Options for field diagnosis of human african trypanosomiasis

Abstract

Human African trypanosomiasis (HAT) due to Trypanosoma brucei gambiense or T. b. rhodesiense remains highly prevalent in several rural areas of sub-Saharan Africa and is lethal if left untreated. Therefore, accurate tools are absolutely required for field diagnosis. For T. b. gambiense HAT, highly sensitive tests are available for serological screening but the sensitivity of parasitological confirmatory tests remains insufficient and needs to be improved. Screening for T. b. rhodesiense infection still relies on clinical features in the absence of serological tests available for field use. Ongoing research is opening perspectives for a new generation of field diagnostics. Also essential for both forms of HAT is accurate determination of the disease stage because of the high toxicity of melarsoprol, the drug most widely used during the neurological stage of the illness. Recent studies have confirmed the high accuracy of raised immunoglobulin M levels in the cerebrospinal fluid for the staging of T. b. gambiense HAT, and a promising simple assay (LATEX/IgM) is being tested in the field. Apart from the urgent need for better tools for the field diagnosis of this neglected disease, improved access to diagnosis and treatment for the population at risk remains the greatest challenge for the coming years.

FIG. 1.

Diagrammatic representation of the life cycle of T. b. gambiense and T. b. rhodesiense in humans and the tsetse fly. Copyright Alexander J. da Silva and Melanie Moser, Centers for Disease Control Public Health Image Library. Reprinted with permission from the Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta, Ga.

FIG. 2.

Geographic distribution of major endemic foci of T. b. gambiense and T. b. rhodesiense human African trypanosomiasis in Africa (1995). Reprinted from reference with the permission of WHO/CPE.

FIG. 3.

Example of CATT performed on 10 serum samples diluted 1:4. Samples 1 to 3 are strongly positive, sample 4 is weakly positive, and samples 5 to 10 are negative.

FIG. 4.

Example of a field algorithm for the diagnosis of T. b. gambiense sleeping sickness according to data from Simarro et al. (112).

FIG. 5.

Bloodstream trypomastigote forms of T. b. rhodesiense on a peripheral thin blood smear. Copyright Jean Jannin (WHO/CPE).