Vaccine produced from cells of Brucella abortus S.19 grown by methods of continuous culture in liquid medium is as safe and immunogenic in guinea pigs as vaccine produced by conventional methods on agar medium.
Summary
The chick embryo has been successfully employed for the quantitative assay of residual equine encephalomyelitis virus in tests with immune serum. Under the conditions of these experiments maximum neutralization of equine encephalomyelitis virus by antiserum was attained within a few seconds of mixing the virus and the serum. Less neutralization was apparent if the virus-serum mixtures were kept at 4 C prior to inoculation. The amount of neutralization which was apparent was related directly to the susceptibility of the embryo or inversely to the number of virus particles necessary to initiate a lethal infection. The greatest neutralization was shown when 15 day eggs were inoculated by the yolk sac route and the least neutralization when 15 day eggs were inoculated by the chorio-allantoic route. Eleven day eggs inoculated by either route showed intermediate degrees of neutralization.
Introduction. Many viruses produce characteristic lesions, known as pocks or plaques, on the chorio-allantois of the developing chick embryo. The first to be successfully propagated on this membrane was fowl pox (1). Since then, Burnet and his collaborators (2, 3) have determined the potencies of suspensions of a number of viruses such as vaccinia (4), herpes simplex (5), influenza (6), ectromelia (7), myxoma (8), laryngotracheitis (9), and fowl pox (10), by estimating the average number of pocks produced at several serial dilutions. Some independent workers have found the technique satisfactory (11), but others have failed to obtain consistent results (12), and the method has not been generally adopted for the titration of viruses outside Burnet's laboratory.
In these Laboratories, various studies on fowl pox virus, for which reliable titration methods are necessary, are in progress. Since titration by application of virus suspensions to the comb or feather follicles of adult birds seemed unsuitable, it was decided to investigate the possibilities of the chorio-allantoic method.
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