The BVD virus is highly infectious and can be spread by nose-to-nose contact, urine, faeces (including slurry) tears, saliva, clothing, equipment, buildings, trailers and, on occasion, semen and embryos. It can stay active out of body for up to four weeks. Sheep can act as ‘reservoirs’ and spread the disease but this is not fully understood. Little risk is thought to exist from wild ruminants but infection has occurred in goats and wild deer. Biting flies are thought to spread infection also.