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Ultrastructural degenerative changes of age-dependent ECHO 9 virus-induced polymyositis in infant mice
Abstract:
Experimental inoculation of newborn NMRI mice with Echo virus, type 9, strain A. Barty *ECHO 9 virus AB) resulted in diffuse polymyositis 4 days later. The disease, after a delay of 1 day, increased in intensity and was accompanied by a rapid, progressive paresis leading to death 7-11 days following infection. As early as 24-48 h after inoculation, we detected initial ultrastructural degenerative changes, characterized by segmental dilation fo the sarcoplasmic reticulum. Disruption and breakage of myofibrils followed, and lead to the formation of increasing numbers of contraction bands. Ultimately, virus-mediated nuclear and other organellar injury resulted in muscle fiber necrosis. In addition, we observed some substructural cellular events related to virus propagation. Beginning on the 4th day after infection, pronounced proliferation of the sarcoplasmic-reticulum membranes became evident in perinuclear and subsarcolemmal areas in the mature muscle fibers, myoblasts, and post-fused myotubes of mice inoculated within 18 h after birth. These cytological alterations were not noted in the myoblasts and myotubes of NMRI mice injected with virus 2 or 4 days after birth.
Insights
Echo 9 virus infection in newborn mice causes polymyositis and muscle fiber necrosis. Early ultrastructural changes include sarcoplasmic reticulum dilation, myofibril disruption, and ultimately, muscle cell death.
Area of Science:
- Virology
- Pathology
- Cell Biology
Background:
- Echo 9 virus (ECHO 9 virus) is known to cause various human illnesses.
- The pathogenesis of ECHO 9 virus-induced muscle damage at the cellular level requires further elucidation.
Purpose of the Study:
- To investigate the ultrastructural changes in muscle tissue following experimental inoculation with ECHO 9 virus in newborn mice.
- To characterize the temporal progression of viral myopathy and identify cellular events associated with virus propagation.
Main Methods:
- Newborn NMRI mice were experimentally inoculated with ECHO 9 virus.
- Muscle tissues were examined using electron microscopy to observe ultrastructural changes at various time points post-infection.
- Histopathological analysis was performed to assess the extent of muscle damage.
Main Results:
- Infection led to diffuse polymyositis within 4 days, progressing to paresis and death between 7-11 days.
- Early ultrastructural changes (24-48 h post-inoculation) included sarcoplasmic reticulum dilation and myofibril disruption.
- Muscle fiber necrosis occurred due to virus-mediated nuclear and organellar injury, with formation of contraction bands.
- Pronounced proliferation of sarcoplasmic reticulum membranes was observed in muscle fibers, myoblasts, and myotubes of mice infected within 18 hours of birth.
Conclusions:
- ECHO 9 virus infection in newborn mice induces significant muscle pathology, characterized by polymyositis and necrosis.
- The study reveals specific ultrastructural alterations in muscle cells, highlighting the role of sarcoplasmic reticulum and myofibrils in viral myopathy.
- Age at inoculation is a critical factor, as cytological alterations were specific to mice infected very early in life.