Microscopic examination of Giemsa-stained blood slides continues to be a major reference standard for the detection, identification and quantitation of malaria parasites. The assessments of antimalarial drug and vaccine efficacy, and the performance of diagnostic devices all require sensitive, accurate and precise measurement of the numbers and species of malaria parasites. The consistency and reliability of microscopy results depend on numerous factors, beginning with the quality of the materials and equipment used, and the protocols applied for slide reading and quality assurance. However, microscopy relies most on the knowledge, level of skill, and judgment of the user, which could influence results.
Global Good’s Dr. David Bell worked together with a group of experts convened by the UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (TDR) to develop a set of procedures for microscopy recommended for use in malaria research studies. The group included representatives from the Foundation for Innovative New Diagnostics (FIND), US Centers for Disease Control and Prevention, Kenya Medical Research Institute, World Wide Antimalarial Resistance Network (WWARN), AMREF Health Africa, Institut Pasteur du Cambodge, Institut de Recherche pour le Développement – Senegal, Mahidol-Oxford Tropical Medicine Research Unit, Queensland University of Technology, and Shoklo Malaria Research Unit.
“Malaria research has been considerably hampered by a lack of standardization in this primary method for detection of parasites,” says Dr. David Bell, Head of Global Health Technologies at Global Good. “This multi-institution initiative will contribute to improving the quality and efficiency of efforts to understand, and eradicate malaria.”
The procedures proposed by this group in the Methods Manual: Microscopy for the detection, identification and quantification of malaria parasites on stained thick and thin blood films in research settings are intended to help researchers working in drug or vaccine efficacy trials or in diagnostics to deliver consistent and reliable data and to promote standardization in reports.
These procedures, and the standards on which they are based, were adapted from the WHO guidelines to cater to the particular requirements of research malaria microscopy. Routine clinical microscopy is typically performed to confirm the diagnosis of malaria before appropriate treatment can be given. In research contexts however, additional information is needed on the species, parasite stages and the density of the infecting parasites. High diagnostic specificity is of particular importance in research microscopy as false positive results can significantly skew efficiency estimates. Accordingly, the recommended procedures incorporate best practices from various published procedures to cover all aspects of malaria microscopy to detect, identify and quantitate malaria parasites from stained blood films. They also include clear guidelines for quality assurance of microscopy and rigorous standards for proficiency testing of microscopists.