September and had the second longest period of activity. Ae. campestris was the first to complete its activity, resulting in a moderate period of activity. Cu. tarsalis and Ae. vexans appeared later in the season, disappeared by late September, and had the briefest periods of activity. Logistic regression was used to estimate relationships between the proportions of traps positive and mean weekly abundance for each species. Fifty percent of the traps were positive when abundance averaged 0.19-0.30 females per trap night. Logistic regression was used to determine the timing of the onset of activity and temperature thresholds for flight. Relationships between the proportion of positive traps and mean weekly temperature indicated that Cs. inornata had the lowest temperature threshold, Cx. tarsalis the greatest, and the remaining species had intermediate thresholds. Logistic regression indicated that mosquito presence was primarily affected by temperature and accumulated degree-days, with only Ae. vexans exhibiting a positive response to precipitation. The models can be used to predict the onset of activity as defined by when populations exceed a particular threshold.

New approaches to detection and identification of Rickettsia africae and Ehrlichia ruminantium in Amblyomma variegatum (Acari: Ixodidae) ticks from the Caribbean

Imported from Africa in the 1700s and despite frequent modern eradication efforts, Amblyomma variegatum (F.) spread through the Caribbean by cattle transport, small ruminants, and migrating birds. A. variegatum is a vector for Rickettsia africae, the causative agent of African tick bite fever, and Ehrlichia ruminantium, the causative agent of heartwater. We examined 95 A. variegatum and six Rhipicephalus (Boophilus) microplus (Canestrini) collected from cattle at an abattoir in Antigua. Engorged tick extracts adsorbed on Nobotu filter paper strips and new nested polymerase chain reaction (PCR) assays for E. ruminantium and Dermatophilus congolensis were used to evaluate these ticks for the presence of these pathogenic bacteria. Amblyomma ticks (62.4%) contained R. africae DNA by PCR/restriction fragment length polymorphism analysis and DNA sequencing of the OmpA and 17-kDa antigen genes. Twenty Amblyomma and two Rh. microplus contained E. ruminantium DNA. No E. chaffeensis, Anaplasma phagocytophilum, Coxiella burnetii, or D. congolensis DNA was detected in these ticks. The continued presence of Am. variegatum in the Caribbean poses a significant risk of infection in cattle with E. ruminantium and in humans by R. africae. Eradication efforts are essential to prevent the further spread of Am. variegatum.

The effects of global change on the threat of exotic arthropods and arthropod-borne pathogens to livestock in the United States

Arthropod-borne diseases are an important part of the group of foreign animal diseases that command attention from federal, state, and local animal health authorities in the United States because of the potential for adverse local and regional animal health impacts and also because of possible losses of export markets. Diseases of concern are listed by the US Animal Health Association and also by the Office International des Epizooties. Global change is causing the emergence of newly recognized diseases and altering enzootic and epizootic circumstances for known disease problems. Selected examples of arthropod-borne diseases of importance are discussed in terms of their potential for introduction, spread, and impact on livestock and human health in the United States.

New strategies for the control of arthropod vectors of disease in dogs and cats

Arthropod-borne diseases (ABDs) in cats and dogs have a major impact on animal health and welfare and, in many cases, also on human health. Many ABDs are expected to increase in prevalence as a result of changing social habits, habitat modifications, introductions of exotic vectors and climate change. Control has, historically, focused on the use of insecticides and chemotherapy. We review alternative, emerging approaches to ABDs that currently offer promise, particularly modelling and molecular techniques and the development of novel vaccines that target molecules produced by arthropods during the bloodmeal. We argue that there is an urgent need to establish effective surveillance systems for most ABDs across various countries in order to facilitate a detailed risk analysis, which should include evaluation of potential spread to new areas and the possible introduction of new exotic species or disease agents. This will require clear and exhaustive knowledge on the distribution of ABDs in different areas, understanding of the diagnostic limitations pertaining to ABDs and standardization of techniques among reference laboratories in different countries. Continuous monitoring of insecticide resistance and the development of management strategies to minimize its onset are also essential. Ultimately, it is probable that approaches which attempt to reduce vector abundance or treat hosts with chemotherapy alone are unlikely to be effective in the long term. More suitable approaches may include greater use of a range of mutually compatible options in integrated management programmes.

