ペストの血清疫学的研究 : Yersinia pestis の驚異的Fraction-1 抗原に対する抗ペスト血清反応とその疫学的応用
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概要
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Rodents were infected experimentally with plague bacilli and examined for antiplague antibody production at fixed intervals. Indirect hemagglutination (IHA) and latex agglutination (LA) tests using the fraction-I (FR-I) antigen of Yersinia pestis were adopted for antibody titration. Technical conditions were determined to insure the specificity and reproducibility of the reactions. Utilizing the methods studied, we carried out antiplague serologic surveillance with sera from wild rats (Rattus norvegicus and R. rattus) captured in the harbor areas of Japan during the period from 1971 to 1979. The results obtained are as follows : 1) No cross reaction was observed between the antibodies against Y. pestis (FR-I) and those against Y. pseudotuberculosis or Y. enterocolitica in the gel diffusion precipitin, IHA, and LA tests. 2) Antiplague immune sera from various species of animals were tests for their IHA titers by the use of tanned fresh sheep red blood cells (RBC) sensitized with various concentrations of the FR-I antigen. It was shown that the FR-I concentrations suitable for reasonably positive IRA were in the range of 12.5-50 μg/ml, and that the antigens 75 μg/mt or more produced nonspecific reactions against both immune and control sera. 3) Specific reactions were confirmed by the FR-I antibody inhibition (FRIAI) and nonspecific hemagglutination (NSHA) tests. Experiments were carried out to investigate how FRIAI tests would be influenced by FR-I concentrations, reaction time or temperature of medium. The FR-I antigen at 25 μg/ml or more produced better results in the FRIAI tests than did the same antigen at 12.5 μg/ml or less ; hence, the 25 μg/mt antigen was regarded as optimal for the reaction. It was also shown that the serum-antigen mixture should be kept at room temperature for 2 hrs before the addition of RBC sensitized with FR-I, and that the specific antibodies were inhibited by FR-I antigen. 4) To examine the specificity of the IHA reaction and the duration of the positive reaction, rodents (rats including wild-captured ones, guinea pig, rabbits and mice) were inoculated with live or killed plague bacilli and the sera taken at intervals thereafter were assayed for IHA titers. The same tests were also performed with acetone-treated or mercaptoethanol-acetone-treated sera. The IHA titers were significantly high at 7-11 days after the inoculation of live bacilli and practically the maximum titers (in the range of 1 : 128 to 1 : 512) were maintained for at least 50 days. The anti plague antibodies produced at 1 to 2 weeks after inoculation of plague bacilli were ME-sensitive, whereas those detected in the later stages or after a second inoculation were ME-resistant. The data indicated that the acetone treatment of sera was useful for screening of anti plague antibodies, and that the treatment with ME was helpful in assessing the time of past plague infections. 5) Antiplague antibodies of sera from mice and rats immunized with plague bacilli were titrated in parallel by the slide-LA, microtiter-LA and IHA methods. The micro-LA titers well correlated with those obtained by the IHA method, although the former tended to be a little lower than the latter. The slide-LA reaction was also shown to parallel both the micro-LA and IHA reactions. The slide-LA became positive when the IHA titers were 1 : 4 or more. The LA tests may be applied to seroepidemiological studies of plague infection in rodents. 6) Bacteriological and serological surveillance was carried out in the harbor areas of Kobe, Osaka and Sakaide, Japan, during the period from 1971 to 1979. Among 1,645 sera of rodents captured in Kobe, four samples (0.24%, all from R. norvegicus) were positive against plague by the IHA test. However, attempts to isolate plague bacilli from those wild rodents as well as from fleas were unsuccessful. It was recommended that the surveillace of plague infection in wild rats, with particular reference to the detection of antiplague antibodies, should be continued for the purpose of monitoring the possible invasion of plague into nonendemic areas.
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