Molecular Monitoring of Knockdown Resistance in Head Louse (Phthiraptera: Pediculidae) Populations in Iran

Knockdown resistance (kdr) is a common mechanism of insecticide resistance in head lice to the conventionally
used pyrethroid pediculosis and can be the result of various amino acid substitutions within the voltagesensitive
sodium channel (VSSC). In this study, 54 sequences from varied specimens were investigated to
monitor well-known resistance mutations and probable new mutations. The Pediculus humanus capitis de
Geer specimens were collected from 13 provinces in Iran. The specimens were stored in 70% ethanol until DNA
extraction and PCR amplification of ~900-bp fragment of VSSC. The sequences were analyzed using different
bioinformatics software for the detection of well-known kdr substitutions and additional mutations potentially
associated with kdr resistance in head lice. There were six new and an old (haplotype I) kdr haplotypes within
the Iranian head louse population. K794E, F815I, and N818D amino acid substitutions were reported for the
first time. The P813H mutation was the most prevalent amino acid substitution in eight provinces. Among
53 sequences, 26 (49%) were homozygous susceptible, and 27 (51%) were heterozygotes. Thus, 51% of the
head lice collected in Iran harbored only the P813H allele. The exact test for the Hardy–Weinberg (H–W) equilibrium
showed that genotype frequencies differed significantly from the expectation in East-Azerbaijan and
Tehran provinces. Moreover, these populations had an inbreeding coefficient (Fis) <0, indicating the excess
of heterozygotes. This observation suggests that the populations of head lice from Iran are currently under
active selective pressure. For the rest of the populations, H–W equilibrium and the expectations were significantly
in harmony. The results of the current study highlight molecular techniques in the accurate detection of