Peroral immunization of adult white mice with the Skalica strain from the tick-borne encephalitis virus complex.

Adult white mice immunized perorally with the infectious Skalica strain from the tick-borne encephalitis (TBE) virus complex did not show any clinical symptoms of illness. 56% of experimental animals immunized with two doses of the Skalica virus (the titer of virus was 6 x 10(10) LD50) were protected against the challenge with the Hypr strain of TBE virus. All mice immunized with the Skalica virus and having haemagglutination-inhibiting antibodies higher than 1:80 survived the challenge with the given dose of virulent TBE virus. No differences in the immunogenicity and protectivity were observed in experimental animals infected with infectious Skalica virus by oesophageal probe, or by drinking virus-containing medium. A higher protective activity against the virulent Hypr virus was observed in adult white mice immunized subcutaneously with the Skalica virus.