In the early 2000's we have started to receive reports of a newly identified cause of weight loss with poor coat and pot belly, depression, diarrhea, and colic in young horses, weanlings to yearlings. The cause is a bacteria labeled Lawsonia intracellularis and has been recognized as a cause of diarrhea in pigs and other species since the mid 1990's. Labelled "proliferative enteropathy", it has now been described in horses in Australia, the USA, Canada, European countries and Latin America. It is believed that it may have world wide incidence. This article presents what is known about this disease including how we think foals get it, clinical signs, diagnosis, treatment, prognosis.

Epidemiology is the study of how a disease is transmitted and unfortunately in this case we know almost nothing for certain in horses. What little we know we extrapolate from work done with pigs. It is thought that young animals are the reservoir for the organism. In herds of pigs it is self-perpetuating as the infected young, infect others around them . In pigs the infection may last up to 10 weeks during which they shed the organism in their feces. L. intracellularis being a obligate intracellular organism may survive up to 2 weeks in the environment.

Currently it is uncertain whether PE infection is self-perpetuating in equine breeding farms. Though there have been outbreaks where multiple foals were affected most reports have been single cases. Wildlife exposure may be involved in the perpetuation of disease in some outbreaks.