An evaluation of the reactivity of the card agglutination test for trypanosomiasis (CATT) reagent in the Fontem sleeping sickness focus, Cameroon

Abstract

The TestrypR Card Agglutination Test for Trypanosomiasis (CATT) used for the serodiagnosis of gambiense trypanosomiasis is based on the variant antigen type (VAT) LiTat 1.3. This antigen is rarely expressed by trypanosomes in the Fontem focus of Cameroon, but the CATT has been used for serodiagnosis in the focus since 1985. We give here a summary of results obtained with the CATT in Fontem from 1985 to 1989. The CATT is specific for trypanosome antibodies since: (a) sera from persons with other parasitoses from areas non endemic for trypanosomiasis fail to react and (b) an enzyme-linked immunosorbent assay (ELISA) based on the detection of antibodies to somatic antigens of T.b gambiense from Fontem concorded with the CATT. CATT reactions in Fontem seem to be specific for the variant surface glycoprotein (VSG) since absorption of CATT reactive sera with formalin fixed bloodstream T. gambiense from Fontem and with culture produced procyclics of T. gambiense from Fontem failed to abrogate CATT reactivity. CATT on serum failed to confirm 37% of CATT positive cases on whole blood. Although immunoconglutinin (IK), anti-human red blood cell (RBC) antibodies and complement fixing immune complexes (ICs) were found in sera from Fontem, our results failed to incriminate immunoconglutination of RBCs, reactions of RBCs with their autoantibodies and immune adherence hemagglutination as contributory factors in this lack of agreement between CATT on serum and whole blood. Further, comparison of whole blood and serum CATT results of parasitologically confirmed patients leads to the conclusion that screening with the CATT in the Fontem focus should be done on whole blood, not serum or plasma. CATT reactions in Fontem are based on cross-reactions with as yet undefined VATs.