An international team of 70 researchers from 28 institutions in the U.S., Europe, Australia and South Korea has decoded the genome of head lice, the smallest insect ever submitted to this exercise. The results have been published in Proceedings of the National Academy of Sciences on June 21, 2010.
The genome of human body lice, which are closely related to head lice, inseparable companions of man over millions of years, has brought to light the genetic secrets of these parasites, and this could well lead to a divorce between humans and lice.
Body and head lice are disgusting, repelling, and the latter are the nightmare of many parents of school aged children. These parasites are 2 to 4 millimeters long, have six legs and a translucent body. Pediculus humanus loves our heads and feeds exclusively on our human blood. Besides the unbearable itching that their presence causes, they are pathogens and are a vector of diseases in developing countries. And according to the researchers, lice would no longer exist without us humans.
The simplicity of the louse’s lifestyle is reflected in its genome as shown by the small number of genes responsible for detection and response to the environment. The sequencing revealed significantly fewer receptors for light, tastes and odors compared to other insects.
The body of lice also has “the smallest number of detoxification enzymes found in any other insect,” said John Clark of the University of Massachusetts, co-author of the study. This reduced number of detoxification enzymes makes lice interesting for the study of resistance to insecticides and other defense mechanisms, observes the other study coordinator Barry Pittendrigh, professor of entomology at the University of Illinois.
Lice, vectors of diseases?
The louse can transmit to humans pathogens such as Rockettsia prowazekii, responsible for typhus, Borrelia recurrentis, responsible for relapsing fever, and Bartonella Quintana, responsible for trench fever, which affected the army of Napoleon during the retreat from Russia in 1812.
However, these diseases are mainly present in developing countries and will not affect children in the U.S. or Europe if they live in good sanitary conditions. As far as head lice are concerned, note that if they are not treated properly the crusts and wounds caused by repeated itching can lead to a bacterial skin infection called impetigo.
On the way to final eradication of lice?
According to the scientists, head and body lice are becoming increasingly resistant to treatment, and the sequencing of their genome could help find new ways to control lice. The team of researchers also sequenced the genome of a bacteria living in symbiosis with the louse, Candidatus Riesia pediculicola.
It turns out that the body louse relies on this bacteria for vitamin B5, which it cannot produce itself and which is absent from human blood. And this bacteria can be eliminated with antibiotics, so finding a way to eliminate the bacteria might also be the solution to getting rid of lice.
According to the team of researchers, the decoding of the genome of lice should help develop better methods for controlling both body lice and head lice. And hopefully we’ll find means to eliminate head lice that do not imply putting pesticides on our kids’ heads.