Genetic Study Finds Head Lice and Body Lice Likely Same Species
Posted on April 9, 2012
A new study, reported here in Insect Molecular Biology, offers genetic evidence that head and body lice are the same species. The finding is of special interest from a health perspective, because body lice can transmit deadly bacterial diseases, while head lice do not. In the CDC image above, a head louse is pictured on the left and a body louse is pictured on the right.
The researchers say scientists have long debated whether human head and body lice are the same or different species. The head louse (Pediculus humanus capitis) lays its eggs in human hair, digging its mouthparts into the scalp and feeding on blood several times a day. The body louse (Pediculus humanus humanus) tends to be larger than head lice, and is a more dangerous parasite. It lays its eggs on clothing, takes bigger blood meals, and can transmit relapsing fever, trench fever and epidemic typhus to its human host.
University of Illinois entomology professor Barry Pittendrigh, who led the study, says, "We were interested in understanding potentially how closely related head lice and body lice are. Do they have the same number of genes? Do those genes look very similar or are they very different? What we found is that these two organisms are extremely similar in terms of their protein-coding genes."
Previous studies have found that head and body lice don't stray into each other's turf even when they are both present on the same host. They don't breed with one another in the wild, but they have been shown to successfully reproduce under specific laboratory conditions. The researchers say that the presence of head lice has little to do with human hygiene. However, body lice seem to appear out of nowhere when hygiene suffers, such as in times of war or economic hardship.
In the study, researchers compared the number and sequences of all of the protein-coding genes expressed at every stage of the head and body louse life cycles. They found only very minor differences in their gene sequences.
Pittendrigh says, "My colleagues at the University of Massachusetts, led by veterinary and animal sciences professor John Clark, collected lice at every developmental stage, exposed them to every pesticide they could get their hands on, multiple bacterial challenges, several physical challenges - cold, heat - to get the lice to express as many genes as possible. The differences in their sequences were so minor that if we didn't know they were separate groups, we would have considered them the same species."