The genomes of two of the parasitic worms that cause schistosomiasis have been sequenced, paving the way for the development of new drugs for the debilitating disease.

Schistosomiasis afflicts hundreds of millions of people in tropical areas. The worms, called schistosomes, burrow through the skin and migrate to the organs. The body's immune response to the worm's eggs causes symptoms such as fever and aches.

The genome sequences of Schistosoma mansoni, the most widespread cause of schistosomiasis, and Schistosoma japonicum, which causes the disease in Asia, were published in Nature last week (16 July).

The genome sequences constitute "a crucial first step towards developing additional drugs and possibly vaccines that are urgently needed to deploy against schistosomiasis", says Najib El-Sayed, associate professor at the US-based University of Maryland and co-author of the S. mansoni study.

El-Sayed's team, consisting of European, Japanese and US scientists, drew a genetic map of S. mansoni, while another team led by Chinese scientists did the same for S. japonicum.

Both studies yielded important findings about the parasites' nerve systems, metabolism and relationships with the host, providing targets for potential new drugs or vaccines, says El-Sayed.

His team looked for targets for which drugs already exist. "The advantage of drug repositioning or repurposing is that candidate drugs would have already passed all the safety and toxicity tests in humans," he says.

S. mansoni and S. japonicum are two of the three principal species of the worm that infect humans. There is currently only one approved drug against the disease, praziquantel, leading to concerns that the worms might become resistant.

Joanne Webster, director of monitoring and evaluation at the Schistosome Control Initiative at Imperial College London in the United Kingdom, hopes that the genomes will lead to new drug targets.

"Knowing more about the genome of these schistosomes will also open up new avenues for related research, such as into the population genetic structure and transmission dynamics of these parasites," she adds.

Webster says she expects the genome of the third schistosome, S. haematobium, which causes urinary schistosomiasis across much of Sub-Saharan Africa, to be sequenced soon.

Source: SciDev.Net
Date: 21 July 2009