In Africa severe malaria is commonly misdiagnosed and the consequence is a failure to treat other life threatening illnesses. In malaria endemic areas, parasitemia does not ensure a diagnosis of severe malaria because it can be incidental to other concurrent disease. Recent investigations suggest that malaria retinopathy with collective sensitivity of 95% and specificity of 90% is better than other clinical or laboratory feature in distinguishing malaria from non-malarial coma (Beare et al., 2006)
The most economic, preferred and reliable diagnosis of malaria is the microscopic examination of blood films because each of the four major parasites specie has distinguishing characteristics. Two sorts of blood films are traditionally used. They include thin and thick films. Thin films afford specie identification because the parasites appearance is best preserved in this preparation. On the other hand, thick films allow the observer to screen larger volume of blood and are about eleven times more sensitive than the thin films, so
Using the thick film, an experienced microscopist can detect parasite levels down to as low as 0.0000001% of red blood cells. Diagnosis of species can be difficult because the early trophozoites (or the ring forms) of all species look alike and it is never possible to identify a specie on the basis of a single ring form; the identification is always based on several trophozoites.
In areas where microscopy is not available, or where laboratory staff are not experienced at malaria diagnosis, there are antigen detection tests that require only a drop of blood (Pattanasin et al., 2003). Immunochromatographic tests also called dipsticks have been developed. These tests use finger-stick or venous blood, the threshold of detection by these rapid diagnostic tests is in the range of 100 parasites per micro litre of blood compared to 5 parasites by the thick film microscopy.
Recently, fluorescent microscopy techniques based on acridine orange and enzyme linked immunosorbent assay of parasites proteins were introduced as diagnostic tools. These techniques are on the whole sensitive, specific and probably less operator dependant than the thick films (Peter Winstanly, 1998). Also, molecular methods based on polymerase chain reactions are available in some clinical laboratories and rapid real-time assay are being developed with the hope of being able to deploy them in endemic areas (Mens et al., 2006).
Other new techniques are OPtiMAL-IT which is said to reliably detect falciparum down to 0.01% parasitemia and non falciparum down to 0.1%, and Parachek Pf that detect parasitemias down to 0.002% but will not distinguish between falciparum and non falciparum malaria. Parasite nucleic acids are detected using polymerase chain reaction (PCR). This technique is more accurate than microscopy. However, it is more expensive and requires a specialized laboratory. Moreover, levels of parasitemia are not necessarily correlative with the progression of disease, particularly when the parasite is able to adhere to blood vessel walls. Therefore, more sensitive, low tech diagnostic tools need to be developed in order to detect low levels of parasitemia in the field (Redd et al.,2006).
When laboratory facilities are not available a diagnosis must be made on the clinical manifestations and history. The onset of intermittent fever accompanied by other clinical features such as splenomegaly, increase in rectal temperature and nail bed pallor should suggest the diagnosis of malaria in endemic areas and can be used as treatment indication.
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