Schistosoma mansoni larva

WHO/TDR

[SAO PAULO] Two teams of scientists — one based in Brazil and the other in China — have sequenced the genomes of two of the parasitic worms that cause schistosomiasis. Their findings, published in the journal Nature Genetics, may help fight the disease, which affects more than 200 million people in 74 countries.

The Brazilian scientists, led by Sérgio Verjovski-Almeida of the University of São Paulo, analysed the active genes of the parasite Schistosoma mansoni, which is found in Africa, the Caribbean and South America.

The Chinese research, carried out by Ze-Guang Han and colleagues of the Chinese National Human Genome Center in Shanghai focused on the genome of Schistosoma japonicum, which causes a different version of the disease in Asia.

The genetic sequences of both parasites hint at therapeutic and vaccine targets that could help to overcome resistance to drugs currently used to treat the disease.

"We wanted to show that a genomics approach could be as useful in fighting a Third World disease as education and prevention," says Verjovski-Almeida.

Popularly known in Brazil as 'water-belly' (due to expansion of the abdomen), symptoms of schistosomiasis appear when adult parasites move to blood vessels in the liver, making it swell. The worm’s eggs make their way to lakes and ponds, where they find their intermediate host, a snail. People swimming or bathing in those waters can then be infected by the parasite's larvae, and the cycle begins again.

The Brazilian scientists' data include information on six phases of the worm’s life cycle. According to Verjovski-Almeida, no one has previously managed to look at the genetics involved in all these phases. "It’s especially hard to extract genetic material from the eggs and larvae, since they are so tiny," he says.

Instead of sequencing the worm’s entire genome, the team focused on analysing those genes that are actually 'turned on', or 'expressed'.

The researchers uncovered a set of genes that help ensure the parasite's survival. For example, they identified those genes that help it to prevent blood from clotting around it. And another set of genes allows the worm to fool the immune system by producing an allergic response similar to that elicited by wasp poison.

Work to apply this information is already under way, according to biochemist Luciana Cézar de Cerqueira Leite of São Paulo’s Butantan Institute. "Two of those proteins have shown promising results in mice," she says.

Link to Nature Genetics paper by W Hu et al
Link to Nature Genetics paper by S Verjovski-Almeida et al