Partial protection against natural trypanosomiasis after vaccination with a flagellar pocket antigen from Trypanosoma brucei rhodesiense.

Cattle that were inoculated with an antigen derived from the flagellar pocket of Trypanosoma brucei rhodesiense and then infected with Trypanosoma congolense and Trypanosoma vivax were compared with unvaccinated cattle when both groups of cattle were placed in regions of Kenya endemic for tsetse flies known to harbour T. congolense and T. vivax. In one trial, 90 cattle were employed, 40 untreated controls, 30 cattle given prior treatment with samorin, and 20 inoculated with a flagellar pocket (Fp) antigen derived from T. brucei rhodesiense, with bovine serum albumin as the carrier and alum as the adjuvant. The animals were monitored for parasitaemia, by buffy coat analysis, during one rainy season. The untreated controls had 58% infection, the samorin-treated cattle had 43% infection, and the immunized cattle had 26% infection. Simultaneously, a second trial was conducted using 250 cattle, 100 untreated controls and 150 inoculated with the above antigen, carrier and adjuvant. At the end of the same rainy season, the untreated controls had 22% infection while the immunized animals had 9% infection. In a third experiment, on the same ranch as the latter experiment, ovalbumin was employed as the carrier. After 15 months, or over three rainy seasons, 13% of the untreated controls became infected while of the 177 immunized animals 0.9% became infected. These results are the first report of heterologous immunoprotection against trypanosomiasis in cattle.