[The resistance of a maternally-derived immunity of baby mice against mousepox--experiments regarding a special possibility of immunization with orthopox viruses (author's transl)].

In the scope of research concerning new proplylactic possibilities against mousepox we tested the resistance of a passive immunity of baby mice whose mothers had been immunized before or during pregnancy several times with either the vaccinia virus strains MVA, CVB or the so-called attenuated ectromelia virus strain "Hampstead" respectively. The vaccines CVB and "Hampstead" were found to cause the production of haemagglutination-inhibiting antibodies only. A passively-transmitted immunity of baby mice was proven to be effective against an intraperitoneal challenge-infection with a virulent ectromelia virus strain for as long a period as 3 weeks after birth, if their mothers had been vaccinated with either of the following: 10(2,0) and 10(4,0) KID50 of the "Hampstead" strain, or one of the vaccinia virus strains in a dosage 100-times as large. The vaccination did not lead to an intrauterine infection of the fetuses. After 224 tissue culture passages in mouse fibroblast cells (line 3T6), THE "Hampstead" strain was found te be still virulent for baby mice; however, female adult mice which had been intraperitoneally inoculated with 10(2,0) and then 10(4,0) KID50 two weeks later demonstrated no signs of mousepox. The possibility for using this ectromelia virus strain instead of vaccinia virus for active immunization against mousepox of young animals under the protection of a homologous passive immunity is discussed.