Basic research for establishing molacular diagnosis of insecticide-resistance in humanlouse

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The cDNA sequences encoding for para-orthologous sodium channel and acetylcholinesterase were newly determined from an insecticide-susceptible bodylice strain, NIID. Insecticide susceptibility of NIID louse were assayed by continuous phenothrin-impregnated filter-contact method and knockdown louse were scored after 3 hours treatment. KCl and KC99 of adult louse were 20mg/m2 and 54 mg/m2, respectively. The KC99 value was used for a minimum resistant-discriminating concentration while the KC1 value was used for a reference in estimating resistance ratio of torelent louse. Ten headlice colonies collected in Saitama Pref. , Tokyo, Kanagawa Pref. were assayed for phenothrin susceptibility and three were resistant. A resistant colony showing the highest resistance ratio in underestimation was 160-fold. The complete coding sequence of sodium channel gene from a phenothrin-susceptible headlice was compared to that from the NIID bodylice and there was a single synonymous base substitution between them. A phenothrin-resistant headlice had 23 nucleotide substitutions in which four resulted in putative amino acid substitutions, structural change in resistant sodium channel should be involved in some of these mutations. The two out of these amino acid substitutions, T952I and L955P, were at least shared among the pyrethroid-resistant headlice colonies in the US and UK reported previously (Lee et al. 2000) and the present Japanese leadlice. Bsed on these resistant-specific point mutations, we would be possible to excute molecular diagnosis of pyrethroid-rsistance with eggs and dead louse which are obtained more easily than alived louse.