Epidemiology of bovine ephemeral fever virus infection in Taiwan

Sick animals with excessive nasal discharges and protruding tongue as a res ult of dyspnea were observed in the August of 1996. Eight strains of BEF vi rus were isolated from heparinized blood samples of the affected cattle. Mo st of the affected cattle were difficult to be treated and had a poor progn osis. A total of 516 farms in the 9 districts of Taiwan were affected in 19 96. Among a population of 110,247 dairy cattle, 14,993 (13.6%) cattle were found to be clinically ill. During the epidemic, 1,685 (11.3%) affected cat tle were culled or dead after the onset of the disease. Furthermore, a stra in of Ibaraki virus was isolated from the blood sample of a sick cattle tha t showed pyrexia, labored respiration and solitary behavior in the affected farm. The cattle with Ibaraki virus infection had typical symptoms of BEF at the early stage of the disease, but neither stomatitis nor pharyngoesoph ageal paralysis was observed at the onset of the disease. The outbreak was presumably brought about by the low level or non-immune status of a large c attle population due to the negligence of BEF vaccination. Therefore, the d isease easily recurred in Taiwan after a typhoon episode in the August of 1 996, which resulted in the proliferation of biting midges in the field. No difference in the antigenicty was found between the new and the previous is olates of BEF virus. As analyzed by cross neutralization test, the isolated BEF viruses showed no relationship to the Kimberley and Berrimah viruses t hat were isolated from the blood of cattle and related to BEF virus in Aust ralia. We have tried to advise farmers that they must vaccinate their cattl e annually to prevent BEF outbreak in the future.