13 Kentucky Potomac Horse Fever Cases

A few cases of Potomac horse fever (PHF) occur each fall in Kentucky. This year they were detected earlier than normal. Nathan Slovis, DVM, MS, Dipl. ACVIM, of Hagyard Equine Medical Institute in Lexington, Ky., said the early occurrence probably was due to the dry weather in July and August.

"It's nothing new or crazy," said Slovis. "We usually see cases this time of year (mid-August). We did, however, see cases last month (July), which is earlier than usual."

Neil M. Williams, DVM, PhD, of the University of Kentucky's Lexington Disease Diagnostic Center, who did his doctoral studies on PHF, said that at the diagnostic laboratory in Central Kentucky, "We usually have a few cases of PHF each year. For the most part, the number of cases has really fallen off dramatically since the 1980s. This year there have been 13 positive PHF cases, one in June, 10 in July, and two so far in August. The fact that it is not very commonly seen, and that the signs can vary greatly from case to case, makes it a diagnostic challenge."

Typically, the first signs of PHF are lethargy, fever, loss of appetite, and often diarrhea. About half of the sick animals were vaccinated for PHF. Slovis said, "The efficacy of the vaccine is still in question."

Owners and managers should watch out for high fevers (104-105º Fahrenheit) of unknown origin in adult horses. "Look for lethargy and inappetence," he added. "They don't necessarily have diarrhea, about 50% didn't have it with the fever."

His advice: "If you can't find cause (for the fever), your veterinarian might want to use tetracycline and test for PHF until you know what is causing the problems."

For more information see www.TheHorse.com/emag.aspx?id=7387.

According to data from the Lucy Whittier
Core Molecular Diagnostic Laboratory
at the University of California, Davis:


Number of states with confirmed cases of
PHF in 2006 (California, Iowa, Kentucky,
Missouri, New York, and Oregon).


Percentage of suspect samples submitted in
the summer and fall that are PHF-positive.


Number of submissions the laboratory
receives annually for PHF testing.


When the lab started detecting positives
in 2006.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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