BVDV rapidly loses infectivity outside the host, and is very susceptible to detergents, light, temperature changes and other environmental conditions. It is mainly transmitted by close contact with persistently infected or acutely infected cattle via the oral or nasal routes. Acutely infected animals only shed the virus for a short time (about 2 weeks1), whereas PI animals shed constantly in all bodily secretions for life. Acutely infected bulls shed virus in their semen for at least 2 weeks; PI bulls shed virus constantly in their semen, thus, semen is another potential source of infection in natural mating. Reputable artificial insemination services will check their bulls and semen for BVDV.2 Sheep, goats, and pigs can become infected from close contact with cattle, and sheep can transmit the virus to cattle in close contact. Needles, rectal sleeves, water troughs, feed bunks, nose tongs, and other equipment can aid the spread of virus.2 It has been shown experimentally that biting insects can also spread the virus.2
1 Smith, B: Bovine Virus Diarrhea; Mucosal Disease: Large Animal Internal Medicine. Mosby Publications, 1996;pp 806-814
2 Tremblay, R: Transmission of bovine viral diarrhea virus. Veterinary Medicine 9:858-866;1996.