15 May 2023

Strangles: Your questions answered

A unique webinar, Taking the Heat Out of Strangles, was held on 3^rd May 2023 as part of the annual Strangles Awareness Week campaign, which aims to help owners protect horses, ponies, donkeys and mules from the UK’s most common equine infectious disease and reduce cases of this often devastating illness.

Hosted by World Horse Welfare in partnership with eminent equine scientist Dr David Marlin, the webinar brought together speakers including Senior Veterinary Advisor to the FEI, Caterina Termine, and Professor Ashley Boyle from the University of Pennsylvania, along with a panel of vets, horse owners and yard managers keen to share their own experiences of dealing with a Strangles outbreak and practical steps to help yards avoid going through the same distressing scenario.

More than 100 attendees were keen to make the most of the event, with a great range of questions being asked, far more than could be responded to in the limited time available. Keen to ensure all queries were answered, world-leading Strangles researcher Dr Andrew Waller (AW) and vet, researcher and veterinary adviser at Bransby Horses, Dr Jeremy Kemp-Symonds (JKS), kindly offered to share their expertise and their answers to questions raised during the seminar here. Both Andrew and Jeremy are also members of the Strangles Awareness Week technical team.

Simply scroll down to find out how Jeremy and Andrew responded!

How long does the horse remain infectious after Strangles symptoms have stopped?

AW: Most equines clear Strep. equi infection within six weeks of recovery. However, around 10% of recovered horses can become persistently infected carriers and can potentially remain infectious for the rest of their lives. Richard Newton (University of Cambridge) and Nic de Brauwere (Redwings) followed one carrier that remained infectious for five years after recovery!

JKS: Testing is essential to ensure an infected horse is completely free of Strep. equi once they are looking better. Using an endoscope to both carry out a visual check of the horse’s guttural pouches and then take samples for laboratory testing is the only way to be confident the horse isn’t still infectious. If the horse is showing signs of becoming a Strangles carrier, the endoscope allows treatment to begin immediately by removing the residual bacterial contamination and instilling antibiotics as needed.

How long should pasture be rested after infected horses have been in it?

JKS: Research shows that the ability of Strep. equi bacteria to survive outside the horse is limited, and the timeframe depends on the environmental conditions. The bacteria prefer cool, damp conditions and can survive for around six weeks in a water trough, making it essential to keep cleaning and disinfecting water buckets and tanks during an outbreak. However, the bacteria don’t live for long in hot, dry conditions, particularly if exposed to direct sunlight.

Click here to find out more about the latest published research.

Please can you tell us about the new Strangles vaccine?

JKS: A new vaccine to help protect horses and ponies from Strangles was launched in the UK in September 2022. The product is the result of more than 20 years of research and development and has several key advantages over previous vaccines. In particular, the vaccine is administered into the muscle, making it safe and easy to use. In addition, it doesn’t affect Strangles blood test results, meaning a vaccinated horse can be differentiated from an infected horse when using blood tests to help screen for the disease. The vaccine is highly effective, tests showing that it helps prevent or reduce disease in up to 94% of cases.

Discover more by clicking here.

What is the reason behind the extreme reluctance to use antibiotics even if horses are suffering with several abscesses over weeks on end?

AW: Antibiotic treatment often cannot penetrate the abscesses at sufficient levels to kill all of the Strep. equi bacteria that are present. This means that the infection often flares up again when treatment stops and this can prolong the time to resolving the infection. Antibiotic treatment may also reduce the effectiveness of the natural immune response, so recovered horses may be reinfected more easily. A further concern is the chance of development of antibiotic resistance. However, sometimes, antibiotics can be a really important tool to help a horse through severe disease.

JKS: In most cases, in our experience, a better option is to encourage drainage of the abscesses through use of hot packs or poultices and/or creating drainage with the use of minor surgery in some more severe cases. Patients often quickly show signs of relief as soon as abscess pressure is relieved and pus can drain.

Is there other daily monitoring other than temperature taking? Like stall-side testing? Or something else.

