Pigeon fever in horses: what it is, how it spreads, treatment and recovery

What is pigeon fever in horses?

Pigeon fever is a group of diseases in horses caused by Corynebacterium pseudotuberculosis, a gram-positive bacterium found worldwide, and in most horses it means abscesses in the chest muscles or along the underside of the belly. The AAEP's 2026 infectious disease guideline, written by Dr. Sharon Spier, defines it as a collection of syndromes caused by this one bacterium. The strain that infects horses is nitrate-positive, while the strains from sheep, goats and camelids are nitrate-negative, and the AAEP notes that natural cross-species transmission does not occur between small ruminants and horses. Researchers call the horse strain biovar equi, as in the title of a 2015 study on Corynebacterium pseudotuberculosis biovar equi in horses.

The disease has collected a lot of names. The Merck Veterinary Manual's owner page lists false strangles, pigeon breast, dry land distemper and ulcerative lymphangitis, and a 2002 Colorado State University release adds breastbone fever, dryland strangles and false distemper. If you have heard someone at the barn talk about dryland distemper, it is the same thing.

Why is it called pigeon fever?

Pigeon fever is named after the swelling on the horse's chest, which looks like a pigeon's breast; birds play no part in the disease, and many affected horses never run a fever. UC Davis explains that the swelling resembles a pigeon's breast, which is how the disease got its name. The University of Florida's IFAS Extension stresses that birds are not involved in how it spreads or develops. As for the fever, Brazos Valley Equine Hospitals in Texas writes that about a quarter of infected horses develop a fever, up to 104°F. Merck counts a high or prolonged fever among the signs of complications, so a reading gives your vet something concrete; our guide to a horse's normal temperature shows how to take one.

What causes pigeon fever, and how do horses get it?

Horses get pigeon fever when Corynebacterium pseudotuberculosis from soil, manure, contaminated objects or flies gets into a scrape, a small wound or a mucous membrane. The AAEP says the bacterium exists in the soil and gains access through skin breaks and mucous membranes, and UC Davis describes infection through small scrapes, either by direct contact with contaminated soil or objects, or by insects that deposit the bacteria on broken skin.

It is a hardy organism. According to the AAEP, it has been shown to survive up to two months in hay and shavings and more than eight months in soil, and manure helped it survive and multiply in experimental studies. VetSpecialists.com describes it as flourishing in manure-contaminated sandy and rocky soils. The University of Florida is broader still and says it can survive for weeks to months, or possibly even years, in the soil.

What about the pigeon fever incubation period? Abscesses form 3 to 4 weeks after infection according to the AAEP, UC Davis gives a lengthy incubation period of 1 to 4 weeks, and the University of Florida says it can vary from days to weeks. So a horse that shows an abscess today was most likely infected several weeks earlier, which is worth remembering when your vet asks which horses he has been turned out with.

Which horses get pigeon fever?

Any horse can get pigeon fever; no breed or sex is predisposed, and young horses and horses out at pasture with other horses appear to be at higher risk. In 538 cases at the UC Davis veterinary teaching hospital from 1982 to 1993, breed and sex did not appear to be associated with infection. A 1998 study of California horses found significantly higher odds for horses aged 1 to 2 and 3 to 5 years, and for horses in contact with other horses or on summer pasture. The University of Florida adds that young horses may be at an increased risk, and Brazos Valley Equine Hospitals writes that horses kept in stalls are at a decreased risk.

How does pigeon fever spread?

Pigeon fever spreads mostly through flies that carry the bacterium from draining abscesses or soil onto broken skin, and through contact with contaminated soil, equipment, hands, hay and bedding. The AAEP names three flies that can act as mechanical carriers: the horn fly, the house fly and the stable fly. A 2004 study that tested 2,621 flies on five farms in northern California found the bacterium in up to 20% of house flies near diseased horses, with the highest percentages in October, when most sick horses were seen. In a 2015 experiment, house flies transmitted the bacterium to ponies: all four ponies exposed to the flies became infected, while three others in the study were inoculated directly.

