Adult Immersion Test for Assessment of Amitraz Resistance in Rhipicephalus Sanguineus Ticks

Ticks are obligate blood sucking ectoparasites recognised globally as vectors of various pathogens, next to mosquitoes. The present study is conducted on brown dog ticks collected from naturally infested dogs in and around Thrissur district. Adult immersion test was performed and the parameters such as engorged tick weight, egg mass weight as well as tick mortality were recorded to derive the reproductive indices, percentage inhibition of oviposition and percentage mortalities. Non-linear regression analysis of the dose response data yielded the LC50 values at 95% confidence intervals and, the slopes and regression coefficients of the different parameters were also derived. The Resistance factors (RF) were calculated to categorise resistance levels into I, II, III and IV. Resistance to amitraz was detected at level II in tick isolates collected from Choolissery and Mundur, at level III and level IV in isolates collected from Mannuthy and Paravattani, respectively. Two isolates collected from Mannuthy were found to be susceptible. One way ANOVA of resistance levels revealed that the resistance levels III and IV were significantly different from that of susceptible and resistance level II. This is the first report on detection of amitraz resistance levels in dog ticks from south India calling for proper implementation of tick control strategies to prevent spread of amitraz resistance.