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日本脳炎の疫学的研究
https://az.repo.nii.ac.jp/records/3338
https://az.repo.nii.ac.jp/records/333883858bca-d4c4-42ce-a14f-8f7a5d30e930
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diss_dv_otsu0207 (5.2 MB)
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diss_dv_otsu0207_jab&rev (401.6 kB)
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diss_dv_otsu0207_jab (263.6 kB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||||||
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| 公開日 | 2013-02-28 | |||||||||
| タイトル | ||||||||||
| タイトル | 日本脳炎の疫学的研究 | |||||||||
| タイトル | ||||||||||
| タイトル | Epidemiological studies on Japanese encephalitis | |||||||||
| 言語 | en | |||||||||
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| 言語 | jpn | |||||||||
| 資源タイプ | ||||||||||
| 資源タイプ | thesis | |||||||||
| 著者 |
板垣, 国昭
× 板垣, 国昭
× Itagaki, Kuniaki
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| 抄録 | ||||||||||
| 内容記述タイプ | Abstract | |||||||||
| 内容記述 | I 緒論 日本脳炎ウイルス(以下:JEV)が，コガタアカイエカ(以下:蚊)によって媒介伝播されることは，三田村(1933)により報告され，JEV分離では，林(1934)，笠原ら(1936)の報告が最初のようである。以来，arthropod-borne Virusの日本における代表的ウイルスとなった。 JEVの宿主は，哺乳類，鳥類および変温動物等極めて広く，高い感受性を示すブタと蚊の間にpig-mosquito cycleが提唱されているが，その他の宿主動物と蚊およびJEV間の相互の生態については，未解明の点が多い。 近年，ヒトの患者は激減と地方病化的傾向がみられるが，1978年以降患者は再び増加する様相を呈している。著者は，現今の自然界におけるJEVのecologyの一端を把握する目的で，病原体(JEV)，媒介者(蚊)および宿主(感受性動物)の生態について，獣医学的領域における調査を行い，過去の流行当時の成績と比較検討した。 II 材料および方法 1)実験動物によるJEV感染実験 人工培地に増進しないウイルスでは，感受性動物を用いた実験病理は不可欠である。あらゆる疾病において健康群の生態と疾病群の病態生理が，感染の本質を知る意味で最も重要であると考え，イヌ，ウサギ，1週令マウス，7週令マウスを用いた感染実験を行い，体重変動，臨床症状，血液像，組織像および赤血球疑集抑制抗体(以下:HI抗体)の変動について，1981年7月5日から同17日の13日間観察を行った。 2)家畜と野生鳥獣の日本脳炎HI抗体の保有状況調査 自然界において，いかなる動物がJEVのamplifier或いはreservoirとして，どのような役割を果しているか究明すべき点も多い。 著者は，1980年と1981年の7月から9月の期間，山口県内のと畜場のブタ(438個体)，同一畜舎内に飼育した動物(ウシ，ブタ，イヌ，ウサギ，ニワトリ，ハトおよびマウス)，両年間に狩猟等で捕獲された野生鳥獣(カラス，ハト，スズメ，カモ，キジ，ヤマドリ，ゴイサギ，ヒヨドリ，イノシシ，タヌキ，ノウサギ，イタチ，クマネズミ，ヘビなど288個体)，1981年の6月から同9月の間に保健所に集められた生後7ケ月未満の幼犬(178個体)および生後2週間以内の哺乳犬(32個体)，1982年7月には出生直後の初乳授乳前後の子イヌ(5個体)，1981年6月から1982年7月の期間に保健所に集められたネコ(33個体)および1982年7月には自然動物園のアメリカクロクマ(7個体)のHI抗体を測定し，JEVの侵淫度について解析を行い，新鮮感染度を把握するため2ME感受性抗体も併せて測定した。 3)コガタアカイエカの消長と周辺動物の感染状況の調査 JEVの伝播に蚊の存在は欠くことはできない。蚊の生態は気象や環境に大きく影響され，これらを考慮した調査が必要である。 著者は，1980年と1981年の7月から同9月の期間に，前述した畜舎内および1981年は犬舎内で捕集した吸血蚊(畜舎1760個体，犬舎160個体)の吸血源動物を知る目的で，動物血球に対する家兎免疫抗血清を作成し，蚊の吸血液を抗原として沈降素法による血清学的検索を行った。なお，山口県における日本脳炎に関する調査地域の概要等について未尾のFig.1に示した。 III 実験結果および調査成績 1)実験動物によるJEV感染実験の結果 供試動物のうち，体重の病的変動，臨床症状の発現，血液の病的変化は，マウスの接種群にみられ，1週令マウス接種群では，体重減少，運動異常，痙攣，麻痺，授乳不能，リンパ球と好中球の増多が3日目よりみられ，5日目にリンパ球，好中球の減少を呈して全て死亡した。7週令マウスでは，死亡個体はみられなかったが，立毛，旋回運動が一部に観察され，白血球の軽い増減がみられた。 病理組織学的変化は，全ての種類の供試動物の大脳に主座し，小円形細胞浸潤，グリア細胞増殖，皮質の浮腫，血管周囲細胞浸潤，神経細胞変性像を呈し，これらはマウスで著明で，イヌ，ウサギで散見された。 HI抗体の変動は，5日に死亡した1週令マウス以外は有意の上昇を示し，抗体価はイヌの320倍が最高値であった。 2)家畜と野生鳥獣の日本脳炎HI抗体の調査成績 1980年と1981年のと畜場のブタは，JEVに対する高い感受性を示し，2ME感受性抗体の上昇は前年が7月下旬，後年は8月下旬で1か月の差がみられた。畜舎内供試動物はイヌ，ブタが両年とも抗体の早期上昇を示し，他の供試動物より抗体価も高く，と畜場のブタ同様両年の抗体上昇時期は，前年が早く約1カ月の差がみられた。1981年の保健所に集められたイヌの成績は，7月下旬より2ME感受性抗体が出現し，同年のと畜場のブタより早期に抗体上昇がみられ，保有率はブタ同様高率であった。また，生後2週間以内の子イヌの抗体価はいずれも10倍以下であり，親の抗体価が80倍の子イヌの初乳授乳前(出産直後)，授乳10日後の抗体価はいずれも10倍以下であった。ネコの抗体保有率は9.1%と低く，保有抗体価は10倍～20倍であった。