The use of a polymerase chain reaction assay for the detection of bovine herpesvirus 1 in semen during a natural outbreak of infectious bovine rhinotracheitis.

Nasal swabs from two bulls at an artificial insemination (AI) station were submitted to our laboratory. The animals showed clinical signs of Infectious bovine rhinotracheitis (IBR), although the station was supposedly free of bovine herpesvirus 1 (BHV1). DNA of BHV1 was detected using a polymerase chain reaction (PCR). Subsequently nasal swabs from 100 animals that could have been in contact were submitted. BHV1 DNA was detected in swabs from 23 animals. Using the PCR, BHV1 could only be detected in a limited number of semen samples over a period of two months prior to the outbreak or two months after the outbreak. Also, not all animals that shed BHV1 from the nose harboured detectable BHV1 in the semen. Finally BHV1 was detected in the semen of one bull, approximately six weeks before seroconversion. Presently the PCR is being used as a means of quality control of fresh semen from bulls that are seropositive for BHV1. We are able to produce a result within 6 h after the semen samples have been submitted, allowing the AI-station manager to take measures before semen distribution in the event of a positive reaction. So far 11 out of 318 samples were shown to contain BHV1 DNA. In order to be able to interpret these results an interlaboratory comparative study is proposed. In countries endemically infected with BHV1 the PCR can be a cost-effective method to minimize the risk of transmitting virus by semen.