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[KOLKATA] Scientists are a step closer to developing the first ever blood test for the deadly infectious disease known as kala-azar, or visceral leishmaniasis.

The researchers identified proteins produced only by Leishmania donovani, the parasite that causes the disease.

The team hope that, as well as overcoming the virtually impossible task of rapidly diagnosing the disease, the proteins could lead to the first vaccine against the disease.

The proteins discovered by Peter Walden of Humboldt University in Germany and colleagues, are targeted by human antibodies — proteins that fight infection.

The researchers screened blood samples from 44 Indian kala-azar patients for these antibodies.

They found that 36 patients had antibodies to the parasite proteins.

The findings — by researchers including those from Banaras Hindu University in India, and the Indian Institute of Chemical Biology — were published in the October 2005 issue of Infection and Immunity.

Walden told SciDev.Net this work is important because knowing more about the microbe's proteins will help understand which ones are produced at different stages of infection. This has implications for monitoring how well a treatment works or detecting whether a patient has been re-infected.

Walden added that scientists must find a combination of proteins that would lead to a diagnostic blood test that is effective enough to detect early cases.

Kala-azar, which is transmitted to people by sand flies, damages internal organs including the liver and spleen. The World Health Organization says there are 500,000 new cases each year. It is fatal if not treated, but quick and easy diagnosis is currently impossible.

Instead, diagnosis relies on physical examinations of the patients. However, other diseases cause similar symptoms, making the method unreliable.

A better approach is to test spleen samples, but this is painful, needs highly experienced doctors — in short supply in poor countries — and can be time-consuming, says Walden.

"Kala-azar still lacks specific diagnostic tools, so these [parasite proteins] are impressive," says Salil Bhattacharya, associate professor of preventive and social medicine at Calcutta National Medical College, India. "But more research will be needed before they become available on the market." 

Walden's team also hopes that the proteins they identified could be used to develop a vaccine.

"There is no vaccine for leishmaniasis yet, though vaccination may be possible for prevention and, maybe, also for therapy," says Walden.

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