Equine Viral Arteritis | BEVA
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Equine Viral Arteritis (EVA)

EVA is a notifiable viral disease that affects horses, mules and donkeys. It is notifiable in all stallions, and in mares that have been mated or inseminated within 14 days.

It occurs in both Thoroughbred and non-Thoroughbred populations and is currently a relatively common disease in Europe and other parts of the world, but is relatively rare in the UK.

While it is rarely life threatening to otherwise healthy adult horses, EVA is of special concern to horse breeders because it can cause abortion in pregnant mares, death in young foals and render breeding stallions permanent carriers of the virus.

EVA Vaccine Updates
January 2024: Changes to the Breeding Regulations for the 2024 season due to an interruption in supply of the Equip Artervac vaccine

Guidance for Mare Owners

After the recent batch of Equip Artervac (Zoetis) failed post-production clearance testing, the absence in availability of this vaccine, which helps protect stallions and the industry against Equine Viral Arteritis (EVA), will mean that stallion immunity will be reduced this year. EVA is a notifiable (in England, Scotland and Wales), viral disease, which is often subclinical and transmitted by close contact, or venereally and is endemic on the continent. Importation of an alternative, live, American vaccine, Arvac is being explored by managers and Defra, but will not be available in time for this breeding season. Most previously vaccinated stallions were correctly blood tested following their last vaccination (with samples stored at Rossdales Laboratories for paired testing), and therefore should comply with Defra regulations (EVA Order 1995).

Following discussions and meetings in December, stallion stud managers agreed that retaining routine post January 1st swabbing and blood testing is important for annual biosecurity screening, but an additional EVA blood test from mares would be needed no more than 30 days before they are covered. If this test is taken close to the covering date, it may also be acceptable for a covering in the subsequent oestrus period if she fails to conceive to the first service (assuming the mare is returning to the same stallion). If the mating is due to take place on a date within 30 days of the routine January screening, a second blood test will still be required (i.e. a minimum of two blood EVA tests will be necessary). As always, mare owners are advised to consult with the stallion stud prior to every covering, to check their specific requirements.

Biosecurity and welfare of the thoroughbred breeding population are paramount and the recommendations within the HBLB International Codes of Practice should be followed at all times. Of particular importance in the context of EVA, are close adherence with quarantine protocols for imported mares and the separation of thoroughbred and non-thoroughbred horses on stud farms.

The updated NSFA guidelines are attached here.

If you have any questions in relation to these recommendations for the 2024 breeding season, please contact the TBA on 01638 661321.

Guidance for Stallion Managers

Dr Richard Newton (FRCVS), Director of Epidemiology and Disease Surveillance at Equine Infectious Disease Surveillance (EIDS) has advised that Defra's Animal Disease Policy Group has approved the proposals (including the decision tree) for clearing seropositive, lapsed EVA vaccinated stallions for the 2024 breeding season - the guidance is now uploaded to the EIDS website and can be accessed here.

December 2023: approaching the 2024 breeding season

BEVA Council member James Crabtree represented BEVA in discussions along with other equine industry representatives, over a strategy of how best to approach the 2024 breeding season in the face of the ongoing unavailability of Equip Artervac (Zoetis) and confirmation that the vaccine will be unavailable until at least the back end of 2024.

Meetings involved Zoetis, DEFRA, members of the Eqiune Infectious Disease Surveilance (EIDS) team, BEVA and representatives of the Thoroughbred Breeding Industry who recommend vaccination of Thoroughbred stallions against Equine Arteritis Virus using Artervac (the only commercially available vaccine in the UK), as detailed in the Horserace Betting Levy Board (HBLB) International Codes of Practice.

Given Artervac is not a 'DIVA vaccine' ie. one can not Differentiate Infected from Vaccinated Animals (DIVA), it was accepted that lapsed vaccinated stallions will likely have positive serology results, meaning that seronegativity will not be able to be used in all instances to confirm disease free status at the start of the breeding season. It was therefore necessary to define an approach that could be used to navigate the different options available for establishing disease free status to safely start breeding in 2024.

