Retrospective epidemiological investigation of an outbreak of bovine ephemeral fever in 1991 affecting dairy cattle herds on the Mediterranean coastal plain

From August to October 1991 bovine ephemeral fever (BEF) occurred sporadically in two localities in Israel. The morbidity and mortality rates reached 2.6% and 0.1%, respectively. Only 12/50 dairy cattle herds were clinically infected with BEF in the dairy community. The total morbidity rate reached 0.8%. The lowest morbidity rate was recorded in young heifers (5.5%) and the highest in adult cows (75%). Only heifers over the age of three months were clinically affected. The spread of the disease apparently followed the local prevailing night winds, which blow from east to west, i.e., from the land toward the sea. The morbidity period lasted 61 days. The low incidence and morbidity rates were possibly due to the low virulence of the virus strain involved in the 1991 epidemic. Retrospective analysis indicates that vectors - apparently mosquitoes - infected with BEF virus could have been overwintering.