Bovine herpesvirus 1 in semen of bulls and the risk of transmission: a brief review.

Outbreaks of bovine herpesvirus 1 (BHV1) infections in artificial insemination centres can run a clinical or subclinical course. Clinical signs vary from mild to severe balanoposthitis and may be associated with a decrease in semen quality. After intranasal as well as intrapreputial infection, BHV1 can replicate in the preputial and penile mucosae, although the pattern of virus shedding in semen differs considerably per individual bull. Beyond the primary phase of a genital infection, BHV1 remains latent in sacral ganglia, and consequently a protracted course of intermittent virus excretion may follow. The seminal plasma rather than the sperm cells contains the BHV1. Diluting the semen before inoculating cell cultures appears to be the best method to neutralize its toxic activity and to achieve optimal virus isolation results. Detection of BHV1 in semen by polymerase chain reaction seems to be more sensitive than virus isolation. Not each extended semen straw contains virus when the virus titre in the ejaculate is low. The minimal dose to infect a cow by artificial insemination may be more than 32 infectious virus particles. Such an infection may lead to fertility disturbances, mainly endometritis. The risk of transmitting BHV1 to inseminated cows by using BHV1-seropositive bulls for artificial insemination is substantially reduced if two straws per semen batch are assayed for virus and if each positive batch is destroyed.