Shedding of bovine alphaherpesvirus-1 in bovine extended frozen semen in Indian semen stations: A longitudinal analysis.

Infectious bovine rhinotracheitis (IBR) caused by bovine alphaherpesvirus 1 (BoHV-1) is an economically important disease of cattle and buffaloes. Following acute infection, the virus usually attains latency in the sensory neurons. Stress-induced reactivation of latency can cause the infected animals to intermittently shed the virus in body secretions including semen. A longitudinal analysis was carried out to study BoHV-1 shedding in the semen of IBR seropositive cattle and buffaloes. The study involved data generated from the screening of 119,850 extended frozen semen (EFS) batches, collected from 1,229 IBR seropositive bulls, over a period of four years (April 2015 to March 2019). A TaqMan based real-time PCR assay was employed to detect the gB gene BoHV-1 DNA in the EFS batch samples. Each sample was tested in duplicate and amplification in any of the replicates at or below the threshold cycle (Ct ≤ 40) was considered positive. The overall positivity of BoHV-1 in EFS batches was 1.18%. About 41% of the bulls (509 of 1,229) were found to have excreted the virus in semen at least once during the study period. The frequency of viral shedding in buffaloes (0.96%) was significantly lower than that of cattle (1.3%) (p < 0.001). No significant difference was noted in the rate of shedding between the first and the second ejaculates collected on the same day (p = 0.607). The rate of shedding also did not vary among various breeds of cattle (p = 0.454) or with the age of the bulls (p = 0.054). No significant variation in the shedding rate was observed in cattle across different seasons (p = 0.101); while in buffaloes, the rate was higher in autumn (1.2%) than in winter (0.7%) (p = 0.037). The difference in positivity among semen stations was statistically significant (p < 0.001). Analysis of data revealed that ≥100 EFS batch samples/bull were screened from 361 of the 1,229 bulls included in the study. None of the EFS batches screened from 39 of these 361 bulls were found positive during the four years, suggesting they were non-shedders. Further research is warranted to delineate the underlying features of the seropositive non-shedders; following which an adequate risk assessment may be made for the maintenance of infected but non-shedding bulls in semen production.