Scientists discover weakness of human louse

Scientists have discovered the human louse's Achilles' heel which could lead to new treatments to rid us of body and head lice infestations.

The University of Reading, in collaboration with Bangor University, has discovered bacteria within the louse which are crucial to its survival. The researchers have established that these bacteria have no immunity to antibiotics and could be treated with antibiotics now clinically ineffective for any other treatment.

The lice have adopted the bacteria to enable them to gain the vitamins they need to survive, which they are no longer able to obtain from ingested human blood.

Although head lice in children are the bane of many parents, both the body louse and head louse can cause serious diseases or conditions. Body lice can transmit endemic typhus, louse-borne relapsing fever and increasingly common trench fever in the homeless population of inner cities.

Head lice, while not transmitting disease, can, as with body lice, lead to unexpected conditions such as cervical lymphadenopathy or corneal epithelial keratitis. They are also increasingly resistant to current insecticidal treatments. This is leading to endemic infestations, particularly among the young in the west and even more so in developing countries.

The work of Dr Alejandra Perotti, of the University's School of Biological Sciences, and Dr Henk Braig, of Bangor University, is reported in a paper in the Proceedings of the National Academy of Sciences today. The research forms part of a larger project to genetically sequence the genomes of the louse and its bacterium with over 25 institutions across the world.

Dr Perotti said: "We have found the human louse's weakness. All human lice depend on this bacterium for reproduction and survival. This bacterium represents a new target for the development of novel anti-louse agents especially for cases where classical treatment fails.

"Antibiotics that have completely lost their therapeutic value could now be tested for this target. The potential of antibiotics to fight human lice is not new but we now have a solid scientific basis for this. Several antibiotics might be efficient and should be systematically tested."

Dr Braig added: "We have established that these bacteria have no immunity to antibiotics as they have been isolated within the body of the lice and transmitted down the generations for millennia with no outside contact. Having had no other contact with external bacteria they have had no need to develop resistance to antibiotics- as they would in the wider environment, in their struggle for survival and dominance."

Professor Barry Pittendrigh of the University of Illinois has led the overall project and co-ordinated the international team of scientists who analysed the sequence. "The body louse genome is the smallest known genome of any insect," he said.

Other project researchers discovered that the body louse also has "the smallest number of detoxification enzymes observed in any insect." John Clark, of the University of Massachusetts at Amherst, and Si Hyeock Lee, of Seoul National University, led this part of the analysis.

The body louse's pared-down list of detoxifying enzymes makes it an attractive organism for the study of resistance to insecticides or other types of chemical defence, Professor  Pittendrigh said. University of Illinois entomology professor and department head May Berenbaum and former graduate student Reed Johnson contributed to this effort.