野生鳥獣のHI抗体の保有状況は，イノシシ，ゴイサギ，ヤマドリ，キジおよびカモが高い保有率を示し，カラス，ハト，スズメ，ヘビ，クマネズミなどに保有率が低い傾向がみられ，保有抗体価は鳥類ではゴイサギの160倍，哺乳類ではイノシシの640倍が最高値であった。また，自然動物園のアメリカクロクマ7個体はいずれも抗体を保有しており，その抗体価は20～40倍で低い値を示した。野生鳥獣のうち，JEV活動期に捕獲されたスズメ(1個体)，ゴイサギ(1個体)，イノシシ(2個体)は2ME感受性抗体を保有し新鮮感染を示した。 3)コガタアカイエカの消長と周辺動物の感染状況の調査成績 1980年と1981年の野外捕集蚊数は前年に多く，捕集蚊数と気象の関係は，気温，降雨量以外はあまり有意でなかった。両年の畜舎内捕集蚊数は前年に多く，捕集蚊数のピークは前年が早く現われ，吸血率も約10%高値を示した。1981年の犬舎内補集蚊数は気温によく相関し，吸血率は各月とも50%前後で一定していた。畜舎内捕集蚊からのJEV初分離は，1980年は7月10日，1981年は8月16日で約1か月の差がみられ，両年の畜舎内供試動物の抗体上昇時期によるJEV出現推定日と，蚊からのJEV分離成績はよく一致した。つぎに，1980年の畜舎内と1981年の犬舎内で捕集した吸血蚊の吸血源の調査成績は，畜舎ではウシを吸血したものが約70%，ブタを吸血したものが約30%で，ほとんどがウシとブタで，犬舎内では96.9%がイヌを吸血していた。 IV 考察 JEV感染実験では，マウスのみ臨床症状が発現し，病理組織像はいずれの供試動物も非化膿性脳炎像を呈し，不顕性に経過したイヌやウサギは，ヒトの不顕性感染像にも似て注目される。また，抗体価の最高値はイヌの320倍であり，JEVに対する高い免疫応答が覗われた。 動物の日本脳炎HI抗体の保有状況調査では，と畜場のブタがJEVに対する高い感受性を示し，1980年と1981年では前年が抗体保有率が高く，2ME感受性抗体の出現も早く，JEVの発現が早期であったことが判明した。 1980年と1981年の畜舎内供試動物の抗体変動は，同種の動物では陽転時期や抗体価の成績がほぼ同じで個体差があまりみられず，動物種類別では差があり各供試動物の感受性差が明確となり，イヌがブタ同様に早期感染型でありブタについで高い免疫応答を示し注目される。1981年に保健所に集められたイヌの成績では，7月下旬に新鮮感染が出現し，と畜場のブタより早期の感染像と高い抗体保有率を示し，夏期におけるイヌのJEV感染がブタに劣らず高率であることが立証され，ブタ血液が入手困難な山口県においては，イヌの抗体調査によってJEVの流行予測を行うことも，充分可能であることが判明した。また，出生後2週間以内の哺乳犬は，いずれも抗体を保有せず，親の抗体価がhigh levelでないと初乳を介して抗体の移行は起らないものと思われ，生後間も無く感染の機会があることが明らかになった。ネコは抗体保有率，抗体価共に低く，JEV伝播にはあまり重要な動物ではないと思考された。野生鳥獣の成績では，イノシシ，ゴイサギ，キジ，ヤマドリ，カモ，タヌキ，イタチ等比較的大型或いは地表棲息性の鳥獣は保有率が高く，スズメ，カラス，ハト，等小型或いは樹上棲息性の鳥類は保有率が低く，地上或は地下棲息性のヘビ，クマネズミは抗体を保有せず，棲息環境別に考察すると，蚊の咬刺吸血の機会に差があることが示唆された。また，輸入動物のアメリカクロクマは日本に在住している過去5年間にJEVに感染したものと思われ，自然界におけるこのウイルスの広い宿主域が再確認された。 媒介蚊の調査では，1980年と1981年の野外捕集蚊数は前年に多く，その要因は降雨量が多く産卵場所が拡大したためと思われる。畜舎内捕集蚊数は前年は早期発生型を示し，後年は遅延型を示し，前述した両年の畜舎内動物の抗体陽転時期，JEV分離時期とよく一致し，前年は蚊の交尾繁殖が早期且活発であったことが明らかになった。ちなみに，県内のヒトの患者発生は前年3名，後年はみられなかった。1981年の犬舎内捕集蚊数は気温によく相関し，吸血率は各月とも約50%と一定しており，犬舎においてかなりの蚊がイヌを吸血し，イヌのJEV感染が高率であることが裏付けされた。畜舎内の吸血源調査では，ウシ，ブタの大動物を吸血した蚊がほとんどであり,体表面積を考慮すべきではあるが，蚊の吸血に嗜好性があることが再確認された。犬舎内の吸血源は，やはりイヌが最も多く96.9%であり，1畜舎1畜種の場合は，蚊の吸血嗜好性は無視され,その動物に吸血が集中することが明らかになった。 このように今回の日本脳炎に関する調査成績では，ヒトの患者の減少した現在も流行時に変らぬ自然界におけるJEVの旺盛な活動が確認された。供試した殆どの宿主動物が高率に感染しているにも係わらず，JEV伝播サイクルはpig-mosquito cycleが主体に提唱され，他のJEV感受性動物に対するamplifier或いはreservoirとしての役割の有無について知見に乏しい。ヒトの患者の多発した流行時に比較して，ブタとニワトリの飼育頭数は現在は約2倍に増加しており，他の動物は激減している。前述したように，と畜場に搬入されるブタは毎年高率にJEVに汚染されており，大規模飼育化されている現在においても，豚舎周囲で保毒蚊の数的密度が高く，飛来可能な地域では，ヒトの患者の発生例があって然りであるが,このような報告はみられない。 著者の行った調査の範囲内で，ヒトの患者の減少要因を考察するならば，ブタ，ニワトリ以外の感受性動物の絶対数の減少と媒介蚊の数的密度の低下が第一義的に挙げられるが，調査対象外の宿主，すなわちヒト側の要因が最も大きいのかもしれない。 V 総括 現今，自然界におけるJEV伝播サイクルの究明は，最も困難な研究として残されている。高い感受性を示すブタは勿論であるが，高い抗体保有率と抗体価を示すイヌやイノシシをはじめ他の家畜および野生鳥獣等についても，ヒトの患者発生との関連において，X-mosquito cycleの可能性を究明すべき点が多い。 特に，今回実施した感染実験，抗体調査，媒介蚊調査のいずれにおいてもdog-mosquito cycleの存在が示唆されるイヌについては，ヒトに身近かな動物であり注目すべきである。自然界におけるこのウイルスの活動状況から思考すれば，ヒトのJEV免疫力が低下した場合は大流行することも考えられ，患者が減少した現今においてこそ，獣医学的領域における基礎的研究を蓄積し，JEVに対するさらに詳細な疫学的観察が必要である。 (以下図表) |
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| Abstract | ||||||||||
| 内容記述タイプ | Other | |||||||||
