Geographical Distribution of Pyrethroid Resistance Allele Frequency in Head Lice (Phthiraptera: Pediculidae) From Argentina

ARIEL CEFERINO TOLOZA,; MARINA S. ASCUNCE; DAVID REED; MARIA INE S PICOLLO

JOURNAL OF MEDICAL ENTOMOLOGY

ENTOMOLOGICAL SOC AMER

Lugar: Lanham; Año: 2014 vol. 50

0022-2585

The human head louse, Pediculus humanus capitisDeGeer (Phthiraptera: Pediculidae),is an obligate ectoparasite that causes pediculosis capitis and has parasitized humans since thebeginning of humankind. Head louse infestations are widespread throughout the world and have beenincreasing since the early 1990s partially because of ineffective pediculicides. In Argentina, the overuseof products containing pyrethroids has led to the development of resistant louse populations. Pyrethroidinsecticides act on the nervous system affecting voltage-sensitive sodium channels. Three pointmutations at the corresponding amino acid sequence positions M815I, T917I, and L920F in thevoltage-gated sodium channel gene are responsible for contributing to knockdown resistance (kdr).The management of pyrethroid resistance requires either early detection or the characterization ofthe mechanisms involved in head louse populations. In the current study,weestimated the distributionof kdr alleles in 154 head lice from six geographical regions of Argentina. Pyrethroid resistance kdralleles were found in high frequencies ranging from 67 to 100%. Of these, 131 (85.1%) were homozygousresistant, 13 (8.4%) were homozygous susceptible, and 10 (6.5%) were heterozygous. Exact testsfor the Hardy-Weinberg equilibrium for each location showed that genotype frequencies differedsigniÞcantly from expectation in four of the six sites studied. These results show that pyrethroidresistance is well established reaching an overall frequency of 88%, thus close to Þxation. With 30 yrof pyrethroid-based pediculicides use in Argentina, kdr resistance has evolved rapidly among thesehead louse populations.