title: Survey of Rhipicephalus microplus resistance to ivermectin at cattle farms with history of macrocyclic lactones use in Yucatan, Mexico.
abstract: Engorged females of Rhipicephalus microplus were collected from 30 cattle farms in Yucatan, Mexico to evaluate ivermectin resistance. The larval progeny of each tick sample were produced in laboratory and evaluated using the larval immersion test to obtain the larval mortality. Concentration-mortality data were subjected to probit analysis to generate lethal concentrations (LC). Resistance ratio (RR) of each tick sample was calculated by dividing its LC with that of an ivermectin-susceptible strain (Deutch). Field populations of R. microplus demonstrated various levels of resistance to ivermectin. The top three resistant populations were CHPAT (RR(50)=10.23, RR(99)=179.6), SDGO (RR(50)=7.37, RR(99)=115.3) and FND (RR(50)=7.09, RR(99)=50.22). The level of ivermectin resistance in most tick samples from cattle farms in Yucatan, Mexico were relatively low. However, the intensive use of macrocyclic lactones to control both endo- and ectoparasites in the region will likely lead to a more serious resistance problem that may cause control failure in the future.
authors.affiliation: Departamento de Parasitología, Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Yucatán, Km. 15.5 carretera Mérida-Xmatkuil, C.P. 97100 Mérida, Yucatán, Mexico.
authors.forename: L C
authors.initials: LC
authors.lastname: Perez-Cogollo
authors.forename: R I
authors.initials: RI
authors.lastname: Rodriguez-Vivas
authors.forename: G T
authors.initials: GT
authors.lastname: Ramirez-Cruz
authors.forename: J A
authors.initials: JA
authors.lastname: Rosado-Aguilar
mesh_terms: D000822:Animal Husbandry / Q000379:methods; D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000469:parasitology* / Q000517:prevention & control; D016009:Chi-Square Distribution; D004351:Drug Resistance / Q000502:physiology; D005260:Female; D007306:Insecticides / Q000008:administration & dosage / Q000494:pharmacology*; D007559:Ivermectin / Q000008:administration & dosage / Q000494:pharmacology*; D007928:Lethal Dose 50; D008800:Mexico / Q000453:epidemiology; D021261:Parasitic Sensitivity Tests / Q000662:veterinary; D048494:Rhipicephalus / Q000254:growth & development*; D011795:Surveys and Questionnaires; D013984:Tick Infestations / Q000469:parasitology / Q000517:prevention & control / Q000662:veterinary*; D014329:Tropical Climate
chemical_list: D007306:Insecticides; D007559:Ivermectin