Update on Equine Influenza 2020

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. Following confirmation of equine flu in three vaccinated racehorses on a racing yard in England the British Horse Racing Association (BHA) postponed races up and down the country at the beginning of February 2019. The outbreak additionally resulted in many venues and yards canceling competitions and caused the general public concern about spread of the disease. Owners were recommended to vaccinate their horses against equine flu if they had not been so in the last 6 months. Since those confirmed cases in February 2019, a total of 228 outbreaks (premises affected) with 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 3 reported outbreaks in 2018 and 15 in 2017. At many of the outbreaks several horses were affected with the condition.

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 virus causes clinical signs including coughing, nasal discharge, fever (>38.5 degrees Celsius), lethargy and inappetence, 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 Equine Influenza (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) in 2019 ran a surveillance scheme for equine flu sponsored by the Horse Betting Levy Board (HBLB) giving free testing and advice for suspected and confirmed cases of equine flu. This was crucial to identifying new strains of the virus so the vaccine companies can be informed and update their vaccines accordingly.

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. Equine flu has a short incubation period of 1-3 days. (This is the time from infection to displaying clinical signs.) Infected patients unfortunately shed the virus before clinical signs are present. 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 2 week (min) intervals because it takes up to 2 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 annual world organisation for Animal Health, as of April 2019, recommend that both the Florida Clade 1 H3N8 and Florida H3N8 strains be included in all current vaccines.

So what are we advised to do now?

• Keeping your horses’ 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 6 months of the competition date. Due to the 2019 outbreak, 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, the 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 number of newly confirmed cases of equine flu per month greatly reduced over tail end of 2019. 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 virus’s ability to constantly mutate in an attempt to succeed with causing disease, it is likely that we will see further outbreaks in the future.

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