The Histology of Equine Encephalomyelitis.

This research investigates the impact of the virus of equine encephalomyelitis on different animals, primarily highlighting how it causes acute nerve cell degeneration and other specific changes in nerve tissues. The work notes a variation in the intensity and scope of the effects when comparing the eastern and western strains of the virus, and different host animals.

Key Findings and Observations

• The article examines the effects of the equine encephalomyelitis virus (eastern strain) on various animals including horses, calves, sheep, and dogs. It reports this strain induces an intense form of encephalomyelitis that’s characterized by certain changes on the cellular and tissue level, such as acute primary degeneration of nerve cells and the masses or clumps (nuclear inclusions) in neurons akin to those seen in Borna disease or poliomyelitis.
• Additional effects at the cellular and tissue level include polymorphonuclear (PMN) infiltration in nervous tissues, which refers to a type of reaction wherein certain white blood cells that are part of the immune response infiltrate the tissue, leading to an early proliferation of microglial cells; these are a type of cell in the nervous system that serve immune system functions. Another noted effect is perivascular cuffing, a condition characterized by inflammation surrounding small blood vessels in the nervous system; this involves mononuclears (single nucleus cells) and PMNs in varying proportions.
• The research notices that the grey matter (areas of the nervous system primarily composed of neuron cell bodies and capillaries) is more impacted by these changes than the white matter. The effects appear to vary across different regions of the brain; lesions are reportedly less pronounced in the striatum, brain stem, and cord than in the cerebral cortex, thalamus, and hypothalamus, while the cerebellum regularly exhibits only low-grade changes.
• Meningeal infiltration, which refers to the spread of inflammatory or cancer cells into the membranes covering the brain and spinal cord, is described as secondary to the other observed effects. The lesions and other changes produced by the western strain of the virus, when compared to the eastern strain, appear less intense and extensive, at least in the horse.
• The eastern virus also causes acute encephalomyelitis in guinea pigs, rabbits, and mice. In these animals, there is a particular tendency for the virus to affect higher olfactory centers. The research also reveals the occurrence of small, red-staining (oxyphilic) bodies in glial (neuron-supporting cells) and mesodermal (middle germ layer in early embryonic development) nuclei in addition to nerve cell inclusions in guinea pigs. In guinea pigs, the disease may complicate and become interstitial or bronchopneumonia.
• In terms of symptoms and changes, the study points out that the disease resulting from infection with the western virus may appear identical to that induced by the eastern strain, at least in guinea pigs.

Implications of the Research

• This research contributes to our understanding of the pathological changes brought on by the virus of equine encephalomyelitis. It provides a comprehensive overview of the varying effects of the eastern versus the western strain of the virus on different domesticated and laboratory animals, enhancing the existing knowledge of the virulence, pathology, and tropism of these viral strains.
• Knowing the specific neurodegenerative changes and inflammatory symptoms that can occur helps guide diagnosis and treatment approaches for these diseases in veterinary medicine. It also can help inform future research on similar viral encephalomyelitis diseases in humans.