Necrotizing myocarditis in mice infected with Western equine encephalitis virus: Clinical, electrocardiographic, and histopathologic correlations.

Western equine encephalitis (WEE) virus was found in myocardial tissue of adult mice during the first five days after inoculation of the virus, with a peak titer (5.0 log plaque-forming units/g) at 24 hr. Light microscopy revealed a multifocal necrotizing myocarditis with a prominent inflammatory response and hyaline and granular degeneration of myofibers. Electron microscopy showed cytoplasmic viral nucleoids and budding and free mature WEE viral particles. Serial electrocardiograms showed the development of disturbances of rate and rhythm, defects in conduction, marked elevation in the ST segment, and low voltage. Myocarditis has not been previously recognized as a complication of alphavirus infection in humans. and we found no evidence for myocardial damage in 11 persons with acute WEE virus infections studied electrocardiographically in 1975. Demonstration of myocarditis in the WEE virus-infected mouse, however, suggests the need to monitor human patients for possible cardiac involvement during future epidemics of WEE virus infection.