Acaricide resistance and synergism between permethrin and amitraz against susceptible and resistant strains of Boophilus microplus (Acari: Ixodidae)

The control of the southern cattle tick, Boophilus microplus (Canestrini), in Mexico and many other countries relies on chemical acaricides. Boophilus microplus has developed resistance to all major classes of acaricides in recent years. To gain a better understanding of the resistance and to develop resistance management strategies that benefit both Mexican ranchers and USDA's cattle fever tick eradication program (CFTEP), the authors used larval bioassay techniques to determine levels of resistance to permethrin and amitraz and then evaluated synergism between these two acaricides in one susceptible laboratory tick strain and four resistant strains originating from Mexico and Brazil. To examine mechanisms of resistance to permethrin in these strains, the frequency of a mutated sodium channel gene was determined using a PCR assay. The tick strains from Mexico and Brazil demonstrated 49.4- to over 672.2-fold resistance to permethrin, and up to 94.5-fold resistance to amitraz. While the San Roman strain from Mexico was the most permethrin-resistant strain, the Santa Luiza strain from Brazil was the most amitraz-resistant strain. A significant correlation was found between the permethrin resistance ratio and the allelic frequency of the sodium channel mutation. Significant synergism between permethrin and amitraz was found when one acaricide was tested in the presence of another. Synergism ratios ranged from 1.5 to 54.9 when amitraz was tested as a synergist for permethrin. Similar synergism ratios were obtained when permethrin was tested as a synergist for amitraz. Permethrin caused virtually no mortality in the San Roman strain, even at the highest concentration (3294 microg cm(-2)). Adding amitraz (11.0 microg cm(-2)) to permethrin led to a dramatic increase in larval mortality, even at very low concentrations of permethrin.

Persistently infected calves as reservoirs for acquisition and transovarial transmission of Babesia bovis by Rhipicephalus (Boophilus) microplus

Babesia bovis is a deadly disease of cattle resulting in severe economic losses in the vast regions of the world where it is endemic. If reintroduced into the United States, babesiosis would cause significant mortality in the naïve cattle population. In order to address the risk to U.S. cattle, it is essential to quantify the transovarial transmission efficiency in adult female Boophilus microplus ticks following acquisition feeding on persistently infected cattle. This study tested the hypothesis that infection rates are the same for larval progeny derived from females fed to repletion during persistent or acute infection. Increasing parasite levels during acute infection correlated with an increasing number of females harboring kinetes detectable in hemolymph (r = 0.9). The percent infected larvae ranged from 0 to 20% when derived from females fed to repletion on persistently infected calves and from 4 to 6% when derived from females fed to repletion during acute parasitemia. There was no significant difference in infection rates of larval progeny, implying that the risk associated with the introduction of either persistently infected or acutely infected cattle is equal. Parasite levels ranged from 2.4 x 10(2) to 1.9 x 10(5) in 3-day-fed larvae derived from females fed to repletion on persistently infected cattle. One group of larvae failed to transmit the parasite, suggesting that a threshold level of parasites must be obtained by larval progeny via transovarial transmission in order for larvae to deliver sufficient parasites to infect a naïve host.

Conservation of transmission phenotype of Anaplasma marginale (Rickettsiales: Anaplasmataceae) strains among Dermacentor and Rhipicephalus ticks (Acari: Ixodidae)

