Strangles is one of the most commonly diagnosed infectious diseases of horses - and one the horse owners and us as vets hate to hear of - as it can result in movement on and off yards being limited and competitions being cancelled! In rare cases strangles can be fatal. In some cases the cost of testing, treating and checking freedom from disease can also be high.
It is caused by a bacterial infection - primarily of the upper respiratory tract - and can spread easily between horses.
Signs of strangles
Loss of appetite
Marked ‘snotty’ nasal discharge
Lymph node (gland) swelling and abscesses - usually around the head and throat
Remember some horses will not show all of these signs, and in some outbreaks or some affected horses will only show a mild short fever and a slight nasal discharge (if any)!
So making a definite diagnosis can rely on tests that can take time to get a result.
Causes / Spread
Horses can become infected with strangles by contact with secretions containing the bacteria (usually nasal or from an abscess) - either directly through contact with other horses, or indirectly - via secretions on walls, buckets, owners hands / clothes etc.
Some horses can also carry the bacteria without showing any signs - for long periods - these carriers can excrete the bacteria intermittently - infecting other horses, but normally show no signs themselves.
Clinical signs can be enough to diagnose strangles, but we will often take tests from affected horses - to attempt to find DNA from the bacteria, or to grow the bacteria after taking swabs or washings from your horse. None of these tests are 100% sensitive, so in some cases need repeating or taking from multiple horses.
A blood test also exists and is useful to test horses that have been showing symptoms for some time - but this is more useful when checking a yard is free from disease, or for preventing horses carrying the disease from entering a yard - see prevention below.
Most treatment is aimed at keeping the horse comfortable and allowing the disease to clear - so making sure your horse maintains their appetite and is drinking, monitoring temperature, we will often use drugs such as bute or flunixin. Antibiotics are only used in very severe cases - this is because the infection forms abscesses which antibiotics do not penetrate well. Horses on antibiotics often improve, but go backwards again when the antibiotics are stopped.
Stopping strangles before it arrives on your yard is difficult but important to try - especially if strangles is known to be in your area - for example:
When away from home use your own buckets, limit mingling with other horses, wash your hands after handling other horses
At home have separate grooming kit, tack and buckets for each horse
Anyone moving between horses on various yards should wash hands, disinfect boots, and if possible change outer clothes
Blood test(s) for horses planning to move to your yard - see Jenny's post from 2017 for more details
Isolation area for 2 weeks once horses move onto your yard
Know what to do if a horse is suspected of strangles
Have a vaccination policy for horses on your yard:
Strangles vaccines exist and can help prevent a limiting and expensive disease - but are much more effective if used by all horses on a yard. They are injected into the upper lip of the horse and are boosted every 3-6 months - and boosted again if any disease is present on the yard or in the area - again more detail on strangles vaccination is another blog post found here.
If strangles is suspected
This fast spread makes it very important to isolate infected horses / areas of the yard.
It is very difficult to have a policy that suits all yards - as the approach would be very different for a home with 2 or 3 horses, to a large livery yard or stud. There are several guides available - one good one is “STEPS” produced by the AHT and the BHS, and it may be worth discussing the best policy for your yard with one of our vets.
The main points are:
Isolate the affected horse and any horses that have had direct contact with it.
Call your vet to arrange appropriate testing and discuss management.
If confirmed implement detailed isolation and handling procedures.
All horses should remain on the premises to protect neighbouring yards and other equine communities.
Isolation of horses in groups depending on the risk they have met - from horses with direct contact, to ones detached in different buildings.
Strict hygiene should be in place for handlers and owners - feeding and mucking out the low risk group first before the high risk (or having different staff for each area) - making sure to wash hands and disinfectant dips for boots between each horse.
Separate feed buckets and grooming kit etc.
Monitor horses temperatures - as this is often the first sign of a problem.
After the disease
Once all horses on the yard are showing no symptoms for at least 4 weeks testing for freedom from the disease - most horses that have shown signs are tested with guttural pouch washes - which involves putting a camera up the horses nose into a pouch in the tube between the throat and ear and taking a sample.
Horses with lower risk and that have shown no signs of disease can be blood tested at this point - but if positive will require the guttural pouch wash from above.
Both groups may require further treatment or tests to check they are free from disease if any tests come back positive.