Veterinary vaccine manufacturer Zoetis has warned of supply problems with its equine viral arteritis (EVA) vaccine, Equip Artervac, which will lead to an as yet undetermined interval in supply after their currently available batch expires on 26th November 2017. This will result in vaccinated stallions and teasers effectively ‘lapsing’ at six months after their last vaccination if Artervac is not available for the next recommended six-monthly booster dose. In August 2017, the Thoroughbred Breeders’ Association advised their members to booster vaccinate or complete a primary vaccine course before 26th November 2017, any stallions/teasers that will be covering/teasing in 2018.
Attending veterinary surgeons will need evidence to satisfy them that lapsed vaccinated stallions and teasers were seronegative before first vaccination (recorded in the horse passport) and that post-vaccination seropositivity, when lapsed, is associated with vaccination and not due to possible challenge by EAV infection. Suspicion of challenge by EAV infection would require notification to Defra/APHA under the terms of the Equine Viral Arteritis Order 1995, with the stallion/teaser being officially investigated to determine whether they are shedding EAV in their semen.
It is recommended that in addition to routine annual Code of Practice blood sampling, serial blood samples (clotted blood) are collected from vaccinated stallions during the period when Equip Artervac vaccine is not available to provide boosters and that the separated serum is tested alongside each other once it becomes clear that Equip Artervac will be available again. Results which show evidence of stable/declining virus neutralising antibody levels (VN antibody titres) against the virus during the period without vaccination should be considered consistent with absence of exposure to EAV infection during that period.
For stallions and teasers last vaccinated in November 2017, the routine January 2018 blood sample should represent the approximate peak post-vaccine VN antibody response from which subsequent antibody levels would follow and be able to be assessed as stable/declining. It is suggested that further samples are taken at approximately 6 month intervals thereafter (so in July 2018 and then January 2019 and in that pattern until Equip Artervac is again available). When Equip Artervac is available again, a final blood sample should be taken at the same time that the stallion resumes vaccination.
In order to assist with careful collation of serum samples, the Animal Health Trust (AHT) has agreed that it will receive, process and store serial samples from stallions as part of this scheme. All samples need to be clearly labelled with the name of the stallion, the stud farm and/or owner, the date that the sample was collected and the name of the veterinary surgeon and practice that collected it.
Samples should be submitted to the AHT using a dedicated submission form specifically designed for this purpose and which can be printed as required (download from HERE). Dates of vaccination must be recorded in horse passports.
Stallions ‘shuttling’ to the 2017/18 and 2018/19 southern hemisphere seasons will have further issues regarding ‘lapsed’ vaccinations and it is recommended that involved stallion owners and managers discuss with their veterinary surgeons the specific implications on the basis of individual stallions’ circumstances. These issues may be more difficult to predict and resolve as government to government discussions may be required with individual countries involved and we cannot currently confirm if or when this might happen.
To view the Program for Equip Artervac vaccinated stallions and teasers who will inevitably ‘lapse’ (six-monthly boosters will not be available during at least 2018). click here.
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