THE FIELD USE OF A GERBIL-DERIVED AND DRUG-CONTROLLED LIVE VACCINE AGAINST BOVINE BABESIOSIS IN IRELAND

Live Babesia divergens parasites in gerbil erythrocytes were used to v accinate cattle on seven farms in Co. Clare, Ireland. the basic vaccin ation regime consisted of pre-treatment of cattle in late winter with 0.5 mg/kg imidocarb dipropionate (imizol; mallinckrodt Ltd) three days before subcutaneous/inoculation of about 10(7) infected gerbil erythr ocytes in RPMI 1640 medium with 40% foetal calf serum. This procedure proved safe and effective in cattle one to two years old and in a seco nd trial 32 out of 35 adult cows were successfully protected in the sa me way. However, the vaccine itself gave rise to babesiosis in two pos sibly three, of the 35 vaccinated cows. Two further trials showed that treatment with imidocarb on the day of vaccination instead of three d ays earlier resulted in decreased seroconversion, although clinical ca ses did not occur subsequently in the seronegative animals. These stud ies showed that live b. divergens, controlled by pretreatment with imi docarb, can be used to vaccinate cattle at one to two years old, the a ge group most often at risk from babesiosis. Although this approach ca n also be applied to cows, more work is required to make the vaccine s afe for animals that are in calf or have recently calved.