Body Lice are Head Lice

Today's gross news:

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. . . .

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.

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.

CDC images of the head louse (upper) and body louse (lower) show the adult forms look quite different. From an evolutionary standpoint, this is another great example of the way that genes and environment interact to produce the adult form of an animal. From a personal standpoint, eeeuuw.