Elisha Dickinson, D.V.M.

Having most likely just worn your thickest insulated coveralls to feed the horses only to spend your time kicking ice out the water buckets, it is hard to imagine that Spring is in fact just around the corner.  Along with the warm weather, however, comes the resposibility of ensuring your horse is protected against certain seasonal diseases, including Potomac Horse Fever.

Potomac Horse Fever is caused by the rickettsial organism, Neorickettsia risticii.  Horses get infected by ingesting aquatic insects and arthropods, in particular, snails.  Horses get exposed to infected snails by grazing near wet, moist environments during the warmer months; primarliy June to September in our region.  Once a horse gets infected, it cannot directly spread the disease to other horses.

Symptoms of Potomac Horse Fever vary greatly and can by highly non-specific.  Most commonly associated with the disease is profuse, water diarrhea.  Classically, a high fever (up to 107°F) will precede the onset of diarrhea.  Other signs, which may occur with or without diarrhea, include depression, inappetance, edema (swelling) of the limbs and neck, colic and laminitis (founder).  Pregnant mares may abort or produce weak, maladjusted foals.  Some horses will get infected with the organism, but will fail to produce any clinical signs at all.

For veterinarins, it can be challenging to diagnose this disease.  Blood samples are collected and submitted for various tests, but often the results are inconclusive.  It is not uncommon to begin treatment and asses the response to treatment to help confirm a diagnosis.

Treatment of Potomac Horse Fever involves administration of tetracycline antibiotics and supportive care.  Many horses require intravenous fluids, anti-inflammatories, and probiotics.  In cases of founder, aggressive treatment is necessary.  Often horses cannot be treated at the farm, and must be sent to a 24-hour referral center.  This disease can result in the death of the horse and treatment should be started early and aggressively.

As you can imagine, the emotional and financial impacts of this disease can be quite devastating.  It is our recommendation that ll horsese be vaccinated annually, in the early Spring.  For horses traveling to known problematic areas, it is advisable to have a booster in mid-summer.  The efficacy of Potomac Horse Fever vaccines has been questioned in the past.  The vaccine does not guarantee your horse will not get infected with Neorickettsia risticii, but it will usually reduce the severity of the disease if your horse does indeed get infected.  Most vaccines are safe for use in broodmares and can be given as early as 3 months of age.  Please take the time to discuss concerns with your veterinarian at the time of vaccination.