Before the eradication of Boophilus ticks from the United States, Rhipicephalus (Boophilus) microplus (Canestrini) and Rhipicephalus (Boophilus) annulatus (Say) were important biological vectors of the cattle pathogen Anaplasma marginale Theiler. In the absence of Boophilus ticks, A. marginale continues to be transmitted by Dermacentor ticks. However, a few U.S. strains are not transmissible by Dermacentor andersoni Stiles, Dermacentor variabilis (Say), or both, raising the question of how these strains evolved and how they are maintained. We hypothesize that the U.S. non-Dermacentor-transmissible strains of A. marginale were formerly Boophilus-transmitted strains that have been maintained by a combination of persistent infection and mechanical transmission since the eradication of their biological vector from the United States. To test this hypothesis, we attempted to transmit a well-documented non-Dermacentor-transmissible A. marginale strain (Florida), by using D. andersoni and the two Boophilus species that formerly occurred in the United States. For comparison, we examined tick-borne transmission of a strain of A. marginale (Puerto Rico), which has previously been shown to be transmissible by both D. andersoni and B. microplus. All three species of tick transmitted the Puerto Rico strain, and immunohistochemical (IHC) analysis confirmed the presence ofA. marginale colonies in their salivary glands. All three tick species failed to transmit the Florida strain. Although both D. andersoni and B. microplus acquired transient midgut and salivary gland infections after acquisition feeding, we were unable to detect colonies of the Florida strain in the salivary glands with IHC. This demonstrates that the transmission phenotype ofA. marginale strains is conserved among tick species, and it suggests that the failure of the Florida strain to be transmitted by ticks is related to a general inability to efficiently invade or replicate in tick cells, rather than to a failure to invade or replicate in cells of a specific tick species.

Detection of Babesia bigemina infection in strains of Rhipicephalus (Boophilus) microplus collected from outbreaks in South Texas

The sudden death of several cattle infested experimentally with Rhipicephalus (Boophilus) microplus led to a clinical investigation into the reasons for the unexpected mortality. Microscopic evidence for Babesia bigemina infection was found in blood smears from the affected animals and a PCR assay was designed to detect the presence of B. bigemina and Babesia bovis in all R. microplus strains received and propagated at the laboratory. The assay utilizes a nested PCR approach with the first PCR amplifying a well-conserved segment from the Babesia 18S ribosomal RNA gene followed by a nested PCR with Babesia species-specific primers and annealing temperatures enabling amplification of the 18S ribosomal RNA gene fragment specific to either B. bigemina or B. bovis. DNA from groups of 50 larvae was extracted using a rapid DNA preparation protocol, which consisted of grinding the frozen tick larvae in PCR buffer and boiling the mixture for 5min. The assay sensitivity allowed for the detection of the equivalent of a single infected tick larva. R. microplus eggs were also analyzed, but yolk protein viscosity created inconsistent results with the crush and boil DNA isolation protocol, necessitating the use of a more extensive proteinase K digestion-based DNA purification method. We detected the presence of B. bigemina in all strains of R. microplus currently reared at the laboratory and 4 of 26 strains collected from infestation outbreaks in Texas by the U.S. Cattle Fever Tick Eradication Program.

Results of a survey of owners of miniature swine to characterize husbandry practices affecting risks of foreign animal disease

OBJECTIVE

To characterize husbandry practices that could affect the risks of foreign animal disease in miniature swine.

DESIGN

Survey study.

STUDY POPULATION

106 owners of miniature swine.

PROCEDURES

An online survey of owners of miniature swine was conducted to obtain information about miniature pig and owner demographics; pig husbandry; movements of pigs; and pig contacts with humans, other miniature swine, and livestock.

RESULTS

12 states, 106 premises, and 317 miniature swine were represented in the survey. More than a third (35%) of miniature swine owners also owned other livestock species. Regular contact with livestock species at other premises was reported by 13% of owners. More than a third of owners visited shows or fairs (39%) and club or association events (37%) where miniature swine were present. More than 40% of owners fed food waste to miniature swine. Approximately half (48%) of the veterinarians providing health care for miniature swine were in mixed-animal practice.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of this study indicated that miniature swine kept as pets can be exposed, directly and indirectly, to feed and other livestock, potentially introducing, establishing, or spreading a foreign animal disease such as foot-and-mouth disease. In addition, the veterinary services and carcass disposal methods used by miniature swine owners may reduce the likelihood of sick or dead pigs undergoing ante- or postmortem examination by a veterinarian.

