In Treasure State, you never know what to expect in terms of our climate. The fall season began with unusually warm temperatures that quickly turned to freezing temperatures. During this time there was another unexpected thing; A disease that afflicted horses in north-central Montana.
The disease is called “pigeon fever.”
Jody Jackson of Carter between Great Falls and Fort Benton was out feeding her horses and noticed something was wrong with one of them.
“A month or six weeks ago I had a mare who didn’t show up for morning chores so I investigated why she wasn’t showing up. She had a big, football-sized lump on her chest, and I was like, ‘Wow, she got kicked.’ Then I remember my friend telling me about pigeon fever and the abscesses the night before so I loaded the mare and took her to our vet and it was definitely pigeon fever.
Pigeon fever is found to be most prevalent in the Southwestern United States, such as Texas, New Mexico, and is even encroaching on parts of California.
The bacterial infection called Corynebacterium pseudotuberculosis, which typically results in the formation of large abscesses in the horse’s chest area or under the abdomen.
The swelling on the horse’s chest resembles a pigeon’s breast, hence the disease’s name.
Clinical signs include:
- External abscesses – Usually in the chest or abdomen, but can also occur on the mammary gland, groin, foreskin, triceps, limbs, and head
- Internal abscesses – most commonly found in the liver, spleen, kidneys and lungs
- Ulcerative lymphangitis (infection of the limbs along the lymphatic system) – This is usually rare but is described as a painful infection of the lymphatic vessels, most commonly affecting the hind legs, causing swelling and weeping sores
Julia Williams is a Certified Vet Tech with Associated Vet Services. She said they’ve seen more than 50 cases in the past month.
Williams said: “In our clinic we saw about 60 cases and diagnosed them as pigeon fever. We also called several people with signs of it, but we hadn’t seen the horses. We’ve seen a lot of cases, and I’m sure there are more that we haven’t made it through, so they’re pretty strict .
Williams noted that the disease is usually transmitted. “The bacteria are in the soil and are transmitted from flies to horses. So if they have cuts, scratches or something like that, the flies get on that wound and that’s how it’s transmitted. It’s also transmitted by pus from the abscesses, so it’s one of the most important things to be aware of to keep that under control, and fly control.”
While antibiotics may seem like an effective treatment, for external cases it is known that it is best to leave the horse in isolation and let the infection heal on its own.
Williams noted, “We’ve found that antibiotics don’t help abscesses, especially if they haven’t opened. It actually slows down the process, so we don’t put these horses on antibiotics unless it’s an internal case. what dr Jack Newman here does He scans the area with ultrasound and see if there is a pocket he can open and empty. They usually go home and are fine. We usually keep them under control and separate from other horses.”
Jackson added that the antibiotics did nothing for the horses.
“I had a vet put a drainage tube in and she drained it for three or four days. I asked if I could give her antibiotics but there are no antibiotics that work against it. I thought ‘maybe I should vaccinate the rest of the horses’, but there is no vaccination either. The hardest part is doing nothing, but that’s what I had to do… If the horse isn’t in a lot of pain, do nothing but it to isolate.”
dr Trace Nydam of Indian Hammer Veterinary Services in Vaughn has experience with pigeon fever in other states, but this is the first year he’s seen a case like this in Montana.
Nydam said: “It’s worrying to a degree. You’ll need to do some treatments on your horse, but most of the time it’s not life-threatening, although it can be… There’s some horse-to-horse spread, but it’s mostly caused by insect vectors.”
He added: “Most of the abscesses we see are external. These generally recover very quickly. We can have internal cases and these don’t have a much less positive outcome… Generally we heal them 100 percent. When we get into the internal abscesses, that can be a bit more difficult, but antibiotics can treat the internal cases. The most important thing when we’re looking at an outbreak is that the boxes are clean.
The prognosis for horses with external abscesses is generally good; most recover within a few weeks. However, for internal infections, the prognosis can range from cautious to good, but early detection and appropriate antibiotic therapy offer the best chance of a full recovery.
Ways to prevent pigeon fever include:
- Fly control with feed and/or fly repellent, especially in horses with open wounds or draining abscesses. Since flies can cause skin infections on the chest or girth area of some sensitive horses (e.g. midline dermatitis), fly control with fly rugs, spray or ointments is important.
- Regular manure management and sanitation programs should also be put in place to control insect populations.
- Quarantine and monitor new horses for signs of infection before introducing them into the resident population. Isolate horses known to be infected when possible and practicable, wash/disinfect hands after handling infected horses and use gloves and protective outerwear. Avoid using the same items (buckets, pitchforks, and other materials) on infected horses and the general horse population. Thoroughly clean and disinfect areas that may be contaminated with pus from draining abscesses. Check stalls, paddocks and fields for sharp edges or objects that could cause sores on your horse’s skin that could later become infected.
No further precautions are needed once infected horses have healed and abscesses are no longer draining.
There is currently no vaccine against pigeon plague. Horses that recover from the disease are often less likely to be affected again in the future.