Lawsonia intracellularis infection in horses: 2005-2007.
Authors: Frazer M L
Journal: Journal of veterinary internal medicine
Summary
# Lawsonia intracellularis Infection in Young Horses: Clinical Presentation and Diagnostic Implications Equine proliferative enteropathy (EPE), caused by the intracellular bacterium *Lawsonia intracellularis*, represents an emerging disease concern in young stock, yet diagnostic and management protocols remain poorly defined. This retrospective analysis examined 57 horses aged 2–8 months (median 6 months) diagnosed with *L. intracellularis* infection between August 2005 and January 2007, evaluating clinical presentation, diagnostic accuracy, treatment outcomes, and subclinical infection rates in exposed cohorts. Ventral oedema and hypoalbuminaemia were hallmark clinical findings, occurring in 81% and 100% of affected horses respectively, though notably only 50% tested positive on both fecal PCR and serum immunoperoxidase monolayer assay (IPMA)—highlighting significant diagnostic discordance. Despite the severe clinical picture, 93% of treated horses survived regardless of antimicrobial choice, though affected yearlings subsequently sold at public auction for an average of 68% less than their unaffected half-siblings, indicating considerable economic impact beyond mortality. Critically, 6% of age-matched clinically normal herdmates tested positive on fecal PCR and 33% on serum IPMA, suggesting asymptomatic carriage may be common within affected populations. Practitioners should maintain high clinical suspicion for EPE in young horses presenting with ventral oedema and hypoproteinaemia between August and January, utilise both PCR and IPMA testing for diagnostic confirmation, and recognise that negative diagnostic tests do not exclude infection in herdmates or recent contacts.
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Practical Takeaways
- •Suspect L. intracellularis in young horses (2-8 months) presenting with ventral edema and hypoalbuminemia between August and January; use both fecal PCR and serum IPMA for diagnosis as single tests miss ~50% of cases
- •Prognosis for infected horses is favorable (93% survival) but significant economic impact exists—infected yearlings sell for substantially lower prices despite treatment success
- •Screen clinically normal herdmates with both diagnostic tests as approximately one-third may carry subclinical infection, with implications for herd management and sale decisions
Key Findings
- •57 horses with L. intracellularis infection ranged from 2-8 months old (median 6 months) and presented between August and January
- •Ventral edema was present in 81% of affected horses and hypoalbuminemia occurred in all cases
- •Only 50% of horses tested positive on both fecal PCR and serum IPMA, indicating single diagnostic tests are insufficient
- •93% of infected horses survived regardless of antimicrobial treatment, but sold for an average of 68% less than unaffected yearlings by the same sire
- •6% of clinically normal herdmates tested positive on fecal PCR and 33% on serum IPMA, suggesting subclinical infection