The efficacy of killed Trypanosoma evansi vaccines in mice.

Four strains of Trypanosoma evarsi (D3, D4, D5 and D6) isolated from German shepherd dogs were inoculated into mice, and infected blood was used to prepare 9 separate killed vaccines. White mice inoculated with 1:100 diluted PBS vaccine, 0.5% carbol vaccine, or 100% Lugol vaccine showed survival rates of more than 60%. Among these 3 vaccines PBS vaccine and 0.5% carbol vaccine showed higher survival rates at 1:500 and 1:1000 dilutions, respectively. When young mice (15-20 g) were immunized with PBS vaccine, they resisted challenge with homologous strains, D3 strain in single injection, D6 strain in double injections and all strains in 5 injections. Protection however was not observed in old mice (25-30 g) give the same vaccine preparation. When mice were vaccinated with a single injection of D3 vaccine and challenged with heterologous strains, only those challenged with D4 strain at 10-5 dilution showed a survival rate of more than 60%. There was no difference in protective ability among PBS vaccine, agar adjuvant and kaolin adjuvant vaccines. Agglutinating antibody was demonstrated in mice receiving 5 injections of PBS vaccine.