Dipstick Gives Rapid Plague Diagnosis

A new dipstick test for bubonic and pneumonic plague will help dramatically reduce the number of cases in countries still blighted by the diseases.

Bubonic plague is highly contagious and spreads rapidly into epidemics. It is almost eradicated in the developed world, but there at least 4000 confirmed cases every year in more than 20 countries, mainly in Africa.

This number is likely to be a vast under estimation, says Suzanne Chanteau at the Pasteur Institute and Ministry of Health in Madagascar, who developed the test.

About 20 per cent of people with the disease die, she says, despite the disease being easily treatable with streptomycin, a cheap and effective antibiotic. However, early detection is crucial. Pneumonic plague is always fatal unless treated within 24 hours.

Until now, the only way to confirm plague cases was by sending off samples for bacterial analysis, a process that is far too slow. "Often the plague occurs in small villages far away from the big cities and laboratories," says Chanteau. "So this can take as long as a month just for transportation." The bacterial analysis itself can take another couple of weeks.

As a result, the only way for doctors in the field to make a diagnosis is to rely upon clinical symptoms, such as the red, swollen lumps - buboes - that give the disease its name. But this is slower and less certain, allowing the disease time to spread.

The new test gives medics a diagnosis in just 15 minutes and is effective in testing people before symptoms appear. Moreover, in 26 pilot studies carried out across Madagascar, the dipstick detected 60 per cent more confirmed cases than the standard laboratory tests.

The test works by detecting a bacterial antigen in a patient's sputum or buboe. "We don't need to cultivate the bacterium, we just need to detect something that is secreted by it," explains Chanteau.

Any diagnostic test for plague to be used in the field must not depend upon electricity, sophisticated equipment or any need for refrigeration, says David Dennis, at the US National Center for Infectious Diseases in Fort Collins, Colorado, commenting on the paper in The Lancet. He says it satisfies all these criteria, describing the new test as "remarkable".

Another advantage of the test is that it can also be used to test for plague in rodents, says Chanteau. "So now they can use exactly the same test to diagnose the disease in dead rodents and prevent the first human case from occurring."

Journal reference: The Lancet (vol 361, p 211, 191)

SOURCE: NewScientist.com on the 17th January 2003

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