| 内容記述 | I. Introduction Mitamura (1933) reported on Japanese Encephalitis Virus (JEV) carried and disseminated by Culex tritaeniorlynchus (hereinafter as mosquito). Hayashi (1934) and Kasahara (1936) first made reports on JEV isolation. JEV has since been a typical species among arthropod-borne Viruses in Japan. A wide varaiety of animals are hosts of JEV; mammals, birds and cold-blood animals. The pig-mosquito cycle between pigs as a highly sensitive animal to JEV and mosquito has been proposed, but most of the mutual ecology among other host-animals, mosquito, and JEV is still unknown. Significant decrease in the number of patients of Japanese Encephalitis and its localization were once a trend but increasing number of patients have been since 1978. For touching on the fringe of JEV's ecology in the natural condition, a survey was made by the author on the ecology of pathogens (JEV), vectors (mosquito) and hosts (sensitive animals) using Veterenary Science Methods for comparison with the past results obtained when Japanese Encepalitis was in prevalence. II. Materials and Methods 1. JEV Infection Experiments to examined Animals Experiment pathology using sensitive animals is inevital for viruses which show no multiplication in artificial culture. In view of the importance to find essential qualities of infection which is detectable from the analysis of the ecology of normal groups and pathophysiology of morbus groups, infection tests were performed on dogs, rabbits, and l-and 7-week old mice to make analysis on body weight, clinical symptoms, hemograms, tissues, and hemagglutination inhibition antibody (HI antibody) during the l3-day period from July 5, 1981 to 17 the same month. 2. Survey on Japanese Encephalitis HI Antibody in Animals Research is required on the roles of animals as amplifiers or reservoirs of JEV in the natural condition. HI antibody measurement were made to analyze JEV infiltration rates and 2-mercaptoethanol sensitivity antibody (2ME-sensitivity antibody) measurement for determing a first infection to JEV in the summer were also made during July-September periods in 1980 and 1981. The examined animals using in this survey were as follows; pigs (438 subjects) in 2 slaughterhouses in Yamaguchi prefecture, animals raising in the same barn (cattle, pigs, dogs, rabbits, domestic fowl, pigeons, and mice), wild animals (289 subjects) captured by hunting etc. during the two years, infantile dogs (l78 subjects) under 7 months after birth, lactated dogs (32 subjects) under 2 weeks after birth collected from June to september l981, newborn puppies (5 subjects) before and after drinking foremilk from their mother collected in July l982, cats (33 subjects) collected from June 1981 to July 1982 and American black bears raising in zoo (Euarctos americans, 7 subjects) collected in July 1982. 3. Survey on Relationship between the Incidence of Vector Mosquitoes and Infection of Decoy-Animals Mosquito is very important for JEV dissemination. The ecology of mosquito is much affected by meteorology and environments. For this, a survey taking into account these factors was needed. A survey was made on the effects of meteorological factors and sprays of agricultural chemicals over propagation of mosquito in a same barn during July - September priods in 1980 and 1981 and in a doghouse located 200 m apart from the same barn in 1981. JE viruses were isolated from mosquitoes captured in the same barn. Further, for determination of animals