Overview and Clinical Importance
Equine proliferative enteropathy (EPE) is an emerging enteric disease caused by the obligate intracellular bacterium Lawsonia intracellularis. This condition primarily affects weanling foals (4-7 months of age) and represents an important cause of protein-losing enteropathy, weight loss, and peripheral edema in young horses. The disease has a characteristic seasonal distribution in North America, with most cases occurring between August and January. EPE is highly board-relevant due to its distinctive clinical presentation and the critical importance of early recognition and treatment for successful outcomes.
| Characteristic |
Description |
| Gram Stain |
Gram-negative |
| Morphology |
Curved, rod-shaped bacillus (1.25-1.75 μm length, 0.25-0.43 μm width) |
| Growth Requirements |
Obligate intracellular; requires dividing cells and microaerophilic atmosphere for in vitro culture |
| Motility |
Single polar flagellum (darting motility when extracellular) |
| Intracellular Location |
Resides freely in the apical cytoplasm of infected enterocytes (not membrane-bound) |
| Environmental Survival |
Survives 1-2 weeks in environment at 5-15°C |
| Culture |
Cannot be cultured on standard media; requires permissive cell lines |
Etiology
The Organism
Lawsonia intracellularis is the sole species in the genus Lawsonia, classified within the Desulfovibrionaceae family based on 16S rDNA phylogenetic analysis.
Organism Characteristics
High-YieldL. intracellularis is an OBLIGATE INTRACELLULAR pathogen - this is critical for understanding why antimicrobials with good intracellular penetration (macrolides, tetracyclines, chloramphenicol) are required for treatment, and why standard culture methods fail.
| Factor |
Details |
| Age Affected |
Primarily weanling foals 4-7 months; range 3-18 months; occasionally young adults |
| Seasonality (North America) |
August through January (peak: November-December) |
| Geographic Distribution |
Worldwide: USA, Canada, Europe, South Africa, Australia, Brazil, Japan |
| Transmission |
Fecal-oral route; ingestion of contaminated feces from infected animals |
| Reservoir Hosts |
Rabbits (cottontail), rodents (mice, rats), dogs, cats, opossums, skunks, deer, pigs |
| Attack Rate |
Approximately 5% clinical disease; additional 5% subclinical infection |
| Incubation Period |
7-14 days |
| Fecal Shedding Duration |
17-27 days (begins 5-17 days before clinical signs develop) |
Epidemiology
NAVLE TipThe classic NAVLE stem for EPE: 'A 6-month-old weanling foal in November with weight loss, diarrhea, and ventral edema.' The combination of AGE (weanling) + SEASON (fall/early winter) + CLINICAL SIGNS (protein-losing enteropathy) should immediately trigger EPE in your differential list.
| Common Signs |
Less Common Signs |
Severe/Complicated Cases |
| Lethargy, depression
Anorexia
Fever (greater than 38.5°C)
Rapid weight loss
Peripheral edema
Diarrhea (variable: soft to watery)
Rough hair coat |
Colic (mild)
Decreased borborygmi
Subclinical disease
Failure to thrive
Normal fecal character |
Necrotizing enteritis
Endotoxemia
Bacteremia
DIC
Rapid deterioration
Pulmonary edema |
Pathogenesis
The unique pathogenesis of EPE involves enterocyte invasion and proliferation rather than typical inflammatory destruction. Understanding this mechanism explains both the clinical presentation and treatment approach.