- an intestinal disease caused by bacteria, which after ingestion causes low-grade fever, lack of appetite, lethargy and mild abdominal discomfort.

The following are various articles and links on Potomac Horse Fever:

Potomac Horse Fever - What is Potomac Horse Fever? 
College of Veterinary Medicine
University of Minnesota

Disease claims local horses;  racehorses not in danger
By Paul Post, The Saratogian
July 26, 2007

Recent Development
Saratoga Equine Veterinary
July 16, 2007

Potomac Horse Fever Cases Popping Up in Ohio
TheHorse.com
By Erin Ryder, News Editor
July 15, 2007

Fast Fact About Potomac Horse Fever (PHF, Ditch Fever)