Flies are not the only route. VetSpecialists.com lists contaminated equipment, hands and hay or bedding, and the AAEP adds that horse to horse transmission is also likely. How contagious that makes pigeon fever is a separate question, and the sources answer it differently further down.

What are the symptoms of pigeon fever in horses?

The usual sign of pigeon fever in horses is a firm swelling on the chest or along the midline of the belly that grows into an abscess and bursts, often in a horse that otherwise seems well; the internal form shows as fever, weight loss and dullness instead. The AAEP notes that horses with external abscesses do not usually develop signs of systemic illness, while the internal form often brings fever and malaise. The three forms look different enough to take one at a time.

Early signs of pigeon fever

The early signs of pigeon fever in horses can be a poor appetite, fever, dullness, swelling along the chest or belly, or lameness, and sometimes a burst abscess is the first thing anyone notices. That list comes from the University of Florida. Colorado State University warned in 2002 that the only early signs can be lameness and a reluctance to move. VetSpecialists.com mentions hair loss and skin irritation around swellings, especially before the abscess ruptures. And Brazos Valley Equine Hospitals points out that the early symptoms may go unobserved, so the ruptured abscess is the first sign noticed.

External abscesses: chest, belly and sheath

A pigeon fever abscess most often sits in the chest muscles or along the midline of the belly, can grow to 8 inches across before it bursts, and drains tan, odor-free pus. The AAEP lists the pectoral region and the ventral midline as the most frequent sites, and adds the prepuce, mammary gland, triceps, axilla, limbs and head. In the 538 UC Davis cases, 308 horses had pectoral abscesses. Merck says the abscesses can reach up to 8 inches (20 centimeters) in diameter before rupturing and take weeks to months to heal. The pus is tan and odor-free.

Pigeon fever in a horse's sheath is easy to mistake for something else. Brazos Valley Equine Hospitals explains that abscesses of the inguinal lymph nodes can show up as swelling of the sheath or around the mammary gland, and that abscesses along the belly can resemble an allergy to biting midges (Culicoides). Our guides to sheath cleaning and a swollen sheath and to flies and sweet itch cover those look-alikes.

Internal pigeon fever

Internal pigeon fever is an abscess inside the body, most often in the liver, lungs, kidneys or spleen, and it shows as fever, weight loss, colic or dullness, sometimes without any abscess on the outside. The AAEP puts it at approximately 8% of affected horses and says it is seen more often one to two months after the peak of external cases, and that horses with internal abscesses may not have external ones. Merck's veterinary chapter lists weight loss, colic, splinted abdomen, or lethargy as possible signs. In a 2005 series of 30 horses with internal infection, the organs affected were the liver in 18 horses, the lungs in 12, the kidneys in 7 and the spleen in 3, and the same study warned that pregnant mares with internal infections are at risk of losing the foal. Brazos Valley Equine Hospitals writes that 63% of internal cases had external abscesses in the preceding months, which is why a horse that seemed to recover and then loses weight deserves a call to the vet. Under the internal form, the AAEP also lists reported cases of joint and bone infection (septic arthritis and osteomyelitis), which come with severe lameness.

Ulcerative lymphangitis

Equine ulcerative lymphangitis is the rarest form of pigeon fever: severe swelling of one or both hind legs with several draining wounds along the lymph vessels, marked lameness and fever. The AAEP calls it the least common form and lists severe lameness, fever, lethargy and a poor appetite, with support limb laminitis as a common complication; Brazos Valley Equine Hospitals sees it in less than 1% of cases.

Is pigeon fever the same as strangles?

