Lawsonia intracellularis infection in horses: 2005-2007.

This study examines the characteristics, clinical symptoms, tests, medication used, and survival rate of horses infected with Lawsonia intracellularis, an equine pathogen known to cause equine proliferative enteropathy. The study also investigates how these infections affect subsequent sale prices of the afflicted horses at public auctions, as well as infection rates in clinically normal herd mates of similar ages.

Study Methods

• The researchers investigated 57 horses that were treated for diseases associated with L. intracellularis infection between August 2005 to January 2007.
• This retrospective study involved the examination of horses showing evidence of L. intracellularis infection and testing either positive for fecal Polymerase Chain Reaction (PCR) or serum Immunoperoxidase Monolayer Assay (IPMA).

Results of the Study

• Horses in the study ranged in age from 2 to 8 months, and all were examined between August and January.
• The most common symptoms were ventral edema, present in 81% of the affected horses, and hypoalbuminemia, which occurred in all affected horses.
• Of those tested, 50% of the horses tested positive on both PCR and IPMA.
• The survival rate was 93%, and the type of antimicrobial administered didn’t impact survival rates.
• Infected horses, when sold as yearlings at public auctions, fetched an average of 68% less than other yearlings sired by the same stallion.
• Normal, similar-aged herdmates of the affected horses also tested positive for L. intracellularis with a prevalence of 6% for fecal PCR and 33% for serum IPMA.

Conclusions

• Young horses with symptoms of ventral edema and hypoalbuminemia that are examined between August and January should be suspected for L. intracellularis infection.
• Both fecal PCR and serum IPMA tests are necessary to help ascertain disease status.
• Although infected horses generally survive after treatment, their market value at public auctions is significantly lower than their non-infected counterparts sired by the same stallion.
• Age-matched, clinically healthy herd mates have a likelihood of testing positive for L. intracellularis via fecal PCR and serum IPMA.