African Horse Sickness

African Horse Sickness is a very real and sometimes frustrating challenge for all of us and our horses. As horse owners, it is our responsibility to ensure that horses are vaccinated every year and that any movement of horses into the Western Cape African Horse Sickness (AHS) Controlled area complies with policy requirements. Apart from mitigating the risks of horses getting the virus and maintaining the free zone for future exports, the vaccination protocol requires some pre-planning to accommodate any competition, breeding and movement schedules.

To clarify some of the queries we often get, this newsletter offers some background on the vaccination process and current movement protocols.

Vaccination
The current available horse sickness vaccine is a polyvalent vaccine containing attenuated strains in two components: one trivalent (containing serotypes 1,3 and 4), and one quadrivalant containing serotypes 2, 6, 7 and 8. Serotypes 5 and 9 are not included in the vaccines because serotypes 8 and 6 are reportedly providing adequate cross protection. The two vaccines should be administered at least 3 weeks apart but the period in-between can be extended.

The vaccine is a modified live vaccine consisting of attenuated microorganisms which, after administration, replicate, resulting in an immune response similar to that induced by natural infection. The effectiveness of the African Horse Sickness vaccine is largely dependent on humoral immunity (otherwise known as antibody-mediated immunity). Therefore, the administration of several serotypes included in the vaccine results in the production of antibodies against each serotype. The response however, of individual horses to vaccine administration may vary and in some individuals, antibodies against one or more of the serotypes might not even be detectable. Despite these limitations, the Onderstepoort Biological Products’ (OBP) AHS vaccine is the only vaccine registered for use in South Africa in terms of the Fertilizers, Farm Feeds, Agricultural Remedies and Stock Remedies Act, 1947 (Act No. 36 of 1947) and remains the only currently approved AHS vaccine in South Africa.
Inactivated or recombinant vaccines may prove to be viable alternatives to the current available vaccine, but are not commercially available at this time.

New vaccination regulations
New regulations regarding the period during which horses should be vaccinated have come into place but currently only pertain to horses residing within the controlled AHS area and the Thoroughbreds registered under the NHRA. New regulations stipulate that horses should be vaccinated between 1 June and 31 October each year. The main reason for this is to try and vaccinate all horses during a time when the midges are less active and minimise the risk of a vaccine related outbreak of African Horse Sickness.

The OBP AHS vaccine is a modified live virus vaccine and as with any live vaccine, there is always a risk that the vaccine strain may be subject to transmission by vectors and other aberrant events. This is well described for other modified live virus vaccines. Vaccination during high vector periods increases the risk of possible antigen transmission between equines by Culicoides vectors and may present a serious threat to maintaining Free Zone status according to the OIE guidelines to implementing any form of equine export. From an ethical perspective, vaccinating during high risk periods of the year may present a greater risk to naive equines residing in the AHS Controlled Area where vaccination is only allowed with permission.

The Department of Agriculture, Fishing and Forestry (DAFF) encourages owners to vaccinate during the lower vector periods of the year when the likelihood of vector transmission is lower. Restricting vaccination to 1 June – 31 October is never going to suit all horse owners but it is the ethical and responsible response to new research information and it should be encouraged for the whole country.
Dispensation for vaccination outside of this time in the AHS controlled areas must be sought from the National Director of Animal Health by an application made via the local state veterinarian and Provincial Director. No application that has not been endorsed by the Provincial Director will be considered.

Can I vaccinate my horses with another vaccine such as Equine Flu at the same time?
Yes, a horse may receive Equine Flu at the same time and it should not interfere with the African Horse Sickness vaccine. The current Equine Flu vaccine is an inactivated vaccine and the immunological response to this vaccine therefore differs from the Horse Sickness vaccine.

The requirements for moving registered equines into the controlled area of the Western Cape
No equine may be moved into or between zones of the AHS Controlled area without a movement permit issued by the state veterinarian, no more than two weeks before the movement.
Permits can be cancelled in the event of an AHS outbreak and regulations may change depending on the season and the state vet’s recommendation.

Horses can currently move within 40 days of their last vaccination (previously 60) but not more than 24 months from last vaccination.
The movement permits will only be issued if no outbreaks are reported within a radius of 30km’s for more than 40 days (previously 30).

The following needs to be submitted by the owner/trainer in order to apply for a permit from the state vet, within two weeks of the proposed travel date:
1. The name of the horse, current holding or yard and yard/farm it is going to in the Western Cape and the transporter. Contact details of the owner/trainer requesting the permit and the details of the contact at the destination.

2. Clear copies of the horse’s ID Page with passport number and the AHS vaccination page or batches and dates.

Once the permit is received it will be disseminated to the relevant owners/trainers and transporters.

Within 48 hours of movement, the health certificate needs to be signed off by a registered vet.
South African Jockey Club passports can just be filled in, in the relevant pages.
For International and FEI passports, the vet must fill out and sign a separate health certificate and send it with the passport.
The vets will then complete and sign a pre-notification document for the relevant horse/horses and will email it to the State Vet Boland.

Permits are valid for two weeks prior to movement, from issue but can be withdrawn at any time by the state vet should a case of Horse Sickness be reported from the area.

Handling a case of African Horse Sickness
Unfortunately there is still no treatment for this disease and supportive therapy remains the only means of treatment at this time. Keeping horses calm and avoiding any form of stress is very important. Should a horse be close to a referral facility, hospitalisation could prove useful, however the risk of stress from transportation should be considered. Supportive therapy such as anti-inflammatories or corticosteroids remain part of the treatment. Antibiotics are rarely indicated unless secondary bacterial infection is suspected. Judicious use of intravenous fluids may be indicated in some cases. Colloidal fluid support such as Voluven may prove valuable. Voluven increases oncotic pull within the vasculature and mimics the function of proteins, maintaining intravenous fluid volume. It is known to maintain these effects even with increased capillary permeability. Unfortunately the cost of these products limits their use in private practice.

Regardless, horses should remain in a stress free environment and have access to good quality water and hay. Monitoring horses for secondary complications is important. These can include biliary, as well as oesophageal paralysis resulting in oesophageal obstruction or ‘choke’. These horses will require more intensive treatment and may require an indwelling nasogastric tube to assist with feeding until oesophageal function returns.

Should a horse survive, it is recommended to rest them for a minimum of four weeks after clinical signs have subsided.

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