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Alberta horse owners struggle with disease

Horse owners and veterinarians in Alberta are on alert after an outbreak of Potomac horse fever, which causes death in up to 30 percent of cases. The disease causes diarrhea, depression and intestinal problems and can occur after horses ingest snails, slugs and insects in their food. (See link for article)



Equine monocytic ehrlichiosis, or Equine neorickettsiosis is commonly known as Potomac horse fever (PHF).  

While PHF occurs typically in late spring and early fall in temperate areas, it is spreading and has been reported in over 40 states, Canada, and Europe.  It tends to occur near bodies of water:

The agent behind it is Neorickettsia risticii, found in flukes (flatworms) that develop through one stage in aquatic snails. Horses drinking from streams swallow them but they are also picked up by aquatic insects – the second stage (caddisflies, mayflies, damselflies, dragonflies) that might transmit it to horse as they graze.

The second link in the cycle are in bats and barn swallows (N. risticci has been found in their intestinal tracts) that feed on the aquatic insects. It is unknown if bat and barn swallow fecal material infects horses as well.

Potomac horse fever can be mild to life-threatening affecting intestinal cells and monocytes. It causes fever, poor appetite, depression, and diarrhea. Possible lameness with limb edema may occur as well as elevated heart rate, dark mucus membranes, sweating, and signs of mild colic.

PHF is confirmed by lab identification in blood or manure samples. It may be confused with salmonella and the horse should be considered contagious to both animals and humans until fecal salmonella tests are negative.

Treatment is antibiotics, particularly oxytetracycline, IV fluids, electrolyte therapy, and non-steroidal anti-inflammatory drugs to alleviate pain.

There was a 2005 outbreak in Minnesota. They theorize mayflies from the Missippi River were attracted to bright lights outside barns which blew into the show grounds and infected at least six horses. Other cases occured on area farms at the same time that had lights by horse barns.

Turn off lights when aquatic insects are hatching in summer.

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According to this article, PHF is NOT considered contagious or is passed between horses with casual contact. If more than one horse is affected it is believed that they all consumed infected insects:

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