Trypanosomiasis: Diagnosis, serology

Antibodies can be detected serologically. Several techniques (immunofluorescence etc.) have been developed. There are also methods for use in primitive rural conditions. A cheap and practical method is a direct agglutination reaction of trypanosomes on a plastic card, with macroscopic read-off (CATT = Card Agglutination Test for Trypanosomiasis). This is a good screening method in population studies for T. b. gambiense. A drop of blood (finger prick) and a drop of reagent that contains blue-coloured parasites of a known serotype are mixed on a white plastic card. The card is mechanically shaken for 5 minutes and then immediately read. When the test is positive (presence of antibodies) the trypanosomes agglutinate and form a blue clot. CATT must not be confused with the CIATT (Card Indirect Agglutination Test for Trypanosomiasis). Another method is to take a blood drop on very small filter papers (confetti) and examine this later in a laboratory. The patient should be called back later if the result is positive. Antigen-detection methods (ELISA) have also been developed, but are not yet in routine use. A problem arises in persons who have a positive serology, but who are asymptomatic and in whom no parasites are found (wait and see with follow-up or treatment with suramin or pentamidine?). After successful treatment the antibodies remain for years. Antibody detection therefore cannot be used for detecting relapse or reinfection. It is hoped that in the future we shall be able to prove a cure by monitoring reductions in the levels of circulating antigens, either directly (e.g. ELISA) or by PCR or variants of these. Such tests remain to be validated by further clinical investigation. Further invention of genetic detection methods will possibly also facilitate the detection of resistant parasites, which may then of course influence treatment

Category: Medicine Notes