Strangles what you need to know

What is strangles?
Strangles is a highly contagious, seriously debilitating disease in horses caused by the bacterium, Streptococcus equi.

What are the clinical signs?
Clinical signs include fever, nasal discharge, cough, depression, anorexia and enlarged glands on the head and neck, which can become abscesses.  The swollen glands can restrict the airway and make breathing laboured, hence the name strangles. Infection is usually restricted to the head and neck, however in up to 10% of cases it can develop in other body organs and cause abscesses.  This is usually fatal and is known as ‘bastard’ strangles.  Another complication is purpura haemorraghica (damage to the blood vessels of the limbs, eye lids and gums), which can be so extreme that it can cause circulatory failure and death.

How common is the disease?
While strangles is rarely fatal (1% of cases), it is one of the most common equine respiratory infections which causes major economic loss to the equine industry worldwide due to its prolonged course, recovery period and associated serious complications.  The International Collating Centre1 reports that strangles is responsible for 30% of infectious diseases.  In Sweden, where strangles and equine ‘flu are notifiable diseases, there are approximately four cases of strangles for every case of ‘flu.

Are younger horses more susceptible?
It can affect horses of all ages and types, but those most at risk are young horses; horses kept in large numbers and horses that travel to shows and competitions.

How is strangles transmitted?
Streptococcus equi is transmitted by horse-to-horse contact or via humans, tack, feed and equipment.  Transmission frequently occurs through shared water sources where the bacterium lives for longer periods of time.

What is the incubation period of the disease?
The incubation period of strangles is approximately a fortnight.  However, new outbreaks can occur up to three weeks or more after the initial outbreak as infected horses can shed the bacterium for long periods.  In addition, approximately 10% of recovered horses, known as ‘carriers’ may harbour strangles with no outward clinical signs, increasing the likelihood of recurrent outbreaks in unvaccinated horses.  It is imperative, therefore, to minimise contact with horses of unknown origin.

Can strangles be treated?
If the disease is diagnosed at an early stage, your vet may decide to treat with antibiotics and insist upon supportive care.  However, if diagnosis takes place after abscesses have been formed, they may need to be lanced by the vet to drain infectious pus.

What should I do if I suspect strangles?
If you suspect that a horse has strangles, contact your vet immediately.  Once the first case of strangles on a yard has been diagnosed, all other horses will be at risk.  The affected horse will need to be isolated and the yard may need to be shut down for several weeks.

What should I do once strangles is diagnosed?
Once the first case of strangles has been diagnosed on a yard, all other horses will be at risk.  It is important that the affected horse is isolated and that the yard is closed to other horses.  All healthy horses should be closely monitored to ensure that new cases of strangles are identified as soon as possible and people who are in regular contact with horses from outside the yard should stay away from the infected premises.  Tack and stable equipment will need to be disinfected and disinfection procedures should be adopted, similar to those used during foot and mouth disease a few years ago.

What can I do to prevent strangles on my yard?
It is advisable to follow good stable management procedures. Ideally these should include keeping horses new to the yard in quarantine for up to three weeks where they should be closely monitored and swabbed for signs of disease.  It is also sensible to ensure that your yard doesn’t become overcrowded and to avoid contact with horses of unknown origin.

In addition, your vet may recommend a strangles yard vaccination policy.*  The unique strangles vaccine can be used in horses from just four months of age and is administered through an innovative injection into the upper lip of the horse, which horses often accept more readily than traditional vaccinations.

Two injections should be given at a four-week interval.  The vaccine has a three-month duration of immunity after the second injection and horses in high-risk situations should be re-vaccinated with a single dose four times a year.  An option for horses in medium-risk situations is to re-vaccinate every six months but administer a single dose booster vaccination immediately if an outbreak occurs and it has been more than three months since the last vaccination.  This will help protect the vaccinated horses or greatly reduce the severity of the disease.  There is generally no need to vaccinate horses in low-risk situations.

The vaccine reduces the clinical signs of strangles and the occurrence of lymph node abscesses in horses that are at risk of Streptococcus equi infection such as competition horses, horses in livery yards, horses at the sales and horses in an outbreak area.

Which risk group does my horse fit into?
In general, the more a horse is in contact with other horses the greater its risk of contracting strangles.  Examples of high, medium and low risk situations are as follows:

High-risk situations

• Horses kept in premises where strangles has been diagnosed in the past
• Horses kept in groups, where new horses of unknown origin are regularly added
• Horses kept in an endemic area (an area where strangles outbreaks are known to occur)

Medium-risk situations

• Horses residing in stables with other horses, but there are no other horses introduced into the group regularly
• Horses frequently travelling to shows, riding club events or competitions

Low-risk situations

• Very little or no contact from other horses

Is it worth only vaccinating some of the horses on the yard?
It is advisable that all horses on a yard be vaccinated against strangles to create herd immunity and prevent non-vaccinated horses being reservoirs for disease.  Individual horses will still benefit from vaccination as their immunity will be higher than any unvaccinated horses.



*Please note that all batches of Equilis StrepE have been withdrawn from the market. An update on its availability can be found here.