Recently doubt has been cast over the validity of the ‘Strangles Blood Test’ for identifying carriers coming onto yards. Increasingly yards are asking for testing of Guttural Pouch Lavage samples which owners regard as more invasive and are still not infallible. Either way these tests do not negate the risk of an outbreak entirely, particularly if the yard is not completely closed.
An adjunctive or alternative approach would be to vaccinate against the disease. Like Covid, when individuals are vaccinated, it gives us the confidence that the risk of getting a nasty form of the disease is reduced significantly.
A relatively new intramuscular vaccine provides immunity against the Strep equi bacteria that we associate with the disease known as Strangles.
Vaccines are useful at providing immunity against a particular disease so that when we are exposed to it, the body already has a degree of protection. The vaccine cannot give a 100% guarantee that your horse will not become infected, however, within a yard outbreak the protection means that for the majority of horses exposed to the disease we would expect to see minimal clinical symptoms. Some horses may still develop symptoms and spread the disease, although this would be at a significantly reduced severity.
The licensed protocol for the vaccine is to give a primary course of two vaccine doses at 4 weeks apart. The onset of immunity is considered to be 2 weeks after the second vaccination dose. In high-risk situations it is suggested to repeat this regime every 2 months.
However, there is now good clinical trial and field data particularly from its use on yards in Europe, on which we can base our decisions for moderate to low-risk situations. Vets will be using different protocols for this, and, like the Covid vaccines, we have to implement a workable and pragmatic protocol utilising the available science and license information. We are advising a primary course, described below, to hit the right balance between clinical efficacy, side effects and practical issues. As we gain more data this protocol may change and as this is not written into the license of the product, it’s use is considered ‘off-license’. Off license use is common for many of the products we use in equine veterinary practice.
Our proposed regime is to follow a similar programme as the Flu vaccinations with a primary course of two vaccine doses at 4 weeks apart. Then a first booster at 4 – 6 months followed by annual booster vaccinations in low-risk situations and every 6 months in moderate risk situations. Booster vaccinations which run over by more than a month should re-start the primary course.
In both moderate and low risk scenarios we would strongly advise re-vaccinating horses that have not had a vaccine within 2 months of become high risk i.e. where there is known/suspected strangles on a yard or within a close vicinity.
This is not a live vaccine so there is no risk of your horse getting Strangles from the vaccine. It will not interfere with interpretation of the strangles blood ELISA test. i.e. it will not raise the levels the labs look at to demonstrate exposure. It will also not interfere with the validity of the results of a PCR from a guttural pouch lavage.
Mild vaccination reactions are more common than horse owners would expect compared to our influenza vaccinations and can include a transient raised temperature, ocular discharge and lethargy. Local reactions at the injection site including heat, pain and swelling are very common and can be worse at subsequent injections. In our experience these have largely resolved without requiring any treatment. At Equitait we used the vaccine on our own horses and then monitored them closely for reactions the results of which are published on our website. The vets at Equitait continue to vaccinate their own horses.
Vaccination should not replace good biosecurity measures as these are still important in preventing Strangles and other infectious diseases. In a gold standard situation starting vaccination at or before the time of a guttural pouch lavage would mean it was starting from a known strangles status.
No information is available on the safety and efficacy of this vaccine when used with any other veterinary medicinal product. In our experience we have widely used it at the same time as other vaccines without issue, although we try to give them at different sites.
True herd immunity is only achieved when a large proportion of the same yard are vaccinated, and this is obviously preferable. However, even if your horse is the only one vaccinated on the yard it is still beneficial, and you can be confident that you are adding to your protection from those around you.
For yard managers, we feel that integrating vaccination into your biosecurity measures would result in a reduce risk in all yards. Many vets now believe that vaccination gives better protection to an established herd than pre-movement serology (bloods).
Insurance companies report that on average a case of strangles in a single horse will cost in excess of £1000. Where businesses are involved the loss of earnings can be considerably more and those who have seen nasty clinical cases will vouch for just how distressing it can be for both the animal and the owner.
If you would like more information or would like to discuss how you could implement vaccination to benefit your horse or yard in your specific situation then please call or e-mail the practice.
For further reading the article “Strangles vaccination: A current European perspective” gives a good overview of where we are now.
Strangles vaccination FAQs
Is the strangles vaccine effective?
The strangles vaccine is fully licensed in the UK for horses, meaning that it has undergone extensive rigorous testing. It has also been used on a large scale in other countries including Sweden where it has been shown to be both safe and effective in real world scenarios.
What are the possible side effects of the strangles vaccine?
horses will often have a transient rise in body temperature of up to 2.6 degrees lasting for 1 to 5 days following vaccination. Horses will often get heat, pain and swelling at the injection site (up to 5cm diameter) lasting for up to 5 days. Discharge from the eyes is common for 1-5 days after vaccination. Less than 1 in 10 horses will have a loss of appetite and change in demeanour for up to 1 day. It is possible to use an anti-inflammatory medication e.g. bute to alleviate pain and inflammation that a horse may experience after the strangles vaccination, however this is rarely required.
How is the strangles vaccination given?
The vaccine is injected into the muscle just like a ‘flu vaccination. If it is given at the same time as another vaccination two different muscle sites are used. Often, we give the strangles vaccine into the gluteal muscles in the hindquarters providing the horse is amenable to this.
Is the strangles vaccine safe?