species from which mosquito sucked blood, lapino-immune antisera were prepared with the hemocytes of examined animals and the serological analyses were made by the precipitin method. Mosquitoes were collected in the same barn in 1980 and in the doghouse in l981 (1760 pcs. in the same barn and 160 pcs. in the doghouse). Districts where our survey on Japanese Encephalitis were made in Yamaguchi Prefecture are shown in Fig. 1. III. Test Results and Survey Outcome 1. Results of JEV Infection Experiments to Examined Animals On the examined animals, body weight changes, appearance of clinical symptoms, and abnormal blood conditions were found in innoculated mice group. In 1-week-old innoculated mice group, body weight decrease, abnormal exertion, convulsion, paralysis, lactation inability, lymphocytosis, and neutrophilia were found from the 3rd day and all died on the 5th day due to lymphopenia and neutropenia. No dead cases were found in 7-week-old mice except piloerection, circling movement found in some subjects, and slight increase of leukocytes. Pathohistological changes were found in cerebrums of all examined animals and minor teres cellular infiltration, glia cell proliferation, cortical edema, periaterial cellular infiltration, and neurocyte denatured images were shown. These findings were appreciable in mice and partly found in dogs and rabbits. Significant increase of HI antibodies were shown in animals except 1-week-old mice which died in the 5th day. Maximum 320 elevated antibody levels were found in dogs. 2. Survey Results of Japanese Encephalitis HI Antibody in Animals Pigs in the slaughterhouse showed high sensitivity to JEV in 1980 and 1981 and a 1-month difference was observed in an increase of 2ME-sesitivity antibody; early July in l981 and late in August in the following year. Both dogs and pigs raising in the same barn showed the higher levels of antibodies than the other examined animals. The increasing time of the positive antibody rates were one month earlier in 1980 than 1981. Infantile dogs collected to the health center in 1981 showed emergence of 2ME-sensitivity antibodies and elevation of the positive antibody rates earlier than pigs in the slaughterhouse. The positive antibody rates of dogs were as high as pigs. In the lactated dogs within 2 weeks after birth and the newborn puppies (drinking foremilk or not drinking it from their mother) no antibody to JEV infection were found in their sera. Low positive rates of antibody and low antibody levels were found in cats. High positive rates of antibody were shown in wild boars, night herons, copper pheasants, pheasants, and ducks. While the low positive rates were shown in crows, pigeons, sparrows, snakes, and rats. High elevated antibody levels were found in wild boars and night herons. Althugh the high positive rates (100%) to JEV infection were found in the American black bears examined in this survey, their antibody levels were relatively low. In which, sparrows (1 subjects), night herons (1 subjects), and wild boars (2 subjects) infected in the summer,i,e the 2ME-sensitivity antibodies were elevated. 