Abstract
Summary
Studies are reported in which the Lederle stock strain of canine distemper virus was adapted and maintained through 74 serial passages on the chorio-allantoic membranes of developing chick embryos. The chick embryo adapted strain retained its capacity to produce lethal infection in ferrets through the 24th egg passage level but apparently lost its ability to do so between the 24th and 28th egg passages. Ferrets inoculated with chick embryo adapted virus of passage levels higher than the 28th transfer failed to show any signs of disease, but were found immune on rechallenge with fully virulent ferret spleen virus. Cross neutralization tests carried out in chick embryos and in ferrets indicate that the chick embryo adapted strain and the parent strain of ferret spleen virus are immunologically related.
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