Relationship of Virulence for Mice to Patient Source of Type 2 Polioviruses

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Abstract
Summary: A total of 104 strains of Type 2 poliovirus, in first or second tissue culture passage, has been tested in mice. Eighty-eight produced paralysis by the intraspinal route; 15, with high titer intraspinally were positive by the intracerebral route. No correlation between tissue culture titer and mouse pathogenicity was apparent. Comparison of clinical status of the patient source with tissue culture pathogenicity in monkey kidney epithelium showed an almost equal distribution of titers between patients with and without central nervous system (CNS) involvement. On the other hand, when the mouse intraspinal pathogenicity of the group of strains derived from patients without CNS involvement were examined in comparison to the results with the group from patients with CNS involvement there was a tendency for less virulence in the former group. This tendency for mouse CNS virulence to reflect virulence for human CNS was apparent only when the results for the entire 104 strains were considered since the whole spectrum of mouse virulence was represented by individual strains in both groups. It is concluded that Type 2 poliovirus isolates obtained from human stools probably represent a mixture of mouse virulent and avirulent virus particles, both of which are pathogenic for monkey kidney epithelium in tissue culture and that the relative proportions of the two kinds of virus particles may be partially related to the type of clinical infection in the patient source.