The results from a five year survey on the antibody rise in summer against JE virus in pigs in Natori District of Miyagi Prefecture were analysed with regard to the time of antibody rise, detection rate of 2-ME sensitive antibodies, level of antibody titers, and duration of high-titered antibodies. These serological results obtained in pigs were finally correlated to the isolation rate of JE virus from mosquitoes collected in the same area and to the incidence of JE patients among 1, 750, 000 residents in Miyagi Pre-fecture.
On the basis of this limited 5 year survey, one can conclude the following:
1. A hundred percent infection among pigs and positive isolation of the virus from mosquitoes have consistently been observed during these 5 years. Thus the cyclic outbreak between mosquitoes and pigs existed every year, even in the absence of the spread to humans.
2. The earlier the appearance of the initial antibody rise and the longer the duration of high-titered antibody among pigs, the higher the incidence of infection among humans.
3. The time of the initial and subsequent isolation of virus from mosquitoes coincided completely with the time of antibody rise among pigs, as was pointed out by us 5 years ago.
4. A minor pre-outbreak and minor post-outbreak of infection among pigs were noticed before and after the main outbreak among pigs. The fact was clearly illustrated by pursuing 2-ME sensitive antibodies.
5. The height of antibody titers in pig sera was assumed to be a reliable indicator to predict the amount of virus harbored by mosquitoes. The titer in pig sera was lowest in a year of the least incidence of human infection, irrespective of the fact that 100% of pigs were infected every year.
6. An assumption was proposed to predict the appearance of virus harboring mosquitoes almost 3 weeks in advance by setting the threshold number of 150 of the candidate mosquitoes trapped per night under a defined condition.

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The virulence and immunogenicity (protectivity) of an attenuated live strain of Paeteurella pestis, EV, were examined in mice. When injected subcutaneously at a dose of 10⁶ bacilli, the organisms survived at the injection site for as long as one week though the population decreased gradually. A small number of EV was recovered from the spleen, liver and kidneys from the second to the fifth days after injection. The optimal doses for immunization ranged 10^6-7 bacilli; a smaller or larger dose resulted in a lower protection. Various organs of mice inoculated subcutaneously with the live vaccine strain EV at a dose of 6.0×10⁶ organisms were subjected to histopathological examination every day. Pathological changes developed at first in the liver on the next day after the injection, and then the lungs and spleen were involved from the 2nd to the 18th days. The changes in the liver were characterized by perivascular and parenchymal infiltration of cells, granuloma and necrosis. The perivascular changes were characteristic to EV strain, in contrast to the sole parenchymal changes caused by virulent strains. The changes in the spleen were hyperplasia of follicles, reticulum cell proliferation in the germinal centers, infiltration of plasma cells and of polymorphonuclear leucocytes and proliferation of pericordial reticulum cells in the regions of red pulp. Changes in the lungs were detected in some mice, but there was no proof to regard them as being specific. These changes induced by the conventional live vaccine strain are discussed in relation to the death of mice.

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