No, pigeon fever and strangles are different diseases caused by different bacteria: pigeon fever by Corynebacterium pseudotuberculosis, strangles by Streptococcus equi equi, which forms abscesses in the lymph nodes of the upper airway and is highly contagious. Merck describes strangles as abscesses in the lymph tissue of the upper respiratory tract and warns that infected horses can become carriers that show no signs but still spread it. The confusion is understandable: "false strangles" is one of pigeon fever's nicknames (UC Davis), and Colorado State University noted in 2002 that pigeon fever can initially resemble strangles. Brazos Valley Equine Hospitals sums up both the overlap and the difference: horse-to-horse transmission does not happen as consistently as with strangles, and as with strangles, lancing and drainage is often the only treatment an external abscess needs. A culture of the pus is how your vet confirms pigeon fever, as the next section explains. Our guide to strangles in horses covers the other disease.

How do vets diagnose pigeon fever?

Vets confirm pigeon fever with a bacterial culture or PCR test of pus from the abscess, use ultrasound to find deep and internal abscesses, and use the synergistic hemolysis inhibition (SHI) blood test only as support for the internal form. The AAEP states that a definitive diagnosis comes from bacterial culture and/or PCR of purulent material. Culture matters because, as UC Davis puts it, not all abscesses are caused by Corynebacterium pseudotuberculosis, and the right treatment depends on the cause.

Ultrasound does two jobs. The AAEP describes abdominal ultrasound as helpful for identifying abscesses, guiding drainage and monitoring treatment, and Dr. Keith Chaffin of Texas A&M explained in 2012 that ultrasound shows whether a swelling has reached the mature abscess stage, that is, whether it is ready to open.

The SHI test is a blood test for antibodies, and its use is narrower than owners often expect. The AAEP says it can support a diagnosis of internal abscesses in horses without external abscesses, is generally not helpful for confirming an external abscess, may be negative early on, and should never be used alone. A 2013 study came to the same conclusion: it was not a useful predictor of internal infection in horses with external abscesses, but was useful when there was no external disease.

Your own observations count as well. UC Davis says the diagnosis is based on clinical signs together with time of year, local prevalence and historical information. When the swelling appeared, where it is, when it opened, whether he had a temperature and whether other horses on the yard have it are the details your vet will ask about.

How do you treat pigeon fever in a horse?

Treatment for pigeon fever in horses with an external abscess is mostly drainage: the abscess is brought to a head with hot packs or poultices, lanced by your vet, flushed and kept clean, with an anti-inflammatory for pain, while the internal form and ulcerative lymphangitis need long courses of antibiotics. The AAEP's rule is that abscesses should be lanced, drained, and flushed whenever possible, and that most uncomplicated external abscesses respond well to drainage and supportive care with hot packing and anti-inflammatories. UC Davis lists hot compresses, poultices, lancing and draining, with collection of the infected material.

Timing is your vet's call. The AAEP describes abscesses ranging from less than 1 cm deep to more than 10 cm under the muscle, which is where ultrasound helps decide when and where to open them.

For pain, UC Davis says nonsteroidal anti-inflammatory drugs (NSAIDs) can ease discomfort before or after drainage, and Merck's veterinary chapter names phenylbutazone or flunixin meglumine; our guide to bute and Banamine explains the difference. The AAEP also recommends a current tetanus vaccination in every case, so check the date of his last shot in his vaccination records.

The AAEP guideline lists specific antibiotics with doses, written for veterinarians. We leave those out on purpose: which drug, how much and for how long is your vet's decision for your horse.

Does pigeon fever need antibiotics?

For a simple external abscess, the AAEP and UC Davis say antibiotics are often unnecessary and can make the abscess take longer to resolve, Merck explains why they can slow healing, and the University of Florida's extension sheet is the exception and says treatment usually includes them. The AAEP writes: "The use of antimicrobials for external abscesses is often not necessary and may prolong time to resolution." UC Davis says the same about most horses, and Merck's veterinary chapter explains why: antibiotics for an uncomplicated external abscess may prolong the disease by delaying abscess maturation. On the other side, the University of Florida's 2023 sheet states: "Treatment of pigeon fever usually involves systemic antibiotics and drainage of external abscesses."

