Demyelination in canine distemper encephalomyelitis: an ultrastructural analysis

Area of Science:

• Veterinary Neurology
• Neuroimmunology
• Pathology

Background:

• Canine distemper virus (CDV) is a significant cause of neurological disease in dogs.
• Encephalomyelitis associated with CDV leads to white matter lesions and demyelination.
• The precise mechanisms of demyelination in canine distemper are not fully elucidated.

Purpose of the Study:

• To investigate the morphological changes associated with demyelination in canine distemper encephalomyelitis.
• To identify the cellular players involved in myelin injury and phagocytosis.
• To determine the role of oligodendrocytes in the demyelination process.

Main Methods:

• Morphological examination of white matter lesions in three dogs with canine distemper encephalomyelitis.
• Light microscopy to observe cellular infiltration and myelin changes.
• Electron microscopy to identify viral nucleocapsids within specific cell types.

Main Results:

• Two stages of demyelination were identified: initial myelin sheath ballooning and subsequent phagocytosis by immune cells.
• Canine distemper viral nucleocapsids were found in astrocytes, macrophages, ependymal cells, and lymphocytes, but not oligodendrocytes.
• Microglial cells and astrocytes were the primary myelin-phagocytosing cells, with some oligodendrocyte involvement.
• Axonal necrosis and evidence of remyelination were observed in established lesions.

Conclusions:

• Myelin loss in canine distemper is likely initiated by astrocyte dysfunction, leading to myelin edema and ballooning, rather than direct oligodendrocyte infection.
• Phagocytosis by macrophages and astrocytes is the primary mechanism for myelin removal.
• Limited remyelination may be hindered by reduced oligodendrocyte numbers and an increase in immature forms.