Virginia Confirms a Potomac Horse Fever Case

The case was reported in Fairfax County, Virginia, Aug. 8, 2022.

Virginia confirmed a Potomac horse fever case. It occurred in Fairfax County, Virginia, identified in red on the map of the state.

Virginia confirmed a Potomac horse fever case on Aug. 8. An attending veterinarian reported a horse in Fairfax County, Virginia, positive for Potomac horse fever. The boarding facility where the horse resides is not under quarantine, and an unknown number of horses might also be at risk.

To read the Equine Disease Communication Center alert about this case and others, click here.

EDCC Health Watch is an Equine Network marketing program. It utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization. It is supported by industry donations in order to provide open access to infectious disease information.

About Potomac Horse Fever

Potomac horse fever is caused by Neorickettsia risticii. This is an organism found in parasites, called flukes (flatworms), which infects aquatic snails and insects. Insects carrying Potomac horse fever infect horses after the horses ingest them. Water containing N. risticii can also infect horses. Additionally, horses can get Potomac horse fever by inadvertently consuming infected insects or parasites in feed, water, or on pasture.

The incubation period for Potomac horse fever is between one and three weeks. In addition, the mortality rate is up to 30%. While vaccines against Potomac horse fever are not 100% effective, vaccinated horses tend to have fewer and less severe clinical signs.

Most reports of Potomac horse fever cases occur in July through September. Outbreaks tend to be seasonal.

Horse owners and caretakers, especially those who keep their horses near creeks and rivers, should watch for signs including:

  • Diarrhea
  • Colic
  • Loss of appetite
  • Lethargy
  • Toxic shock
  • Dehydration
  • Abortion in pregnant mares
  • Laminitis
  • Mild to severe fever

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