Development of Trypanosomosis Agglutination Card Test (TACT) utilizing fixed and stabilized procyclic antigen from culture derived Trypanosome brucei Gambiense and its evaluation in Uganda

Abstract

In a bid to improve field diagnosis of animal trypanosomosis in tsetse-infested African countries, TACT utilizing fixed and stabilized procyclic antigen from culture-derived Trypanosoma brucei gambiense isolate IL2343 was developed and evaluated in Uganda. Its diagnostic sensitivity was evaluated using blood samples from 64 confirmed trypanosome-infected cattle, and its diagnostic specificity using blood samples from 328 trypanosome-free cattle from non-tsetse infested high altitude areas on Mt Elgon. Diagnostic sensitivity and specificity of TACT were also evaluated at varying dilutions of the antigen (1:10, 1:100 and 1:500). Suitability of whole blood and plasma for performing TACT was tested using 50 negative and 133 positive samples. In addition, the detection rate of TACT in comparison to the parasitological test (Haematocrit Centrifugation Technique) was assessed using blood samples from 145 anaemic cattle (PCV≤24), 642 non-anaemic cattle (PCV ≤24), 433 cattle from trypanosomosis-endemic areas, and 500 cattle from a Rhodesiense sleeping sickness focus. Findings revealed that TACT had a diagnostic sensitivity of 94% and a diagnostic specificity of 100%. Its diagnostic sensitivity declined with increasing dilution of antigen while its diagnostic specificity remained constant. Either whole blood or plasma was equally suitable for performance of TACT. Regarding cattle with different pathological status, TACT was three times as sensitive in detecting trypanosome infection in anaemic cattle (clinical cases) but five times as sensitive in detecting trypanosome infection in non-anaemic cattle as compared to the parasitological test. Furthermore, 95% of anaemic cattle and 84% of non-anaemic cattle detected positive parasitologically were also detected positive by TACT. Regarding cattle in trypanosomosis-endemic areas, TACT was twenty times as sensitive as the parasitological test in detecting trypanosome infection. Interestingly, 100% of the cattle detected positive parasitologically were also detected positive by TACT. Regarding cattle reservoirs in a Rhodesiense sleeping sickness foci, TACT was three times as sensitive as the parasitological test in the detection of trypanosome infection. 100% of the cattle detected positive parasitologically were also detected positive by TACT. In conclusion, the rapid nature of TACT, affordability, easy of testing and impressive sensitivity for detection of animal trypanosomosis were its major advantages.

Keywords: Animal trypanosomosis; Diagnosis; Card Agglutination; Sensitivity; Specificity