INVESTIGATIONS ON NATURALLY-OCCURRING TRYPANOSOMA-EVANSI INFECTIONS IN HORSES, CATTLE, DOGS AND CAPYBARAS (HYDROCHAERIS-HYDROCHAERIS) IN PANTANAL-DE-POCONE (MATO-GROSSO, BRAZIL)

The prevalence of Mal de Cadeiras - Portuguese for Trypanosoma (T.) evansi infections in horses - as well as the prevalence of T. evansi infections in cattle, dogs and free-ranging capybaras (Hydrochaeris hydrochaeris) was investigated in Pantanal de Pocone (Mate Grosso, Brazil). In 0.3, 8.6 and 8.0% of the horses, dogs and capybaras, respectively, infection was detected using standard parasitological methods. A seroprevalence of 4.1, 2.3, 7.1 and 22.0% was found in horses, cattle, dogs and capybaras, respectively, using an enzyme-linked immunosorbent assay for the detection of T. evansi antigen (Ag-ELISA), whereas 9.6, 4.2, 18.6 and 14.0% of the animals investigated were reactive in a T. evansi antibody (Ab-) ELISA. Positive ELISA results ('high responders') were identified using computer-assisted mixture analysis (C.A.MAN). Agglutinating antibodies were detected by the T. evansi card agglutination test for trypanosomiasis (CATT/T. evansi) in 14.6%, 1.3%, 15.7% and 22.0% of the horses, cattle, dogs and capybaras, respectively. A moderate but significant (kappa test; p < 0.05) agreement beyond chance level was observed between Ab-ELISA and CATT results but generally not between antibody and antigen detection tests. Therefore, in an attempt to maximize the information yield of the three serodiagnostic tests, their results were numerically scored (negative=0, intermediate=1, positive=2) and added up to a total score (TS) which was considered indicative for infection when TS greater than or equal to 4 (results of the Ag-ELISA received double weight). Estimates of seroprevalence according to TS were 13.2, 4.7, 30.0 and 24.0% for horses, cattle, dogs and capybaras, respectively. Identical isoenzyme profiles, known as zymodeme 58 (T. evansi MCAN/BR/86/H), were found in all T. evansi stocks isolated in the study area (six from dogs, one from a horse and one from a capybara). From the results of this study it can be inferred that Mal de Cadeiras is endemic in Pantanal de Pocone. Although clinical and parasitological findings support the possible role of the capybara as a reservoir host of T. evansi, dogs and cattle - due to their close contact with horses should rather be regarded as efficient reservoir hosts for Mal de Cadeiras in the study area.