Avaliação de resistência cruzada e efeito da ciclosporina A em populações de Rhipicephalus microplus resistentes a lactonas macrocíclicas no Semiárido Nordestino.

Abstract

The cattle tick, Rhipicephalus microplus, is the hematophagous ectoparasite with the greatest economic and health impact on Brazilian cattle. The most used method of controlling this parasite is the application of synthetic chemical acaricides, with emphasis on drugs of the macrocyclic lactone class, such as ivermectin. There are different mechanisms involved in antiparasitic resistance, including the increased activity of cellular efflux pumps such as ABC membrane transporters (ATP binding cassettes), which aid in cellular detoxification of parasites, causing drug resistance. This resistance mechanism has already been described in ivermectin­resistant populations of R. microplus. As macrocyclic lactones are similar compounds, we investigated the hypothesis of cross­resistance between different drugs of this group (ivermectin, eprinomectin and moxidectin) and the participation of ABC transporters as the resistance mechanism involved. Four populations of resistant R. microplus were analyzed, from the semi­arid region of Northeast Brazil, from the states of Paraíba and Ceará, with two properties in each state. For this, Larval Immersion Tests were performed with and without the use of Cyclosporine A (CsA), comparing with the susceptible and reference strain Porta Alegre, observing the synergism between CsA and ivermectin, eprinomectin and moxidectin in these populations. Among the populations analyzed, cross­resistance between moxidectin and ivermectin was observed and CsA acted as a synergist, reducing its lethal doses, while for and eprinomectin the results were different from those found for the other macrocyclic lactones used. It is suggested that other resistance mechanisms may be involved for eprinomectin in resistant populations in the semiarid region of Northeastern Brazil.