Recent Upticks in Equine Influenza and Pigeon Fever

  |   Animal Health

Noticeable upticks in the number of cases of Equine Influenza Virus and Pigeon Fever have been reported by private veterinarians to the Washington State Veterinarian’s Office in the past two months. You can find the full list of diseases that veterinarians are required to report by visiting the Washington State Department of Agriculture’s website and searching for ‘reportable diseases.’

Here are overviews of both diseases and steps that can be taken for prevention.

Equine Influenza Virus (EIV) 

There have been 23 cases of Equine Influenza Virus reported since early September. Veterinarians have reported cases in Pierce, Thurston, King, Mason, Lewis, Snohomish, and Spokane counties. Some reports are associated with larger outbreaks of disease in stables where horses have returned from events, but it is likely that there are more cases than those that have been reported.

EIV is caused by influenza type A virus subtypes. It is highly contagious between horses, primarily through direct contact and inhalation of aerosolized virus. The virus can survive on surfaces for up to 60 hours and is susceptible to common disinfectants.

Clinical signs of Equine Influenza include:

  • Fever
  • Depression
  • Lethargy
  • Nasal discharge
  • Coughing
  • Reduced appetite.

Viral shedding is significant by both clinical and subclinical animals. In unvaccinated populations, all horses may become infected and ill, but death rates are low.

Anti-inflammatories address the fever and make animals more comfortable. Some cases may require antibiotics to treat secondary bacterial infections but such treatment should only be given with veterinary guidance. Affected horses need rest and slow return to work, and an infected premise should be quarantined.

Diagnosis is via clinical signs, vaccination history, barn disease status, viral isolation, and antibody testing.

Prevention includes twice-yearly vaccination of at-risk animals (including those that travel and mix with other horses or are stabled with such horses), strict biosecurity practices, isolation of sick horses especially after returning from a show, event or exhibition, and quarantine of new animals.

Pigeon Fever 

Pigeon Fever gets its name from an affected horse’s swollen chest, which looks similar to that of male pigeons in display. Since September, there have been 13 cases reported in Yakima, Lewis, Thurston, Kitsap, King, Pierce, Spokane and Clark counties. Pigeon fever is a bacterial disease caused by Corynebacterium pseudotuberculosis, a variant of the agent causing caseous lymphadenitis in small ruminants.

This organism can survive for long periods in the environment, including soil. It is transmitted by biting flies, skin punctures, and wound contamination. The disease manifests as abscesses, most commonly on a horse’s pectoral region or abdomen; internal abscesses and ulcerative lymphangitis are less common conditions.

Clinical signs depend on where the abscesses are located and can include fever, depression, lethargy, lameness, anorexia, weight loss, colic, and respiratory signs.

Diagnosis is through clinical signs, local history of cases, and antibody detection. Treatment includes lancing and draining external abscesses with painstaking collection and disposal of exudate, anti-inflammatories, wound care, and insect repellant. Antibiotics are only recommended for the internal abscessation and ulcerative lymphangitis forms under veterinary guidance.

To prevent this disease, focus on fly control, wound prevention, and practice good biosecurity, especially in locations with current cases. Visit the Equine Disease Communications Center at to sign up for equine disease alerts.

Dr. Brian Joseph is Washington’s State Veterinarian at the Wash. Dept. of Agriculture.


Posted November 20, 2020