November 18, 2010
Pigeon fever is contagious but rarely deadly.
By Andrea Caudill in The American Quarter Horse Journal
Pigeon fever typically presents as external abscesses around the chest and midline, giving the horse a “pigeon chest” appearance.
When Mary Townsend of Amarillo headed out to feed horses one late September evening, she noticed something unusual about her horse, Taylormaid Legend. The 10-year-old gelding had severe swelling around his chest and the right side of his neck. She immediately pulled “Legend” out of his pasture and called her veterinarian.
Legend had a slight fever and was limping on his right foreleg. He was diagnosed with pigeon fever and was quarantined to prevent spreading the infection to other horses. Ultrasound located the deep abscesses in the right side of the gelding’s chest, explaining a mysterious and intermittent lameness he suffered in the months prior to the abscess emerging. During the next few weeks, he was treated to draw the abscess to the surface.
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When the abscess came to a point on Legend’s chest, Mary’s veterinarian lanced and drained it. A few weeks later, Legend was healthy and sound and returned to regular work. The other horses on the property, despite sharing a pasture prior to Legend showing symptoms, never developed the disease.
Previously confined to the arid, western United States, pigeon fever is rapidly spreading across the country. When it strikes, although rarely fatal, it can take weeks or months for an affected horse to heal. The American Quarter Horse Foundation is funding an ongoing research project to learn more about the disease. Conducted by Occidental College in Los Angeles, the ultimate goal of pigeon fever research is to develop a preventative vaccine. The research has been headed by Roberta Pollock, a professor at Occidental College who uses molecular and cell biology to study the immune system; and Drs. Sharon Spier and Nicola Pusterla, veterinarians and researchers at the University of California at Davis.
“Pigeon fever has been known to horsemen for decades,” says Dr. Spier, who has spent many decades researching the disease. “It was first recognized in California in the San Francisco Bay area in 1915. But in the last 10 years, we have been experiencing more outbreaks. The disease is increasing in numbers of horses affected and is spreading from the West to the East.”
The disease has, so far, been reported as far north as Washington and as far east as Kentucky.
What Is It?
The bacterial infection by corynebacterium pseudotuberculosis goes by several different monikers in the horse world. Its most common name is pigeon fever or pigeon breast fever. It is also known as dryland distemper, breastbone fever, false strangles or dryland strangles.
The disease is not related to the bird that shares its nickname; instead, it gets it name from the symptomatic abscesses and swelling that develop along the horse’s chest and midline, giving the horse a puffed-chest appearance that resembles a pigeon.
The disease typically occurs in warmer, more arid places, such as the western United States and most commonly appears in the summer and fall months. The bacteria live in the soil, and hot, dry weather tends to accelerate bacterial growth. Horses are usually infected with the bacteria through fly bites, open wounds or when the bacteria come in contact with mucous membranes.
The classic first symptom of pigeon fever is swelling around the chest or abdomen as abscesses develop. The horse might develop a fever but typically continues eating and acting normally. An affected horse might become sore or lame after developing swelling or abscesses. A definitive diagnosis of the disease can be made via bacterial culture.
The abscesses typically form around the chest, midline along the belly and groin area but can develop anywhere.
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“This disease doesn’t just occur in the classic ‘pigeon breast’ or pectoral abscesses,” Dr. Spier explains. “You can see abscesses almost anywhere on the body during an outbreak. Some horses will develop very deep abscesses in the upper leg under the triceps muscle, which causes severe lameness. A veterinarian needs to drain these surgically – you can’t just wait for them to mature and drain on their own or the horse will remain very lame for weeks to months. Horses might have internal infection, involving the liver, kidney, lungs or spleen – and we’ve had rare cases of bone or joint infection, due to Corynebacterium pseudotuberculosis.”
Internal abscesses occur in approximately 8 percent of cases and are a more serious complication, requiring expensive diagnostics and antibiotic treatment.
Less frequently, infected horses can develop ulcerative lymphangitis, which is an infection of the lymphatic vessels in the lower leg. It causes ulceration of the skin, limb swelling, pain and lameness and can be difficult to cure, usually requiring months of treatment.
Horses with external abscesses have a low mortality rate of less than 1 percent, while those with internal abscesses rocket to a mortality rate of 30 or 40 percent.
The disease is unrelated to the more well-known bacterial infection referred to as strangles, an infection by Streptococcus equi, which typically infects the horse’s lymph nodes in its jawbone, swelling and potentially causing the horse’s breathing to be affected. In rare cases, strangles can also take the form of “bastard strangles” or internal infections and abscessing.
Click here to read Part 2.
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