Susceptibility to insecticides of body lice, Pediculus humanus, collected in Tokyo
(IASR 2000; 21: 57-58)

Body lice, Pediculus humanus and head lice, Pediculus capitis are widely observed among the homeless people and children respectively in Japan and other industrialized countries. WHO announced a warning that insecticide use will be more difficult to control pediculosis in near future due to development of insecticide resistance of body lice and head lice. Investigations of insecticide susceptibility against these species are urgently needed in Japan. Using body lice, collected from 5 homeless people and one elderly person who lived alone in Toshima City during May 1999 to January 2000, susceptibility of 3 insecticides was measured. Phenothrin, one of the pyrethroids, which is solely approved by the Government for delousing agent, permethrin, which is another pyrethroids, and DDT, which is employed during a certain period after the World War II and its development of drug resistance is concerned, are examined.

The examination was carried out by counting survived body lice number after 24 hours contact with impregnated filter paper. As control louse, the NIID strain, which has been maintained at NIID since 1953 was employed. The 50% lethal concentration (LC₅₀) of body lice against phenothrin was 10-30mg/m², which was almost same or slightly lower than that of the controls (40-70mg/m²), thus result was susceptible. The LC₅₀ of lice from a homeless person against permethrin was 8mg/m², and that from the elderly person was 4mg/m². These results are apparently lower than that of control (17mg/m²). The LC₅₀ from a homeless person against DDT was 0.3mg/m², and that from the elderly person was 1.5mg/m². These results were the same or lower than that of control (1.8mg/m²).

These results indicate that body lice, which were collected in Tokyo maintained high susceptibility against the approved insecticide, thus development of drug resistance was not observed. However, both body and head louse cases are increasing in Japan, susceptibility monitoring should be continued. In particular, it should be conducted against head lice, since it has not carried out before.

Reported by Takashi Tomita, Masakazu Takahashi, Mutsuo Kobayashi, and Noriaki Agui, Dept. of Medical Entomology, NIID; Minoru Mihara, Dept. of Environmental Biology, Japan Environmental Sanitation Center; Noboru Yaguchi, Ikebukuro Public Health Center; Naomi Seki and Kuniko Makigami, Central Health and Welfare Center, Toshima City, Tokyo.

Correspondence: Takashi Tomita;
E-mail: tomita@nih.go.jp

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