Intestinal lesions in a horse associated with eastern equine encephalomyelitis virus infection.

This research article discusses a rare and unique case where a 6-month-old male Tennessee Walking Horse received a vaccination for various diseases, including Eastern Equine Encephalomyelitis (EEE) virus. Unfortunately, the horse developed unusual intestinal lesions linked to EEE virus infection, in addition to the typical changes in the brain and spinal cord characteristic of the disease.

Eastern Equine Encephalomyelitis and Its Typical Lesions

• The paper starts by pointing out that the usual primary lesions (abnormal changes in body tissues) associated with Eastern Equine Encephalomyelitis (EEE) virus infection, a rare and serious equine illness, are typically found in the brain and spinal cord of horses.
• The EEE virus usually affects the central nervous system, causing inflammation of the brain and spinal cord.

An Unusual Case

• However, the researchers encountered a unique case in a 6-month-old male Tennessee Walking Horse. This colt was inoculated with vaccines for a number of diseases, including EEE, one week before it died.
• Unexpectedly, in addition to the regular disturbances in its central nervous system, this horse also developed intestinal lesions.

Clinical Signs and Gross Lesions

• In terms of symptoms, this young horse exhibited ataxia (lack of muscle coordination) and rear-end weakness. The animal also had an elevated body temperature, indicating the presence of a fever.
• On examination, the researchers found several gross anomalies. These included a yellowish discoloration, swelling, edema (excess fluid), and hemorrhage in the brain stem, along with a dark discoloration in the gray matter of the spinal cord.

Microscopic Findings

• In addition to these gross lesions, the investigators also identified abnormalities under microscopic examination. In the small intestine, there were main lesions in the muscle layer, characterized by multiple areas of muscle cell death (myonecrosis) and white blood cell infiltration. They also observed few regions of mild fibrous connective tissue proliferation.
• In the brain and spinal cord, the researchers found widespread areas of inflammation near small blood vessels (perivascular lymphomonocytic cuffing), certain areas of tissue death (necrosis), inflammation involving neutrophils, hemorrhage, and neuronal degeneration (death of nerve cells).
• The study also recorded hepatic changes, including an immune response within the liver and mild degeneration of liver cells.
• In summary, these findings indicate a significant and widespread impact of the EEE virus on this horse’s body.

EEE Virus Isolation

• The researchers were also able to isolate the EEE virus from the horse’s intestine and detect it through DNA in situ hybridization, which confirms that the observed lesions were indeed caused by an infection with this virus.
• This evidence supports the idea that, in this unusual case, the EEE virus affected not only the central nervous system but also the digestive tract of the horse.