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Rapid malaria tests can better
22 June 2011
Institute of Tropical Medicine Antwerp
Rapid diagnostic tests for malaria are simple, reliable and robust. But errors occur, through misuse or because they aren’t designed for primitive circumstances. Researcher Philippe Gillet put them to the test and made a series of suggestions for improvement. It resulted in a PhD at the Institute of Tropical Medicine Antwerp and Maastricht University.
Malaria is caused by a Plasmodium parasite infecting red blood cells. Humans can be infected by five species of Plasmodium, but most cases are caused by Plasmodium falciparum. The parasites are transmitted by blood-sucking mosquitoes. Worldwide, some 225 million people have malaria and 780 000 people a year die from it. This makes malaria the number one cause of death worldwide. Until recently treatment was initiated based on clinical suspicion, but since a few years the World Health Organisation advises to start treatment only after laboratory confirmation of the diagnosis. Then a microscopic blood examination is needed, demanding tools, time and experts. Therefore in tropical circumstances often a rapid diagnostic test is used, applying a drop of blood to a strip and waiting for some coloured lines to appear, a bit like a pregnancy test. Very helpful in the field, but no panacea.
Existing tests for instance are not powerful enough to differentiate between P. falciparum and P. vivax, a parasite from the subtropics (even if their label and even brand name suggest differently). Not all tests react good to high concentrations of parasites – strangely enough, this overloading leads to a negative result or a very weak line, often read by inexperienced users as “no malaria”.
And not only by inexperienced users. More people than one thinks need reading glasses, certainly in the tropics, where presbyopia starts earlier in life. But many don’t have them…
In the field, people sometimes replace the liquid (the ‘buffer’) in the test by tap water, or by the buffer of a different kit. Because the flask was empty, or lost, or swapped. Gillet discovered that the rapid tests then see malaria where there isn’t.
The rapid tests also aren’t suitable to see if a treatment catches on. Some tests read positive up to weeks after the infection, even when in the mean time the infection is under control.
Gillet also criticises design and packaging: instructions in small print and in a complicated jargon, unclear reading scales, awkward pipettes. “All of it easily and cheaply to remediate. It already would make a large difference if WHO and EU would sharpen their rules for registration.”
Though not everything should be blamed on the manufacturers. When Gillet in Belgium, Congo, Cuba and Cambodia asked health workers about the international danger symbols on the products, less than half of them could give the right answers.