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Diagnosis of malaria in resource-poor settings and Rapid Diagnostic Tests

Overview:

Diagnosis of malaria must be prompt, as even a few hours delay in treatment can mean the difference between life and death. For centuries now, the gold standard for diagnosing malaria has been microscopy to visualise parasites directly in a blood film. This requires a laboratory set-up with a good microscope, reagents, slides and a trained microscopist. However, in many malaria-endemic countries, most of the smaller health facilities do not have laboratories, so malaria is commonly diagnosed on clinical grounds alone. As a result, many people receive drugs unnecessarily, as almost all fever cases are treated for malaria. In recent years, in response to growing resistance by the parasite to the existing drugs - chloroquine and sulfadoxine-pyrimethamine, the majority of endemic countries have switched their national drug policy for first-line drug to artemisinin-based combination therapy (ACT). This strategy is significantly more expensive than before, so accurate diagnosis of malaria has become much more important.

A third option is the Rapid Diagnostic Test (RDT), which detects markers in the blood that indicate a malaria infection. These RDTs can be performed on a fingerprick of blood with very little training and give a result in about 15 minutes. Thus they are suitable for use where there is no laboratory such as smaller health centres and even at community level. The RDTs can be roughly divided into two groups, those that detect falciparum malaria only (this causes the often fatal cerebral malaria) and those that detect all four malaria species. Although the RDTs currently available have levels of accuracy comparable to routine microscopy, they all have incidents of giving false results, especially if not performed correctly. A very important factor when selecting a RDT is its heat stability, as it will often be used in situations where there is little or no refrigeration. It is also important to be aware that RDTs do not give as much information as microscopy as they are not quantitative and do not indicate what stages of the parasite are present in the blood.

With the advent of more expensive antimalarials and increasing use (and better targeting) of antibiotics RDTs will become more cost effective.

Regardless of whether microscopy or RDT is used for malaria diagnosis it is very important to have quality control and assurance systems in place to ensure the diagnosis is of a high standard. This is very important as many clinicians still treat the patient based on clinical symptoms, even if a parasitological test is negative, as they have low confidence in the test used. If they continue to do this it is very unlikely that the use of microscopy or RDTs will give any benefit and their use, instead of being cost effective will, in fact, increase the overall cost of treatment. However there are other benefits to having a clear parasitological diagnosis: improved clinical management; prevention of unnecessary treatment and therefore exposure to antimalarials (therefore reducing selection pressure for resistance) and improved disease reporting. In areas of high HIV levels, parasitological diagnosis is important because of the high incidence of other fever-causing infections. In areas of low endemicity, fever is more likely to be caused by another infection, but when malaria does occur, infection is more likely to develop into severe or complicated malaria.

Key Points:

  • Rapid Diagnostic Tests are preferred in a poorly resourced healthcare setting, where microscopy is not possible.
  • RDTs are quick and easy to use, but drawbacks are the heat stability of some tests and the limited shelf life.
  • Some RDTs detect all species of malaria parasite, others only falciparum malaria.
Programme Activities:

The Malaria Consortium is involved in three studies in Uganda evaluating the cost effectiveness, suitability, sensitivity and performance of RDTs in field settings, in comparison to microscopy or clinical diagnosis. One looking at sensitivity and specificity (funded by COMDIS), one pilot study on the suitability of RDT's in health centres (in partnership with DFID Drugman) and one (in partnership with WHO TDR, Ugandan Institute of Public Health and Mbarara University) on the use of RDTs at a Home Management level looking at cost effectiveness, suitability and reliability.

In Ethiopia, an assessment of strategy for quality assurance of RDTs and microscopy is being carried out.

In northern Sudan (Darfur) local health workers have been trained by the Malaria Consortium in using RDTs. [Link to RDTs]

References:

  1. WHO (2000). New Perspectives: Malaria Diagnosis. Report of a joint WHO/USAID informal consultation 25-27 October 1999. Geneva, World Health Organization. Link
  2. WHO (2003). Malaria Rapid Diagnosis: Making it Work. Meeting report 20-23 January 2003. Manila, World Health Organization. Link
  3. WHO-WPRO (2005). Malaria Rapid Diagnostic Tests: Making Rapid Diagnosis Work. World Health Organization - Regional Office for the Western Pacific. Link (accessed 25/08/05)
  4. WHO (2005) LIST OF KNOWN COMMERCIALLY-AVAILABLE ANTIGEN-DETECTING MALARIA RDTS (Information for national public health services and UN Agencies wishing to procure RDTs) Link (accessed 26/08/05)
  5. * WHO (2004) Trials of RDTs, Guidelines for the Field Evaluation of Rapid Diagnostic Tests for Malaria.
  6. WHO (2004b). The Use of Malaria Rapid Diagnostic Tests. Manila, World Health Organization-WPRO. Link
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  9. * Bell, D. (2004). Is there a role for malaria rapid diagnostic tests in Africa? WHO MERA Sept: iii - iv.
  10. * Huong NM, Davis TM, Hewitt S, et al. (2002). Comparison of three antigen detection methods for diagnosis and therapetic monitoring of malaria: a field study form southern Vietnam. Tropical Medicine and International Health 7(4): 304-308.
  11. * Leke RFG, Djokam RR, Mbu R, et al. (1999). Detection of the Plasmodium falciparum histidine-rich protein 2 in blood of pregnant women : Implications for diagnosing placental malaria. Journal of Clinical Microbiology 37 (9): 2992-2996.
  12. Bell, D. & Peeling, R. (2006) Evaluation of rapid diagnostic tests: Malaria. Nature Reviews Microbiology 4 (9): 1524. Link (available if register with journal)
  13. WHO: Informal Consultation on Quality Control of Malaria Microscopy , 2006
  14. Reyburn, H., Ruanda J., Mwerinde O., Drakeley C. (2006) The contribution of microscopy to targeting antimalarial treatment in a low transmission area of Tanzania . Malaria Journal 5: 4-10.
  15. Shillcut, S. (2006) Assessing RDT cost-effectiveness. Supported by: LSHTM/TDR/WPRO (2006) http://www.wpro.who.int/sites/rdt/Assessing+RDT+Cost-Effectiveness.htm
  16. Rafael, M.E., Taylor, T., Magill, A., Lim, Y-E, Girosi, F. & Allen, R. (2006) Reducing the burden of childhood malaria in Africa: the role of improved diagnosis . Nature Diagnostics 39:48.
  17. * Shillcutt, S.D., Morel, C.M., Coleman, P.G., Mills, A.J. & Goodman, C.A. (2006) WHO Report: Cost effectiveness of malaria diagnosis in sub-Saharan Africa: the role of rapid diagnostic tests in rural setting with high Plasmodium falciparum transmission.WHO.