We are one year since the beginning of the equine influenza (flu) outbreak of 2019 – the first of its like seen in Britain since 2003.

The outbreak was part of a larger outbreak that affected many countries in Europe and Africa. The confirmation of equine flu being found in three vaccinated racehorses on a racing yard in England, caused the British Horse Racing Association (BHA) to postpone races up and down the country at the beginning of February, 2019.

It additionally resulted in many venues and yards cancelling competitions and caused the general public concern about spread of the disease. Owners were additionally recommended to vaccinate horses against equine flu if they had not done so in the last six months.

Since those confirmed cases in February, of last year, a total of 228 outbreaks (premises affected) of equine influenza have been documented between Scotland, England and Wales, with the highest number of these found in Durham and Swansea regions (Animal Health Trust 2019).

These 228 outbreaks were huge in comparison to the three reported in 2018 and 15 in 2017. At many of the outbreaks, several horses were affected.

Equine flu is endemic in the UK, which means it is commonly found here. It is a highly infectious respiratory disease caused by the equine influenza (EI) virus.

This causes clinical signs including coughing, nasal discharge, fever (>38.5 degrees Celsius), lethargy and inappetance, which can vary in severity depending on the horse or pony’s immunity.

Immunity can be achieved by previous infection or vaccination and enables the animals’ body to be primed to fight the virus. This is why vets recommend horse owners vaccinate their horses against equine flu.

Transmission of the EI virus occurs through horse to horse contact via respiratory secretions and aerosols, which can travel in the air for long distances, increasing the risk of infection from nearby yards.

Complications of equine flu result from the reduced ability of the airway tract to clear mucous and other debris. This can lead to secondary bacterial infections, and problems such as sinusitis, pneumonia and in severe cases it can be fatal.

The concern with the 2019 outbreak was that it was confirmed in vaccinated horses. Horses that should have had sufficient immunity to the virus due to being vaccinated.

Vaccines are manufactured based on the types of EI virus strains that have been detected in previous outbreaks, therefore, priming your horse or pony’s immune system accordingly. Viruses have one goal in their life- to evade the host’s (in the case your horse) immune system and cause disease.

The virus can also do this by changing how they appear on their surface, through mutations during replication, and so change how they are recognised by the immune system of the host.

Virtually all the outbreaks of equine flu in 2019 involved the Florida Clade 1 H3N8 of the EI virus. The protection provided by the current vaccinations appears not to have been sufficient to prevent the spread of the disease.

The Animal Health Trust (AHT) run a surveillance scheme for equine flu sponsored by the Horse Betting Levy Board (HBLB) which gives free testing and provides free advice for suspected and confirmed cases of equine flu.

This is crucial to identifying new strains of the virus so the vaccine companies can be informed and update vaccines. Sampling involves taking a blood sample and a swab from the back of the nose and throat, which can then be tested to determine what strain of the EI virus is causing the disease.

The flu has a short incubation period of 1-3 days (the the time from infection to displaying clinical signs.) Infected patients unfortunately shed the virus before clinical signs are present, so this means that this is a good time to swab to look for the virus.

Taking blood samples to show evidence of EI virus exposure need to taken at two-week (min) intervals because it takes up to two weeks for an immunity to build to the virus. At this stage, a blood sample will show a rise in antibodies if the virus had been encountered. Below is a table to help detail when such testing should take place.

The World Organisation for Animal Health, as of April, 2019, recommended that both the Florida Clade 1 H3N8 and Florida H3N8 strains be included in all current vaccines.

So what are we advised to know?

Keeping your horse's vaccinations up to date is a good place to start. If not competing, most horses will be vaccinated annually according to the individual vaccine protocol.

However, most affiliated associations, and possibly some competition venues, will have specific requirements involving the horse or pony being vaccinated for flu within the last six months of the competition date.

Due to the outbreak last year, passports are being checked at competitions and livery yards are questioning the vaccination status of new horses arriving onto the yard. Please check with your specific association and/or venue before setting of for competition.

If your horse or pony has never been vaccinated against equine flu they will be required to have an initial course of three vaccinations. Following the first vaccination the second needs to be given 21-92 days later.

Following the second vaccination, 150-215 days after this, a third must be given. From the date of the third vaccination, the annual booster must be given on or before this date.

Adhere to isolation protocols when moving yards and being sensible while at competitions is very important.

Any horses displaying equine flu like symptoms should be isolated and tested.

Additionally any un-vaccinated, in contact animals should also be tested as precaution.

The Animal Health Trust have an Equiflunet webpage with lots of helpful information for owners and what to do if you suspect a case of equine flu.

Currently, the number of newly confirmed cases of equine flu per month has greatly reduced over tail end of last year. No new cases were reported in September, 2019, and only one outbreak per month from October to December, 2019, were recorded, according to the data collected by the AHT surveillance scheme.

Due to its ability to constantly mutate in an attempt to succeed in causing disease, it is likely that we will see further outbreaks in the future.

For now, following guidelines should help prevent severe infection, identify new cases promptly and help limit the rate of spread of any new cases of equine flu within the UK.