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Age dependence of paralysis induced by echovirus type 9 in infant mice
Abstract:
Newborn mice of different strains (including NMRI) infected with 2-5 x 10(6) pfu of echovirus type 9 strain A. Barty developed progressive flaccid paralysis five days after inoculation, followed by death. Suckling mice injected with the same infective dose two, four, or six days after birth disclosed at most transient paresis and survived. Infectivity titrations revealed in all groups a similar rate of virus multiplication exceeding 10(8) 50% tissue culture infective doses per mouse four days after virus inoculation. Histologically, polymyositis resulting in muscle fiber necrosis was seen. The percentage of damaged muscle tissue declined with increasing age of the experimental groups. It is concluded that in order for paralysis to occur, at least 50% of skeletal muscle tissue must be destroyed by virus-induced lesions before the sixth day of life. Electron microscopy demonstrated additional age-dependent, virus-mediated disturbances of postnatal muscle growth. Reparative events in destroyed muscle fibers seemed to be unaffected in all age groups.
Insights
Echovirus type 9 infection in newborn mice causes paralysis and death due to polymyositis. Muscle damage must exceed 50% before six days of life for paralysis to occur in these mice.
Area of Science:
- Virology
- Neurology
- Pathology
Background:
- Echovirus type 9 (EV-A9) is a known human pathogen.
- Viral infections can cause neurological damage in neonates.
- Age-dependent susceptibility to viral diseases is a critical factor in disease outcome.
Purpose of the Study:
- To investigate the age-dependent effects of echovirus type 9 infection on newborn mice.
- To determine the pathological mechanisms underlying EV-A9-induced paralysis.
- To establish the critical threshold of muscle damage required for paralysis.
Main Methods:
- Newborn mice of different ages were inoculated with EV-A9.
- Virus infectivity and multiplication were assessed via titration.
- Histological and electron microscopy were used to examine muscle tissue.
- Neurological symptoms, including paralysis and survival rates, were recorded.
Main Results:
- Infection led to progressive flaccid paralysis and death in newborn mice.
- Older mice exhibited only transient paresis and survived.
- Virus multiplication was high across all age groups.
- Histopathology revealed polymyositis with muscle fiber necrosis, declining with age.
- Over 50% skeletal muscle destruction by day six was required for paralysis.
Conclusions:
- Age is a critical factor in EV-A9 pathogenesis, influencing disease severity.
- Significant muscle destruction is necessary for EV-A9-induced paralysis in mice.
- EV-A9 also disrupts postnatal muscle development in an age-dependent manner.