Lawsonia intracellularis is the causative agent of Equine Proliferative Enteropathy (EPE). The disease in horses is often referred to as “Lawsonia.” L. intracellularis is an obligate intracellular bacteria found in the proliferating crypt epithelial cells of the intestine. It causes hyperplasia, or thickening of the walls of the intestinal tract, which leads to malabsorption and protein loss. The method of transmission in the horse is still unknown, but a fecal oral route is most probable.


Lawsonia is most common in young horses between two and eight months of age, but rarely adult horses may be affected. Horses present during late fall or early winter (August through January). The most consistent clinical sign in affected horses is ventral edema (jaw, leg or abdomen), but horses may also exhibit lethargy, diarrhea, fever, colic, potbelly appearance, poor haircoat and/or weight loss. The most common finding on blood work is low total protein and low albumin levels. Most affected horses have an albumin level below 3.0 mg/dL (reference range: 3.4-4.1 mg/dL). Typically, the thickened, edematous intestinal walls can be visualized with transabdominal ultrasound.


Lawsonia is diagnosed by observation of typical clinical signs in conjunction with a positive fecal PCR and/or a serum IPMA titer greater than or equal to 1:60. For the most accurate diagnosis, a fecal sample as well as a blood sample in a red-top tube should be submitted to the laboratory for analysis. The most reliable diagnosis is a silver stain or PCR of a section of intestinal wall, but the tissue sample can only be obtained via surgery or in postmortem cases. Our laboratory is one of only 3 in the United States that performs Lawsonia titers.


Affected animals should be treated with an antimicrobial with good intracellular penetration. Oxytetracycline (LA200), doxycycline, chloramphenicol and clarithromycin are all good choices. Metronidazole may also be used in conjunction with one of these antimicrobials. Antimicrobials may have to be given for several weeks or until the albumin level shows a trend upward toward the reference range.

Horses with severe edema (intestinal or subcutaneous) and those with very low protein levels should be given Hetastarch, a synthetic colloid, and/or plasma. Affected horses may also require intravenous fluid therapy to correct dehydration and electrolyte abnormalities.


Affected horses that are treated aggressively usually survive the infection. However, these horses may take months to “catch up” to their herd mates in body condition. Severely affected horses may not survive.


Until we know how the disease is spread and where the organism is harboured in the environment, taking precautions to prevent the disease is impossible. Instead, be familiar with clinical signs of the disease so that infected horses can be diagnosed and started on appropriate therapy quickly. Sick animals should be separated from the rest of the herd during treatment. There is an intra-rectal vaccine that Hagyard Equine Medical Institute veterinarians conducted research on with good clinical outcomes. Please ask your veterinarian about this product as a prevention of this disease.