Status of Rhipicephalus microplus resistance to ivermectin, fipronil and fluazuron in Mato Grosso do Sul, Brazil

Abstract

Southern cattle tick resistance to pour-on and injectable acaricides has yet to be evaluated on a broader scope, and the paucity of information on the subject may hinder efforts to control this parasite. The objective of this study was to evaluate the resistance profile of ten populations of Rhipicephalus microplus to the acaricides fluazuron, fipronil and ivermectin in cattle herds in Mato Grosso do Sul, Brazil. The larval immersion test (LIT) was used to evaluate susceptibility to ivermectin and fipronil and the adult immersion test (AIT) was performed to evaluate fluazuron. Samples were randomly obtained in ten farms, and in general, we found resistance in five samples to fluazuron and in four samples to ivermectin and fipronil. Six samples showed incipient resistance to ivermectin and fipronil. Five of the ten evaluated samples showed resistance and/or incipient resistance to all the active ingredients, and the other five to two active ingredients. Among the samples classified as resistant, the average resistance ratio for ivermectin was 2.75 and 3.26 for fipronil. These results demonstrate the advanced status of resistance to the most modern chemical groups for the control of R. microplus in the state of Mato Grosso do Sul.

Brazil's battle against Rhipicephalus (Boophilus) microplus ticks: current strategies and future directions

“…The historical massive use of chemical acaricides led to reports of multiple resistance against the main classes of acaricides in all regions in which the cattle tick is found. Of the seven classes of chemical acaricides marketed in Brazil, resistance to six of them has been reported ( Reck et al, 2014a ; Valsoni et al, 2021 ). To date, there is no report of resistance against isoxazolines, which have been released to the market for cattle in 2022.…”

The current status and outlook for insecticide, acaricide and anthelmintic resistances across the Australian ruminant livestock industries: assessing the threat these resistances pose to the livestock sector

“…112 Recent reports have described isolates of cattle tick in Brazil that are resistant to all of these chemical classes as well as fluazuron. 113,114 Control of the buffalo fly appears to not be under immediate threat while MLs and OPs remain effective. However, resistance to OPs has been reported in the closely related horn fly in the USA.…”

“…Resistance to SPs, OPs, amitraz and MLs is widespread in cattle tick populations across the world, particularly in Latin America and South America 112 . Recent reports have described isolates of cattle tick in Brazil that are resistant to all of these chemical classes as well as fluazuron 113,114 …”