Baseline susceptibility of a laboratory strain of Pediculus humanus humanus (Anoplura: Pediculidae) using a modified World Health Organization testing protocol

The World Health Organization (WHO) protocol for determining resistance in body lice, Pediculus humanus humanus (L.), requires holding lice for long periods, which makes successful execution of the test difficult in field settings. The purpose of this study was to modify the WHO test procedure to make the holding period of lice shorter and the handling of lice easier. Susceptible lice from a laboratory colony were placed in a petri dish containing a paper that had been treated with an insecticide solution. After 6 h, the petri dish was turned on its side and lightly tapped on the table. Lice that were unable to cling to the paper were counted as knocked down. The KD(50) in mg (AI)/ml of the insecticide solution used to treat the papers was as follows: lindane 0.060, permethrin 0.115, d-phenothrin 0.554, and malathion 1.008. If the diagnostic dose is set at 2 times the KD(99), for this test procedure the diagnostic doses and WHO equivalent dose would be lindane, 0.368 mg (AI)/ml (WHO 0.132%); permethrin, 0.498 mg (AI)/ml (WHO 0.206%); d-phenothrin, 2.680 mg (AI)/ml (WHO 1.107%); and malathion, 5.212 mg (AI)/ml (WHO 2.020%).