28/11/2025
What most people don’t understand about strangles and testing from a frustrated vet!!
*Backstory*
Around 10% of horses infected with strangles go on to store the infection in their guttural pouches, while outwardly appearing to be a completely healthy horse. We call these ‘latent carriers’ and they can cause a strangles outbreak years after they initially came into contact with it.
Problem 1
If a livery yard lets one of these latent carriers on to their yard and it causes an outbreak, they are subjected to a 16th century witch hunt, publicly shamed and the centre of a 20 mile hysteria - yard owners want to avoid this!
Problem 2
The ONLY way of knowing which horses are latent carriers is to stick a camera down every horses’s throat, into the guttural pouches and wash out a sample to test in the lab.
*The Practical Solution*
Given its expensive (£300-500) and invasive to perform these guttural pouch washes, it seems sensible to first rule out the horses that have never come into contact with strangles, and only stick a camera down the ones who have. This is were the blood test comes in!!
The blood test tells us (with 98% specificity using the latest lab test available - ie 98% of negatives are truly negative) which horses have not come into contact with strangles. If the blood result is negative we can save the horse (and owner) the need to perform a guttural pouch wash, they are free to move yard - great success!
If the horse has a positive blood result then we need to wash its guttural pouches and find out if they are a latent carrier - remember we expect 90% of horses with a positive blood result to come back with a negative guttural pouch wash. A positive blood result and a negative wash does not mean the blood result was wrong, it means the horse has been exposed but was not part of the 10% that went on to store the infection. The horse is free to move yards - great success!
If the guttural pouch wash is positive then we have found ourselves a latent carrier, we can clear the infection from the pouches until no infection is left and the horse is free to move yards. Testing prevented a strangles outbreak - great success!!
*The Complication*
The blood test won’t pick up a new recent infection (so if the horses was infected in the days leading up to the blood sample) and there are other - arguably worse - infectious diseases that can cause outbreaks not being tested - Equine Influenza and Equine Herpes Virus [even if vaccinated] to name two.
*The Grand Conclusion*
Strangles testing is a useful PART of biosecurity BUT IT MUST be done in CONJUNCTION with other measures - critically an ISOLATION PERIOD to avoid disease outbreaks.