Importance of ticks and their chemical and immunological control in livestock

The medical and economic importance of ticks has long been recognized due to their ability to transmit diseases to humans and animals. Ticks cause great economic losses to livestock, and adversely affect livestock hosts in several ways. Loss of blood is a direct effect of ticks acting as potential vector for haemo-protozoa and helminth parasites. Blood sucking by large numbers of ticks causes reduction in live weight and anemia among domestic animals, while their bites also reduce the quality of hides. However, major losses caused by ticks are due to their ability to transmit protozoan, rickettsial and viral diseases of livestock, which are of great economic importance world-wide. There are quite a few methods for controlling ticks, but every method has certain shortcomings. The present review is focused on ticks importance and their control.

Bluetongue virus and double-stranded RNA increase human vascular permeability: role of p38 MAPK

Endothelial cell (EC) involvement in viral hemorrhagic fevers has been clearly established. However, virally activated mechanisms leading to endothelial activation and dysfunction are not well understood. Several different potential mechanisms such as direct viral infection, alterations in procoagulant/anticoagulant balance, and increased cytokine production have been suggested. We utilized a model of EC barrier dysfunction and vascular endothelial leakage to explore the effect of bluetongue virus (BTV), a hemorrhagic fever virus of ruminants, on human lung endothelial cell barrier properties. Infection of human lung EC with BTV induced a significant and dose-dependent decrease in trans-endothelial electrical resistance (TER). Furthermore, decreases in TER occurred in conjunction with cytoskeletal rearrangement, suggesting a direct mechanism for viral infection-mediated endothelial barrier disruption. Interestingly, double-stranded RNA (dsRNA) mimicked the effects of BTV on endothelial barrier properties. Both BTV- and dsRNA-induced endothelial barrier dysfunction was blocked by treatment with a pharmacological inhibitor of p38 MAPK. The induction of vascular permeability by dsRNA treatment or BTV infection was concomitent with induction of inflammatory cytokines. Taken together, our data suggest that the presence of dsRNA during viral infections and subsequent activation of p38 MAPK is a potential molecular pathway for viral induction of hemorrhagic fevers. Collectively, our data suggest that inhibition of p38 MAPK may be a possible therapeutic approach to alter viral-induced acute hemorrhagic diseases.

Abundance and species composition of Culicoides (Diptera: Ceratopogonidae) at cattle facilities in southern Alberta, Canada

Culicoides fauna was examined at seven feedlots and one rangeland site (Warner) in southern Alberta, Canada, during a 3-yr period. Eight species and species groups accounted for > 99% of the Culicoides (Diptera: Ceratopogonidae) captured. The most abundant species or groups were Culicoides gigas Root and Hoffman, Culicoides sonorensis (Wirth and Jones), Culicoides (Selfia) group, and Culicoides palmerae group. These accounted for 78-88% of the Culicoides captured, with the balance being members of the Culicoides cockerellii section, Culicoides crepuscularis Malloch, Culicoides wisconsinensis Jones, and Culicoides yukonensis Hoffman. Univariate and multivariate analyses indicated that the rangeland site was characterized by greater abundance of C. sonorensis and C. palmerae and lower abundance of C. (Selfia) compared with the feedlot sites. The Culicoides fauna was more dissimilar among sites as geographic distance between sites increased. Species of Culicoides captured in this study showed three broad patterns of seasonal abundance. The C. palmerae group had the earliest seasonal activity, with an increase in June, peak in July, and greatly reduced abundance thereafter. C. crepuscularis, C. (Selfia), C. wisconsinensis, and C. gigas had later periods of activity, with peak abundance in July, but moderate abundance in June and August. C. cockerellii, C. yukonensis, and C. sonorensis had the latest periods of activity, with populations increasing through June and July, peaking in August, and declining thereafter. C. sonorensis was somewhat unique on that it was the only species with moderate abundance as late as September.

