Virus vaccine and passive immunization for the prevention of viral myocarditis in mice

The effect of an inactivated virus vaccine and passive immunization was studied in an animal model of viral myocarditis. Encephalomyocarditis (EMC) virus was inactivated by 1:4000 formalin. Four-week-old CD-1 mice were injected subcutaneously and after 7 days intravenously with 0.1 ml vaccine. Seven days after the second vaccine, live EMC virus was inoculated intraperitoneally. None of ten mice with vaccine treatment died or showed myocardial lesions after challenge with EMC virus, whereas all ten mice without vaccine died 5-7 days after EMC virus inoculation and showed severe myocardial lesions. Hyperimmune rabbit serum, made by inactivated EMC virus, had a neutralizing antibody titer of 1:3000. Four-week-old BALB/c mice were injected intramuscularly with 1:10 dilution of hyperimmune rabbit serum in 6 groups (each, n = 10) on day -2, -1, 0, 1, 2, or 3, respectively, after inoculation with 10 plaque-forming units of EMC virus, and observed for 14 days. Eight mice infected with the virus without immune serum died and all ten mice showed severe myocardial lesions. No death or myocardial lesion was seen in mice with hyperimmune rabbit serum given on days -2 to 2. In this model, the virus vaccine prevented development of myocarditis, and passive immunization had a protective effect if given early after infection.