Effects of acaricide treatment and host intrinsic factors on tick acquisition and mortality in Boran cattle.

Ticks and associated pathogens pose serious threats to the health of livestock. To assess the efficacy of acaricide dip treatment (cypermethrin, chlorpyrifos, piperonyl butoxide, citronella), we assessed post-treatment tick acquisition and tick mortality of free-ranging Boran cattle inhabiting a wildlife-cattle ranch in Northern Tanzania. Because host intrinsic variables and exposure to ticks may substantially affect tick acquisition, we incorporated host sex, body mass, health condition, and distance traveled in models of tick acquisition. Using generalized linear mixed models that accounted for non-independence of individuals, we found that tick species richness increased with host body mass but was not significantly related to other factors. In contrast, tick abundance increased with time since acaricide treatment, was positively correlated with host body mass, and was higher in female than male cattle. Distance traveled and health condition did not predict tick acquisition. Overall, these patterns were similar when separately analyzing acquisition of the more common tick species (Rhipicephalus pulchellus, R. sanguineus sensu lato, and R. praetextatus). Logistic regression models suggested that tick mortality was high for a few days after acaricide dip treatment but declined steeply post-treatment; 3.5 days after treatment, only 50% of ticks were dead, and mortality declined further thereafter. Our results provide new information regarding tick acquisition patterns in this system including female-biased tick parasitism and support for the hypothesis that increased host body mass provides greater resources and thus supports higher ectoparasite abundance and species richness. The limited acaricide duration of action and effectiveness on all tick species calls for adjusting tick management practices.