A new study seeks to determine how one parasitic species can give rise to two drastically different outcomes in its host: The human body louse (Pediculus humanus) can transmit dangerous bacterial infections to humans, while the human head louse (also Pediculus humanus) does not. A report of the new study as published online on January 9, 2014 in the journal Insect Molecular Biology. "Body louse-transmitted diseases include trench fever, relapsing fever, and epidemic typhus," said University of Illinois entomology professor Dr. Barry Pittendrigh, who led the research. In a previous study, Dr. Pittendrigh and his colleagues compared the sequences of all protein-coding genes in head and body lice and determined that the two belonged to the same species – despite the fact that body lice are bigger than head lice, cling to clothing instead of hair, and can transmit disease. Since the early 2000s, Dr. Pittendrigh has worked with Dr. John M. Clark, a professor of environmental toxicology and chemistry at the University of Massachusetts, on the molecular biology and genomics of lice. Dr. Clark was a collaborator on the 2012 study, and the two have had "a long-term goal of trying to solve this question of why body lice transmit bacterial diseases and head lice don't," Dr. Pittendrigh said. In the new study, Dr. Clark's group infected head and body lice with Bartonella quintana, the bacterium that causes trench fever. Dr. Pittendrigh's laboratory then looked at gene expression in each to see how the insects responded to the infection. "Our experiments suggest that the head louse immune system is fairly effective in fighting off the bacteria that cause trench fever," Dr. Pittendrigh said.Login Or Register To Read Full Story