In vitro susceptibility assessment of various tick species against fipronil

Abstract

The number of infections transmitted by ticks has significantly increased over the last decades. It is of importance that ticks are controlled in order to prevent the transmission of tick-borne infections. Humans are also susceptible to some of the tick-borne infections that occur in dogs and cats; therefore controlling ticks on cats and dogs is also of importance for public health.

It is desirable for an acaricide to exhibit specificity to insects over mammals and birds. Fipronil shows specificity to insects over mammals by binding to GABA and glutamate receptors in the arthropod cell. Binding to these receptors causes inhibition of chloride channels leading to hyper excitation of the nerve cell of the tick and death of the tick.

To determine the susceptibility of known and unknown acaricides, in vitro testing of acaricides is the best possible way because there is no influence from a host. In this in vitro study the efficacy of fipronil in killing adult ticks was tested. Fipronil produced 100% mortality in all tick species tested. The LD50 value of fipronil in adult Amblyomma americanum, Rhipicephalus turanicus and Rhipicephalus sanguineus at 24 hours was 3,558, 0,094 and 0,283 respectively. The LD50 value of fipronil in Amblyomma americanum, Rhipicephalus turanicus and Rhipicephalus sanguineus at 48 hours was 0,022, 0,006 and 0,005 respectively. Fipronil was shown to be least effective against Amblyomma americanum, compared to the other tick species tested. From the tick species tested fipronil is most effective against adult Rhipicephalus ticks. The efficacy of fipronil against adult Rhipicephalus turanicus and adult Rhipicephalus sanguineus was highly comparable.