Ivermectin resistance of three Rhipicephalus microplus populations using the larval immersion test

Abstract

SummaryBackground: in Colombia, the control of tick infestation in cattle is almost exclusively performed with chemical acaricides. It is important to determine the degree of resistance of Riphicephalus microplus field populations to ivermectins (IVM) as the first step to design strategies to increase the useful life of acaricides and decrease the reliance on chemical controls. Objective: to test the degree of resistance to IVM. Methods: three cattle farms in Antioquia (Colombia) where IVM had previously failed to control infestations of R. microplus ticks were studied. Ticks were collected several months apart in 2013, and the larval immersion test (LIT) was performed on the progeny of the adult females. Concentration-mortality data were subjected to probit analysis. Results: the three populations showed lethal concentrations (LC) 50 and 99 of ≥ 30 ppm and ≥ 400 ppm, respectively. There was no difference observed in the LC at different times of collection for each population studied. Such high values for LC, together with very low regression slopes (≤ 2), indicated a very heterogeneous response to increasing concentrations of IVM, which is common for resistant populations. At two farms, subcutaneous injection with a long-acting formulation of IVM at a dosage of 630 µg/Kg was ineffective at eliminating existing infestations and protecting against reinfestations, confirming farmer suspicions of lost efficacy. Conclusion: epidemiological studies are necessary to assess the current status of resistance to IVM in this region of Colombia, and it is likely that the intensive use of IVM will aggravate this situation in the future.

Resistencia in vitro a acaricidas tópicos de poblaciones de garrapatas Rhipicephalus (Boophilus) microplus provenientes de cuatro departamentos de Colombia

“…microplus que no responden a los acaricidas convencionales. Por ejemplo, en el caso de Antioquia, los estudios in vivo e in vitro en algunos municipios han mostrado que efectivamente existe un problema de resistencia a la mayoría de acaricidas comerciales Puerta et al, 2015;Villar et al, 2016). Para demostrar que se trata de una resistencia innata y no de una mala aplicación o preparación de los productos, se han realizado pruebas in vitro recomendadas por la FAO (2004); simultáneamente se han hecho estudios de campo empleando las guías recomendadas por la Asociación Mundial para el Avance de la Parasitología (Holdsworth et al, 2006).…”

Identification and prevalence of ticks (ACARI: Ixodidae) in bovines in five municipalities of the Popayán plateau (Colombia)

“…Two methods of acaricide resistance development by ticks are known; one is metabolic resistance and the other is target site insensitivity (Diaz, 2012;de Oliveira Souza Higa et al, 2015). In Colombia, there are reports of resistance to acaricides including organochlorines, formamidines, organophosphates, synthetic pyrethroids, and ivermectin (Benavides et al, 2000;Abbas et al, 2014;Araque et al, 2014;Villar et al, 2016). Information gathered in this study regarding estimated prevalence of ticks, degree of tick infestation, types of acaricide used and frequency of acaricide application (Table 1) suggest there is acaricide resistance in the Cauca province and highlights the need for further research on the subject in order to propose more pertinent strategies for tick control.…”

“…Economic losses caused by ticks in Colombia, as reported by Garcia in 1983, were $5,000 million COP (equivalent to $1.6 million USD) without taking into account the cost of treatments (PolancoEcheverry and Rios-Osorio, 2016). Furthermore, there are reports of tick resistance to acaricides including organochlorines, formamidines, organophosphates, synthetic pyrethroids, and ivermectin (Benavides et al, 2000;Abbas et al, 2014;Araque et al, 2014;Villar et al, 2016). …”

Resistance profile and molecular characterization of pyrethroid resistance in a Rhipicephalus microplus strain from Colombia

“…The LIT with ivermectin was conducted as described previously (Villar et al ., ). A control solution containing 1% ethanol and 0.02% Triton X‐100 in distilled water was used to prepare all immersion dilutions and to test control larvae.…”

“…The traditional method of control used throughout the country has been the application of injectable and topical chemical acaricides. However, recent in vivo and in vitro studies conducted across the country have revealed widespread resistance to most commercial acaricides (López‐Arias et al ., ; Puerta et al ., ; Villar et al ., , ). The findings have revealed that pyrethroids, in particular cypermethrin and deltamethrin, are no longer effective in Colombia and most farmers have now abandoned their use for tick control.…”