An outbreak of babesiosis (B. divergens) in a dairy herd comprising different age groups of cattle.

Outbreaks of acute bovine babesiosis affecting several individuals within a herd are well known among veterinary practitioners and farmers within different parts of Sweden. Although outbreaks may not occur every year, they are feared by the farmers due to the unpredictability of the disease, its suddeness of onset, its rapid course, and the high mortality unless treated. Sporadic outbreaks of acute bovine babesiosis comprising several animals within a limited time period have been previously reported in Sweden (Linnaeus 1747, Bergman & Waxberg 1915, Heijbel 1928), in Finland (Hinderson 1928), in Norway as cited by Tambs-Lyche (1943), in the United Kingdom (Donnelly et al. 1970) and elsewhere within the area where B. divergens is distributed (Tambs-Lyche 1943, Purnell 1980). In all of these cases groups of animals had been transferred onto pastures where clinical cases of bovine babesiosis were known to occur from areas where the disease was rare or had never occurred; i.e. unexposed animals were transferred onto pastures with Babesia infected ticks. The farmers first became aware of this situation after the outbreak had occurred.