TICK VECTOR AND DISEASE PATHOGEN SURVEILLANCE OF NILGAI ANTELOPE (BOSELAPHUS TRAGOCAMELUS) IN SOUTHEASTERN TEXAS, USA

Abstract

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.

Enhanced biosurveillance of high-consequence invasive pests: southern cattle fever ticks, Rhipicephalus (Boophilus) microplus, on livestock and wildlife

“…Over the last four decades, ungulate wildlife such as WTD and nilgai have adversely affected success of the CFTEP [ 7 , 10 , 19 ]. In 2010, the need to refine current SCFT tick models to include SCFT host interactions was identified as a key research goal for success of the eradication programme [ 12 ].…”

“…Currie [ 39 ] reported an average infestation of 13 adult SCFT per WTD in south Texas (Zapata County). Olafson et al [ 19 ] reported a mean of 5.4 SCFT per nilgai in south Texas (Cameron and Willacy counties). The relative metabolic body size and agility of nilgai indicate they are as ill-equipped as cattle to remove ticks by grooming, suggesting that 5.4 may be at the low end of probable per capita tick loads.…”

“…Blood from free-ranging nilgai in northern Mexico tested PCR-positive for both B. bigemina and B. bovis , although no SCFT were found on the nilgai from which the blood was sampled [ 18 ]. It remains unknown whether either bovine Babesia species can establish an infection in nilgai [ 19 ]. Further studies are needed to evaluate the biological performance of SCFT on nilgai and to determine whether nilgai can sustain a population of SCFT in the absence of cattle and/or WTD [ 7 ].…”

Research on Integrated Management for Cattle Fever Ticks and Bovine Babesiosis in the United States and Mexico: Current Status and Opportunities for Binational Coordination

“…populations, but they did not find evidence of deer being able to allow either B. bovis or B. bigemina to complete their transmission cycles. It was further studies by Ueti and collaborators [ 29 ] that confirmed that deer cannot be infected with virulent B. bovis isolates.…”

“…For example, a knowledge gap exists on CFT infestation and the circulation of Babesia pathogens in wildlife and the actual infection rate in Mexican cattle. These aspects are of grave concern for the U.S. [ 29 , 30 ]. In particular, participants in the meeting were most interested in understanding the ecology of R. microplus and R. annulatus in the Texas–Mexico transboundary region, as well as how white-tailed deer, Odocoileus virginianus (Zimmerman) and nilgai, Boselaphus tragocamelus (Pallas) complicate CFT and hemoparasite management efforts.…”