Schistosomiasis: new genetic blueprint revealed
18 August 2009: An analysis of the DNA blueprint for Schistosoma mansoni, the organism responsible for Schistosomiasis, has been published in Nature. The work done by an international research consortium and supported in part by TDR helps shed light on the role that schistosome genes and gene products play in schistosome-host interactions. "Knowing the organism’s genetic codes will help researchers develop better medication for infections, a diagnostic field test and even a vaccine", said research co-author Phil LoVerde, Professor of Biochemistry and Pathology at The University of Texas Health Science Center at San Antonio.
Schistosomiasis, a neglected tropical disease, is a major cause of morbidity in 76 countries. Infecting over 200 million people, it ranks second only to malaria in terms of socioeconomic and public health importance worldwide. The disease is widespread throughout Africa, the Middle East and the Americas. An estimated 500–600 million people worldwide are at risk. Although the mortality rate is relatively low, the morbidity rate is high, with infection causing severe debilitating illness in millions of people. In many areas, schistosomiasis infects a large proportion of children under 14 years of age.
The disease is often associated with water resource development projects, such as dams and irrigation schemes, where the snail intermediate hosts of the parasite breed. Larval forms of the parasites (known as cercariae), released by the snails, penetrate the skin of people in the water. The snails themselves become infected by another larval stage of the parasite, known as a miracidium, which develops from eggs passed out in the urine or faeces of infected people.
The research team hopes to identify genes that allow the parasite to take advantage of human signals in order to develop; they also are using the genome sequence to give them new clues about drug resistance which in turn will help identify better ways of controlling the disease.
LoVerde, in collaboration with Timothy Anderson of the Genetics Department at the Southwest Foundation for Biomedical Research, produced the first microsatellite-based genetic linkage map for Schistosoma mansoni, just published in BioMed Central’s open access journal Genome Biology. This map represents another tool for researchers that will stimulate research and open doors to new advances in combating this human pathogen.
“Every day of their lives, people are exposed to S. mansoni in areas where it is endemic,” LoVerde said. “Existing drugs don’t prevent reinfection, so some people have repeat cases. With the sequencing of this helminth’s genome, we can develop better treatments at unprecedented speed.”
Implications for this pioneering work are clear. Knowing the genetic sequence should make it possible to identify the genes responsible for the severity of infections, and help understand why some people seem to develop immunity to repeat infections while others do not. This latest genomic information will serve as a valuable platform to help develop much needed new control tools for the treatment and eradication of this important and neglected disease.
The project was supported in part by the National Institute of Allergy and Infectious Diseases, the John E. Fogarty International Center for Advanced Study in the Health Sciences, the Burroughs Wellcome Fund and TDR.