Evaluation of a polymerase chain reaction assay for the diagnosis of bovine trypanosomiasis and epidemiological surveillance in Bolivia

BACKGROUND: Sporadic outbreaks of bovine trypanosomiasis have been reported in Bolivia since 1996 when T. vivax and T. evansi were identified for the first time by parasitological means. However, comprehensive epidemiological information concerning T. vivax and T. evansi in the country is lacking. Current parasitological and serological diagnostic methods for trypanosomiasis have important limitations either in their sensitivity or specificity, which can result in unreliable data when applied in epidemiological studies. PCR assays are a recently developed procedure that might help to overcome the constraints of parasitological and serological assays. Therefore, the objective of this study was to evaluate PCR assays as a diagnostic tool for epidemiological studies in Bolivia. RESULTS: PCR assays for diagnosis of trypanosome infection in cattle were evaluated for their ability to detect trypanosome DNA in blood spots samples collected from cattle in four different provinces from the Bolivian lowlands and the results compared with those obtained with standard parasitological Micro Haematocrit Centrifugation Technique (MHCT) and stained smears and serological methods (Card Agglutination Test for T. evansi (CATT), and Antibody ELISAs for T. vivax and T. congolense). Kappa agreement analysis showed a significant agreement between PCR assays and results from parasitological methods but there was no agreement when PCR was compared with serological assays. Some samples from T. vivax smear positive animals were negative by PCR, therefore modifications to the PCR assay conditions were undertaken to try to improve agreement between PCR and parasitological assays. Changes in the template DNA concentration or the use of an alternative primer set resulted in improvements in the PCR detection rate, but not all the parasitologically positive samples were detected by PCR. Results from PCR assays for T. vivax and T. evansi were combined with results from parasitological and serological assays to provide information on prevalence rates for the four provinces from where the samples were obtained. CONCLUSION: The present study established evidence of the usefulness of PCR as diagnostic tool for epidemiological studies and confirmed that cattle trypanosomiasis appears to be endemic in several regions of the Bolivian lowlands.