Body louse genome sequenced: time to go, critters An international team of scientists has sequenced the genome of the human body louse (Pediculus humanus humanus) and of a type of bacteria (Candidatus Riesia pediculicola) crucial to its survival. The findings, published in the Proceedings of the National Academy of Sciences (... An international team of scientists has sequenced the genome of the human body louse (Pediculus humanus humanus) and of a type of bacteria (Candidatus Riesia pediculicola) crucial to its survival. The findings, published in the Proceedings of the National Academy of Sciences (PNAS) journal, provide insights that could lead to better controls of this disease-spreading pest. Body lice feed on human blood and can spread epidemic typhus, relapsing fever and trench fever. (The head louse, a close relative, mostly makes little kids' heads itch but can also lead to cervical lymphadenopathy or corneal epithelial keratitis.) Lice are naturally deficient in vitamin B5 (pantothenate); fortunately for them, the louse-dwelling Candidatus Riesia pediculicola produces enough B5 to keep them both going. The two species have enjoyed a symbiotic relationship for millions of years. Body lice, which take up residence in the folds and seams of clothing, thrive in conditions of poor hygiene and are ubiquitous in disaster areas. They have become increasingly resistant to insecticidal treatments, which has led to endemic infestations. In this latest research, scientists from 25 institutions around the world pooled their resources to sequence the genomes of both the louse and its pal. Among other things, they established that Candidatus Riesia pediculicola are not immune to antibiotics. 'We have found the human louse's weakness,' said Dr Alejandra Perotti of the University of Reading in the UK. 'All human lice depend on this bacterium for reproduction and survival. [Candidatus Riesia pediculicola] represents a new target for the development of novel anti-louse agents, especially for cases where classical treatment fails.' Dr Perotti added that 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,' she said. 'Several antibiotics might be efficient and should be systematically tested.' Dr Henk Braig of Bangor University in the UK explained that the bacteria are not immune to antibiotics because 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,' he said. Julio Rojas of the University of Barcelona in Spain observed that the louse has shed many non-essential genes, but is nevertheless highly functional. 'In the case of the insulin signal transduction pathway, there is only one copy of each important gene, unlike in other insects, which generally have more copies of certain genes,' he said. 'Mapping the genome is important for identifying the target that should be acted on,' explained Dr Rojas. 'The important thing is to act directly on the louse: if we can identify the genes that contribute to host recognition, we will be able to target the parasite directly. Given that the bacterial endosymbiont contains genes essential to the survival of the parasite, we are probably talking about another potential genetic target in the fight against these lice.' The body louse genome is the smallest known genome of any insect, and has the smallest number of detoxification enzymes observed in any insect. This makes it ideal for studying insecticide resistance and other types of chemical defence. In addition, its remarkable completeness makes it a natural evolutionary reference point for studies of all sequenced insect species. Countries Spain, United Kingdom
