Equine Influenza

What is equine influenza?

Equine influenza (EI) is a highly infectious viral respiratory disease. It is characterised by fever and coughing, which can spread rapidly among susceptible horses.

What are the signs of equine influenza?

The incubation period (that is the time between infection and the horse showing clinical signs) is 1 to 3 days, therefore your horse will rapidly start to show signs if they have become infected with EI.

Clinical signs are highly variable in severity and depend on natural and/or vaccine immune status. Fully vaccinated horses will usually show none or very few clinical signs when infected with EI, whereas young horses are very susceptible.

  • Fever up to 41oC (106oF)
  • Depression
  • Watery nasal discharge
  • Dry, non productive, harsh cough
  • Watery eyes (conjunctivitis)
  • Swollen submandibular lymph nodes
  • Filled, swollen legs

In uncomplicated cases, clinical signs usually disappear over 3 – 7 days, however coughing may continue for weeks once the larynx has been irritated and damaged by repeated coughing. Mildly affected horses usually fully recover over 2 – 3 weeks, however severely affected horses may take as long as 6 months to return to full health and performance.

Severely affected horses may also develop complications, normally due to secondary bacterial infections that invade when the immune system is compromised, there include: Pneumonia, vasculitis, myocarditis and others. These conditions can be serious, requiring intensive care in a specialist hospital facility, and may cause prolonged debilitation.

What causes equine influenza?

EI is caused by a virus in the orthomyxoviridae family, belonging to the H7N7 and H3N8 subtypes. Unfortunately, influenza viruses gradually change with time, therefore it allows the virus to evade both natural and vaccine stimulated immunity.

As EI is transmitted from horse to horse in close proximity (by coughing and inhaling live virus), this form of transmission is intensified in stabled horses, particularly in stables with shared air space. Live virus is also spread from horses to other horses via hands, clothes, grooming equipment or tack contaminated with infectious material.

How is equine influenza diagnosed?

Any horses showing the before mentioned clinical signs, particularly in non vaccinated horses, should be considered to have EI until proved or disproved by laboratory testing. Blood samples taken at the time clinical signs first appear, then again 10-14 days later, can be examined for rising antibody levels, which confirm significant challenge. There is also now a human influenza A virus antigen detection rapid test which is available at a number of equine veterinary laboratories, which will give a reliable same day result. Your vet may also advise that a naso-pharyngeal swab is taken, so the virus can be grown and types to survey strain type and to look for signs of antigenic drift.

How is equine influenza treated?

Effective antiviral drugs are currently unavailable, therefore treatment is primarily aimed at stopping exercise and providing supportive care for fever and depression, as well as improving access to clean, fresh air with low dust and mould content.

EI virus replicates in the respiratory tract lining the cells, resulting in their destruction and loss of function. Once the virus has been overcome and expelled, the lining cells require 3 weeks to recover, so it is important that infected horses are given at least 3 weeks rest (and sometimes more) from exercise to reduce the risks of secondary bacterial infection and the development of serious secondary problems.

Can I prevent my horse from getting equine influenza?

There are a number of safe and efficacious vaccines to protect against EI. It is important that vaccinations are kept up to date, as immunity will lapse when vaccination is stopped.

Prevention and control also depends upon good biosecurity measures, such as:

  • Early detection of cases
  • Isolation of cases
  • Environmental cleaning and disinfection

Useful links:

Preventative Healthcare

Tetanus Vaccination:

We believe that every horse should be vaccinated against tetanus as this fatal disease can be prevented at relatively low cost. The initial course of vaccination requires two doses 4-6 weeks apart followed by a booster after one year. Boosters are then given every two years.

Influenza Vaccination:

Equine Influenza (flu) is a serious respiratory disease that can cause widespread problems in unvaccinated horses eg. the Australian outbreak in 2007. Influenza can be effectively prevented by vaccination which we would recommend and is also required by many shows/event organisers/racing authorities. If your horse’s vaccinations do not comply with the regulations below, your horse may be refused entry:

Initial influenza vaccination
Second influenza vaccination 21-92 days after the first
Third influenza vaccination 150-215 days after the second
Annual boosters thereafter not exceeding 365days after previous vaccination.

Vaccinations are not permitted within 7 days of racing/competition.

We endeavour to send out reminders for third and annual booster vaccinations but it is your responsibility to ensure that your horse’s vaccinations comply with the appropriate regulations.

FEI vaccinations:

Horses competing under FEI rules are required to have two initial vaccinations 21-92 days apart followed by a third vaccination within 6 months and 21days following the second dose with at least annual (within 365 days) boosters given subsequently. When competing at an FEI competition, the last vaccination must have been given within 6 months +/- 21 days of the competition date. No vaccinations to be given within 21 days of the competition.

For further details please visit: www.inside.fei.org

EHV ( Equine Herpes) vaccinations:

Horses can be vaccinated against EHV in order to protect against respiratory disease and/or abortion. For the prevention of respiratory disease the schedule is:

First EHV vaccination
Second EHV vaccination 4-6 weeks later
Booster EHV vaccination every 6 months
Pregnant mares can be vaccinated at 5,7 & 9 months of pregnancy to protect against abortion. EHV vaccinations are compulsory on many stud farms before your mare can be admitted to foal down.

Microchipping & Passports

We support microchipping of horses to provide permanent identification as well as being a legal requirement for horses born since 1st Jan 2010. The microchip is implanted in the left side of the crest and horses are routinely checked for microchip at vettings, events, auctions & racing. We offer a combined package of microchip implantation and passporting for foals, please contact the office for details.

Equine Healthcare Plan

We have developed our Healthcare Plan to allow you to spread the cost of your horse’s preventative healthcare as well as save money. It provides regular health and dental checks, vaccinations and worm egg counts. Find out more

Worming Programme

We offer an annual worming programme- we will perform as many worm egg counts as we deem necessary, advise on the results and tailor an individual worming program for each horse. Find out more