Strangles Testing: All You Need To Know
Strangles testing can sometimes be a bit of a minefield, especially with the different tests available. Hopefully this guide can help highlight the pros and cons of each type of test, and when they are best used.
1.Swab - (Nasopharyngeal PCR)
Just like a COVID-19 test, this involves passing a (very large) cotton swab up the nasal cavity.
Pros: It is relatively easy and non-invasive to perform. At the lab, they will be looking for bacterial DNA, which lets us identify if an active infection is present.
Cons: Active infections can be missed if the bacteria are only in the guttural pouches, and not in the nasal cavity.
When we will recommend this test: If we are coming to see a horse with signs consistent with Strangles, and there is a large volume of mucous/snot.
2.Bloods - (Serum ELISA)
This test looks for antibodies to Strangles bacteria in the bloodstream.
Pros: It is very easy to perform, and is generally the cheapest form of testing.
Cons: It only identifies that a horse has had exposure, which could have been up to six months previously. Antibodies only indicate a normal immune response following exposure, and will last in the bloodstream for a long time, meaning they don’t necessarily indicate current infection.
When will we recommend this test: Because of the shortfalls of this test, we will not commonly recommend its use for diagnostic purposes. It is commonly requested by external parties prior to movement of horses, however we are unable to diagnose a current infection without further testing via a guttural pouch wash.
3. Guttural pouch wash - (Guttural pouch PCR)
The guttural pouches are two sacs that sit at each side of the back of a horse’s head, and are where Strangles bacteria will sit if there is a current or persistent infection. Therefore, getting a sample from these pouches is the most definitive method of ruling out a current Strangles infection. We could send the sample for ‘culture’ - where the lab will try to grow the bacteria from the sample. However this takes several days and isn’t completely reliable. The quickest, and easily most reliable test is via a PCR reaction, which just looks for the presence of bacterial DNA in the sample.
Pros: This is gold-standard testing which provides a definitive answer whether there is or isn’t a current Strangles infection. It is by far the most reliable test and very rarely provides inaccurate answers.
Cons: Because it requires specialist equipment and is a relatively specialist skill to perform competently, it has an associated increased cost.
Overall, a swab is generally used if we have lots of nasal discharge and a high suspicion of strangles. A blood test is a cheap and fairly quick way to identify horses who haven’t been exposed to Strangles in the last six months, however if you get a positive result (approx 25% of horses), you will likely need to have a guttural pouch wash performed to ascertain the true Strangles status of your horse, costing more time and money. A guttural pouch wash is the quickest, most reliable route to understanding the Strangles status of your horse, but with a higher cost.
4. Strangvac - The Strangles Vaccination
Wouldn’t it be great if there was a vaccine to help reduce the Strangles burden in our horse population? Strangles vaccines are already produced globally, however more recent data shows that there is a product available which has increasingly positive research behind it.
Will this vaccine eradicate Strangles?
Theoretically, if every horse was vaccinated, then yes Strangles could be eliminated from the population. However, establishing and/or maintaining this scenario would be nigh on impossible. So why vaccinate at all? The evidence shows that vaccinated horses are much less susceptible to getting clinical signs when faced with bacterial challenge; In one outbreak in Sweden, over 70% of unvaccinated horses became clinically infected whilst only 10% of vaccinated horses were affected (Rendle et al., 2024).
Which horses/yards would be best to use a Strangles vaccine?
- Premises frequently accepting new horses
- Premises where maintaining optimal biosecurity is difficult
- Livery yards where there is frequent movement of horses
- Studs accepting visiting and walk-in mares
- Horses attending competitions with suboptimal biosecurity
- Equestrian businesses where closure would be untenable
What is the vaccination schedule?
As with all vaccines, there are times when we would recommend differing schedules but most courses will start with 3 injections;
- 1st Vaccination from 5 months
- 2nd Vaccination 4 weeks later
- 3rd Vaccination 6 months following the first vaccination
Does the vaccine mean my horse can’t be tested for Strangles?
No. The vaccine will not affect any of the above tests, so all three options will still be available if they are required. Having your horse vaccinated will not make it positive on testing.
Will the vaccine give my horse Strangles?
No, it has been formulated so that it won’t cause clinical disease.
Like any injection there can be local reactions, and from 20,000 injections, less than 6% of horses had any reaction. From those that did have a reaction, the vast majority had some local swelling which self-resolved within 5 days (Rendle et al., 2024).
My yard has an outbreak of Strangles. Should I vaccinate?
There is no published data looking at this, but theoretically it may help. It is best to discuss this with the vet managing your yard’s outbreak.
Can Strangvac be used in pregnant mares?
There have been no specific safety tests for use in pregnant mares or stallions, but unpublished data from use in 73 brood mares reported no adverse events. We recommend discussing with one of our vets if you know or suspect your mare is pregnant and you are considering vaccinating for Strangles.
If you have any questions about vaccinating against Strangles, or want to discuss any of the above points further, please do not hesitate to contact us.
All of the above procedure options are available to book via our team on 01323 815120. If you have any queries about any of the above information, or want to discuss anything regarding Strangles testing, please do not hesitate to contact us.