The sources agree on when antibiotics do come in. For an external abscess, VetSpecialists.com names complicating factors such as persistent fever, depression, lameness, or cellulitis, Brazos Valley Equine Hospitals adds drainage beyond two weeks or repeated infection, and the AAEP adds deep abscesses in the muscle that need extensive dissection to drain. For the internal form and ulcerative lymphangitis, the AAEP says horses should be treated early and aggressively with antimicrobials, and Merck gives a minimum of 1 month or as directed by follow-up ultrasound. The University of Florida notes that the bacterium is usually sensitive to most antibiotics, including penicillin, but that a culture and sensitivity test of the pus is often recommended. Ulcerative lymphangitis also needs anti-inflammatories, hydrotherapy, hand walking and limb bandages to prevent permanent swelling.

What you can do at home

At home, your part of pigeon fever treatment is flushing the wound the way your vet showed you, catching and throwing away the pus, keeping flies off the wound, and keeping the horse, his kit and your hands apart from the rest of the barn. If you're looking for pigeon fever treatment at home, these are the steps the sources give owners:

1. Hot packs or poultices, if your vet asks for them. UC Davis lists hot compresses and poultices among the treatments for external abscesses.
2. Flush daily as instructed. Brazos Valley Equine Hospitals writes that daily flushing with saline or water for 3 to 5 days often resolves the infection; Merck's owner page mentions iodine solution and says your vet can recommend the most effective treatment. Use what your vet chose.
3. Catch the pus. The AAEP says to collect and dispose of all purulent material and contaminated supplies and not to let it drain onto the floor; the University of Florida adds that bedding from infected horses should be collected and disposed of too.
4. Treat on a floor you can disinfect. Ideally concrete or rubber flooring, according to the University of Florida.
5. Keep flies off the wound. The same sheet calls topical fly treatment around wounds and draining areas critical.
6. Gloves and clean hands. The AAEP advises exam gloves and diligent hand washing when you flush abscesses and handle infected horses.
7. His own buckets and tools. UC Davis says not to use the same buckets, pitchforks, and other materials for infected horses and the rest of the herd.

You'll find "natural treatment for pigeon fever" and cooling clay products recommended online. None of the veterinary or university sources we read supports them, and we won't guess. What they do describe is the list above.

How long does pigeon fever last in horses?

Most horses with an external pigeon fever abscess recover in 2 to 3 weeks according to UC Davis, ulcerative lymphangitis takes about a month, and the internal form needs antibiotics for 4 to 6 weeks on average according to the AAEP, or 2 to 3 months or more according to UC Davis. Large or deep abscesses can take longer than the typical case: Merck's owner page says abscesses take weeks to months to heal. Here is how long each stage lasts, with the sources that disagree side by side:

The sources that describe the end point agree: once the abscesses have stopped draining, VetSpecialists.com says most recovered horses need no aftercare and pose no risk of passing it on, and UC Davis says no further precautions are needed once there is no drainage.

Is pigeon fever contagious?

Pigeon fever is contagious in the sense that a horse with a draining abscess sheds bacteria that flies, hands and shared kit can carry to other horses, but it doesn't pass between horses as readily as strangles, and the sources describe that in very different words. Oregon's Department of Agriculture states that "Pigeon fever is a contagious disease in horses" and that it spreads easily, the AAEP says horse to horse transmission is also likely, and Colorado State University called it highly contagious in 2002. Brazos Valley Equine Hospitals is more cautious: "Direct transmission (horse to horse) does not appear to occur as consistently as with strangles". You will also see pigeon fever described online as non-contagious; none of the veterinary sources we read says that.

The way through the disagreement is the drainage. Dr. Keith Chaffin of Texas A&M said in 2012 that a recently drained abscess is potentially contagious, and that horses are generally no longer contagious once the abscesses have been drained, treated and healed. Our view is that a horse with an open or draining abscess should be treated as contagious until nothing drains, because every precaution the sources ask for is cheap compared with a second case on the yard.

Do you need to quarantine a horse with pigeon fever?

