Strangles – the key facts

What is strangles?

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

What are the symptoms?

Symptoms 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 (bleeding from 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, recovering period and associated serious complications.  The International Collating Centre¹ reports that strangles is responsible for 30% of infectious diseases.  InSweden, 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 equiis transmitted by horse-to-horse contact or via humans, tack, feed and utensils.  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 week.  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 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, it may be treated with antibiotics.  However, if diagnosis takes place after abscesses have been formed, your vet may need to lance them.

What should I do if 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 from others and that the yard is closed to foreign 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.

What can I do to prevent strangles in my yard?

It is advisable to follow good stable management procedures.  These include keeping new horses to the yard in quarantine for a few weeks where they should be closely monitored closely 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.

Is there a vaccine to protect my horse from strangles?

Equilis StrepE^® is theUK’s first strangles vaccine for horses which helps protect against the disease.  This unique vaccine, which has been developed following 12 years of intensive research, 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.  In trials conducted by Intervet, horses tolerated this novel injection method. 

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.

Equilis StrepEreduces 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.

For further information about strangles orEquilis StrepE, please contact your vet or Intervet’s Veterinary Support Group on 01908 685685 or by Email.

1. The International Collating Centre (ICC) was established in 1987.  Participating countries nominate a vet who is responsible for reporting episodes of infectious disease from their country on a quarterly basis. In turn the ICC provides quarterly disease reports and supplementary reports as necessary to subscribers worldwide.  The data is the only sort of its kind for non-notifiable diseases such as equine influenza and provides a unique global perspective.