By Dr. Tom Lenz, special contributorThe American Quarter Horse JournalJune 14, 2013
An abscess on the horse's chest is the result of fever. (Journal photo) BELOW: Learn how to take equine vital signs – pulse, respiration and temperature – and find out the acceptable ranges of each.
The incidence of pigeon fever, also known as dryland strangles and dryland distemper, has been on the increase in the last few years. The disease is caused by Corynebacterium pseudotuberculosis, a bacterium that causes abscesses in affected horses.
The disease is called pigeon fever not because it’s spread by pigeons, but because the abscesses caused by the bacteria frequently localize in the pectoral (chest) muscles and ventral abdomen of the horse giving the horse’s chest a pigeon-breasted appearance. Pigeon fever was first diagnosed in 1915 in San Mateo, California, but is now routinely found throughout the arid regions of the West and Midwest.
Most outbreaks occur during periods of high climatic temperatures and dry conditions, and it appears the recent drought conditions across the United States have aided the disease in moving as far east as Kentucky and Florida.
C. pseudotuberculosis survives in the soil and is spread to horses primarily by flies or through open wounds. It occurs most commonly in the fall during periods of dry weather when horses and insects congregate.
The first signs of the disease are usually swelling of the chest and lower abdomen. Horses may run a slight fever, greater than 101.5 degrees F, but usually act normally and continue to eat.
Other areas of the horse’s body where abscesses can develop include the mammary gland, sheath or legs, which are areas where flies often feed or congregate. Horses with multiple abscesses often go off feed, become lethargic and run a fever. The swellings are often deep in the muscle and might take weeks to months to mature into an abscess that can be lanced and drained.
About 3 percent of horses develop internal abscesses that are much more serious, as they often develop in the horse’s chest or abdomen where they can interfere with internal organs. In rare occasions, the infection can spread to a horse’s legs, causing a syndrome called ulcerative lymphangitis, which is difficult to treat. Your veterinarian can determine whether your horse is suffering from pigeon fever through bacterial cultures, clinical signs, blood work and by ultrasounding the swellings.
The American Association of Equine Practitioners has released new pigeon fever control guidelines. Download the disease control guidelines now.
Treatment of pigeon fever consists primarily of applying warm compresses or ointments, such as Ichthammol, that aid in bringing the abscesses to a head. Once that has occurred, the abscess can be lanced and flushed daily with a dilute Betadine or Nolvasan solution. Antibiotics should not be administered until the abscesses have been lanced and drained, as they will delay maturation of the developing abscesses and might facilitate the development of internal abscesses.
In most cases where the abscess has been lanced and flushed and the horse appears healthy with a normal temperature and appetite, antibiotics might not be needed. If the abscesses are painful, nonsteroidal anti-inflammatory drugs might be indicated. Complete recovery can take several weeks.
Since flies are a major vector of the disease, apply insect repellent to affected horses and isolate them whenever possible.
Of course, like all diseases, prevention is key. Although there are no vaccines to prevent this disease, there are a number of preventive measures. Good sanitation is important, so stalls and paddocks should be kept free of manure. Fly control is important, as flies are the main vector of pigeon fever, so apply insect repellents daily, and use predator wasps or provide feed-through fly-control products.
Humans can spread the bacteria on their shoes, hands, tack, etc., so make sure you maintain good hygiene and consider disinfecting the area and tack with diluted disinfectants or chlorine. To find out whether pigeon fever is a problem in your part of the country, talk to your local veterinarian. Be sure to consult the American Association of Equine Practitioners new pigeon fever control guidelines.
Thomas R. Lenz, DVM, M.S., Diplomate of the American College of Theriogenologists, is a trustee of the American Horse Council, chairman of AQHA’s research committee and is past president of the American Association of Equine Practitioners. Dr. Lenz's Horse Health column can be found in every issue of The American Quarter Horse Journal.
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