Abstract
Although the virus of encephalitis of St. Louis type has been successfully cultivated by Maitland technic and on the chorio-allantoic membrane of developing chick 1-4 the titer obtained in these cultures has been invariably low. None of the cultures showed a titer as high as 10-6 even after repeated passages. Recently Kawakita 5 has reported successful cultivation of Japanese encephalitis virus in a special medium containing chick allantoic fluid. It has occurred to us to attempt to cultivate the virus of St. Louis type on the agar-tissue medium which has been found to be satisfactory for the growth of various types of rickettsiae. 6 , 7 The results of such a study together with a preliminary study on the immunizing value of vaccine prepared from these cultures are hereby communicated.
The virus, Webster No. 3. which has full virulence for mice, was propagated in the following fashion: Infected mouse brain, diluted with serum-Tyrode solution mixture (1:5) to 10% by weight was filtered through Seitz E. K. pad after brief centrifugalization. A small amount of the filtrate was inoculated on to a small piece of young mouse embryonic tissue in a sterile Petri dish. These were minced together, and after being allowed to stand for 15 to 20 minutes at room temperature, the finely cut tissue bits were carefully laid on the surface of agar slants employed for the cultivation of rickettsiae. These cultures were incubated at 37°C, and transferred every 5-8 days. By this method, the virus has been carried for over 40 generations in a period for more than 10 months. The activity of the virus for Swiss mice by intracerebral injections of different generations was found to be as follows: 10-6 for the sixth, 10-6 for the sixteenth, 10-7 for the twenty-first, and 10-6 for the thirty-fourth generations of cultures.
Get full access to this article
View all access options for this article.