Almost fixation in knockdown resistance alleles to pyrethroids in head louse (Pediculus humanus capitis) populations from Argentina

TOLOZA A; ASCUNCE M; REED D.; PICOLLO M.I.

Park City, Utah

Congreso; 5º International Conference on Phthiraptera 2014; 2014

University of Utah

In Argentina, the overuse of products containing permethrin (a common used synthetic pyrethroid) in the last three decades has led to the development of resistant louse populations. Pyrethroid insecticides act on the nervous system affecting voltage-sensitive sodium channels (VSSC). Two point mutations at the corresponding amino acid sequence positions T917I and L920F in the voltage-gated sodium channel gene are responsible for mainly contributing to knockdown resistance (kdr). The management of pyrethroid resistance requires either early detection or the characterization of the mechanisms involved in head louse populations that are essential to perform optimal control strategies. In the present study, we estimated the geographical distribution of kdr alleles in 154 head lice from six geographic regions throughout Argentina. Pyrethroid resistance kdr alleles were found in high frequencies ranging from 67 to 100%, reaching almost fixation. Of these, 131(85.1%) were homozygous resistant, 13 (8.4%) were homozygous susceptible, and 10 (6.5%) were heterozygous. Exact tests for Hardy-Weinberg equilibrium for each location showed that genotype frequencies differed significantly from expectation in 4 of the 6 sites studied (67%). These results show that pyrethroid resistance is well established and has evolved rapidly among head louse populations from Argentina.