Estimation of trypanosomal status by the buffy coat technique and an antibody ELISA for assessment of the impact of trypanosomosis on health and productivity of N'Dama cattle in The Gambia

The buffy coat/dark ground phase contrast technique (BCT) and an indirect a ntibody enzyme immunoassay (ELISA) were employed to assess the trypanosomal status of 32 N'Dama cattle, aged 19-28 months, exposed to natural challeng e of Glossina morsitans submorsitans and C. palpalis gambiensis. Prior to t he start of the investigation animals experienced 9-16 months of tsetse cha llenge in the study area. Blood and corresponding serum samples were examin ed monthly for a period of 8 months for patent parasitaemia by BCT and pres ence of Trypanosoma vivax and T. congolense antibodies by ELISA. In the ELI SA, the reactivity of sera to anti-trypanosomal antibodies was expressed in percent positivity (pp). Packed cell volumes (PCV) and body weights were a lso recorded monthly, and daily weight gain (DWG) computed to assess the im pact of trypanosomal status on health and productivity. During the study pe riod, the overall parasitaemic trypanosome prevalence was 3% (6/199), while the serological prevalence was 54.7% (109/199). Both diagnostic tests reve aled a predominance of T. vivax over T. congolense infections in N'Dama cat tle. Sensitivity of the immunoassay was 83.3%. In ir: vivax-parasitaemic ca ttle, antibodies persisted for 4-6 months after the parasite was detected b y BCT. A significantly higher overall mean PCV level was observed in blood samples obtained from cattle found, in any particular month, negative by BC T and ELISA, compared with those blood samples from animals responding sero logically positively for anti-trypanosome antibodies. Likewise, mean DWG wa s significantly higher in cattle found negative for both tests in compariso n to animals presenting detectable anti-trypanosome antibodies and those de tected positive by both tests. A significant negative relationship was obse rved between pp values and PCV levels in animals seropositive for T. vivax and/or T. congolense. Similarly, a negative relationship was observed betwe en DWGs and pp values. PCV levels were significantly positively correlated with DWGs. It was concluded that serological screening could provide useful information complementary to that obtained by the use of BCT not only to a ssess more accurately the trypanosomal status of cattle populations, but al so to evaluate the effects of trypanosome infection on animal health and pr oductivity and estimate the trypanosomosis risk. (C) 2001 Elsevier Science B.V. All rights reserved.