Potomac Horse Fever - contd.
The cause of PHF is an organism called Ehrlichia risticii, a parasite that infects the white blood cells, as well as the epithelial or tissue cells of the small intestine and colon. The exact route of infection is not known at this time, but it is suspected that PHF is transmitted by the bite from an arthropod such as a tick; other possible vectors are being investigated at this time. A horse can not infect another horse directly.
Transmission is most common in horses living near the Potomac River in the states of Maryland and Virginia. However, evidence of PHF has been confirmed serologically in many other states and Canada, although the disease has not been documented outside of North America. Horses living near a river are at a higher risk of disease than animals living in drier regions. Most cases of PHF occur seasonally in the summer and autumn months.
