Experimental influenza B viral myositis.

[focal myositis]

To investigate the pathogenesis of influenza myositis in animals , juvenile BALB /c mice were inoculated with influenza B /Lee virus intramuscularly into the right quadriceps muscle . Chicken normal allantoic fluid (NAF ) or phosphate-buffered saline (PBS ) was injected into the left quadriceps of control mice and in some virus-infected mice . Serum creatinine phosphokinase (CPK ) levels rose significantly on days 1 and 2 post-inoculation (PI ) in only virus-inoculated mice . On days 2 and 3 PI , right quadriceps muscles developed scattered foci of a predominantly mononuclear inflammation in the perimysial connective tissue often adjacent to degenerating or necrotic muscle fibers . Immunofluorescent staining with specific anti-influenza B virus antisera showed muscle fibers that contained specific staining in nuclei and adjacent cytoplasm . Skip areas of staining within muscle fibers suggested that not all muscle nuclei within an individual muscle fiber were infected . A continuous fall in infectious virus titer in the right quadriceps muscles suggested the initial virus inoculum became inactivated and progeny virions were not produced . Left quadriceps muscle never had muscle necrosis or endomysial inflammation , specific staining of viral antigen , virus isolation , or viral RNA detected by the reverse transcriptase polymerase chain reaction assay . These findings support the hypothesis that a non-permissive influenza viral infection can develop in murine skeletal muscle that can damage specific nuclear domains of muscle fibers producing muscle degeneration or necrosis . A similar type of muscle infection may develop in humans that occasionally develop focal myositis during influenza .