The group reviewed the current situation and discussed the diagnostic options available resulting in the formulation of a decision tree to help clinicians navigate the options available for individual stallions depending on their vaccination status and whether or not they were blood sampled and serum stored post their last vaccination in 2023.

It is important to note that if stallions have incomplete vaccination histories or lapsed vaccinations not as a result of the 2023 shortage of Artervac, this strategy WILL NOT apply to them and they may need a bespoke screening strategy, depending on their risk of exposure, since their last vaccination. Members are reminded that it is BEVA's recommendation that all stallions are screened at the beginning of the breeding season to establish freedom from infection with Contagious Equine Metritis, Equine Viral Arteritis and Equine Infectious Anaemia, prior to commencing breeding activities. If you require further guidance see EVE article EVA: a potential trapdoor for the practicing veterinary surgeon in the United Kingdom, or contact us at membership@beva.org.uk.

View full guidance and flowchart

July 2023: Zoetis Equip Artervac Update


We would like to update you regarding the supply of Equip Artervac. Unfortunately, there has been a further delay in supply with availability now anticipated in December 2023.

We are working hard to resolve this situation and apologise for the inconvenience this may cause.

The Thoroughbred Breeders Association earlier this year published advice for a blood sampling scheme to help manage re-vaccination of stallions when stock of Equip Artervac becomes available. Please note for stallions sampled and the blood stored for testing according to this protocol, there is no further action required at this time.

If you require further information please speak to your Zoetis account manager or call Head Office on 0345 300 8034.

Yours sincerely,

Tim Burgess
Ruminant & Equine Business Unit Director UK

February 2023: Zoetis Equip Artervac Update

Zoetis Ltd today announced that there will be a supply issue with Equip® Artervac.

Equip Artervac is a part of the Zoetis Equip range of vaccines. It is indicated for the active immunisation for horses against equine viral arteritis (EVA) to reduce the clinical signs and shedding of the virus in nasal secretions following infection.

The current inventory of Equip Artervac has an expiry date of March 29, 2023 and Zoetis is not expecting a new batch to be available until the end of September 2023.

We have been working closely with the relevant organisations to implement a plan to mitigate the impact to breeders.

The Thoroughbred Breeders Association has published advice for a blood sampling scheme, find out more here.

Please note this requires action two weeks after the most recent EVA vaccination so please ensure you familarise yourself with these guidelines in plenty of time.

We sincerely apologise for any inconvenience that may be caused with this supply issue. Zoetis confirms its commitment to providing further information as soon as possible.

The VMD and DEFRA have been notified about the situation.

For further information contact your Zoetis Account Manager or the Zoetis Technical Team on customersupportUK@zoetis.com or 0345 300 8034

About Zoetis

As the world’s leading animal health company, we are driven by a singular purpose: to nurture our world and humankind by advancing care for animals. After 70 years innovating ways to predict, prevent, detect, and treat animal illness, we continue to stand by those raising and caring for animals worldwide – from livestock farmers to veterinarians and pet owners. The company’s leading portfolio and pipeline of medicines, vaccines, diagnostics and technologies make a difference in over 100 countries. A Fortune 500 company, Zoetis generated revenue of $7.8 billion in 2021 with approximately 12,100 employees. For more information visit the Zoetis website.

February 2023: BEVA Guidance on supply of Equip Artervac

The current supply of Equip Artervac has an expiry date of 29 March 2023 and due to supply issues Zoetis are not expecting a new batch to be available until the end of September 2023 meaning that all previously vaccinated stallions may go beyond the 6 month booster interval and therefore go ‘out of date’. It has been estimated that approximately 160 stallions may be affected by this. As there should be no issues in obtaining vaccine up to the date of expiry of the current batch of Artervac, it should be possible to bring vaccinations forward up to and before the 29 March 2023, making them next due for booster vaccination by 29 September 2023.

