In a recent news release, Penn State (Pennsylvania) extension specialists Danielle Smarsh and Laura Kenny stressed that pigeon fever has “nothing to do with pigeons and everything to do with horses.” This bacterial infection, caused by Corynebacterium pseudotuberculosis, gets its unusual name from the characteristic swollen-chest appearance it creates in affected horses, resembling a pigeon’s puffed-out breast.

No longer merely a regional threat, pigeon fever is now a concern around the nation. One horse at a boarding facility in Lebanon County, Pennsylvania, recently tested positive for pigeon fever, highlighting the disease’s continued spread beyond its traditional western United States range.

Over the last few years, more states have reported cases of pigeon fever for the first time ever, with confirmed cases now documented in Massachusetts and New York.

This northern and eastward expansion underscores the importance of vigilance among northeastern horse owners.

Causes and transmission

The disease is caused by the soil-dwelling bacterium Corynebacterium pseudotuberculosis, which can survive in the environment for extended periods. The bacteria enter horses through small wounds, insect bites or mucous membranes.

Pigeon fever spreads primarily through direct contact with infected drainage from abscesses, contaminated soil, or shared equipment. Flies are an important and common mechanical vector, carrying bacteria from infected animals to susceptible horses.

The disease is not directly contagious between horses but spreads through environmental contamination.

Clinical signs

Pigeon fever presents in three distinct clinical forms. The most common and recognizable form involves external abscesses that cause characteristic swelling of the chest and ventral (underneath) abdomen, creating the distinctive “pigeon-breasted” appearance that gives the disease its name. However, these abscesses can occur anywhere on the body and may eventually rupture, draining thick, purulent (pus and pus-like) material.

The second form involves internal abscesses that typically develop in vital organs such as the liver, spleen and lungs, making diagnosis more challenging.

The third form, ulcerative lymphangitis, is characterized by severe limb swelling accompanied by cellulitis and skin ulceration. Regardless of the form, affected horses commonly exhibit systemic signs including fever, lethargy and decreased appetite. Early recognition of these symptoms is crucial for prompt treatment and management.

Prevention

The press release encourages horse owners to maintain good wound care by promptly cleaning and treating cuts, scrapes and insect bites. Do not share equipment such as water buckets and tack, but if you must, disinfect shared equipment regularly. Also, avoid overcrowding in pastures and facilities. Keep horses in good body condition, as stressed or immunocompromised animals are more susceptible to disease. During outbreaks in your area, consider limiting horse movement and contact with unfamiliar animals. 

Fly management is key, as flies are the primary vector for transmitting these infections from the soil and between horses. You need to fight flies in several different ways:

• First, clean up manure every day, because flies lay eggs in fresh manure. Also, eliminate standing water around your barn by emptying buckets, fixing leaky hoses and filling in puddles where flies tend to breed.
• Use fly sprays. Fly sprays containing fatty acids, such as Ecovet or Ultrashield Gold and other non-permethrin-based products like Out Smart and Equiderma, are potentially more effective in the laboratory (Tuorinsky and Machtinger, 2020). Read the label and spray your horse as often as directed during fly season. You can also use fly sheets, masks and leg wraps to create a barrier between flies and your horse. Ensure these fit well so your horse can move around easily. Pay extra attention to protecting the area around your horse’s eyes, as flies tend to gather there.
• Put fans in stalls and other areas where your horse spends time. Moving air makes it hard for flies to land on your horse. You can also set up fly traps around your property, but don’t rely on just traps alone.

The most important thing is to be consistent. You can’t just do fly control sometimes; you need to keep it up throughout fly season, when these infections occur most often. Also, experts say that the organism that causes pigeon fever prefers hot and dry conditions, so extra vigilence during the hot, dry season is warranted. The same is true in regions where climate change has brought temperature increases and more arid conditions.

What to do if you suspect pigeon fever

Contact your veterinarian immediately for proper diagnosis and treatment. Your veterinarian may recommend blood tests, an ultrasound or a bacterial culture to confirm the diagnosis and determine the appropriate antibiotic therapy. Do not attempt to open or drain abscesses yourself, as this can spread infection.

Isolate the affected horse and practice strict hygiene when handling the animal. For example, feed or groom this horse last, and wash your hands after handling the horse. Do not share grooming tools or buckets between the affected horse and others.

Pigeon fever is being reported more frequently on the East Coast. Horse owners should familiarize themselves with the signs of this bacterial infection. Early veterinary intervention is crucial for successful treatment and the prevention of complications. Maintain fly control measures and proper wound care as preventive strategies for your herd.

References

EDCC Health Watch. (2025, June 11). Pennsylvania horse tests positive for pigeon fever. The Horse.

Tuorinsky, E. V., & Machtinger, E. T. (2020). Behavioral inhibition of the house fly, Musca domestica (Diptera: Muscidae), when exposed to commercial equine fly repellents. Journal of Economic Entomology, 113(1), 518–526. doi.org/10.1093/jee/toz243