3. Survey Results of Relationship between the Incidence of Vector Mosquitoes and the Infection of Decoy-Animals Mosquitoes Captured in the field were larger in number in 1980 than 1981 and no significant relations between the number of captured mosquitoes and meterology were found except tepperture and rainfall. The number of mosquitoes captured in the same barn were larger in 1980 than 1981 with its peak shown earlier in 1980 and blood-sucking rates were approx. 10% higher. The number of mosquitoes captured in the doghouse in 1981 were proportionte to temperture and the suking rates were stable with around 50% each month. First isolation of JEV from mosquitoes collected in the same barn was made in July 10, 1980 and about a month later on August 16 in the following year. Coincidence was fownd with the time of positive antibody comversion and JEV isolation in the same barn. The survey on blood souces of the mosquitoes collected in the same barn and doghouse showed approx. 70% from cattle, approx. 30% from pigs in the same barn and 96.9% from dogs in the doghouse. IV. Discussion 1-week-old mice showed significant changes in JEV infection tests, which reveald high sensitivity of infantile animals. Dogs and rabbits were notable for submerged symptoms accompanied by slight pathohistological changes and high antibody levels on account of its similarity to submerged infection found in humans. High elevated antibody levels in dogs(maximum 320) revealed a possibility of severe viremia and dogs' role as amplifiers or reservoirs in the JEV dissemination cycle in natural condition should also be clarified. We think that the condition of epidemics of JEV infection in the summer can be expressed by testing the sera from dogs. Animals used in this survey showed a high sensitivity based on the elevated HI antibody levels. Positive rates of the antibody from pigs in the slaughterhouse were higher in 1980 than in 1981. This suggests early appearance of 2ME-sensitivity antibody and JEV spread. Expansion northward of JEV was found earlier in the slaughterhouse at Bofu than that at northern Iwakuni. Individual difference was small in antibody changes of examined animals of the same species in the same barn in 1980 and 1981, but difference was among each species of animals. This shows sensitivity difference in each species of animals. Dogs showed 2nd high sensitivity after pigs. New infected bodies were found in late July in infantile dogs collected to the health center in 1981. It was the infection appearance earlier than in pigs in the slaughterhouse and proved dogs' high JEV contamination as high as pigs' in summer. No antibody was found in the lactated dogs within 2 weeks after birth and the newborn puppies (before and after drinking foremilk). The fact suggests that the JEV infection to dogs easily caused. Cats may not play the important role to the JEV dissemination cycle. It seems that American black bears infected to JEV during past 5 years after being imported from USA. Comparatively large terrestial wild life like wild boars, night herons, pheasants, copper pheasants, and ducks have high antibody positive rates, small arboreal birds like sparrows, croes, pigeons, etc. low rates, and underground-dwelling