抄録
In the previous paper the isolation of SG strain of Izumi-fever virus from feces of a sporadic case was reported.
The present report describes the preparative methods of the Izumi-fever vaccine and the relation between degree of immunity of mice following vaccination and the titer of neutralizing antibodies in the serum.
In this experiment formalinized vaccine, Merzonin vaccine and ultraviolet-irradiated vaccine were prepared.
The brain of a mouse infected with SG strain was ground in a mortar under sterile conditions. The emulsion thus obtained was diluted by ten volumes of phosphatebuffered saline of pH 7.0. After the diluted emulsion was centrifuged at 3, 000 r.p.m. for 15 minutes, the supernatant was used for the starting material of the following vaccine.
The supernatant fluid was added with formalin in 0.1 and 1.0 per cents, or with Merzonin in 0.01 and 0.1 per cents, respectively. A portion wasi ncubated at 37°C and the other portion was kept in a refrigerator of 4°C, each for 5 days. After the incubation 1 per cent formalinized vaccine was dialysed against distilled water until the vaccine indicated negative Fehling's reaction. To test the infectivity of the each portion, samples were injected daily for 5 days into the mouse brain. The complete inactivation was observed only in 1 per cent formalinized vaccine which was incubated for 5 days, whereas it was not found in other vaccines in the same periode of days.
Ultraviolet-irradiated vaccine was prepared in the following manner. About 2.0ml of the vaccine material were placed in a Petri dish in a distance of 9cm from the ultraviolet lamp. The virus solution was irradiated for 5 minutes and then tested for the infectivity by injecting 0.03ml intracerebrally into mice. Consequently it showed no infectivity after exposure under the condition mentioned above.
The immunizing potency of the formalinized and ultraviolet-irradiated vaccine were determined in the following way. Each of test mice were injected 0.5ml of the vaccines intraperitoneally every other day for 2 doses. The challenge virus was injected intracerebrally or intraperitoneally into mice 2 weeks after the final immunizing administration.
In the experiments vaccinated mice showed about 100 to 1000 times of resistance being compared with non-vaccinated controls.
Neutralization tests were done with pooled sera obtained from mice by heart pucture or cutting the axiillary artery 3 to 14 days after vaccination. The broth was used instead of serum in the control test. These sera or broth were mixed with virus solution diluted 10 times serially and injected intracerebrally into mice, and the inoculated mice were observed for 14 days. Consequently the sera collected from mice 3 days after vaccination showed already a little neutralizing power. Then the antibodies were increasing daily, and finally showed a titer as high as 2.6 in neutralizing logarithm 14 days after vaccination.
