Evaluation of the antigen detection test for the diagnosis of trypanosomes using monoclonal antibodies. Experimental and natural infections

Abstract

An antigen detection ELISA for the diagnosis of trypanosomes was recently proposed by NANTULYA and LINDQVIST (1989). Based on species-specific monoclonal antibodies, this test could be used to diagnose a current infection and to identify the causing trypanosomes. The test was evaluated at CRTA during experimental infections in small ruminants and with sera from naturally infected cattle, thanks to reagents supplied by the International Laboratory for Research on Animal Diseases (ILRAD). Sera from cattle sampled in France were also tested. Cattle sera from France gave optical densities (OD) from0.007 to 0.009 with three monoclonal antibodies against T. congolense, T. vivax and T. brucei. These OD values were well below 0.050, which is considered as a positive threshold OD reading. In the small ruminant experimental infections, the sensitivity of the test was 63.2 % for T. congolense-infected animals and 9.9 % for T. vivax-infected animals. The sensitivity of parasitological tests was 55.1 and 48.6 %, respectively. The combination of the antigen- and parasite-detection tests increased the sensitivity to 82.4 and 52.8 %, respectively. Means of OD values, with the naturally infected cattle sera, were 0.116 ± 0.030 for T. congolense, and 0.011 ± 0.028 for T. vivax-infected animals. Sixteen out of 20 T. congolense-infected sera (sensitivity of 80 %) and one out of 20 T. vivax-infected sera (sensitivity of 5 %) gave an OD value exceeding 0.050. The determination of a threshold OD reading lower than 0.050 would greatly improve the sensitivity of the test. This determination could either be done by studying the preinfection sera or a local population of animals living in an area free from trypanosomosis. Our results have been obtained during the acute phase of infection. Results from ILRAD show that this test is much more reliable during the aparasitaemic chronic phase. Other evaluations for epidemiological surveys in the field are being carried out at CRTA.