Sequencing a new target genome: the Boophilus microplus (Acari: Ixodidae) genome project

The southern cattle tick, Boophilus microplus (Canestrini), causes annual economic losses in the hundreds of millions of dollars to cattle producers throughout the world, and ranks as the most economically important tick from a global perspective. Control failures attributable to the development of pesticide resistance have become commonplace, and novel control technologies are needed. The availability of the genome sequence will facilitate the development of these new technologies, and we are proposing sequencing to a 4-6X draft coverage. Many existing biological resources are available to facilitate a genome sequencing project, including several inbred laboratory tick strains, a database of approximately 45,000 expressed sequence tags compiled into a B. microplus Gene Index, a bacterial artificial chromosome (BAC) library, an established B. microplus cell line, and genomic DNA suitable for library synthesis. Collaborative projects are underway to map BACs and cDNAs to specific chromosomes and to sequence selected BAC clones. When completed, the genome sequences from the cow, B. microplus, and the B. microplus-borne pathogens Babesia bovis and Anaplasma marginale will enhance studies of host-vector-pathogen systems. Genes involved in the regeneration of amputated tick limbs and transitions through developmental stages are largely unknown. Studies of these and other interesting biological questions will be advanced by tick genome sequence data. Comparative genomics offers the prospect of new insight into many, perhaps all, aspects of the biology of ticks and the pathogens they transmit to farm animals and people. The B. microplus genome sequence will fill a major gap in comparative genomics: a sequence from the Metastriata lineage of ticks. The purpose of the article is to synergize interest in and provide rationales for sequencing the genome of B. microplus and for publicizing currently available genomic resources for this tick.

BmiGI: a database of cDNAs expressed in Boophilus microplus, the tropical/southern cattle tick

We used an expressed sequence tag approach to initiate a study of the genome of the southern cattle tick, Boophilus microplus. A normalized cDNA library was synthesized from pooled RNA purified from tick larvae which had been subjected to different treatments, including acaricide exposure, heat shock, cold shock, host odor, and infection with Babesia bovis. For the acaricide exposure experiments, we used several strains of ticks, which varied in their levels of susceptibility to pyrethroid, organophosphate and amitraz. We also included RNA purified from samples of eggs, nymphs and adult ticks and dissected tick organs. Plasmid DNA was prepared from 11,520 cDNA clones and both 5' and 3' sequencing performed on each clone. The sequence data was used to search public protein databases and a B. microplus gene index was constructed, consisting of 8270 unique sequences whose associated putative functional assignments, when available, can be viewed at the TIGR website (http://www.tigr.org/tdb/tgi). A number of novel sequences were identified which possessed significant sequence similarity to genes, which might be involved in resistance to acaricides.

Genome size and organization in the blacklegged tick, Ixodes scapularis and the Southern cattle tick, Boophilus microplus

Genome sizes and the organization of repetitive DNA were determined in the hard ticks Ixodes scapularis and Boophilus microplus using reassociation kinetics. The I. scapularis genome contains approximately 2.15 pg (2.1x10(3) Mbp) of DNA and consists of no foldback (FB), 27% highly repetitive (HR), 39% moderately repetitive (MR), and 34% unique DNA. The B. microplus genome contains 7.5 pg (7.1x10(3) Mbp) DNA, and consists of 0.82% FB, 31% HR, 38% MR, and 30% unique DNA. In both species, repetitive sequences occur in a mixture of long and short period interspersion but most (65-80%) of the DNA follows a pattern of short period interspersion. Genome size and organization in the three tick species so far examined are distinct from other arthropods in having a greater proportion of MR, a lower proportion of unique and HR DNA of very low sequence complexity.

