Expansion of the Knockdown Resistance Frequency Map for Head Lice

A new study has produced further information on the spread of lice resistance to pyrethrin-type treatments.

A study by Gellatly et al., published in the March 2016 edition of the Journal of Medical Entomology suggests a correlation between the decrease in effectiveness of pyrethrins or pyrethroid insecticides and the increase in knockdown resistance (kdr) type mutations in lice over time.

The study compared the changes in the frequency of the kdr-type mutations from lice collected from over 130 collection sites in the continental USA. Quantitative sequencing was used to examine the extent and magnitude of the kdr mechanism in lice responsible for the lice resistance to pyrethrins.

The overall average percentage of resistance alleles (indicating knockdown resistance) was 98%. The frequency of kdr-type mutations did not differ regardless of the human population size that the lice were collected from, indicating that resistant alleles are uniformly spread over the population.