LIVE VACCINES AGAINST HEMOPARASITIC DISEASES IN LIVESTOCK

Live vaccines against hemoparasitic diseases in livestock are based on parasites derived from culture (Theileria annulata), from blood of in fected animals (Babesia bovis, Babesia bigemina, Anaplasma centrale, ( attenuated) Anaplasma marginale and Cowdria ruminantium), and from tic ks (Theileria parva). The T. annulata attenuated cultured schizont vac cine is safe for all varieties of cattle. Blood derived vaccines are r ecommended mainly for young cattle, the age limit varying with the dif ferent vaccines and breeds of cattle. In older animals, monitoring of the individual response is needed. Immunization against T. parva requi res simultaneous or postinoculation chemotherapy. The potential for ac cidental transmission of disease agents exists with all blood derived vaccines. Various degrees of resistance to field infection have been r eported in animals immunized with live vaccines. Nevertheless, all of them engender a level of protection against natural challenge that jus tifies their use in field vaccination. Chemotherapy or chemoprophylaxi s may prevent establishment of infection with the vaccinal parasites, and thus may interfere with elaboration of immunity. Outbreaks of dise ase in vaccinated herds, caused by antigenic variants among the tick-t ransmitted parasites, have been observed mainly in Babesia infections. In recent years, the main efforts towards improvement of live vaccine s have been in the direction of replacing blood- and tick-derived para sites by those cultured in vitro under controlled standardized conditi ons.