Equine influenza virus on the rise again in Washington

By Dr. Amber Itle, WA State Veterinarian
Washington State Department of Agriculture (WSDA)

Horses are on the move and so are equine diseases. Just this week a quarantine was released at the polo facility where 600 horses were exposed to Equine Herpes Virus (EHV) in California. That is a good reminder to everyone of how important vaccination is to mitigate disease severity and allow for continuity of business. Now is the time to encourage your clients to get up to date on EHV, Flu/Rhino and West Nile Disease in addition to the core vaccines recommended by AAEP. This is especially critical in boarding facilities where horses come and go to shows, events and even trail rides. Any commingling event is an opportunity for viral spread. Although horses that are vaccinated can still contract the virus and spread it, the course of disease should be less severe.

In the last few weeks, WSDA is starting to see an uptick in cases of Equine Influenza Virus (EIV) in Western Washington. Equine Influenza virus is a very contagious infectious respiratory disease of horses and is a reportable disease to the State Veterinarian. In recent years, we have seen high morbidity in stables across 13 counties in the State. As soon as the attending veterinarian gets positive laboratory results, EIV must be reported through the Reportable Animal Disease database. Once reported, a field veterinarian will follow up with you to see how we can best support you. WSDA also reports to the Equine Disease Communication Center and they distribute minimal information that protects personally identifying information through an alert to subscribers. Usually, private practitioners manage individual cases of EIV by performing diagnostics, addressing individual horse treatment, implementing on farm biosecurity practices, and helping the barn manager institute a self-quarantine of infected or exposed horses.

In some cases, when morbidity is high and/or stable compliance is a problem, the State Veterinarian can be requested to assist. WSDA field veterinarians can issue quarantines in order to mitigate the spread of disease and protect horse health and the economic vitality of the equine industry across the state. A quarantine will be in place until 14-21 days after the last “new” case, allowing for a full incubation period to pass by without clinical signs. Horses can remain contagious for 10 days after clinical signs or fever starts. The quarantine will require that rectal temperatures be recorded daily whenever possible so that febrile horses can be rapidly isolated, tested and monitored for clinical signs. Often viral infections can be “dose dependent” so rapid removal of sick horses can reduce viral load and transmission.

Airborne transmission is the most common way horses become infected. Infected horses release infective droplets into the air by coughing or snorting which are then inhaled by horses in close proximity. Horses can also be exposed to the virus by coming into contact with contaminated surfaces such as stalls, wash racks, stocks, water sources, feed, tack, grooming equipment such as wipe rags, and transport vehicles. Humans can spread the virus from horse to horse by contaminated hands and clothing, so the adoption of biosecurity measures is paramount.

WSDA Field veterinarians can also assist private practitioners with on farm biosecurity plans to help mitigate viral spread. Here are some biosecurity tips you can customize for your clients during a (self or state mandated) quarantine period to help ensure the health and welfare of your client’s horse.

1. Observe Strict Biosecurity
   1. Limit Stress to horses
   2. Control flies, vermin, vectors
   3. Monitor all horses’ rectal temperatures on the premises twice a day
   4. Keep hoses out of free-standing water such as ponds or creeks
   5. Promptly remove compost and manure
   6. Wash hands frequently
   7. Prevent direct contact with infected horses
   8. Do not share equipment, buckets or tack
   9. Tape off an “off limits” perimeter outside any symptomatic horse stall approximately 3 feet by six feet. Only people that need to enter the stall are permitted into this area.
   10. Place a foot bath outside the stall with disinfectant, to dip feet into prior to entering and again after exiting the stall. Be sure to clean your boots before you disinfect.
   11. Frequently clean and disinfect the stall
   12. Designate one person to care for your horse and limit contact of personal with exposed horses
   13. Notify your veterinarian immediately if you notice any clinical signs or changes in behavior. Horses with EIV are prone to secondary bacterial infections.
   14. Coughing horses aerosolize the organism and can spread the virus as far as 150 feet
2. Horse Management
   1. Supportive care and treatment at prescribed by your veterinarian
   2. Keep in well-ventilated stall and or paddocks to reduce inhalation of dust
   3. Consider staggering outdoor paddock access to avoid nose to nose contact
   4. Spray any common contact areas with 10% bleach.
   5. Consider physical barriers between outdoor runs to avoid nose to nose contact
   6. Keep dust down in the stall and hay (by wetting if needed)
3. Exercise – No sick horses should be allowed in the main arena or in shared wash racks.
   1. Symptomatic horses (fever, lethargy, nasal discharge, coughing, etc.)
      1. Febrile horses should remain in their stalls and allowed to rest.
      2. Avoid strenuous exercise and hand walk or exercise lightly for short periods of time.
         1. Remember, your horse is not feeling well and may be lethargic, have painful muscles or a cough that can be exasperated by exercise. The idea is to stretch the horses legs and provide some stress relief from being stalled.
      3. Lightly exercise horses in the designated round pen area away from other horses
      4. When moving horses down the alleyway, use the closest exit and be cautious to avoid direct nose to nose contact with other horses.
      5. Only one horse should be exercised at a time and a schedule should be posted if needed.
   2. Exposed, non-clinical horses (No fever, no nasal discharge, rare or occasional cough)
      1. Avoid strenuous exercise, but light riding or exercise is acceptable.
         1. Remember that your horse’s immune system may be under stress from recent exposure and fighting off potential infection. Too much exercise may exasperate clinical signs or illness.
      2. All horses should exit the barn on the north side.
      3. Exercise horses in the designated outdoor arena space
      4. Only one horse should be exercised at a time and a schedule should be posted if needed.

Mapping the farm can also be helpful when thinking about horse movement patterns on the farm as well as identifying access points, parking, cleaning and disinfection stations and carcass pick up areas.

Practitioners can find this graphic on the WSDA website to be printed and provided to your clients. We also have large, printed posters available upon request.

Additional Equine Biosecurity Resources can be found on the WSDA website.