Efficacy of Theileria parva stabilate kept on melting ice in immunisation against East Coast fever

Abstract

The effect of increasing the shelf life of equilibrated Theileria parva stabilate beyond the recommended shelf life of one hour was studied in immunization against East Coast fever. In a preliminary experiment, groups of five cattle were immunized with stabilize material which had been kept on melting ice at 0, 1, 2, 4, 8 and 24 hours after equilibration. The material was ineffective up to 24 h and all animals developed high antibody titres to T. parva schizont antigen. The animals were challenged with a lethal dose of the homologous material thirty five days later. Animals inoculated with 2 to 8 hour old stabilate resisted homologous challenge while both controls and an animal in each of the other groups required treatment. In a subsequent experiment, twenty cattle were immunised with the same stock of parasite, which had been kept for four hours on melting ice. Thirty five days later, they were divided into two equal groups and challenged with the homologous or heterologous stabilate. Ninety and seventy percent of the animals resisted the homologous and heterologous challenge respectively, while all controls developed severe disease.