A prospective strategy is in place to monitor stallions by serological screening. Blood should be collected 2-3 weeks after the stallion receives it’s Artervac booster, when peak antibody levels should be present. This sample should be submitted to Rossdales laboratory, Newmarket, using the special submission form. A further blood sample should be taken at the time that the stallion receives their next Artervac booster when the new batch of vaccine is available. Paired serological testing will be performed to demonstrate that infection has not occurred and these results should be certified in the stallion’s passport. DEFRA’s Animal Disease Policy Group (ADPG) have approved the proposed approach for blood testing however, this strategy will only work if blood is taken in the proposed window post vaccination to provide a reference point for the paired serology. Stallions that do not follow this strategy will likely need a rely on a retrospective approach involving screening of semen for EAV to demonstrate they are free from infection before vaccination resumes. Stallions that were not sampled after they were last vaccinated could be boosted early on or before the 29 March 2023, and then sampled 2-3 weeks later.

December 2022: Equip Artevac supply issue

On the 23rd December Zoetis (UK) announced that the current inventory of Equip Artervac has an expiry date of 29th March 2023 and due to supply issues they are not expecting a new batch to be available until the end of September 2023. The currently available licensed batch of Equip Artervac is still in plentiful supply so there should be no problems with vaccinating stallions ahead of the 2023 breeding season. A precise date for re-supply is not currently available and we therefore have to assume the worst-case scenario that it may not be available until after the 29th September; a gap of over six (6) months. Unfortunately, Zoetis have indicated that it will not be possible to extend the vaccine’s expiry date nor is importation of an alternative product a realistic possibility.

Equip Artervac (Zoetis) is the only licensed vaccine in the UK & European Union against equine arteritis virus (EAV) and is recommended for use by the HBLB’s International Code of Practice for the prevention of equine viral arteritis (EVA). The data sheet states that boosters should be administered at six (6) month intervals. This will present stallion owners with an issue if stallions’ vaccinations lapse as EVA is a notifiable disease in the UK under the Equine Viral Arteritis Order 1995. Under this legislation seropositive stallions with lapsed vaccinations, will need to demonstrate they have not been infected during a period when they were considered susceptible i.e. when they were outside of the data sheet recommendations. Disease freedom needs to be demonstrated, ideally prior to re-vaccination.

The Thoroughbred Breeders Association (TBA) have offered guidance to its members and have presented a strategy to manage Thoroughbred stallions and teasers which may not be vaccinated when their boosters are due. They are again recommending a practical means by which stallions/teasers can be monitored by antibody analysis of stored blood samples; the same approach that was adopted in 2018, when Equip Artervac last had supply issues.

Many Thoroughbred stallions will be vaccinated in January ahead of the breeding season and six months later, however, BEVA and the wider industry appreciates that Sports horse stallions may be routinely vaccinated at different times of year to Thoroughbreds and therefore we recommend veterinary surgeons looking after Equip Artervac vaccinated Sports horse stallions should consider discussion of this with their clients/stallion owners.

As there should be no issues in obtaining vaccine up to the date of expiry of the current batch of Equip Artervac (29th March 2023), it should be possible to bring vaccinations forward up to and before the 29th March 2023, making them next due for booster vaccination by 29th September 2023. Stallions due imminently could be vaccinated and then potentially re-vaccinated early up to and before the 29th March 2023 making them also next due by 29th September 2023.

If the worst-case scenario happens and Equip Artervac is not available by the 29th September then one could plan to collect a semen sample from the stallion and submit for EAV virus isolation and/or PCR to demonstrate the stallion is not a carrier, prior to restarting vaccination. One must also however give consideration to the fact that the stallion will have been outside of data sheet recommendations and may therefore have been susceptible to infection. As such a risk assessment should be performed to determine if additional sampling above and beyond a single semen test is necessary as per the guidance given in Crabtree & Newton 2020. Clients should be reminded of the increased risks of contracting the infection through international travel and breeding activities in circumstances where biosecurity measures are either minimal or inadequate with respect to EVA, for example, where potential in-contacts are not screened for EVA and/or are not of equivalent health status.

