A global research team led by scientists from the J. Craig Venter Institute (JCVI) today published a new study in the Proceedings of the National Academy of Sciences describing the sequencing and analysis of the body louse genome. Lead author, Ewen Kirkness, Ph.D., JCVI, directed the sequencing and gene-finding efforts in the project. Detailed analysis of the genome was then conducted by a large international group of 71 scientists, coordinated by Barry Pittendrigh, University of Illinois, and Professor Evgeny Zdobnov, University of Geneva Medical School. Comparative studies of the body louse genome with other sequenced species revealed features that will enhance our understanding of the relationships between disease-vector insects, the pathogens they transmit, and the affected human hosts.
The human body louse, Pediculus humanus humanus, is a human parasite and is responsible for the transmission of bacteria that cause epidemic typhus, relapsing fever and trench fever. The team at the JCVI focused on the DNA sequencing, genome assembly and identification of genes. In addition to the targeted louse genome, the project unexpectedly yielded the complete genome sequence of a bacterial species, Riesia, that lives in close association with lice, and which is essential for survival of the insects. This study revealed that, despite having the smallest known insect genome (108 Mb) and a parasitic lifestyle, the body louse has retained a remarkably complete repertoire of 10,773 protein-coding genes. The compactness of the louse genome helped to predict the encoded genes accurately. The researchers believe that the genome will be a valuable reference for evolutionary studies of insect species, especially in the areas related to insect growth and development.
The body louse usually lives in clothing, with infestations associated with unwashed clothes for prolonged time. Infestations of body lice and the closely related head lice can cause a range of problems in humans from mild irritations to serious disease. The body louse can carry harmful bacteria, such as Rickettsia prowazekii that causes epidemic typhus, and is classified as a category B bioterrorism agent. Body and head lice are also becoming increasingly resistant to traditional pesticides so the sequencing of the body louse genome will help in the important search for new control methods facilitated by detailed molecular studies. Having the complete genome of the bacteria, Riesia, that lives within lice and provide the lice with essential nutrients such as vitamin B5, provides additional potential targets for lice eradication.
According to lead author Dr. Kirkness, "With the genome sequences of the human host, the body louse parasite, and the Riesia endosymbiont now in hand, researchers have the opportunity to gain greater insights into the co-evolution of a host-parasite-symbiont trio with the potential outcome being eradication of the body louse."
J. Craig Venter Institute