MULTIPLICATION OF THE NEWCASTLE DISEASE VIRUS IN TISSUE CULTURE

In tissue cultures of rabbit, guinea pig or mouse tissues, either adult or embryonic, multiplication of the Newcastle Disease virus has never been evidenced. In these cultures, the end titer of virus after different periods of incubation was always found lower. than the virus titer at the start. In the presence of rabbit brain, however, the end virus titer after a few days incubation was usually a little higher than in the control culture which contained no tissue. This is considered to be due to a favourable influence of the tissue on the survival of the virus in the medium. Such an effect of tissue remained unaltered after the tissue was dipped in the boiling water bath for five minutes.In the culture with chicken embryo tissue fragments (brain mostly used) simply suspended in Tyrode solution, the virus multiplied easily, and the culture fluid reached the virus titer of 10-6.5-10-7.5 (chicken embryo MID) within 3 days of incubation. In this culture, the same level of maximum virus titer was obtained from different amounts of starting virus, i.e. 102, 104 and 106 MID. Addition of embryo extract and/or serum, or fixation of tissue fragments in blood plasma or on a paper piece did not appear to increase the maximum virus titer of the culture. When the tissue previously dipped in the boiling water bath was used, the virus never multiplied, but maintained the same level titer as in the rabbit tissue culture.In the culture with abult chicken tissue fragments (spleen mostly used) suspended in Tyrode solution, multiplication of the virus was demonstrated by periodical titrations of the culture fluid, though the maximum titer (about 10-4.5) never reached the level so high as in the culture of the embryo tissue. In this tissue culture, however, multiplication of the virus was remarkably increased, when chicken serum was added to the medium, or the, tissue fragments were fixed on the paper. By the combination of these two conditions, the virus titer became comparable with that which was obtained in the embryo tissue culture.