You can stop scratching your head about the origins of human body lice.
Body lice, which cause highly lethal epidemics (trench fever, typhus and relapsing fever Borrelia), originate from head lice, an international group of scientists reported today.
Image of body louse (Pediculus humanus humanus) courtesy of CDC
The discovery indicates that it is not possible to eradicate body lice without first eradicating head lice, which until now has proved impossible, according to the researchers.
“This has recently been shown by a team from the Emerging Infectious and Tropical Diseases Research Unit (CNRS/IRD/Université de la Méditerranée), in collaboration with researchers from the Universities of Florida and Illinois” in the U.S., says a news statement released by the French National Center for Scientific Research (CNRS).
“Until now, head lice, which feed on the scalp and lay their eggs on hair, and body lice, which feed on the rest of the body and live in the creases of dirty clothes, were thought to be different species. However, researchers from the Emerging Infectious and Tropical Diseases Research Unit (CNRS/IRD/Université de la Méditerranée) and two U.S. teams have shown that these lice have the same origin,” CNRS said.
Image of head louse (Pediculus humanus capitis) courtesy of CDC
Through genetic analysis of the louse genome, the researchers observed that “it was impossible to distinguish the head louse from the body louse at the genetic level,” CNRS added.
“In addition, fieldwork has shown that, in populations living in extreme poverty, the proliferation of head lice led to the emergence of lice able to adapt to clothes and turn into body lice. These body lice were then able to cause epidemics of body lice and bacterial epidemics.”
“This discovery shows that it is not possible to eradicate body lice without first eradicating head lice, which until now has proved impossible. In addition, this explains the regular appearance of body lice in areas where they were previously unknown, when sanitary conditions rapidly deteriorate.
“Head lice are therefore permanently in an endemic state. In highly unfavorable sanitary conditions, head lice proliferate, and some of them migrate into clothes, triggering a new epidemic of body lice,” CNRS said.
Life cycle of the head louse
Information provided by U.S. Centers for Disease Control & Prevention
The life cycle of the head louse has three stages: egg, nymph, and adult
Eggs: Nits are head lice eggs. They are hard to see and are often confused for dandruff or hair spray droplets. Nits are laid by the adult female and are cemented at the base of the hair shaft nearest the scalp (no. 1 in the illustration above). They are 0.8 mm by 0.3 mm, oval and usually yellow to white. Nits take about 1 week to hatch (range 6 to 9 days). Viable eggs are usually located within 6 mm of the scalp.
Nymphs: The egg hatches to release a nymph (no. 2). The nit shell then becomes a more visible dull yellow and remains attached to the hair shaft. The nymph looks like an adult head louse, but is about the size of a pinhead. Nymphs mature after three molts (no. 3, no. 4 ) and become adults about 7 days after hatching .
Adults: The adult louse is about the size of a sesame seed, has 6 legs (each with claws), and is tan to grayish-white (no. 5). In persons with dark hair, the adult louse will appear darker. Females are usually larger than males and can lay up to 8 nits per day. Adult lice can live up to 30 days on a person’s head. To live, adult lice need to feed on blood several times daily. Without blood meals, the louse will die within 1 to 2 days off the host.
How do you get head lice?
Getting head lice is not related to cleanliness of the person or their environment, according to the CDC.
“Head lice are spread by direct contact with the hair of an infested person. The most common way to get head lice is by head-to-head contact with a person who already has head lice. Such contact can be common among children during play at school, home, and elsewhere (e.g., sports activities, playgrounds, camp, and slumber parties).
“Uncommonly, transmission of head lice may occur by wearing clothing, such as hats, scarves, coats, sports uniforms, or hair ribbons worn by an infested person; using infested combs, brushes or towels; or lying on a bed, couch, pillow, carpet, or stuffed animal that has recently been in contact with an infested person, the CDC says.