Such a retrospective approach, with semen sampling, may be relatively simple for some stallions to achieve, however, it is acknowledged that this may not be straightforward for some stallions that are either not trained for semen collection, or that need to visit a semen collection centre for collection (noting that such a centre may require a stallion to demonstrate freedom fromEAV infection to enter in the first place).

Consequently, one could alternatively follow the prospective approach and monitor antibody levels as per the TBA’s guidance for Thoroughbred stallions and teasers. The strategy is to collect a blood sample around 2-3 weeks after the stallion receives their booster dose of Equip Artervac up to 29th March 2023, by when peak antibody levels from vaccination should be present. This sample should be sent by the vet, accompanied by the special submission form specifically designed for this purpose, for storage and later testing by Rossdales Laboratories, Newmarket. A further blood sample should be taken at the time that the stallion receives their next Equip Artervac booster when the new batch of vaccine is available; with this sample also sent to Rossdales Laboratories for pairing up with the previous sample and testing together as necessary. DEFRA agreed this approach in 2018 and the industry are hopeful that it will again be acceptable. Should there be any issues it may be necessary to revert to semen testing.

December 2022: Letter to TBA members regarding supply of Equip Artervac

Equip Artervac (Zoetis) vaccine provides stallions and teasers with some protection against challenge with equine arteritis virus (EAV) and is recommended for use by the HBLB’s International Code of Practice for equine viral arteritis (EVA). Booster doses are required to be administered every six months; usually in January before the breeding season and later in the summer when the six-month booster date comes due. The currently available licensed batch of Equip Artervac is still in plentiful supply so there should be no problems with vaccinating stallions ahead of the 2023 breeding season. However, the current batch of Equip Artervac is due to expire in late March 2023.

On 21st December 2022 the TBA was made aware by Zoetis (UK) that due to a vaccine constituent supply problem, that they do not expect a new batch of Equip Artervac to be available from their European production plant until September 2023; a precise date for re-supply is not currently available. Unfortunately, Zoetis have indicated that it will not be possible to extend the vaccine’s expiry date nor is importation of an alternative product a realistic possibility.

Therefore, as things stand there will be no licensed Equip Artervac EVA vaccine available in summer 2023 to booster vaccinate European stallions and teasers in accordance with the manufacturer’s product datasheet requirements, leading to stallions having ‘lapsed’ EVA vaccination records later in 2023. This will present issues for Defra as EVA is a notifiable disease in the UK under the Equine Viral Arteritis Order 1995. Under this legislation seropositive lapsed vaccinated stallions may need semen sampling and testing to prove that they are not shedding EAV in their semen and unfortunately using out of date vaccine supplies does not solve the ‘lapsed’ vaccination issue.

A similar problem with potential interruption of supply of Equip Artervac occurred back in 2018 and we are again recommending a practical means by which stallions/teasers can be monitored by antibody analysis of stored blood samples. Evidence of stable/declining antibody levels during the period when EVA vaccination lapses occur will be consistent with absence of exposure to EAV infection and preclude the need for semen testing. Defra agreed this approach in 2018 and we are hopeful that it will again be acceptable; Defra are also now aware of the potential 2023 Equip Artervac supply issue.

The proposal is that in addition to routine annual Code of Practice blood sampling, a further blood sample is collected from vaccinated stallions around 2-3 weeks after they receive their booster dose of Equip Artervac vaccine in January 2023, by when peak antibody levels from vaccination should be present. This sample should be sent by the vet, accompanied by the special submission form specifically designed for this purpose, for storage and later testing by Rossdales Laboratories, Newmarket. A further blood sample should be taken at the time that the stallion receives their next Equip Artervac booster when the new batch of vaccine is available; with this sample also sent to Rossdales Laboratories for pairing up with the previous sample and testing together as necessary.

Further guidance on stallions ‘shuttling’ to the southern hemisphere seasons in 2023 will be issued in due course.

Page last updated July 2023