Impact of bovine herpesvirus-1 infection on fertility in dairy cattle

Bovine herpesvirus-1 (BoHV-1) is an important pathogen of cattle throughout the world. It is an alpha-her-pesvirus that can be subdivided into types 1.1, 1.2a and 1.2b (Muylkens et al, 2007), but only types 1.1 and 1.2b are thought to occur in the UK (Nettleton and Russell, 2017). Subtypes 1.1 and 1.2a are associated with respiratory disease (infectious bovine rhinotracheitis) and abortion, while type 1.2b has been isolated from genital lesions (infectious pustular vulvovaginitis and infectious balanoposthitis) (Raaperi et al, 2014). However, this distinction is not absolute, and is influenced by the route of infection with either subtype able to establish infection in either the reproductive or the respiratory tracts (Nettleton and Russell, 2017).

Infection is widespread and is present on all continents (Ackermann and Engels, 2006). While there has been no national herd prevalence survey carried out in Great Britain, surveys of herds in England and Wales in 1970–72 and 1984–86 found the proportion of herds with antibody-positive animals increased from 18% to 48% (Edwards, 1988) with a subsequent increase to 69% in 1996 when bulk tank milk was examined (Paton et al, 1998). These studies were limited by the lack of information on the BoHV-1 vaccinal status of the surveyed herds, but nevertheless were taken together to indicate a long-term trend of increasing herd seroprevalence that was considered likely to continue (Paton et al, 1998). In a survey conducted in the southwest of England that excluded herds that had been vaccinated, but where the vaccinal status of purchased animals was unknown, 83% of 114 herds had at least one animal that was seropositive to BoHV-1 (Woodbine et al, 2009), and a survey completed in 2015 found that of 118 unvaccinated herds 62% had bulk tank antibody to BoHV-1 (Velasova et al, 2017). There is therefore a lack of information on the proportion of dairy herds in Great Britain that currently have endemic BoHV-1 infection or the rate at which outbreaks of BoHV-1 occur. This lack of information has not prevented the creation of formal control programmes for this infection, firstly by the Ministry of Agriculture Fisheries and Food in the 1980s and subsequently by the Cattle Health Certification Standards (2023) in 1999. However, pedigree beef cow herds have been the predominant participants in these programmes. In contrast, in 2021 there were 15 countries in the European Union with compulsory control programmes and eight countries were officially free from BoHV-1 infection (Hodnik et al, 2021). An initial low herd level prevalence was an important factor in the decision of some countries to pursue eradication, but experience has shown that herd vaccination with BoHV-1 glycoprotein-E deleted vaccines can be an effective tool for those herds with endemic infection that are required to progress to freedom from infection (Raaperi et al, 2014). Therefore, while the limited survey work indicates that a high herd seroprevalence should be expected in Great Britain, this is not necessarily a barrier to achieving effective control of BoHV-1 either through formal control or herd vaccination programmes.