Vaccination more reliable than observation for bovine herpesvirus

By Sarah Guy

Vaccination halts the circulation of bovine herpesvirus type 1 (BHV1) in dairy herds and should been seen as the best way to eradicate the virus, despite it disappearing without intervention in some herds after long periods, report researchers in the Veterinary Record.

Leaving animals unvaccinated has an "unpredictable outcome" says the team, which compared outcomes in vaccinated and unvaccinated dairy herds in Estonia.

Kerli Raaperi and colleagues from the Estonian University of Life Sciences in Tartu explain that BHV1 is an important pathogen of cattle that causes substantial economic losses due to reproductive failure and increased calf mortality, as well as respiratory disease.

"Eradication of the infection may have direct economic benefits for the farm and for the cattle industry of the whole country," they say.

Raaperi and co-workers assessed the efficacy of existing BHV1 vaccination programs in lowering seroprevalence of the virus within 12 dairy herds that were (n=7) and were not (n=5) vaccinated but which contained uninfected replacement heifers. They vaccinated all cattle with a gE marker to identify those with NHV1 antibodies.

After 1 year, calves born after the first vaccination in the seven vaccinated herds were all negative to BHV1 antibodies. By 2 years, the same animals in six of the herds remained seronegative, although 7% of 10-month-old animals in one herd showed antibodies against the gE marker.

Within 1.5 years, the mean prevalence of BHV1 decreased from 90% to 76%, giving an odds ratio of 0.3 compared with the pre-vaccination era, report the researchers.

By contrast, in the unvaccinated herds, they found that the mean BHV1 antibody prevalence decreased from 55% to 42% by 2 years, giving an odds ratio of 0.6; a significant decline.

However, results were not consistent across herds and sampling sessions; in one herd, seroprevalence to BHV1 antibodies among young stock increased significantly with each sampling, resulting in 68% prevalence at the third testing. Furthermore, after 2 years, the mean BHV1 seroprevalence among heifers increased from 2% to 14%; a significant rise, note the authors.

"The results of the current study indicate that using inactivated vaccines, without deviation from the vaccination protocol, may lead to rapid reduction in gE seroprevalence among young stock and cows in herds with high seroprevalence, giving good grounds for the possibility of eradication of BHV1 from herds," they conclude.

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