Preventing disease in horses

Infectious diseases such as equine influenza, strangles and herpes can have devastating effects on an event horse’s health. Vet Sarah Hunter discusses how you can keep your horses and yard healthy.

Respiratory infections are the most prevalent contagious diseases among the horse population in the UK. These include the influenza virus, equine herpes viruses-1 and -4, and strangles. 

Equine influenza

  • Equine influenza’s incubation period is just two to three days, meaning the virus can spread quickly and infected horses can shed the virus for up to 10 days. 
  • Horses of all ages are susceptible, but infection is most common in young horses and unvaccinated horses
  • Low-level infection may occur in vaccinated horses, but they are unlikely to develop serious disease and are less likely to spread the virus. 

Symptoms: a high temperature of 39-41 degrees celcius which lasts for one to three days; a frequent harsh, dry cough that can last for several weeks; a clear, watery nasal discharge that may become thick and yellow or green; enlarged glands under the lower jaw; clear discharge from the eyes and redness around eyes; depression and loss of appetite, and filling of the lower limbs.

Prevention: Vaccination is key to preventing the spread of the disease and limiting the effects on horses and is mandatory for BE competition.

Equine herpes viruses

  • There are a number of equine herpes viruses, but types 1 and 4 are the most important. 
  • Infection by equine herpes virus-4 usually results in respiratory disease, whereas type 1 can result in respiratory disease, abortion, the birth of sick foals and neurological disease.
  • Infection occurs by inhalation.
  • The incubation period is two to 10 days. 

Symptoms: early signs include an increased temperature, coughing, nasal discharge and lack of interest in food.

Prevention: A vaccine against equine herpes virus types 1 and 4 is available, which provides some immunity against the respiratory and abortion forms. Vaccination against equine herpes virus is recommended if going to large competitions, especially if international horses will be present.


  • Strangles is a highly contagious bacterial infection that causes upper respiratory mucus and abscess formation in the lymph glands around the head. 
  • Infection is most common in young horses, but any age can be affected. 
  • Although highly contagious, spread is slow compared with the respiratory viruses and requires direct contact. 

Symptoms: strangles sufferers will present with a temperature, depression, loss of appetite and thick, yellow mucus draining from both nostrils. Hot, painful abscesses may develop on the sides of the head and throat, which can burst and discharge pus. The horse may experience difficulty eating or extending his head.

Prevention: The copious discharges result in the quick contamination of the environment so avoid contact with horses showing any symptoms, do not travel your horse if they are showing symptoms. Most recovered cases develop a good immunity, but there is also a vaccination available to help protect horses against strangles.

Reducing the risk

  • There are plenty of measures that can be taken to reduce the risk of disease infection, including:
  • Be familiar with the clinical signs associated with the main infectious diseases.
  • Keep a close eye on your horse after coming back from a competition, paying attention to appetite, demeanour, nasal discharge and temperature.
  • If you have any concerns that your horse may be ill, limit contact with other horses and avoid travelling.
  • Seek immediate veterinary advice if you suspect your horse has a contagious disease. Confirmation is vital so that control measures can be put in place.
  • If there is a known outbreak in the area, talk to your vet about the risks and the measures you can take to minimise the chance of infection.
  • Ensure your horse follows an effective and regular vaccination programme. 
  • Establish a three-week quarantine procedure for new arrivals on to a yard. 
  • Uphold high levels of yard hygiene.
  • Ensure there is a contingency plan in place at your yard to be used in the event of an outbreak.

First published in the Jan/Feb 2020 issue of British Eventing Life, original words by Stephanie Bateman