It’s called “pigeon fever” in horses, and it’s caused by the organism Corynebacterium pseudotuberculosis. It doesn’t have anything to do with either pigeons or tuberculosis, and ordinarily it’s not seen in this region of the country. But over the last couple of years, it’s come on strong.
Dr. Philip Johnson, a professor of equine medicine and surgery with the University of Missouri College of Veterinary Medicine, blames the weather. “The organism is more likely to ‘thrive’ such that it can cause animal infections in dry arid conditions,” Johnson told Ozarks Farm & Neighbor. The disease is usually seen in typically dry regions of the country like California, and Johnson said climate change has gotten the blame for the fact that the disease is becoming more common east of the Pacific.
The bacterium is soil-borne; horses contract infections through wounds, and the reason it’s more prevalent in the arid West is it’s carried in dust. Johnson said it can live for at least eight months in the soil. “It is regarded as an ’emergent’ disease – we have been warning our DVM students that they should anticipate more cases in the mid-west,” he said.
Dr. Jesse Clement of Lake Hamilton Equine Associates in Hot Springs, Ark., said it’s called “pigeon fever” because the horse typically gets a swelling in the middle of its chest. “It can be the size of a volleyball, and it gives the impression of a pigeon, with the prominent breast,” he told OFN. “The abscess is deep in the chest under the muscle and it works its way out, and then it will rupture and drain.”
Clement said up until 2011, he hadn’t seen any cases in 20 years; in the last two years, there’ve been more than 100. The abscesses can occur elsewhere than in the horse’s chest. “I’ve seen it break out in the hips, the back, the side of the head and a lot of places,” he said, “and especially in old horses that do not have an immune system that will contain it into a single abscess…. I’ve seen it in a foal, and it recurred a year later because his immune system wasn’t working like it would when he was a 2-year-old.” The concern in susceptible animals is that the abscesses will grow in the lungs or other internal organs then, Clement recommends a veterinarian’s care. But in most cases, the disease simply needs to run its course. “It has taken sometimes 6-8 weeks for these abscesses to become mature to where it can either be drained, or Nature takes care of it on its own,” he said. “It has to work its way all the way out through the muscle layers, through the skin, and then the horse rubs against something and it ruptures on its own.” In most cases, antibiotics are actually a hindrance because they retard the development of the abscess. Many times, he said, the best treatment is letting the horse run in the pasture, rather than keeping it cooped up in a stall.
Johnson recommended that owners quarantine any horses they believe might be infected, as draining abscesses can spread the disease to healthy horses. He said horse owners can also help prevent the disease by minimizing flies to the extent that is practical, and by minimizing human handling of affected horses. “This infection has been a big problem across our state this fall,” he said. “We do not normally see many cases at all… I, and others, have been surprised by this year’s incidence.”
