The effect of Trypanosoma evansi infection on pig performance and vaccination against classical swine fever.

Although Trypanosoma evansi is not considered as an important pathogen in pigs, it may interfere with other pathogens or vaccinations by its immunosuppressive nature. In order to determine whether T. evansi alters pig performance and induces immunosuppression in pigs, induction of immune responses by vaccination against classical swine fever (CSF) and by immunization with a control antigen, human serum albumin (HSA), was assessed in T. evansi-infected and non-infected animals. Although T. evansi infection did not have a significant influence on growth performance, feed conversion or PCV, antibody responses against both the test antigen HSA and the CSF vaccine were significantly reduced in T. evansi-infected animals as compared to uninfected animals. Moreover, the reduced response against the CSF vaccine appears to be accompanied by a less well-developed protection against CSF with higher fever responses and leukopenia. This immunosuppression might explain the accounts of poor protection of CSF-vaccinated pigs reported in T. evansi-endemic areas of Vietnam, and suggests that prior treatments with trypanocidal drugs to improve the efficacy of CSF vaccination, may be justified.