With the recent occurrence of Equine Herpes Virus (EHV) infections (including the neurological form of EHV) in the UK, including the recent case in Kent, we have received many queries from our clients regarding vaccination against Equine Herpes Virus.
There are several different strains of EHV that can infect horses, the most important being EHV-1 and EHV-4. Both viruses can cause respiratory disease (characterised by an elevated temperature, cough, and nasal discharge), but EHV-1 can also cause abortion in mares and, rarely, neurological disease. Respiratory disease caused by EHV is extremely common in the UK (up to 90% of horses will be infected as foals / yearlings / two-year-olds), and in many cases infection by EHV-1 and EHV-4 causes only very mild or subclinical (silent) disease. Many horses become life-long carriers of the virus and the virus can re-emerge, for example at times of stress. The neurological form of EHV is very serious and can often be fatal. It is not well understood why the same strain of virus can cause such mild signs in some horses but such severe neurological signs in others.
EHV-1 and EHV-4 spreads similarly to how Covid-19 spreads in people – close horse-to-horse (nose-to-nose) contact, aerosol spread over short distances (up to about 5 metres), and indirect spread from shared tack and mucking out tools. People might also inadvertently spread the virus by touching an infected horse and then touching another horse without washing their hands.
The most effective way to prevent infection in your horse(s) is to maintain good biosecurity, including quarantine of new arrivals on the yard, cleaning and disinfecting equipment and transport after events, and close monitoring of horse health including their temperatures. See advice published by the BHS for some practical tips on maintaining good biosecurity.
Unfortunately, there is no vaccine available currently that is effective at preventing the neurological form of EHV-1 and neurological disease can occur in vaccinated horses. However, vaccination can reduce viral shedding in infected horses and therefore may reduce the extent to which an outbreak spreads between horses. Vaccination can also reduce the severity of respiratory disease due to EHV infection, and reduce the risk of abortion in broodmares. We recommend that broodmares receive the EHV vaccine every year (at 5, 7 and 9 months of pregnancy). We do not advice vaccination in the face of an outbreak (i.e. in horses that may have already been exposed to EHV close to the time of vaccination) as this may be detrimental.
EHV vaccination should be considered as part of a group preventative health care programme according to the risks and consequences of an outbreak in that group. Vaccination is often advised in competition yards – particularly horses which are living on yards where other horses travel away to competitions frequently, and horses which travel away for competitions themselves, particularly when this involves overnight stays in shared stabling. In these circumstances it is important to vaccinate all horses on the yard – it is not likely to help to vaccinate individual horses unless all horses on the yard are vaccinated – it is the level of “herd immunity” that is important to reduce the overall levels of virus being spread by infected horses.
Currently (12th April) there is a nationwide shortage of EHV vaccines, and supplies are extremely limited. We are prioritising broodmares for what limited stocks of vaccine are available. We are hoping that new stocks of vaccine will be available in 3-4 weeks, however it is likely that the vaccine will still be in short supply. If you are interested in getting your yard vaccinated, then please contact us.