Potomac Horse Fever Alert

Horse owners in the mid Atlantic region should be aware of the increased potential for Potomac horse fever (PHF). The heavy rains and high heat and humidity make insects thrive, which increases the chances of your horse becoming infected. ?Threats include areas of standing water, ponds, streams.

PHF is spread by the Neorickettsia risticii, basically a fresh water fluke that infects snails and insects. Horses contract PHF by ingesting water or feed that was contaminated by a snail or insect or even by ingesting a the creatures themselves.

Horses at pasture are at greatest risk. Although it’s not contagious and it is curable when caught early, but left undetected, it can be fatal. Fatality rates are between 5 to 30+%. Eventual euthanasia because of laminitis, a frequent complication, accounts for some of the deaths. Pregnant mares may abort.

Horses develop a fever soon after they’re infected, but symptoms otherwise usually take about two weeks to appear. At that time, the horse may again have a fever. The blood may show elevated monocytes and depressed numbers of lymphocytes initially. Once damage to the colon is severe, clotting tests may be abnormal and white counts may drop.

Symptoms usually include:

  • Fever
  • Loss of apptite
  • Diarrhea
  • Complications can include laminitis/founder.

Treatment involves:

  • Antiobiotics
  • Fluids
  • Electrolytes
  • Fever management

There is a PHF vaccine, but it isn’t highly effective at preventing the disease. ?It is believed by some experts that it may reduce the severity of the illness. Instead :

  • Clean water bucks and troughs thoroughly
  • Keep barn lights off to discourage insects
  • Restrict access to streams, ponds, standing water in pastures
  • Monitor the horse’s body temperature and contact your veterinarian if you detect a fever.

For more information visit: www.aaep.org/Potomac_fever.htm