Pigeon Fever Prevalence Evaluated

Pigeon Fever Prevalence Evaluated

Photo: Sharon Spier, DVM, PhD, Dipl. ACVIM

Researchers have confirmed what many veterinarians have feared in recent years: The number of cases of Cornyebacterium pseudotuberculosis infection—more commonly known as “pigeon fever”—in U.S. horses has risen dramatically over the past 10 years, and the affliction now affects horses in most areas of the country.

Pigeon fever is an equine disease that can cause external or internal abscesses and/or an infection or ulcerative lymphangitis in the limbs. While not often deadly, it can pass from horse to horse and generally requires veterinary treatment.

University of California, Davis, (UC Davis) researchers worked with 15 laboratories across the United States that provided data on 2,237 culture-positive samples from horses in 23 states from 2003 through 2012.

They determined that the number of pigeon fever cases rose dramatically in 2011 and 2012, with cases from those years comprising approximately one half of the total reported. And, although there were no significant associations between the number of occurrences and breed or sex, the clinical signs observed in infected animals differed significantly by both sex and geographic area.

Internal abscesses, which only developed in 2% of the total cases examined, were most frequently seen in mares, with the majority of such cases reported in California. The researchers suggested that this could be due to the state’s veterinarians' familiarity with pigeon fever's signs. Also, although the researchers observed ulcerative lymphangitis in only 1% of cases, all but one were reported in Texas. This, they said, could be due to a unique population of organisms spreading the disease in that state.

Study author Sharon Spier, DVM, PhD, Dipl. ACVIM, professor of medicine and epidemiology at the UC Davis School of Veterinary Medicine, noted that pigeon fever has spread to every region of the country—“east to west and north to south.” Traditionally a disease found in the western United States, veterinarian have reported pigeon fever cases in Louisiana, Michigan, North Carolina, South Carolina, South Dakota, Vermont, and Wisconsin, all of which had no previous record of the infection.

The highest proportion of cases occurred during the fall and early winter months. However, there were seasonal differences between years, with high numbers of cases in Texas seen during the late spring and summer months during 2011 and 2012.

“While there was some seasonality to the numbers of cases, the disease can occur year-round,” said Spier.

Although further research is needed to confirm their hypothesis, the study authors postulate that changing environmental factors might be playing a role in pigeon fever's spread. For instance, Spier said, Texas—which was home to 70% of the cases over the 10 years examined in the study--suffered extreme drought during that time frame. These environmental changes likely had a significant effect on the lifecycles of organisms that transmit the infection, such as fly populations or other unknown factors, the team said. The authors also cite the work of other researchers who have suggested that periods of drought might lead to more robust breeding and increased survival of the fly populations thought to transmit the infection.

The study, “Frequency of Corynebacterium pseudotuberculosis infection in horses across the United States during a 10-year period,” was published in the Journal of the American Veterinary Medical Association. http://www.ncbi.nlm.nih.gov/pubmed/25029310

About the Author

Liz Walsh

Liz Walsh has covered the equine industry as a freelance writer for the past five years. Walsh graduated from Columbia University in May 2014 with a degree in anthropology. She and her four horses live on a small farm just outside of Manhattan.

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