|Malaria Diagnosis: New Perspectives (WHO - OMS, 2000, 57 p.)|
In malaria patients, a prompt and accurate diagnosis is the key to effective disease management. The two diagnostic approaches currently used most often, however, do not allow a satisfactory diagnosis of malaria. Clinical diagnosis, the most widely used approach, is unreliable because the symptoms of malaria are very non-specific. Microscopic diagnosis, the established method for laboratory confirmation of malaria, presents technical and personnel requirements that often cannot be met, particularly in facilities at the periphery of the health care system. In addition, delays in the provision of the microscopy results to the clinician mean that decisions on treatment may be taken without the benefit of the results.
Thus, the recent introduction of rapid diagnostic tests (RDTs) for malaria is of considerable interest. Such tests use immunochromatographic methods to detect Plasmodium-specific antigens in a finger-prick blood sample. The tests can be performed in approximately 15 minutes by individuals with minimal training, using test kits (available from several manufacturers) that require no electricity and no special equipment. The RDTs have detection capabilities that are in general comparable to those generally achieved by microscopy in the health services. Compared to microscopy, the main disadvantages of currently available RDTs are: lack of sensitivity at low levels of parasitaemia; inability to quantify parasite density; inability to differentiate between P. vivax, P. ovale and P. malariae, as well as between the sexual and asexual stages of the parasite; persistently positive tests (for some antigens) in spite of parasite clearance following chemotherapy; and relatively high cost per test.
Diagnostic tests (microscopy and RDTs), used correctly, can contribute to better and more cost-effective disease management and can reduce the unnecessary and irrational use of antimalarial drugs.
In areas with high rates of transmission (mostly in Africa south of the Sahara), where asymptomatic infections are frequent and health infrastructures are often inadequate, most malaria treatment is based on clinical diagnosis alone. In some situations, however, the clinical diagnosis would benefit from laboratory confirmation by microscopy or RDTs. Such situations include suspected cases of severe malaria; suspected treatment failures; disease management by private-sector health providers in urban areas; and multidrug resistance (which is not yet a problem in Africa south of the Sahara).
In areas with low to moderate rates of transmission (mostly in Asia and the Americas, and in parts of Africa), most infections are symptomatic and multidrug resistance occurs in some areas (especially South East Asia). These factors are strong incentives for laboratory confirmation of malaria as a component of disease management. While microscopy is generally available at the more central levels, it is often absent or unreliable in remote areas. In such isolated localities, RDTs performed by local health workers or community volunteers can be used to diagnose malaria, which can then be treated immediately, with the aim of reducing morbidity and mortality and the incidence of severe malaria. Where multidrug resistance occurs, the cost of the recommended anti-malarial drugs is higher, thus justifying the use of RDTs when microscopy is not available.
Certain other circumstances offer a potential role for RDTs in support of microscopy. These include complex health emergencies where malaria is a risk, suspected malaria epidemics, and the diagnosis of malaria in travellers and in military forces and organized workforces.
However, the microscope is a key tool in the integrated management of disease in resource poor settings, and the optimal role and conditions for the use of RDTs in relation to microscopy remain to be determined. Several issues need to be addressed through laboratory or field research, situation analysis, modelling and institutional strengthening. These issues include: further improvement of the technical characteristics of RDTs (e.g. sensitivity, specificity, ease of performance by users and robustness); a system of international quality control and quality assurance outside the commercial sector, including the development of a bank of reference reagents and a network of field test sites; and a multidisciplinary analysis of the cost of deploying RDTs in various situations, as well as their potential for reducing malaria morbidity and mortality and delaying the emergence of drug resistance.