Bovine babesiosis: steps towards an irradiated vaccine.

A series of experiments leading towards the field trial of an irradiated blood-derived vaccine against Babesia divergens, common cause of redwater in cattle in Europe, is described. Initially a number of isolates of B. divergens were made from the blood of sick animals in a variety of localities in the british Isles. These isolates were cryopreserved and then characterised by inoculation into groups of spenectomised Friesian calves, whose reactions were statistically analysed. Attempts were made to prepare a vaccine against B. divergens infection using diluted infected blood, but when these failed it was found that irradiation of infected blood within the range of 24 to 32 kilorads and its intravenous inoculation into calves produced the required immune response without pathogenic effects. An irradiated blood-derived vaccine produced by the irradiation of infected blood at 25 or 30 kilorads was used in a field trial in Ireland, and vaccinated calves were protected against a field challenge which caused redwater in 10 control cattle, six of which had severe reactions.