Potential Causes of Acaricide Resistance in Rhipicephalus and AmblyommaTicks (Acari: Ixodidae) in Namwala District, Zambia

Acaricide resistance in ticks poses a great threat to livestock production in many parts of the world where ticks are a problem. The objectives of this study were to screen for acaricide resistance in Rhipicephalus and Amblyomma ticks using phenotypic and molecular assays, and to assess current tick control practices used by cattle farmers in the traditional sector of Namwala District. The larval packet test was used to screen for acaricide resistance in ticks covering concentrations up to twice the discriminatory dose for amitraz, diazinon and cypermethrin. Genetic mutations associated with resistance to amitraz (A22C-T8P and T65C-L22S), and organophosphates/ pyrethroids (G1120A) were screened using polymerase chain reaction and sequencing. Information on tick control practices at the household level was collected using a semi-structured questionnaire. Intermediate resistance (21-50%) to amitraz and cypermethrin was detected in both Rhipicephalus and Amblyomma ticks, with both tick genera showing susceptibility to diazinon (<10%). None of the ticks in this study had the reported acaricide resistance-conferring molecular markers that were screened for. The findings suggest that the resistance detected in the studied tick population may be due to other mechanisms yet to be identified. Tick control practices observed amongst the farmers, such as the incorrect use of acaricide concentrations and rotations, could be fuelling the development of acaricide resistance. Considering that acaricide treatment is the mainstay of tick control in the country, it is thus, critical to comprehensively unravel the factors contributing to treatment failure as this would allow for the application of appropriate remedial actions for effective tick control in Zambia.