Tick vector and disease pathogen surveillance of nilgai antelope, Boselaphus tragocamelus, in Southeastern Texas

Authors: Olafson, Pia; Thomas, Donald; May, Melinda; Buckmeier, Beverly - Greta; DUHAIME, ROBERTA - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Journal of Wildlife Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2018
Publication Date: 7/1/2016
Citation: Olafson, P.U., Thomas, D.B., May, M.A., Buckmeier, B.G., Duhaime, R.A. 2016. Tick vector and disease pathogen surveillance of nilgai antelope, Boselaphus tragocamelus, in Southeastern Texas. Journal of Wildlife Diseases. 79:1135-1142. https://doi.org/10.4315/0362-028X.JFP-15-414.
DOI: https://doi.org/10.4315/0362-028X.JFP-15-414

Interpretive Summary: Nilgai are non-native bovines originally introduced as game animals to one large, south Texas ranch but 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. These animals were either hunter-killed or 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 north to south pattern, and this is at least partly attributed to differences in habitat. The southerly area is a lowland floodplain predominated by halophytes while 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 several livestock pathogens since wildlife can intermingle with cattle in this region. All nilgai were negative for the agents that cause equine piroplasmosis. All animals were PCR negative for the parasite that causes bovine babesiosis (Babesia bovis and B. bigemina), while a single nilgai was seropositive for both these species by a complement fixation assay. It remains unknown whether cattle Babesia spp. can establish an infection in nilgai.

Technical Abstract: Nilgai are non-native bovines originally introduced as game animals to one large, south Texas ranch but 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 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 north to south pattern, and this is at least partly attributed to differences in habitat. The southerly area is a lowland floodplain predominated by halophytes while 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. While 11 animals were seropositive for Anaplasma marginale by cELISA, these were interpreted with caution due to 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.