Granulomatous typhlocolitis, lymphangitis, and lymphadenitis in a horse infected with Listeria monocytogenes, Salmonella Typhimurium, and cyathostomes.

The research article discusses a rare case of a horse suffering from severe diarrhea, attributed to a simultaneous infection from Listeria monocytogenes, Salmonella Typhimurium, and cyathostomes, which resulted in a condition known as granulomatous typhlocolitis.

Objective and Background

• The paper discusses a rare medical case involving a 15-year-old American Quarter horse mare, which was euthanized due to the unsuccessful treatment of severe diarrhea.
• The infections causing the illness were quite unusual, comprising of Listeria monocytogenes, Salmonella Typhimurium, and cyathostomes, which resulted in the development of granulomatous typhlocolitis – a condition that is characterized by inflammation in the colon and other related tissues. The presence of these diseases together in a horse is seldom seen.

Research Findings

• Upon analyzing the horse’s condition post-euthanasia, gross pathological findings were limited to the large intestines of the animal. The walls of the cecum and colon were found to have thickened and there were scattered nodules in the mucosa and submucosa. These extended into the enlarged colic lymph nodes of the horse.
• A microscopic view revealed severe granulomatous typhlocolitis, lymphangitis, and lymphadenitis. These conditions involve inflammation and the formation of granuloma, or small nodules, in the colon, lymphatic vessels, and lymph nodes respectively.
• In these inflamed, nodule-filled regions, numerous Gram-positive, non-acid-fast coccobacilli, and few cyathostomes were found. These are characteristic of L.monocytogenes and cyathostomes infections.

Diagnostic Techniques

• To confirm the presence of these bacteria, Immunohistochemical tests and polymerase chain reaction (PCR) assays were carried out. Both tests positively identified the presence of Listeria monocytogenes in the intralesional bacteria.
• Concurrently, the presence of Salmonella was detected, specifically the serovar Typhimurium, as confirmed by PCR tests and bacterial culture methods.

Conclusions and Insights

• The study thereby concludes that the unusual aspect of this case was the coinfection of Salmonella Typhimurium, and cyathostomes along with rare Listeria monocytogenes.
• The researchers suggest that the coinfection played a role in the development and severity of the granulomatous typhlocolitis in the horse, contributing to its poor response to treatment and eventually to its demise.