The Effects of Rapid Embryo Passage upon the Infectious Bronchitis virus

Abstract

T HAS been well established that the virus of infectious bronchitis (IB) of chickens changes its immunogenic properties upon repeated embryo cultivation.5'89 It is equally well known that the Beaudette strain 42 of virus, when propagated in embryonating chicken eggs, has been prone to develop titers of 10-5-0 to 10-7.0, which makes end-point titrations of immune sera impossible without resorting to a diluted serum method. This investigation was conducted to determine whether rapid embryo passage [i.e., passage of the infectious bronchitis virus (IBV) at the peak of the logarithmic phase of growth] would change the characteristics of a virulent strain of virus in regard to virus concentration, embryo mortality rate, and pathogenicity for the host. In addition, it was expected that rapid embryo passage of the Beaudette strain 42 of IBV would result in an increase of the EID0o. IBV was first reported by Beaudette and Hudson' to be readily propagated in embryonating chicken eggs. Continued serial passages of the virus in embryos increased the virulence of the virus for embryos and was accompanied by a decrease in virulence for chickens.