AW: Temperature-taking is the best and most sensitive way of identifying equines that are incubating Strangles. At the Animal Health Trust we tested various other methods and none were as reliable as taking temperatures.

JKS: It's important to know what is normal for an individual horse, pony, donkey or mule. Taking temperatures in the morning and afternoon can pick up the first signs of Strangles, and other diseases, early. As always, it’s also important to be aware of your equine’s demeanour and appetite to spot subtle and early signs of a health issue. Are they standing at the back of the stable when they would normally come over to greet you? Are they less interested in their companions or surroundings? Are they leaving food or taking longer to finish than usual? Changes like this are always worth looking out for.

Here is a short 'How to film' on taking temperatures.

What is the treatment for Strangles? Any new developments on the horizon?

JKS: While veterinary support, such as anti-inflammatory medication, is important for Strangles patients, good nursing care is equally important to keep the horse comfortable and help relieve clinical signs as their immune system fights the infection. Rest, somewhere quiet and dry to lie down, soft palatable food and plenty of clean drinking water support recovery.

Raised feed bowls can help a horse with swollen glands to keep eating while feeding from the floor can help nasal discharge to drain once abscesses have burst. Regular application of warm compresses on developing abscesses can help them to mature and burst. Continuing to bathe ruptured abscesses with warm water can encourage pus to drain and keep the area clean. Remember to collect and dispose of all cleaning materials and water with care as pus is extremely infectious to other horses.

The horse's immune response will kill Strep. equi, but it needs time to cope with the many ways that the bacteria subvert and evade the immune system’s efforts to overcome infection.

Are there any tips for taking temperatures safely?

JKS: One of the many benefits of routinely taking horses’ temperatures is that the horse can become familiar and comfortable with the procedure. When introducing any new interaction with an uncertain horse, pony, donkey or mule, it’s important to break training down into small steps and use positive reinforcement to create pleasant associations with the process and help keep the horse relaxed.

If an equine has developed a more deep-rooted aversion to having their temperature taken, a more systematic approach is usually needed to help them become accepting. Equine Behaviourist Gemma Pearson shares her approach here as part of the British Equine Veterinary Association’s series of videos below. It’s essential to prioritise safety at all times when introducing a new interaction with any horse. Speaking to an equine behaviourist can be an important step to help a horse overcome stress and anxiety in particular situations and give you confidence in steps to train them positively and effectively.

Any advice about cleaning up once horses have the all-clear?

JKS: It’s important to carefully remove and dispose of as much potentially infected material as possible after a Strangles outbreak. This includes all bedding, drinking water and so on. The next step is to clean and disinfect all equipment and surfaces using a suitable disinfectant at the correct dilution rate and for the recommended contact-time.

When selecting a disinfectant, remember that not all disinfectants are equal, so firstly ensure it is effective against Strep. equi. It’s also important to be mindful of any factors that can impair its effectiveness. Some disinfectants become inactivated by organic matter, such as mud or faeces. This is one of the reasons that cleaning is as important as disinfecting to ensure bacteria are killed.

It is also important to consider how safe a particular disinfectant is for humans, animals, wildlife and the environment. Some products are more toxic than others, meaning special consideration is needed to decide how used disinfectant is disposed of.

A list of DEFRA-approved disinfectants is available by clicking here.

For livery yards, how can we get everyone onboard with upping their daily biosecurity routine without experiencing an outbreak?

AW: Strangles is a horrible disease but can affect any horse (even Princess Anne's horses were affected in the past). Being able to talk openly about disease risks and make biosecurity part of everyday yard routines is an important part of protecting horses from infection.

Having clear protocols for new horses, horses returning from events and visiting horses helps everyone know what is expected of them. Having disinfectant available and displaying information posters also helps make biosecurity normal. Making temperature checking part of everyday horse care will help any yard spot an infectious disease early and can be the difference between one sick and a whole yard of sick horses.

Do horses develop any immunity to Strangles?