The new vaccine that we are using for strangles has been shown to be safe both in rigorous clinical trials and as it has been rolled out to the wider horse population in the UK and Europe over the last few years. In addition to this we have conducted a field trial on four of our own horses at Equitait which were monitored very closely in the days following each vaccination. We saw some mild, short-lived effects from using the vaccine including a mild transient rise in temperature and some mild skin swelling at the vaccination site. All of the horses had completely recovered within 7 days of being vaccinated.
Does the strangles vaccination cause the blood test or nasal swab for strangles to be positive?
The strangles vaccine does not cause any change to a blood test or nasal swab test. A horse is no more likely to test positive after vaccination with the strangles vaccine.
How often does my horse have to have boosters with the strangles vaccine?
We recommend that the dosing intervals of the strangles vaccine are based on an individual risk assessment. The data sheet protocol was developed for horses facing a very high strangles challenge e.g. in an outbreak situation to give the best possible levels of protection. The data sheet recommends vaccines 1 and 2 are given 28 days apart, and then booster courses are given every 2 months. Field trials have shown that after the first two injections which are given 28 days apart, horses have a decent level of protection against strangles. After the second injection boosters given at 6-12 month intervals have been shown to give a good level of protection. In the face of a local outbreak horses could have an extra booster to ensure maximum protection.
Can the strangles vaccination give my horse strangles or cause it to shed strangles?
No, the strangles vaccine that we use is a subunit vaccine not a live vaccine. There is no risk of the vaccine causing clinical disease or shedding of strangles bacteria.
Can the strangles vaccination be given at the same time as a ‘flu / ‘flu & tetanus vaccination?
Yes, it is possible to give strangles at the same time as other vaccinations. We give the vaccinations in different muscle sites e.g. neck & rump or neck & chest.
Can strangles vaccination be used as an alternative to blood tests and / or guttural pouch lavages when horses move yards?
We consider the gold standard of biosecurity for incoming horses to be a guttural pouch lavage combined with strangles vaccination. Whilst the vaccination has been shown to massively reduce shedding of the strangles bacteria in infected horses, it does not completely eliminate it. Therefore, if a horse had contracted strangles prior to being vaccinated it could still be shedding some bacteria and pose a risk to other horses. Obviously, the risk of clinical disease would be massively reduced if all of the resident horses on the yard were vaccinated against strangles. A one-off blood test is of limited value for detecting horses that are carriers of strangles, or horses that have been very recently infected. Therefore, we do not recommend the blood test as a gold standard for yard biosecurity. We would still recommend isolation of incoming horses for three weeks to protect the resident horses from other potential disease risks such as ‘flu and ringworm.
Can the strangles vaccination be given to mares that are in foal?
The strangles vaccination is not licensed for use in pregnant and lactating mares, however since its development it has been used routinely. An unpublished study in 73 brood mares was recently reported where the vaccine was used in combination with ‘flu vaccination and herpesvirus vaccination and it was not associated with any major adverse effects. A panel of medical specialists have reviewed the data available on the vaccination and currently recommend vaccinating pregnant mares at months 5, 6 and 9 months of gestation. This is likely to give some immunity to the foal for the first few months of life via the colostrum. It would be possible to combine with herpesvirus (EHV) vaccinations which are often recommended for pregnant mares.
Can the strangles vaccination be given to breeding stallions?
The strangles vaccination is not currently licensed for use in breeding stallions. Recently a panel of medical specialists have reviewed the data available on the vaccination and see no reason why there would be adverse consequences to vaccinating breeding stallions.
Can the strangles vaccination be given to foals?
Foals can be vaccinated from around 5 months of age. In a high risk situation, we would advise on a case by case basis and may recommend vaccinating younger foals. Vaccination of pregnant mares is likely to give protection to foals via the colostrum for the first few months of life.
Can the vaccine be used when there is already strangles infection going around a yard?
Using the strangles vaccination in the face of an outbreak has been trialled and results have been very promising. We would definitely consider using this approach in a yard outbreak situation. In horses that have already had the primary vaccination course we would give a top up booster in the face of a strangles outbreak if it had been more than 2 months since their last booster, in order to give the highest level of protection.
Can the strangles vaccination be used in donkeys and mules?
No vaccinations are specifically licensed for donkeys or mules. As with ‘flu and tetanus vaccinations we commonly use vaccinations licensed for horses in other equine species. Therefore, we would be happy to recommend the use the strangles vaccine “off license” in donkeys and mules.
Will my horse need time off after the strangles vaccination?
Some horses will be completely unaffected by the strangles vaccination and able to continue with their normal workload. A small percentage of horses will have a transient temperature rise and a small swelling at the injection site which may be painful, and we would advise that horses are rested until these clinical signs have resolved, which is likely to take 2-7 days. Anti-inflammatory medication such as bute can be used to alleviate any muscle soreness. Therefore, we would advise that you choose to vaccinate your horse when there is a clear window in the diary to allow for a quiet few days if required. At least 7 clear days before competition is recommended.
If my horse never goes out of the yard is there any benefit to vaccinating?
Risk of infection really depends on whether other horses move on and off the yard, proximity to neighbouring horses and overall yard biosecurity. Bear in mind that people, tack, trailers, buckets, grooming kit etc can all be a source of infection via contact with infected horses or asymptomatic carrier horses.
How serious is strangles in an unvaccinated horse?
Strangles is a very contagious disease. A high number of horses will become infected when exposed to strangles and whilst most horses will recover in time, the mortality (death) rate can be as high as 10%. Abscesses under the jaw are common in infected horses, which are painful and take several weeks to heal. As well as causing pain and distress to individual horses and owners, a strangles outbreak can also have a significant financial impact on a yard.
