The Disease
Equine viral arteritis (EVA) is caused by the equine arteritis virus (EAV). The virus occurs worldwide in Thoroughbred and non-Thoroughbred populations. EVA was reported in the UK in 2019 with two separate, unconnected subclinical outbreaks.
The first involved presumed respiratory (non-venereal) spread of infection. Both outbreaks involved non-Thoroughbred horses imported from other EU countries where EVA is endemic. One outbreak involved subsequent respiratory spread of
infection associated with attendance at equine competition events in the UK.
Recommendations for the prevention of EVA in the face of an interruption to
vaccine availability
In the absence of EVA vaccines, enhanced surveillance and biosecurity
measures are essential to mitigate the risk of EVA, especially for stallions. The virus
remains endemic in mainland Europe and poses a significant risk of importation,
as evidenced by an imported subclinically infected stallion confirmed in Scotland
in April 2024.
Veterinary surgeons and equine keepers are advised to implement enhanced
testing for stallions. As Artervac does not have DIVA capability (differentiating
infected from vaccinated animals), sequential serological testing of lapsed
vaccinated stallions is recommended.
1. Serum samples taken before the last vaccine booster and at intervals after
can confirm stable or declining titres, verifying no new exposure to EAV and
that serum positivity is due to prior vaccination.
2. Where prior serum samples are unavailable, PCR testing of semen is advised
to confirm that the stallion is not shedding the virus as a single serum sample
would not suffice in determining if seropositivity was due to prior vaccination
or infection.
Mares recently covered by a stallion with a lapsed vaccination status provide
an opportunity for enhanced monitoring to ensure no exposure of stallions while
they are at risk of infection for the duration of the time the vaccine is unavailable,
conducted alongside the sequential blood testing of the stallion. Testing the
mare before and at least two weeks after covering, with paired negative
EAV titres, confirms that the stallion is not actively shedding the virus. Fruther
details can be found at https://equinesurveillance.org/landing/resources/
eids2025ActionWithoutArtervac.pdf
