L. intracellularis Infections in Foals on the Rise

Lawsonia intracellularis, a bacterium causing equine proliferative enteropathy (EPE) in mostly young horses, can result in thickening segments of small intestines and sometimes large intestines. L. intracellularis does not grow in routine aerobic/anaerobic culture and can only grow in vitro (in the lab) in cell culture, which is not practical. Therefore, several quick and reliable PCR tests have been developed to directly detect the bacteria.

Besides horses, L. intracellularis infects pigs and many other domestic and wild animals, including hamsters, rabbits, foxes, deer, ferrets, ostriches, and non-human primates. Previous studies have shown that a variety of wild and domestic animals, including dogs, cats, rabbits, opossums, skunks, mice, and coyote, shed L. intracellularis on farms with diagnosed EPE cases. Fecal-oral transmission of L. intracellularis has been documented in naïve foals housed with clinically infected foals experimentally challenged with an equine isolate of L. intracellularis (Pusterla et al 2010).

Clinical signs of EPE include depression, anorexia, fever, peripheral edema (fluid swelling of the throat latch, sheath, and distal limbs), hypoproteinemia (low blood protein levels), hypoalbuminemia (low levels of the protein albumin in the blood), weight loss, colic, and diarrhea in affected foals. Early clinical signs are generally unspecific and include mild depression, partial anorexia, and fever. Signs of EPE might resemble those of other gastrointestinal disorders such as parasitism, bacterial infections (Clostridium spp., Salmonella spp., Neorickettsia risticii), rotavirus, coronavirus, ulcerations, sand accumulation, intestinal obstruction, and intoxication with plants, chemicals, and pharmacologic agents such as non-steroidal anti-inflammatory drugs or antimicrobials (Pusterla and Gebhart, 2013). Therefore, treating veterinarians should rule out other diseases with diagnostic tests.

Practitioners generally make a presumptive EPE diagnosis based on age of the affected animal, hypoproteinemia/hypoalbuminemia, fever, and presence of thickened small intestinal loops on ultrasonographic evaluation.

Laboratory diagnosis is through PCR detection of L. intracellularis in feces or rectal swab. For these results to be accurate, samples should be obtained before any antimicrobial treatment. Interested owners can send serum for albumin ($5) and total protein ($5) evaluations (the equine Serum Chemistry Panel can also be requested, $17). Owners can also submit fecal specimens, rectal swabs, or mucosal scraping for PCR confirmation in clean screw tubes, not in gloves (in-state fee is $35). Post-mortem diagnosis is achieved by PCR combined with thickening of the mucosa of the ileum and cecum grossly and compatible histopathologic lesions.

1. Positive PCR Equine Lawsonia Cases: 2010-2013

Figure 1 (at left) depicts the total number of cases submitted to UKVDL between 2010 and 2013. We are seeing an increasing trend of positive cases submitted this year as compared to recent years. This might be due to a higher number of ante-mortem cases being submitted for diagnosis than in previous years.

Please read the article by Pusterla and Gebhard, available online.

Information provided by:

  • Erdal Erol, DVM, PhD Head, Diagnostic Microbiology, UKVDL
  • Jackie Smith, PhD Head, Epidemiology, UKVDL
  • Craig N. Carter, DVM PhD Dipl. ACVPM Director & Professor, Epidemiology

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