Ivermectin resistance status and factors associated in Rhipicephalus microplus (Acari: Ixodidae) populations from Veracruz, Mexico.
The objectives of the present study were to (1) determine the status of resistance or susceptibility to ivermectin (IVM) in Rhipicephalus microplus tick populations in Veracruz, Mexico, (2) determine the level of resistance (resistance ratios [RR] and lethal concentrations for 50% [LC(50)] and 99% [LC(99)]) mortality in each R. microplus population, and (3) identify factors associated with resistance. Populations of R. microplus were sampled from 53 cattle farms to evaluate their resistance using the larval immersion test. Mortality data were subjected to probit analysis to calculate LC(50) and LC(99). Resistance ratios were calculated in relation to a susceptible reference strain. A logistic regression model was used to evaluate the relation between resistance and possible associated factors. Thirteen tick populations were susceptible to ivermectin, eighteen had incipient resistance and twenty-two had significant resistance. RR(50) of the susceptible tick populations varied from 0.59 to 1.07. The populations that showed the highest level of resistance were: ANTE (RR(50)=8.21; RR(99)=46.0), PALO (RR(50)=6.25; RR(99)=35.47), P.VIE (RR(50)=5.89; RR(99)=180.3), AURO (RR(50)=5.36; RR(99)=13.82 and CEDR (RR(50)=4.11; RR(99)=26.47). Cattle farms that used macrocyclic lactones ≥ 4 times per year were more likely to develop R. microplus resistant to ivermectin (OR=13.0; p=0.0028). In conclusion, more than two-thirds of the farms sampled in Veracruz, Mexico, showed some level of ivermectin-resistant R. microplus populations and the number of ML applications per year is factor associated with the resistance of R. microplus to IVM.
Centro de Enseñanza, Investigación y Extensión en Ganadería Tropical, Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México, Km. 5.5 Carretera Federal Tlapacoyan-Martínez de la Torre, C.P. 93600, Martínez de la Torre, Veracruz, Mexico.
A
A
Fernández-Salas
R I
RI
Rodríguez-Vivas
M A
MA
Alonso-Díaz
H
H
Basurto-Camberos
D056810:Acaricides / Q000494:pharmacology*; D000818:Animals; D000977:Antiparasitic Agents / Q000494:pharmacology; D001681:Biological Assay; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000469:parasitology* / Q000517:prevention & control; D004351:Drug Resistance; D005260:Female; D005838:Genotype; D007559:Ivermectin / Q000494:pharmacology*; D007783:Lactones / Q000494:pharmacology; D007928:Lethal Dose 50; D016015:Logistic Models; D047028:Macrocyclic Compounds / Q000494:pharmacology; D008800:Mexico / Q000453:epidemiology; D048494:Rhipicephalus / Q000187:drug effects*; D013984:Tick Infestations / Q000453:epidemiology / Q000469:parasitology / Q000517:prevention & control / Q000662:veterinary*
D056810:Acaricides; D000977:Antiparasitic Agents; D007783:Lactones; D047028:Macrocyclic Compounds; D007559:Ivermectin