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

Abstract

Background Some tick species are invasive and of high consequence to public and veterinary health. Socioeconomic development of rural parts of the USA was enabled partly through the eradication by 1943 of cattle fever ticks (CFT, Rhipicephalus (Boophilus) annulatus and R. (B.) microplus). The southern cattle fever ticks (SCFT, R. (B.) microplus) remain a real and present threat to the USA animal agriculture because they are established in Mexico. Livestock-wildlife interactions in the Permanent Quarantine Zone (PQZ) established by the century-old Cattle Fever Tick Eradication Programme (CFTEP) in south Texas endanger its operations. Methods We describe a spatially-explicit, individual-based model that simulates interactions between cattle, white-tailed deer (WTD, Odocoileus virginianus), and nilgai (Boselaphus tragocamelus) to assess the risk for SCFT infestations across the pathogenic landscape in the PQZ and beyond. We also investigate the potential role of nilgai in sustaining SCFT populations by simulating various hypothetical infestation and eradication scenarios. Results All infestation scenarios resulted in a phase transition from a relatively small proportion of the ranch infested to almost the entire ranch infested coinciding with the typical period of autumn increases in off-host tick larvae. Results of eradication scenarios suggest that elimination of all on-host ticks on cattle, WTD, or nilgai would have virtually no effect on the proportion of the ranch infested or on the proportions of different tick habitat types infested; the entire ranch would remain infested. If all on-host ticks were eliminated on cattle and WTD, WTD and nilgai, or cattle and nilgai, the proportions of the ranch infested occasionally would drop to 0.6, 0.6 and 0.2, respectively. Differences in proportions of the ranch infested from year to year were due to primarily to differences in winter weather conditions, whereas infestation differences among tick habitat types were due primarily to habitat use preferences of hosts. Conclusions Infestations in nilgai augment SCFT refugia enabled by WTD and promote pest persistence across the landscape and cattle parasitism. Our study documented the utility of enhanced biosurveillance using simulation tools to mitigate risk and enhance operations of area-wide tick management programmes like the CFTEP through integrated tactics for SCFT suppression.

Simulated dynamics of southern cattle fever ticks (Rhipicephalus (Boophilus) microplus) in south Texas, USA: investigating potential wildlife-mediated impacts on eradication efforts

“…To investigate potential causal mechanisms responsible for wildlife-mediated impacts on SCFT eradication efforts, we used the model described by Wang et al [ 18 , 20 ]. The model is spatially explicit and individual-based [ 25 , 26 ], and is designed to simulate effects of shifts in the spatiotemporal patterns of host (cattle, white-tailed deer, and nilgai) habitat use on the dynamics of SCFT populations (Fig.…”

“…There is a wide variety of CFT models focused on questions dealing with both basic biology and management on four continents [ 15 ]. However, relatively few models have included explicit representation of wildlife hosts [ 16 – 19 ], and only one has included nilgai [ 20 ]. Based on results of a simulation modeling study focused on CFT–livestock–wildlife interactions, it has been suggested that refugia for CFT could be created by white-tailed deer during acaricide treatments directed at cattle via deposition and subsequent collection of CFT in habitats favorable for survival of off-host life stages [ 18 ].…”

“…Based on results of a simulation modeling study focused on CFT–livestock–wildlife interactions, it has been suggested that refugia for CFT could be created by white-tailed deer during acaricide treatments directed at cattle via deposition and subsequent collection of CFT in habitats favorable for survival of off-host life stages [ 18 ]. Further simulation studies have suggested that nilgai, which roam widely over parts of south Texas and northeastern Mexico [ 21 ], could augment the role of white-tailed deer in sustaining CFT infestations by facilitating widespread redistribution of CFT from refugia [ 20 ]. Nilgai activity ranges are larger than those of white-tailed deer by almost an order of magnitude; the maximum axis of home ranges of radio-tracked nilgai have exceeded 30 km [ 11 ].…”

“…One of the major uncertainties in dealing with potential wildlife-mediated impacts on CFT eradication efforts remains our lack of knowledge about the combined effects of host species composition and host habitat use patterns on tick infestation dynamics. Wang et al [ 20 ] conducted a preliminary evaluation of the sensitivities of southern cattle fever tick (SCFT, R . ( B .)…”

Effects of white-tailed deer habitat use preferences on southern cattle fever tick eradication: simulating impact on “pasture vacation” strategies

“…Serologic and molecular evidence suggests that WTD in northern Mexico and southern Texas carry bovine babesiosis [ 17 ], and genetic data suggest WTD likely serve as a source for tick populations that will eventually feed on cattle [ 18 ]. Both field and modeling studies have examined the potential role of ungulate hosts related to disease transmission [ 19 ], the effects of seasonal fluctuations in host communities on the dynamics of infectious disease [ 20 ], and the efficacy of targeting acaricides at specific types of hosts [ 21 ]. Wang et al [ 10 ] focused specifically on modeling the impact of interactions between cattle and WTD on SCFT-eradication methods.…”