A PRELIMINARY-STUDY ON THE ATTENUATION OF TUNISIAN SCHIZONT-INFECTED CELL-LINES OF THEILERIA-ANNULATA

Four Theileria annulata cell lines were characterised at low passage l evels using two polymorphic markers and then used to infect calves. Th eir virulence seemed to be related to the number of genotypes present within the cell line. In all, 3 of the 4 cell lines were cultured up t o passage 100 or 200 and inoculated into calves. Their characterisatio n using the same markers indicated that the attenuation was related to a reduction in the parasite polymorphism down to a single genotype, T he immunogenicity of the three attenuated cell lines was assessed in c alves using two types of challenge. Optimal protection was observed ag ainst homologous challenges. The level of immunity to heterologous cha llenges appeared to decrease with attenuation and seemed to depend on the cell line used.