Yes, keep a horse with a draining pigeon fever abscess apart from the others until the drainage stops, preferably in a stall rather than in the field, with his own buckets, fork and grooming kit. The University of Florida says horses with draining abscesses should be isolated and that stalling them reduces contamination of the pasture, and the AAEP says to separate infected horses from naive and/or unvaccinated herd mates. Brazos Valley Equine Hospitals notes that some large boarding facilities may require individual stalls until the drainage has ceased, and recommends cleaning the infected horse's stall last and sanitizing grooming equipment. Oregon's agriculture department adds tack, buckets and grooming tools to the list of things not to share, and in Oregon pigeon fever is immediately reportable. We found no source on reporting rules in other states, so ask your vet what applies where you live.

New horses are the other half. The AAEP's general rule for new arrivals is isolation for a minimum of 7 to 14 days, longer if the yard they come from had a recent infection, and UC Davis advises you to quarantine and observe new horses. Keep in mind that the AAEP also gives 3 to 4 weeks for abscesses to form, longer than that minimum. Our new horse records guide and the new horse checklist cover the first weeks.

All of this only works if everyone who handles him knows it, from the barn manager to the person who brings him in on Saturdays. Our guide to sharing care and the care handover sheet help you set it out.

How do you prevent pigeon fever?

The best way to prevent pigeon fever is fly control started early in the season and used on every horse on the property, together with manure management, careful wound care and removing sharp edges that cause scrapes. UC Davis calls fly control, using feed-through products and repellents, key to prevention and control, especially on horses with open wounds or draining abscesses. The AAEP says feed-through insect growth regulators are highly effective when started early in the season, and Brazos Valley Equine Hospitals stresses that all horses on the property should receive the feed-through.

The rest of the list from the sources:

• Repellent on the belly. The AAEP advises regular insect repellent, particularly to the ventral midline.
• Fly sheets, sprays or ointments. UC Davis notes that flies can cause midline dermatitis on the chest and girth of sensitive horses.
• Manure management. UC Davis recommends regular manure management and sanitation to control insect populations.
• Sharp edges. Inspect stalls, paddocks and fields for sharp edges or objects that could cause wounds (UC Davis).
• Wound care. The AAEP asks for meticulous wound care with fly repellents, antimicrobial ointments and bandages.

Be realistic about what this buys you. Merck's owner page says the disease occurs even under excellent management, and UC Davis notes that in many parts of California there is no practical way to eliminate the bacteria from soil. Our guide to flies and sweet itch covers fly control through the season.

Is there a vaccine for pigeon fever?

There is no commercially available vaccine for pigeon fever in horses, according to the AAEP's 2026 guideline, although Merck's veterinary chapter, last fully reviewed in November 2023, still says a conditionally licensed one is available. The AAEP states: "There is currently no commercially available vaccine against C. pseudotuberculosis." UC Davis (2019) and Brazos Valley Equine Hospitals (2026) also say there is no vaccine. Merck's chapter, by contrast, says a conditionally licensed bacterin or toxoid is currently available for horses.

The story in between explains the confusion. In March 2015, Boehringer Ingelheim Vetmedica announced that the USDA had granted it a conditional license for a pigeon fever vaccine. A month later, as of April 9, 2015, the company placed a voluntary stop sale on it after reports of unexpected gastrointestinal problems in some horses after vaccination. We found no source saying that stop was ever lifted, so we go with the AAEP's 2026 position and suggest you ask your vet. The vaccine that does matter for pigeon fever is tetanus, which the AAEP wants current in every case.

Where is pigeon fever most common?

Pigeon fever is most common in California and Texas and has spread through the western and midwestern United States and into Canada, with outbreaks in new areas during droughts, mostly in the dry months from late summer into early winter. Merck calls it a common infectious disease of horses in California and Texas that is increasingly seen in other western and midwestern states. The AAEP says equine cases have been reported throughout the United States and in areas of Canada, that its distribution appears to be expanding, and that outbreaks in new areas have occurred during droughts. VetSpecialists.com (2020) lists confirmed cases in Utah, Colorado, Wyoming, Kentucky, Oregon, Idaho, Washington and Florida, as well as Alberta.

