Abortions usually not observed. Usually seasonal in late summer and fall during insect season. Can be in semen. Rate low, incubation to abortion variable. Some calves infected in utero born chronically infected and some with deformity including hydroencephally.
Infected animals carry virus up to several months.
If infected in utero may carry virus for life. Control Culicoides by spray and treating gnat hatching sites. Usually no signs in cow. May have been respir- atory or eye form of disease before abortion. History of keeping cows that have aborted or introduction of infected animals.