Immunization of mice against encephalomyocarditis virus. II. Intraperitoneal and respiratory immunization with ultraviolet-inactivated vaccine: effect of Bordetella pertussis extract on the immune response.

Mice were immunized by intraperitoneal (ip) or respiratory administration of ultraviolet-inactivated virus alone or with Bordetella pertussis extract (BPE) as an adjuvant. The effect of immunization was tested by determination of antibody titers and by survival of a lethal challenge with 200 LD(50) of a virulent (large-plaque variant) strain of EMC virus. For plain vaccine the ip 50% effective dose (ED(50)) was 37 hemagglutination units (HAU; ca. 4 x 10(6) plaque-forming unit equivalents); with adjuvant the ip ED(50) was reduced to 20 HAU. After respiratory immunization by intratracheal injection, an ED(50) value of 100 HAU was found, which was not affected by BPE. After ip vaccination the primary immune response was enhanced by BPE, but the challenge response, measured 3 weeks after challenge, was unaffected. Respiratory immunization induced a primary response which was not influenced by BPE, but here the challenge response was enhanced by the adjuvant. After secondary treatment (challenge or booster vaccination) serum antibodies and protection against challenge persisted for at least 1 year.