Page 54 - July 2017

Fly control and proper wound care are some of the best ways to help prevent spread of this disease.
McGee Medical and Critical Center at Hagyard Equine Medical Institute Director Nathan Slovis, DVM, Diplomate ACVIM
priate treatment. Pigeon fever is fairly common in
California, but still sporadic. The past 15 years have seen
a large number of cases in certain areas of Kern County, California, for instance, but not every year. It tends to go in cycles and the hot spots are dif- ferent every year.
In 2002 and 2003, there
were outbreaks in Kentucky, Wyoming, Utah, and Colorado—
Abscesses are localized infections that are gen- erally just a nuisance to treat, and typically you can get rid of the infection by lanc-
ing, draining, and flushing. There are some nasty ones, however, that require more care and concern, especially abscesses associated with an infection
in horses called pigeon fever. Other names for this disease include pigeon breast, dryland distemper, and Colorado strangles.
This bacterial infection is caused by a gram-posi- tive bacterium, Corynebacterium pseudotuberculosis, found worldwide. Bacteria that tests positive in the Gram stain test is considered gram-positive due to their cell wall taking up the crystal violet stain used in the test, the color of which can be seen under a microscope.
Once this bacteria becomes established by entering the body through a fly bite or any break in the skin, the infection causes deep intramuscular abscesses in horses and sometimes internal abscesses in various organs. On rare occasion, it can cause an infection in the limbs, called ulcerative lymphangitis.
According to Sharon J. Spier, DVM, PhD, Diplomate ACVIM (Professor, Department of Medicine and Epidemiology, UC Davis School of Veterinary Medicine), this disease was first reported in horses in San Mateo County of California in 1915. Since then, it has been recognized in many states and the incidence of this disease seems to be increasing.
Nathan Slovis, DVM, Diplomate ACVIM, Director of the McGee Medical and Critical Center at Hagyard Equine Medical Institute in Lexington, Kentucky, says their hospital began seeing an increased number of cases about 15 years ago. “We’ve always had it here, but by increased incidence we sometimes see several cases on the same farm. We have nowhere near the numbers of cases seen on
the West Coast, but this disease has been here in Kentucky a long time,” says Slovis.
“In recent years, our hospital has only three or four cases a year diagnosed by one of our veterinari- ans. But for a few years, we had a big increase in cases being diagnosed at our laboratory at Hagyard. Some were horses that were shipped here from other parts of the country, but some of them had never left their own farm. We don’t know if the increased incidence was because more animals are being brought into this
A Disease Occurring More Frequently In Recent Years
by Heather Smith Thomas
area for sales, racing, etc., or if the weather was just perfect for it during those years,” he says.
Horse owners need to be aware of this disease. Since flies can spread the disease, they could play
a factor, and weather patterns may also play a role. “People are traveling farther with horses. Some horses are flown from coast to coast and there’s intermin- gling of horses at shows, sales, races, etc. Even though pigeon fever has not proven to be infectious horse to horse, flies can be a source of transmission if a horse has an open wound or a break in the skin,” Slovis says.
Strangles can also cause abscesses, so proper diag- nosis is very important in order to initiate the appro-
Pigeon Fever
Heather Smith Thomas
states where the disease had only been rarely encoun- tered. In 2005 and 2007, outbreaks were reported in Oregon and Idaho. In 2012, more than 60 cases were reported in the northwestern panhandle of Florida. “It is now recognized in Mexico and western Canada, as well as all across the U.S., and it also appears in all seasons of the year,” says Spier. “We used to think it mainly showed up during summer and fall with fly season, but we are now seeing it year round,” she says. There is speculation that environ- mental and climatic conditions may lead to chang- ing insect populations, or there may be a variety of conditions that promote survival of the bacteria in the soil.
52 SPEEDHORSE, July 2017
equine health