Proteome analysis of abundantly expressed proteins from unfed larvae of the cattle tick, Boophilus microplus

Protein expression in unfed larvae of the cattle tick, Boophilus microplus, was characterized using gel electrophoresis and mass spectrometry in an effort to assemble a database of proteins produced at this stage of development. Soluble and insoluble proteins were extracted and resolved by two-dimensional (2D) gel electrophoresis. Twenty abundantly expressed larval proteins were selected for peptide mass mapping and for peptide sequencing by matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) and quadrupole time-of-flight (Q-ToF) tandem mass spectrometry (MS), respectively. Only one protein, tropomyosin, was unequivocally identified from its peptide mass map. Ten proteins were assigned putative identities based on BLAST searching of heterologous databases with peptide sequences. These included a cytoskeletal protein (troponin I), multiple cuticular proteins, a glycine-rich salivary gland-associated protein and proteins with a presumed housekeeping role (arginine kinase, a high-mobility group protein and a small heat shock protein). Eight additional proteins were identified by searching translated open reading frames of a B. microplus EST database (unpublished): putative fatty-acid binding protein, thioredoxin, glycine-rich salivary gland protein and additional cuticular proteins. One remaining protein was not identifiable, suggesting it may be a novel molecule. The ongoing assembly of this database contributes to our understanding of proteins expressed by the tick and provides a resource that can be mined for molecules that play a role in tick-host interactions.

Mode of inheritance of amitraz resistance in a Brazilian strain of the southern cattle tick, Boophilus microplus (Acari: Ixodidae)

The southern cattle tick, Boophilus microplus (Canestrini), has developed resistance to amitraz in several countries in recent years. A study was conducted at the USDA Cattle Fever Tick Research Laboratory in Texas to investigate the mode of inheritance of amitraz resistance with cross-mating experiments. The Muñoz strain, a laboratory reared acaricide-susceptible reference strain, was used as the susceptible parent and the Santa Luiza strain, originating in Brazil, was used as the resistant parent. A modified Food and Agriculture Organization Larval Packet Test was used to measure the levels of susceptibility of larvae of the parental strains, F1, backcross, F2, and F3 generations. Results of reciprocal crossing experiments suggested that amitraz resistance was inherited as an incomplete recessive trait. There was a strong maternal effect on larval progeny's susceptibility to amitraz in both the F1 and the subsequent generations. The values of the degree of dominance were estimated at -0.156 and -0.500 for the F1 larvae with resistant and susceptible female parents, respectively. Results of bioassays on larval progeny of the F1 backcrossed with the resistant parent strain and that of the F2 generations suggested that more than one gene was responsible for amitraz resistance in the Santa Luiza strain. Comparisons of biological parameters (engorged female weight, egg mass weight, and female-to-egg weight conversion efficiency index) indicated significant differences between different genotypes. The differences appeared to be heritable, but not related to amitraz resistance. Results from this study may have significant implications for the management of amitraz resistance.

Detection and characterization of amitraz resistance in the southern cattle tick, Boophilus microplus (Acari: Ixodidae)

Amitraz, a formamidine acaricide, plays an important role in the control of the southern cattle tick, Boophilus microplus (Canestrini), and other tick species that infest cattle, dogs, and wild animals. Although resistance to amitraz in B. microplus was previously reported in several countries, the actual measurement of the level of amitraz resistance in ticks has been difficult to determine due to the lack of a proper bioassay technique. We conducted a survey, by using a newly reported technique that was a modification of the standard Food and Agriculture Organization larval packet test, to measure the levels of resistance to amitraz in 15 strains of B. microplus from four major cattle-producing states in Mexico. Low-order resistance (1.68- to 4.58-fold) was detected in 11 of those strains. Our laboratory selection using amitraz on larvae of the Santa Luiza strain, which originated from Brazil, achieved a resistance ratio of 153.93 at F6, indicating the potential for high resistance to this acaricide in B. microplus. Both triphenylphosphate and piperonyl butoxide significantly synergized amitraz toxicity in both resistant and susceptible tick strains. Diethyl maleate synergized amitraz toxicity in one resistant strain but had no effect on the susceptible strain and had minor antagonistic effects on two other resistant strains. Target site insensitivity, instead of metabolic detoxification mechanisms, might be responsible for amitraz resistance observed in the Santa Luiza strain and possibly in other amitraz resistant B. microplus ticks from Mexico. The Santa Luiza strain also demonstrated high resistance to pyrethroids and moderate resistance to organophosphates. Multiple resistance shown in this strain and other B. microplus strains from Mexico poses a significant challenge to the management of B. microplus resistance to acaricides in Mexico.