Studies on the Serotherapy of Japanese B Encephalitis

Report II: On the Susceptibility of Mice to the Japanese B Encephalitis Virus and the Distribution of the Virus

Abstract

In making virus inoculation experiments, it is essential to keep the susceptibility of the animals in a constant level.
There are many factors which determine the susceptibility ; especially in case when the intraperitoneal inoculation of Jacan ese B encephalitis virus is made, postnatal date and body weight of the mice used are important in determining the susceptibility.
The present author examined these factors along with the influences of room tem-perature. It is also assumed important in elucidating the cause of changes of susceptibility to confirm whether the difference in body weight has influence on the rise and fall of the virus population after intraperitoneal inoculation. The results were as follows:
1) The postnatal date of mice has the close connection with their body weight; the 3-week-old one weighed 8 g, the 4-week-old 10 g, the 5-week-old 15 g on the average.
2) Susceptibility of mice to the virus intraperitoneally inoculated decreases as their body weight increases, but there is no definite interrelation between fatality rate and a challenge dose of the virus, in the case of mice over 15g.
In the mice of body weight from 8 to 10 g, susceptibility is considerably high and it draws a parallel line between the onset and the virus dose inoculated.
Therefore, it is preferable to use the mice of 8 to 10 g for the intraperitoneal chal-lenge of the virus.
3) Susceptibility to the intracerebral and intraperitoneal inoculation of Japanese Bencephalitis virus of the mice which were raised in the high room temperature for a long time is higher than that of those bred in the low room temperature.
4) It is after 48 hours that the virus is recovered from the brain of mice weighing 8 g which was intraperitoneally inoculated with the 10-1 dilution of the infected brain. And 98 hours after the inoculation, recovery of the virus attains the uppermost amount, then the virus nearly corresponds in potency to that from intracerebral inoculation.
In the brain of the 20 g mice, even if the attack is not manifest, no small amount of the virus is demonstrated though less in comparison with that of 8 g mice.
The virus is detected in the blood of 8 and 20 g mice in high concentration up to 12 hours after the challenge, null 48 hours later, and 72 hours later again demonstrated. Thereafter no virus is detected.