Diseases, Equine Health, Vaccines

West Nile Virus in Horses

What is West Nile virus in horses? West Nile Virus (WNV) first arrived in the USA in 1999 from Asia/Europe/Mid-Eastern countries via infected mosquitos hiding in shipping containers. West Nile Virus can affect both humans and horses, but this virus is a relatively new disease in horses in the United States.

How Does a Horse Get West Nile Virus?

Horses with West Nile virus are infected with West Nile only one way – bite from a mosquito infected with the virus that injects it into a horse when the mosquito feeds on bloodmeal from a horse. Mosquitos get the virus by biting infected wild birds with the virus then later that mosquito bites a horse. Mosquitos do NOT get the virus from a horse infected with equine WNV. Horses are NOT a reservoir of disease. They can’t give WNV to another horse or a human being. Because of this, a horse with WNV will not require a farm to be quarantined. Touching a horse with WNV will not transmit WNV to a horse or a human being. Wild birds with WNV are all over North America. Every state, every country, so every horse has the chance to be bitten by a mosquito infected by WNV.

Signs of Equine WNV

When it comes to symptoms of West Nile in horses, most WNV infections in horses are mild; symptoms include fever, off feed and most horses recover in approximately 2/3rd’s of infections. However, in 1/3rd of infections, equine West Nile progresses to moderate or severe and can lead to horse death. Moderate signs of equine WNV include: muscle tremor/stumbling/incoordination. Severe signs are due to an inflamed central nervous system and inflamed muscles. Symptoms of West Nile in horses include sitting like a dog with its rear on ground / front legs extended, can’t get up, full out laying down, can’t get up, and death (via virus or euthanasia). Antibody testing of limited use due to large exposure possible, so it is difficult to tell if it’s a current case or mild previous / recent case. The incubation time of WNV in horses from bite to signs of disease is 3 to 15 days.

Equine Encephalitis

The West Nile virus is a mosquito-borne disease that can cause Encephalitis in horses. There are three viral encephalitis forms in horses; Eastern Equine Encephalitis, Western Equine Encephalitis and West Nile. West Nile Encephalitis is described as an inflammation of the central nervous system. Younger and older individuals are the most susceptible to the virus. The good news, the Prestige® 5 + WNV with Havlogen® vaccine for horses protects against all three forms of equine encephalitis.

West Nile Treatment in Horses

West Nile treatment in horses involves support care. There are no immunoantibody serums available. When it comes to severe cases, a majority end in death. That makes prevention even more vital to your horse’s health.

Prevention with the West Nile Vaccine for Horses

The Equine West Nile vaccine is the only protection available for horses. This prevention costs pennies a day. The initial wnv vaccine for horses is a series of two. Give dose one, then skip three to six weeks, then give the second dose. The horse will be protected from West Nile four to six weeks after the second dose of vaccine. The WNV vaccine for horses are given intramuscular. After the initial two vaccines, you’ll only need one vaccine for WNV once a year. WNV is a AAEP Care Vaccine. Buy the Equine WNV Vaccine Here

Mosquito Protection for Horses

Mosquito control and fly spray is also important to protect animals and humans. To repel mosquitos from biting your horse, spray horses two times a day- a.m. and p.m. Mosquitos can bite anytime of day. Not only at night. Eliminate standing water and containers that hold standing water. Discourage birds from living around your stable. Use sprays that are safe for the environment to control the mosquito population. Cedarcide™ YardSafe, Country Vet® Mosquito & Fly Spray, or Permethrin 10% work to kill mosquitoes and are long-lasting.

If you have more questions on West Nile in horses, call us at 800.786.4751.

Written by: Frank Reilly, DVM

Senior Doctor at Equine Medical & Surgical Associates

Frank Reilly, DVM has been in equine practice for 36 years and has worked on six world-record racehorses. He is the Senior Doctor at Equine Medical & Surgical Associates, Inc. and a member of the AVMA, AAEP, NAEP, and IAPF. Dr. Reilly specializes in Equine Cushings, Insulin problems, Summer Eczema, Vitamin E deficiencies, COPD/Asthma, and Horse Foot Canker. Dr. Reilly is a 35+ year member of American Veterinary Medical Assoc. and the American Assoc. of Equine Practitioners. He is also a member of Pennsylvania Veterinary Association, the Northeast Assoc. of Equine Practitioners and is on the Board of Directors and Treasurer of Ryerss Farm-America’s First Horse Retirement and Rescue, established in 1888.

If you need help, call us at 800.786.4751.