PROPHYLAXIS OF SALMONELLA-ABORTUS-OVIS-INDUCED ABORTION OF SHEEP BY ASALMONELLA-TYPHIMURIUM LIVE VACCINE

A Salmonella typhimurium live vaccine with optimal level of attenuatio n for sheep, constructed by means of 'metabolic drift' mutations, was tested for its efficacy in preventing Salmonella abortus ovis-induced abortions. In two field trials in Kirgiziya, 78 000 to 100 000 first d elivery sheep received a fully tolerated single dose of 10(9) c.f.u. l ive vaccine 2 months before to 4 months after insemination. Alternativ ely, they were immunized twice with commercial inactivated S. abortus ovis vaccine, or they served as non-immunized controls. The S. abortus ovis-induced abortion frequency in the controls was greater-than-or-e qual-to 30%, in sheep immunized with inactivated vaccine greater-than- or-equal-to 11%. In flocks immunized with live vaccine, the S. abortus ovis-induced abortion frequency did not exceed 0.1%. Thus, use of 'me tabolic drift' mutations for construction of stable vaccine strains op timally attenuated for the particular host species proved to be releva nt to practice.