Studies on the population of head-lice, Pediculus humanus var. capitis De G

Abstract

The following is a summary of our studies on population of head lice, adults and nits.1. Out of a total of 8702 adult lice, the male population comprised 2031. The gross infestation rate per head was 129.9 and the maximum number found on a single head was 1434. A disproportion in the distribution of the two sexes was a marked feature.2. Patients below the age of 11 showed a lower infestation rate than those above this age, and short-haired individuals were more heavily infested than long-haired ones.3. Frequent combing of the hair and the use of oil did not seem to dislodge the adults or to prevent the females from laying eggs.4. The maximum larval count on a single head was found to be 4260, the average number of larvae per single head was 418·8, and 9 to 1 was the maximum proportion of larvae to females.5. The maximum number of nits on a single hair was found to be 17 and 5·06 was calculated as the average number per hair.6. Treatment with kerosene and pyrethrum killed all the lice and nits, and reinfestation did not occur.7. The infestation did not spread to healthy patients in the hospital ward; it is thought that the poor migratory habits of lice are responsible for this.8. From studies on the reinfestation of an individual after treatment it is concluded that head-lice cannot establish themselves on any part of the body except the head, and if their access to the head is prevented, the lice will not survive for more than 24 hr.