Drug-resistant lice

IN THIS ISSUE, Yoon et al1 compare the effects of Ovide (Medicis Pharmaceutical Corporation, Phoenix, Ariz) and its active ingredient (malathion) with Nix (Pfizer/Warner-Lambert, Morris Plains, NJ) and its active ingredient (permethrin), using in vitro filter paper and contact bioassays. Lice from one location in Ecuador were compared with lice from 3 locations in the United States. In their assay, lice from a location in south Florida showed a slower response to permethrin compared with the Ecuadorian lice. In the Florida lice, Ovide and malathion showed an effect earlier than Nix or permethrin. The presence of 2 gene mutations (T929I and L932F) in permethrin-resistant lice from south Florida was confirmed by DNA sequencing. These mutations have been associated with knockdown resistance (kdr). In this assay, south Florida lice showed evidence of resistance to permethrin, but not to malathion.