Malaria tests largely unreliable, say researchers

Katherine Nightingale | 26 May 2009
SciDev.Net
Soaring demand for the fast diagnosis of malaria is only likely to be met when more reliable tests are invented, according to a leading diagnostics expert.

As the need for rapid diagnostic tests (RDTs) rises, manufacturers face the challenge of improving test standards while also increasing supply, says David Bell, head of malaria diagnostics at the Foundation for Innovative Diagnostics (FIND).

There is also a growing demand for tests that identify low levels of infection in people without symptoms, adds Bell. This follows a rise in health programmes that aim to eliminate malaria, not just treat patients.

Bell was speaking after the publication of an evaluation of 41 commercially available RDTs for malaria. The research was carried out by FIND, the WHO and the WHO-based Special Programme for Research and Training in Tropical Diseases (TDR).

RDTs employ antibodies to detect proteins from the malaria parasite. Using the tests — which are compact and relatively easy to use — saves patients from taking antimalarial medication when their fever is caused by another disease. Diagnosing and treating patients appropriately has the added benefit of cutting medical costs and minimising drug resistance.

But the market for RDTs for malaria is unregulated and some manufacturers produce tests that perform poorly and have been inadequately tested, Bell told the news agency IRIN.

FIND's results, published in April, show that some tests currently in use in developing countries give false results. To complicate the situation further, quality can vary from batch to batch even among RDTs of a given brand. Moreover, the reliability of some tests varies according to the levels of parasite found in blood samples, malaria types and atmospheric temperature.

Only a few tests passed the combined hurdles of being able to consistently detect low levels of two malaria parasites (Plasmodium falciparum and P. vivax), producing low false-positive rates, remaining stable at tropical temperatures and proving easy to use.

In an interview published on the FIND website earlier this month, Bell said: "The product testing results demonstrate there are RDTs currently available that are adequate for malaria case management in most areas. However, it's important to have tests that maintain this high level of performance and that remain stable during long-term storage in all malaria endemic areas."

He added that FIND is working on finding more stable antibodies for the tests. It is also working to develop DNA-detection tests that should spot low levels of parasite density at a reasonable cost. This would make large-scale population surveys possible, he said.

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