The numbers back that up. A 2014 study of 2,237 positive cultures from laboratories in 23 states found that 54% came from 2011 and 2012 alone, against 46% over the eight years before, including horses in states where the disease was not considered endemic; only 15 of the 44 invited labs took part, so it is a sample rather than a full count. In 2012, during a severe drought, Dr. Keith Chaffin of Texas A&M said the clinic was seeing three or four cases a day. Kansas had an unprecedented outbreak in the fall of 2012, and a study of it found that higher soil moisture was protective while land surface temperatures of 35°C (95°F) or more raised the risk. In Colorado, the 2002 release counted 76 confirmed cases that fall, against 12 the year before.

When in the year depends on whom you ask:

Read together: expect it from late summer into winter, and in the dry season of your own region. The AAEP adds that the number of cases fluctuates considerably from year to year, presumably because of herd immunity, rainfall and temperature.

Can pigeon fever kill a horse?

Pigeon fever rarely kills a horse with external abscesses, with a case fatality of 0.8%, but the internal form is fatal in 30 to 40% of cases according to the AAEP, and infections in the abdomen are fatal if left untreated. The AAEP gives 0.8% for external abscesses, 30 to 40% for internal abscesses, and a considerably higher rate than external for ulcerative lymphangitis, without a figure. The 538 UC Davis cases from 1982 to 1993 gave an overall case fatality of 3.9%, 0.8% for external and 40.5% for internal abscesses. UC Davis puts it plainly: "Infections within the abdominal cavity are fatal if left untreated."

The outlook for the internal form is not as grim as the older figure suggests. In a later series of 30 horses with internal infection, antibiotic treatment gave an overall survival rate of 71%. Brazos Valley Equine Hospitals points out that the 40% figure comes from an older study of advanced cases, and that in their experience most cases respond to treatment, at a large cost in money and time. UC Davis describes the prognosis for internal infection as guarded to good, while the University of Florida calls it generally poor. What they share is that early recognition matters, which is why weight loss or a fever in the weeks after an external abscess is worth a call.

Can a horse get pigeon fever twice?

A horse can get pigeon fever more than once, but it is uncommon: in the largest case series, 91.4% of horses had a single episode with no recurrence in later years. That figure covers 492 of 538 horses, and UC Davis says horses that recover are often less likely to be affected again. The exception is ulcerative lymphangitis: UC Davis warns that without early, aggressive treatment it can leave some residual lymphatic damage that makes the leg prone to swelling and recurrence.

Can humans get pigeon fever?

Humans catching pigeon fever from horses is rare: the AAEP's 2026 guideline knows of a single case of pneumonia after exposure to an infected horse, the University of Florida says no infection of people by horses has been reported, and both advise gloves when you treat an infected horse. The AAEP mentions rare human infections from contact with infected sheep, particularly during shearing, plus that one pneumonia case, presumably from inhaling the bacteria, and says gloves and a mask may be considered when treating infected horses. The University of Florida writes: "Although no reports exist of humans being infected by horses, humans have reportedly been infected by the sheep strain of the disease." Colorado State University went further in 2002 and said the disease is not transmissible to humans, while warning that people can carry it to another animal on shoes, clothing, hands or barn tools. Whichever source you follow, the habits are the same: gloves while flushing, and a thorough hand wash afterward.

Can cattle, sheep, goats or dogs get pigeon fever?

Cattle can be infected by both the horse strain and the sheep and goat strain of Corynebacterium pseudotuberculosis, while sheep and goats get their own strain, known in them as caseous lymphadenitis, which does not naturally pass to horses. The AAEP says natural cross-species transmission does not occur between small ruminants and horses, but cattle can be infected by either biotype, and lists equids, sheep, goats, cattle, buffalo and camelids among its hosts. Brazos Valley Equine Hospitals calls transmission between cattle and horses theoretically possible but not confirmed, and the University of Florida notes that in goats the disease is known as caseous lymphadenitis. We found no veterinary source on pigeon fever in dogs, so we can't tell you either way.