Genome of parasitic flatworm that causes schistosomiasis decoded

An international team of scientists has sequenced the genome of Schistosoma mansoni, a parasitic worm, commonly known as a blood fluke, that infects 210 million in 76 countries through freshwater snails, and each year causing 280,000 deaths in sub-Saharan Africa alone. The research, said to be the largest genome sequencing of a parasite to date, is the cover article in the 16 July issue of Nature.

'This genome sequence catapults schistosomiasis research into a new era,' says Dr Matthew Berriman of the Wellcome Trust Sanger Institute and first author and co-leader of the study. 'It provides a foundation for understanding aspects of the parasite's complex biology as well as a vehicle to immediately identify new targets for drug treatment.'

Knowing the organism's genetic codes will help researchers develop better medication for infections, a diagnostic field test and even a vaccine, said co-author Phil LoVerde, professor of biochemistry and pathology at the University of Texas Health Science Centre at San Antonio. He has studied the parasite, and its close relatives, for more than three decades.

The researchers sequenced the parasite genome using the whole-genome shotgun method. They found that the genome - about ten times the size of the malaria parasite genome - contained almost 12,000 genes.

Schistosomiasis, a neglected tropical disease, ranks with malaria and tuberculosis as a major cause of disease worldwide. Currently, there is only one drug treatment that is used to treat schistosomiasis and - with mounting fears that the parasites will become resistant - researchers have been looking at ways to find new drug targets. Today's publication provides the first steps.

Individuals in Africa contract the S. mansoni infection, known as schistosomiasis or 'snail fever,' by coming into contact with freshwater that contains the infected snails. Ten percent of infected persons develop an enlarged liver or spleen, as the body encapsulates S. mansoni eggs that have been deposited by the adult worms living in their victims' blood vessels. The disease is common among children who live in areas where the water is unsafe, sanitation is poor and basic health care is unavailable.

S. mansoni is classified as a helminth, a family of worms that includes roundworms, pinworms and tapeworms. S. mansoni male and female pairs produce 300 eggs a day, each of which can infect a freshwater snail that produces the infectious form of the parasite. When humans come into contact with freshwater that contains the infectious larvae, the larvae can burrow through unbroken skin and develop into an adult worm. The disease is caused by the egg stage.