Rhipicephalus microplus infestation in sheep from Yucatán, Mexico, and its toxicological response to coumaphos, cypermethrin, and ivermectin.

Rhipicephalus microplus (R. microplus) is the most significant tick in cattle worldwide, including Mexico; however, its presence in sheep is infrequent and typically associated with accidental exposures in production systems where they coexist with infested cattle. The objective of this study is to describe R. microplus infestation in sheep from Yucatán, Mexico, and to determine their toxicological response to coumaphos, cypermethrin, and ivermectin (IVM). The animal population of the production unit under study was examined for the presence of ticks, revealing infestations in sheep and cattle. Cattle exhibited between 12 and 21 standard ticks/animal, whereas six young sheep showed high infestation levels (35.1 standard ticks/animal). Engorged female ticks were collected for morphological identification and progeny collection. The larval packet technique was used to assess susceptibility to coumaphos and cypermethrin, and the larval immersion technique was used to assess susceptibility to IVM. Lethal concentrations at 50% (LC50) and 95% confidence intervals (CI95%) were determined using Probit analysis, as well as resistance ratios (RRs). All collected ticks were identified as R. microplus. The LC50s were 0.003 (0.002-0.004), 0.007 (0.005-0.009), and 0.0004 (0.0003-0.0005) for coumaphos, cypermethrin, and IVM, respectively. The evaluated population was susceptible to the acaricides, with RRs of 0.14, 0.53, and 0.8 for coumaphos, cypermethrin, and IVM, respectively. It is concluded that young sheep in a production unit in Yucatán, Mexico, had high infestations of R. microplus, and toxicological evaluation showed susceptibility to the evaluated compounds.