AW: Yes. In one study, 75% of foals that had recovered from Strangles were resistant to the disease when exposed to an infected horse six months later. However, this also means that 25% of the foals were already vulnerable to disease six months later, showing that immunity is not consistent and will wane over time.

Is it rare for horses to contract Strangles more than once?

AW: No. At the Animal Health Trust we even found one horse that was infected with two different strains at the same time! Over time a horse’s immune response wanes and so 25% of recovered foals fell ill with Strangles when they came into contact with the disease six month later.

JKS: Although Strangles generally stimulates a very good immune response from the patient, sadly, just as with COVID in humans, prior infection does not preclude subsequent re-infection. The duration of immunity from a previous infection will vary according to many factors, such as the immune function of the patient and how large a dose of bacteria they were infected with.

What can you do if your yard has nowhere for isolation?

JKS: Isolation can be set up effectively without the need for dedicated facilities. As Strangles is not an airborne disease, any stable or field shelter where direct contact between horses can be prevented and quarantine measures put in place for people entering to care for the horse can be effective at containing infection.

AW: Isolation can even be set up in a paddock by using a double-layer of electric fence at least two metres apart so horses cannot have nose to nose contact and do not share food or drinking water. Providing equipment that stays within the quarantine area and overalls, foot dips and hand sanitiser for people will mean horses can continue to be monitored and well cared for.

Does Strangles cross species and does having sheep in to graze break any cycle or does it compound the problem?

AW: Strangles has jumped into and caused disease in dogs, but this is extremely rare. The bacteria, Strep. equi, has evolved to specifically cause strangles in horses. Co-grazing sheep may become transiently infected but are extremely unlikely to fall ill. However, moving a sheep from a field with infected horses to a field with healthy horses could increase the risk of spreading Strangles to the healthy horses.

JKS: There are also some incredibly rare reports of Strep. equi - and its close relation Strep. zoo - infections in humans. These individuals usually had a history of close contact with infected equines. So, although the risks appear extremely small, it would be sensible to keep dogs away from suspected or confirmed cases (and any potentially contaminated waste material), while handlers should take precautions such as the use of disposable gloves, regular hand-washing and so on.

What are the main things to look out for in horses in terms of symptoms/change in characteristics if you suspect they may have contracted Strangles?

AW: A high temperature is usually the first clinical sign of Strangles. Horses may then become depressed, develop swollen lymph nodes and then thick, discoloured nasal discharge. Horses may develop a soft moist cough and abscesses may begin to physically burst through the skin.

JKS: While most people are aware of the ‘classic’ signs of Strangles, it’s important to be aware that we know many equines only develop very minor signs of disease. They may only have a fever and be a bit off-colour for a couple of days. However, even horses with mild signs of infection are still infectious to others and the next horse may become much sicker.

Can a carrier brood mare give strangles to her foal?

AW: Yes. Foals are usually immune to Strangles in their early months of life through acquiring immunity from the mare. However, they become susceptible as that immunity wanes over time and certainly by four months of age. Foals with Strangles can also transfer Strep. equi back to the mare, increasing the risk of mastitis. Therefore, carrier mares should be treated to clear Strep. equi as soon as the vet is happy about the possible impact of treatment on pregnancy or the foal.

JKS: Sadly, yes this is possible. I was involved in an outbreak at a stud in Newmarket in which such cases occurred.

How long do antibodies show up on blood tests for?

AW: The average time to return to a negative test result after recovery is eight months. However, some horses can test positive for much longer, even over a year after they became infected.

Is it possible, even just theoretically, to completely eradicate Strangles?

AW: It is theoretically possible to eradicate Strangles and Strep. equi has been eradicated from many yards that have previously had recurrent outbreaks for many years. We hope that the number of outbreaks in the UK, and elsewhere, can be greatly reduced over time as more cases are identified early and new preventative tools become available.

You can watch the recording of Taking the Heat Out of Strangles below to find out why we know more about Strangles than ever before and are better placed to protect horses from the disease. From the importance of temperature checking to a free website that shows where Strangles has been recently diagnosed in the UK, it’s full of fascinating facts and practical guidance.