Meningoencephalomyelitis in horses associated with equine herpesvirus 1 infection.

The research article discusses an outbreak of a neurological disease in mares, caused by the equine herpesvirus 1. The disease resulted in dullness and uncoordinated movements, with the virus identified in the brain and lungs of two severely affected mares.

Introduction and Outbreak

• This research was triggered by an outbreak of abortion in horses which was linked to the equine herpesvirus 1, a common virus in horses that generally causes respiratory disease, abortion in pregnant mares, and occasionally, a severe neurological disease.
• During the outbreak, several mares exhibited signs of a neurological disease. The symptoms included mental dullness and ataxia, a lack of muscle coordination that can affect the animal’s gait, balance, and ability to swallow.

Identification of the Virus and Symptoms

• In two of the severely affected horses, the equine herpesvirus 1 was isolated from the brain and lungs. This was significant as it indicated a correlation between this virus and the observed neurological disease.
• On a microscopic level, both mares that were tested had disseminated meningoencephalomyelitis, a severe inflammatory disease of the brain and spinal cord. This condition was characterized by necrotizing arteritis, a rare form of vasculitis that results in inflammation and cell death in the arteries.
• Additional symptoms observed in the horses included focal malacia in the brain and spinal cord’s grey and white matter. Malacia refers to the softening of tissues, usually due to necrosis or degradation.

Morphological Changes

• The research also found an accumulation of lymphocytes and neutrophils in paravertebral ganglia, the group of nerve cells located near the vertebral column. This indicated an immune response in the affected area.
• In addition, eosinophilic intranuclear inclusion bodies were found in the thyroid adenomas of both mares. These are abnormal cellular formations, often associated with viral infections. The presence of these formations within thyroid adenomas specifically suggests that the virus had an impact on multiple organs and not just the nervous system.