These Park County horses owned by Jennifer Fernandez contracted Potomac horse fever
in summer 2020. The foal survived, but the mare did not. UW Extension recently released
a bulletin publication titled “Potomac Horse Fever Is in Wyoming and Adjacent States”
that describes the disease, how it infects horses and what horse owners can do to
prevent or treat the disease. (Jennifer Fernandez Photo)
Scott Schell owns horses and has lived in Wyoming for 59 years. Until he met Jennifer
Fernandez, a horse owner in Cody, Schell had never heard of Potomac horse fever (PHF)
in Wyoming.
After Fernandez lost a mare to the disease, she wanted to raise awareness among other
horse owners to the hazard PHF poses. Schell, an entomology specialist in the University
of Wyoming College of Agriculture and Natural Resources’ Department of Ecosystem Science and Management, agreed with her and started working on a UW Extension education effort to do it.
UW Extension recently released an awareness poster titled “Potomac Horse Fever Is
in Wyoming and Adjacent States” that describes the disease, how it infects horses
and what horse owners can do to prevent or treat the disease.
“I think that, in the PHF-endemic region of the state, people who have had their horses
get the disease or had a friend’s horse get it are very aware,” Schell says. “Additionally,
many veterinarians in those known PHF areas recommend vaccination for the disease.
However, I think many people from other areas of the state aren’t aware of PHF.”
PHF is a warm-season disease of equines. Horses, mules and donkeys contract PHF after
accidentally eating adult aquatic insects, such as mayflies and caddisflies, infected
with a bacterium. The disease begins with mild symptoms, usually one to three weeks
after ingestion of the infected insects.
According to the poster, symptoms horse owners should watch for are depression, lack
of appetite, watery diarrhea -- mild colic, with watery but decreased gut sounds --
and laminitis symptoms on all hooves. If a horse is depressed, owners should check
the animal for a fever ranging from 102 to 107 degrees.
As PHF progresses, more severe symptoms such as acute laminitis can occur, and the
disease can cause up to 30 percent mortality. Mares that are 100 to 160 days pregnant
when infected with PHF may abort at 190 to 250 days in pregnancy after appearing to
recover from the disease.
“It is part of good horse management to observe what is normal for your animals and
then to watch for the abnormal every time you are around them,” Schell says.
Because PHF is a bacterium, it is treatable with the correct antibiotics, according
to the poster. If a PHF infection in a horse is recognized, diagnosed and treated
quickly, an animal’s prognosis is greatly improved.
While he admits he is no veterinarian, Schell says, according to the literature he
has read, initiating the intravenous antibiotic treatments before a horse exhibits
the extreme diarrhea symptoms of the disease will reduce the probability of a bad
outcome.
Besides vaccinations, a good way to protect equines from becoming infected is to turn
off barn lights during summer nights when aquatic insects are flying. This action
can help prevent the insects from ending up in water troughs and food mangers, where
they could be consumed by horses.
Schell has a number of ideas as to where to release the poster.
“I think any place the horse-owning public may be visiting or spending time waiting
at will be a good place for the poster -- so, veterinarian offices, feed stores, boarding
stables, extension offices, etc.,” he says. “I plan to get some printed; get them
to the 4-H horse programs around the state; and have the members ask to post the posters
in appropriate places around the state. I think the poster needs to go up in places
where it is a known risk for horses; where there are horse owners new to an endemic
area; or just visiting there to know what the symptoms are to watch for.”
Schell adds that horse owners from parts of Wyoming where PHF may not be present need
to be aware of the symptoms in case the disease is spreading to other river basins.
In 2002, PHF was diagnosed in the Big Horn Basin. Before then, the disease was only
known to be present in the far southwestern part of the state.
“Hopefully, it doesn’t spread everywhere,” he says. “But we need to determine PHF’s
current extent and monitor for expansion.”
PHF is currently known to occur in western Wyoming and adjacent areas of Idaho, Utah
and Montana. PHF also occurs in parts of Nebraska and South Dakota.
Schell hopes to develop a project in cooperation with some researchers to look at
both the prevalence rate of PHF in the state and where the disease is present or absent.
Information on this is important for improving PHF management and providing guidance
to both veterinarians and horse owners.
“For example, if we randomly sample horses 5 years and older that have lived all of
their lives in a PHF-endemic river valley and find that 95 percent have been previously
infected, it will indicate that a new horse from a PHF-free area brought there will
probably contract PHF, and vaccination to reduce the severity of the disease is a
very good idea,” Schell says. “My hope is to involve 4-H members with their horses
and make it a ‘citizen science’ project.”
The poster can be found at www.wyoextension.org/publications/Search_Details.php?pubid=2091&pub=B-1375.
For more information about the PHF awareness poster, call Schell at (307) 399-9344
or email sschell@uwyo.edu.
