Other Tests

Alternative microscopy techniques for the identification of malaria parasites are based on fluorochromes such as Acridine Orange. Staining with fluorochromes is rapid (<1 minute) and slides can be rapidly screened at low magnification (x 400), even with low parasitaemia. Acridine dye-stained buffy coat examination (the 'QBC' technique) has been shown to increase the sensitivity of microscopy, but cost and technical concerns have limited its use (Levine et al., 1989; Wongsrichanali et al., 1991; Warhurst and Williams, 1996).

Rapid diagnostic antigen tests using monoclonal antibodies to the P. falciparum histidine-rich protein-2 have been shown to be highly sensitive and reliable (Shiff et al., 1993; Beadle et al., 1994; Garcia et al., 1996; Humar et al., 1997). These tests employ an impregnated strip that gives a colour change when blood containing parasites is added. These tests could be used at the primary health care level in malaria-endemic areas, where microscopy is often unavailable, but, as explained above, may have little influence on the decision to treat and are currently too expensive for most health budgets (although a test costing as little as 0.25 US$ is now available). They could also be invaluable as a screening test in laboratories in non-endemic areas, where low throughput means that personnel often have little experience in the microcopic diagnosis of malaria. They may also assist travellers in the decision to take presumptive self-treatment when in remote areas where medical care is not available. New antigen tests, which differentiate between P. falciparum and other species, are currently being field-tested (Figure 3.8).

Gene amplification methods for the detection of malaria parasites have also been developed (McLaughlin et al., 1993). PCR techniques could have application with low parasitaemia, possible mixed infections or uncertain parasite speciation, as well as for reference studies and microepide-miology (Barker et al., 1992; Snounou et al., 1993; Oliveira et al., 1995) or as research tools for detection of low parasitaemia in sophisticated laboratories (Chen et al., 1998).

IFA, IHA and ELISA assays using cultured P. falciparum-infected erythrocytes as antigen are well-characterised for antibody detection (Lobel et al., 1973; Spencer et al., 1979; Schapira et al., 1984; Srivastava et al., 1991) but are inappropriate for use in the diagnosis of acute malaria, as they reflect exposure rather than acute infection

Fig. 3.8 Positive immunochromatographic test for mixed P. vivax and P. falciparum malaria

or clinical immunity. However, in non-endemic areas, serology may be useful for retrospective diagnosis in patients thought to have had malaria and who received therapy. They are untried for excluding malaria in patients with chronic or recurrent febrile illness, and are too insensitive for transfusion blood screening. In areas where malaria is endemic, serological techniques are useful for epidemiological purposes and for the assessment of infection in mosquitoes.

In vitro tests for sensitivity to antimalarial drugs are valuable tools for establishing prevalence and likely degree of clinically relevant drug resistance, but do not help individual patients. Similarly, examination of PCR products for mutations known to be associated with resistance to sulfa drugs or pyrimethamine is of use in research and epidemiological studies.

clinical assessment, and instituting appropriate antimalarial therapy as soon as possible. Treatment depends not only on the species of malaria but also on the severity of illness, the likely susceptibility to antimalarial drugs, and the age and background immunity of the patient.

The clinical examination should focus on temperature, pulse rate, respiratory rate, blood pressure, hydration, pallor, jaundice, splenomegaly, hepatomegaly, neck stiffness, other CNS signs, urinalysis and weight. A lumbar puncture should be performed to exclude bacterial meningitis in patients with suggestive CNS symptoms or signs. Future studies may resolve the issue of whether possible raised intracranial pressure, which is known to be associated with cerebral malaria in some patients, is a contraindication to lumbar puncture on presentation (Newton et al., 1991). If this were the case, it is likely that appropriate therapy for both bacterial meningitis and cerebral malaria would need to be instituted and continued until lumbar puncture was considered to be safe and results were available. The CSF should be normal in cerebral malaria.

P. vivax, P. ovale and P. malariae very rarely produce fatal disease (except as a predisposing factor for a ruptured spleen) but P. falciparum infection may progress rapidly to multi-organ failure and death.

It is important to weigh children so that accurate mg/kg doses of antimalarial drugs can be administered.

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