Excretion of bovine herpesvirus 1 in semen is detected much longer by PCR than by virus isolation.

To compare the sensitivities of PCR and virus isolation and to examine the course of virus excretion in semen, we intrapreputially inoculated eight bulls with bovine herpesvirus 1 (BHV1) and used two bulls as sentinels. From these bulls, we collected a large panel of semen samples during 65 days postinfection (dpi). At 44 dpi the bulls received dexamethasone to reactivate putatively latent virus. We analyzed the semen samples by virus isolation on egg yolk-extended semen (VIE test), by virus isolation on fresh semen (VIF test), and by a PCR test on egg yolk-extended semen. Of the 162 semen samples that were collected, the VIE test scored 24 positive, the VIF test scored 51 positive, and the PCR test scored 118 positive. At 6 dpi all samples from the inoculated bulls were found to be positive by all three tests. From 9 to 44 dpi most samples were found to be negative by both virus isolation tests but positive by the PCR test. From 48 to 55 dpi the dexamethasone treatment induced virus reactivation, which was evidenced by an increase in the number of positive VIE, VIF, or PCR tests. From 58 to 65 dpi all samples were found to be negative in both virus isolation tests, but several samples were still found to be positive by the PCR test. To determine whether BHV1 DNA was present in the dorsal root ganglia of the infected bulls, we analyzed by PCR several thoracic, lumbar, and sacral ganglia collected at 65 dpi. BHV1 DNA was frequently present in the third, fourth, and fifth sacral ganglia, and semiquantitative PCR analysis showed that the highest amounts of BHV1 DNA (10 to 30 molecules of BHV1 DNA per 10(5) cells) were present in the third sacral ganglion, The results demonstrate that the PCR test detected five times as many positive semen samples as the VIE test. Hence, intrapreputially infected bulls excrete BHV1 in semen much longer than recognized until now.