Low level deltamethrin resistance in ticks from cattle of Kerala, a south Indian state.

The deltamethrin resistance status in Rhipicephalus (Boophilus) annulatus and R. (B.) microplus ticks collected from cattle of five organized farms of Kerala, south India was evaluated. Resistance was characterized using biological (larval packet test), biochemical (esterase enzyme activity assay) and molecular tools (PCR amplification and sequencing of deltamethrin resistance-associated genes). Characterization of field isolates revealed level I resistance in ticks collected from four out of five farms. Elevated level of α/β esterase activity was not recorded in isolates showing level I resistance. Previously reported point mutations in the carboxyl esterase (G1120A) and sodium channel (T2134A and C190A) genes were not observed in any of the field isolates. The present study showed a low level (level I) resistance is developed in the most economically important ticks infesting cattle of this state and it cautions the development of large scale resistance in future.