Head lice, Pediculus capitis, were collected from children aged 3-12 years in Maale Adumin, a town near Jerusalem, after reports of control failure with the pyrethroid insecticide permethrin. A total of 1516 children were examined: living lice and eggs were found on 12.1% of the children; or another 22.8% of the children only nits were found. Twice as many girls as boys (8.1% v 4%) were infested with lice and or nits. Head lice collected from infested children were exposed to permethrin impregnated filter-papers. Log time probit mortality (ltp) regression lines were calculated for mortality data and compared to ltp lines for a similar collection of head lice made in 1989. The regression lines for the two years were significantly different, with a 4-fold decrease in susceptibility at the LT50 level between 1989 and 1994. The slopes of the lines also suggested that the 1994 population was more heterogenous in its response to permethrin than the 1989 population. In contrast, a laboratory population of body lice (Pediculus humanus) tested with the same batch of permethrin-impregnated papers showed a slight but non-significant increase in susceptibility between 1989 and 1994. The results suggest that resistance to pyrethroids has developed rapidly among head lice since permethrin was introduced in 1991 as a pediculicide in Israel.

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Of 3,079 children in a medium-sized community near Jerusalem, 11.2% were found to be infested with living lice and eggs and another 23.4% had only nits. Boys and girls were equally infested. The incidence of infestation was highest among children 4-11 years of age. About 78% of the infested children had from one to ten lice. Approximately 80% of the infested children had nits that were 2-5 cm away from the scalp. Boys with medium length hair and girls with short hair showed the highest incidence of lice infestation. Children with brown and red hair were more infested than those with black and blond hair. Boys and girls with straight and wavy hair were more infested than those with curly and frizzy hair.

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