Immunological Distinction Between St. Louis and Japanese B Encephalitic Viruses

Abstract

Experiments by Perdrau published posthumously indicated that St. Louis encephalitic virus, Strain No. 3, and Japanese B encephalitic virus, Strain No. 2, furnished by us, were immunologically identical. 1 These results are contrary to our previous findings 2 and hence have been checked in this laboratory.

Perdrau's technic was followed in preparing immune sera. The standard technic for setting up neutralization-tests used in both sets of experiments was continued. Serum-virus mixtures were tested after 4 hours according to our method, and again after 20 hours according to Perdrau's method.

We found at once that immune sera prepared as above 1 were equal or superior to ours in neutralizing capacity and that 20 hours' standing reduced the activity of the serum-virus mixtures one hundred- to one thousandfold, yet brought out any neutralizing effect more dramatically. Most important, however, was the ready confirmation of Perdrau's results with St. Louis No. 3 and Japanese No. 2 strains (Table I). Further tests in animals showed that the St. Louis strain had retained its distinguishing characteristics, whereas the Japanese virus behaved in every way like the St. Louis virus. Questions arose, therefore, as to whether (a) our previous findings 2 were erroneous, (b) the Japanese virus had become altered through repeated passage, or (c) the Japanese virus had at some time been erroneously labeled.

That an error had occurred in labeling was indicated by the following tests. Seven strains of virus were secured from outside sources. Dr. G. O. Broun kindly supplied St. Louis strains from the 1933 and 1937 epidemics, Dr. E. H. Lennette, the Japanese strains Nakayama and Sasaki, Dr. R. Kobayashi, the Japanese strains Sakurai (1939) and Sawatani (1939), and Dr. T. Mitamura the Japanese strain Calinina (1935).