snakes and rats have no antibody, respectively. The analysis of animals by habitual environment revealed differences in mosquito's opportunity to bite and suck blood and sensitivity of each group of animals. Survey on Vector Mosquito and Decoy-Animals showed the number of mosquitoes captured in the field larger in 1980 than 1981, which was attributable to much rainfall and resultant expantion of oviposition places. The number of mosquitoes captured in the same barn peaked in July 1980; showing the early-appearance type, and in August l981; the delayed type. Coincidence was found with the time of positive conversion of antibody and JEV isolation in the same barn. This shows positive copulation-propagation of mosquito in the previous year. Japanese encephalitis patients in the Yamaguchi Prefecture were 3 in 1980 and none in the following year. The number of mosquitoes collected in the doghouse in 1981 were proportionate to temperture with stable blood-sucking rates at approx. 50% presenting many materials for later analysis. Most mosquitoes sucked blood from large animals like cattle and pigs in the same barn showing their sucking habit, despite large surface area of those animals to be taken into account as a factor. Blood sources in the doghouse were of course dogs with as much as 96.9%. No such blood-sucking habit was noticeable when one species of animals were raised in one cage and blood-sucking was concentrated on that animal. V. Conclusion In the past, JEV was active in the natural condition. At present, the JEV activity is the same as the past condition. It was demonstrated from these findings that the JEV spread is mainly dependent on the Pig-Mosquito Cycle. Their are few reports that describe the other animals (X-Mosquito Cycle) as amplifiers or reservoirs. It is necessary to studies on various animals; not only pigs which show high sensitivity to JEV but other animals. From the results obtaind above, a possibility of Dog-Mosquito Cycle ageinst JEV infection may be concedered. The condition of JEV infection in the summer can be expressed by testing the sera from dogs. Further studies are necessary for the Animal-Mosquito Cycle such as wild boars and dogs, in particular, becouse dogs live closely with human enveronment. In the field of JEV studies, at present, one of the most difficult subjects is to dissolve the JEV dissemination cycle in the natural condition. Although human cases of JEV infection gradually decrease during the past decade, the JEV and its spread in the natural condition did not decreased according to our reports. From the point of view, the fundamental studies based on Veterenary Science Methods and its application of the epidemiological investigations are required for exterminating the Japanese Encephalitis Epidemics. (Chart) |
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| 学位名 | ||||||||||
| 学位名 | 獣医学博士 | |||||||||
| 学位授与機関 | ||||||||||
| 学位授与機関名 | 麻布大学 | |||||||||
| 学位授与年月日 | ||||||||||
| 学位授与年月日 | 1982-12-01 | |||||||||
| 学位授与番号 | ||||||||||
| 学位授与番号 | 乙第207号 | |||||||||
| 著者版フラグ | ||||||||||
| 出版タイプ | AM | |||||||||
| 出版タイプResource | http://purl.org/coar/version/c_ab4af688f83e57aa | |||||||||
