DDT Resistance in Egyptian Body Lice

Abstract

Summary 1. The average mortality for adult Egyptian body lice from the vicinity of Cairo when exposed to DDT powder for 24 hours was 31 per cent for one tenth per cent DDT, 70 per cent for one per cent DDT, and 89 per cent for ten per cent DDT, giving an LD50 of 0.33 per cent. After four days of wear, sleeves which had been treated with 10 per cent DDT killed only 14 per cent of the lice exposed to them. 2. The results of a field test showed that 10 per cent DDT powder is still effective in reducing lousiness. The percentage of heavily infested people (harboring 10 lice or more) was reduced from 56 per cent before treatment to 9 per cent four weeks after treatment while the control group remained approximately the same. When 10 very heavily infested people were treated once each month for five months the number of lice was markedly reduced but about half remained relatively heavily infested. 3. Tests on cloth treated by dipping in acetone solutions of DDT showed that Egyptian body lice could be propagated on cloth which had been treated with a 1–5,000 dilution of DDT. After two generations these lice were established on cloth treated with a 1–2,000 dilution and maintained on it for four generations. The 1–10,000 dilution proved to be lethal to lice from four localities where it is unlikely that there had been previous contact with DDT.