Virulence and Immunogenicity in Mice of Airborne Encephalomyocarditis Viruses and Their Infectious Nucleic Acids

Mice were exposed to aerosols of different strains of the encephalomyocarditis virus group. Responses in mice were different according to strains, virulence being correlated with plaque size. Small plaque-forming strains, ME and Mengo-37A (a heat-resistant mutant of Mengo), were essentially avirulent. The avirulent strains were immunogenic when in sufficient concentration. Aerosol studies with infectious RNA extracted from Mengovirus, ME, and Mengo-37A indicated that the responses in mice were similar to those observed with intact virus. Mengovirus RNA aerosols were lethal for mice, whereas Mengo-37A and ME RNA were avirulent and were not immunogenic in the limited aerosol concentration tested. Mice immunized with intact Mengo-37A virus were refractory to Mengo RNA aerosol challenge.