Evaluation of a simple PCR technique for the diagnosis of Trypanosoma vivax infection in the serum of cattle in comparison to parasitological techniques and antigen-enzyme-linked immuno sorbent assay.

Polymerase chain reaction (PCR) with specific oligonucleotides for the amplification of Trypanosoma vivax DNA has been developed by Masiga et al. (1992) to detect the presence of T. vivax DNA in biting flies. The aim of this experiment was to evaluate the efficacy of this technique when applied directly on cattle serum, without DNA purification, to detect infection. The sensitivity of this PCR technique was compared with parasitological techniques, namely haematocrit centrifuge technique (HCT) and buffy coat method (BCM), and with the antigen-enzyme-linked immunosorbent assay (Ag-ELISA) for T. vivax developed by Nantulya and Lindqvist (1989). Blood and serum samples were collected from four calves experimentally infected with a stock of T. vivax from French Guyana (IL4007). During the first 51 days of infection, a total of 164 samples were collected and processed using the four tests. Mean percentages of positive results were 68% with HCT, 59% with BCM, 4% with Ag-ELISA and 64% with PCR. Parasitological and PCR techniques yielded approximately the same sensitivities. PCR was able to detect active infection in serum samples when parasitaemia was over 10(3) trypanosomes/ml. With this isolate of T. vivax the Ag-ELISA was not found to be sensitive enough to be used as a diagnostic tool. The sensitivity of this PCR technique is not greater than parasitological techniques but it allows delayed processing of the samples and gives a highly species-specific diagnosis. This simple PCR technique should be evaluated for field diagnosis because it makes retrospective epidemiological survey using serum banks possible. Moreover, it can be substituted to parasitological techniques when immediate examination is not feasible.