Species identification and global positioning system coordinates of infestations of cattle fever ticks, Rhipicephalus (Boophilus) annulatus (Say) and Rhipicephalus (Boophilus) microplus (Canestrini), were determined for 790 specimens submitted to the National Veterinary Services Laboratory between 1 October 1999 and 30 September 2010. Cattle fever tick specimens obtained by personnel of the United States Department of Agriculture-Animal and Plant Health Inspection Service-Cattle Fever Tick Eradication Program from infested cattle and wildlife along the Texas/ Mexico border were submitted for identification, as required by the program. A geographic information system database was developed that incorporates location, collection, and infestation records. Submitted ticks came from 11 Texas counties and were comprised of 19.5% R. (B.) annulatus and 80.5% R. (B.) microplus. Maps produced from this study locate and define the parapatric boundary between R. (B.) annulatus and R. (B.) microplus.
Nilgai ( Boselaphus tragocamelus) are nonnative bovines that were originally introduced as game animals to one large, south Texas, US ranch but that are now present throughout southeastern Texas from Baffin Bay to Harlingen and in northern Mexico at least as far west as Durango. Between October 2014 and January 2017, nilgai ( n=517) were examined for the presence of tick ectoparasites, with particular interest in the cattle fever tick, Rhipicephalus ( Boophilus) microplus. These animals were either hunter killed or they were culled as part of federal cooperative harvesting from Cameron and Willacy counties in southeastern Texas. The proportion of fever tick-infested animals differed in a N-to-S pattern, and this was at least partly attributed to differences in habitat. The southern area is a lowland floodplain predominated by halophytes, whereas the northerly area is upland thorn scrub, the latter of which provides a vegetative canopy that is more conducive to tick survival and persistence. A subset of nilgai, all from the Texas-Mexico border area, were screened for livestock pathogens using molecular and serological assays. All nilgai were seronegative for Babesia ( Theileria) equi and Babesia cabalii. Although 11 animals were seropositive for Anaplasma marginale by competitive enzyme-linked immunosorbent assay (cELISA), these were interpreted with caution because of the lack of concordance between cELISA and molecular detection assays. All animals were PCR negative for presence of Babesia spp. DNA, and a single nilgai was seropositive for Babesia bovis and Babesia bigemina by complement fixation. It remains unknown whether cattle Babesia spp. can establish an infection in nilgai.
The Cattle Fever Tick Eradication Program was the first parasite eradication program of veterinary importance in the United States and is considered to be one of the greatest disease eradication programs of all time. The program's utilization of pasture vacation and dipping of cattle in acaricide has been extremely successful for controlling Rhipicephalus (Boophilus) microplus (Canestrini) and R. (B.) annulatus (Say), collectively known as cattle fever ticks, on cattle along the Texas border with Mexico for decades. However, the increase of white-tailed deer, Odocoileus virginianus (Zimmermann), populations in South Texas over the last 50 yr has compromised the success of the program. R. (B.) microplus and R. (B.) annulatus infestation data have confirmed that O. virginianus can support the maintenance and movement of both species of cattle fever tick within the permanent quarantine or buffer zone in South Texas along the Rio Grande, and also in the cattle fever tick-free area north and east of the buffer zone. Over the last two decades, increasing populations of exotic nilgai antelope, Boselaphus tragocamelus (Pallas), in South Texas have further complicated cattle fever tick eradication efforts. Historical cattle fever tick infestation data, host source data, and geographical data support the continued role of O. virginianus in maintaining reinfestations of R. (B.) microplus and R. (B.) annulatus in South Texas as well as the increasing role of nilgai antelope in cattle fever tick maintenance and dispersal.
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