Abstract
BackgroundThe human head louse, Pediculus humanus capitis, is a cosmopolitan blood-sucking ectoparasite affecting mostly schoolchildren in both developed and developing countries. In Honduras, chemical pediculicides are the first line of treatment, with permethrin as their main active ingredient. Despite the extended use of these products, there is currently no research investigating insecticide resistance in Honduran head lice. In head lice, the most common mechanism is knockdown resistance (kdr), which is the result of two point mutations and the associated amino acid substitutions, T917I and L920F, within the voltage-sensitive sodium channel (VSSC).MethodsGenomic DNA was extracted from 83 head lice collected in the localities of San Buenaventura and La Hicaca, Honduras. Polymerase chain reaction (PCR) was used to amplify a 332-bp fragment of the VSSC gene that contains a site affected by C/T mutation which results in a T917I amino acid substitution on each human head louse genomic DNA fragments.ResultsThe C/T non-synonymous mutation which results in the T917I kdr amino acid substitution was detected in both head lice populations at frequencies ranging between 0.45–0.5. Globally, the frequency of this substitution was 0.47. Of these, 5 (6.1%) were homozygous susceptible and 78 (93.9%) were heterozygotes. The kdr-resistant homozygote (RR) was not detected in the studied populations. Thus, 93.9% of the head lice collected in Honduras harbored only one T917I allele. Exact test for the Hardy-Weinberg equilibrium for both localities showed that genotype frequencies differed significantly from expectation. In addition, San Buenaventura and La Hicaca populations had an inbreeding coefficient (Fis) < 0, suggesting an excess of heterozygotes.ConclusionsTo our knowledge, this is the first study showing the presence of the C/T mutation responsible of the T917I kdr allele associated with pyrethroid resistance in P. h. capitis from Honduras. The PCR-restriction fragment length polymorphism (RFLP) employed here has demonstrated to be a reliable, economic, and reproducible assay that can be used to accurately genotype individual head lice for the mutation encoding the resistance-conferring T917I amino acid substitution. This highlights the necessity of proactive resistance management programmes designed to detect pyrethroid mutations before they become established within populations of head lice.
Highlights
The human head louse, Pediculus humanus capitis, is a cosmopolitan blood-sucking ectoparasite affect‐ ing mostly schoolchildren in both developed and developing countries
Head lice infestation is known as pediculosis capitis which can result in pruritus, loss of sleep, attention deficit, and is associated with secondary skin infections due to scratching of an irritated scalp [1]
The diagnostic genetic marker linked to permethrin resistance consists of the presence of one or two fragments after the digestion with SspI
Summary
The human head louse, Pediculus humanus capitis, is a cosmopolitan blood-sucking ectoparasite affect‐ ing mostly schoolchildren in both developed and developing countries. Pediculus humanus capitis De Geer, commonly known as the human head louse, is a cosmopolitan and obligate ectoparasite found both in developed and developing countries. Head lice infestation is known as pediculosis capitis which can result in pruritus, loss of sleep, attention deficit, and is associated with secondary skin infections due to scratching of an irritated scalp [1]. The control of pediculosis among populations comprises both individual and collective approaches The former includes the use of mechanical or chemical methods, while the latter is based on limiting exposure through behavioral modifications. Specific treatment for this infestation relies heavily on the topical use of pediculicides, compounds with toxic or otherwise deleterious effects to lice. Chemical pediculicides are still recommended as first line of treatment worldwide and consist of over-the-counter (OTC) products, as well as products only available under medical prescription
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