Communicable disease - densenbyo (English spelling)

Japanese: 伝染病 - でんせんびょう（英語表記）communicable disease

A general term for diseases in which a pathogen spreads from host to host, and is often used synonymously with infectious disease, but infectious disease has a broader meaning. In other words, infectious disease refers to infectious diseases that can spread from person to person and become epidemic, such as dysentery and influenza, and does not usually include non-communicable infectious diseases that cannot be spread from person to person, such as tetanus and septicemia. In addition, infectious diseases caused by organisms that are more advanced than bacteria or viruses, such as roundworms and lung flukes, are generally treated separately as parasitic diseases. A term similar to infectious disease is epidemic, which is an old term that refers to infectious diseases that show systemic symptoms, take an acute course, and occur in groups, that is, become epidemic, but it can also be interpreted as synonymous with infectious disease.

[Noriaki Yanagishita]

Classification

Infectious diseases are classified from various viewpoints, including classification based on the onset and progression of the disease, classification based on the main part of the body that is affected, classification based on the route of infection, classification based on the microbiology of the pathogen, and legal classifications such as Class 1 to Class 5 infectious diseases, new influenza and other infectious diseases, designated infectious diseases, and new infectious diseases designated by the Infectious Disease Prevention and Medical Care Act (Infectious Diseases Act), quarantinable infectious diseases designated by the Quarantine Act, and school infectious diseases designated by the School Health and Safety Act.

In addition to these, there is also the administrative name of international infectious diseases. This refers to Lassa fever, Marburg fever, Ebola hemorrhagic fever, etc., all of which are not endemic in Japan and have no established prevention or treatment methods, and are highly contagious and have a high mortality rate, so they are specific infectious diseases that require special facilities to handle patients and samples. Other diseases that have recently attracted attention include AIDS, Hepatitis B, and Hepatitis C.

[Noriaki Yanagishita]

Hospitalization and treatment

In addition to treating the disease itself, infectious diseases require that patients, suspected patients, carriers, and people who have come into contact with the disease, who may be sources of infection, be separated from the general social environment for a period of time to prevent the disease from spreading to others. In particular, under the Infectious Disease Prevention and Medical Care Act, patients with infectious diseases classified as Class 1, Class 2, new influenza, and new infectious diseases must be hospitalized at designated infectious disease medical institutions with specific facilities. Those infected with a quarantine infectious disease virus and those who may have come into contact with the virus are isolated for a certain period of time for observation, which is called quarantine. Patients with Class 3, Class 4, and Class 5 infectious diseases may be treated at home or at a general medical institution.

Although contracting an infectious disease is due to personal carelessness, there are many cases where it is unavoidable, and hospitalization and treatment are partly for the sake of one's own treatment, but also partly for the sake of personal inconvenience in order to prevent infection to those around one, i.e., at designated infectious disease medical institutions, going out or being discharged is not an option for individuals. Therefore, it is for these reasons that some hospitalization and treatment fees are free, and that consideration is given to keeping the burden on patients to a minimum by having the national and local governments cover the costs.

[Noriaki Yanagishita]

Treatment advances and their impact

With the emergence of chemotherapy drugs such as sulfa drugs and antibiotics in the 1930s and 1940s, the treatment of bacterial and rickettsial infectious diseases improved dramatically, and the suffering of illness was quickly alleviated and the mortality rate dropped significantly. For example, in the case of bacterial dysentery, before the advent of chemotherapy drugs, patients usually suffered from frequent diarrhea and abdominal pain for about a week, and the risk of death was high at around 10-20%. However, after chemotherapy drugs were used, the main symptoms disappeared within 1-2 days of starting treatment, patients recovered rapidly, and the mortality rate dropped dramatically to less than 1%. The same can be said for scarlet fever, typhoid fever, rash typhoid, epidemic meningitis, etc. However, as a result, people are prone to underestimate illness, and this trend has become a problem in terms of disease prevention.

[Noriaki Yanagishita]

Prevention and measures

The three most important points for preventing infectious diseases are (1) protecting the entire country from exotic infectious diseases, (2) preventing the spread of infectious diseases that are endemic in the country, and (3) preventing infection at the individual level. To achieve these goals, it is necessary to (1) carry out quarantine perfectly, (2) detect patients and carriers who are the source of infection early and hospitalize them for treatment, as well as disinfect excrement, clothing, bedding, etc., exterminate insects that transmit disease, improve the environment such as water supply and sewage systems, and implement vaccinations as appropriate, and (3) avoid opportunities for infection, maintain personal hygiene, strengthen the body's resistance, and receive vaccinations as necessary. Ultimately, it all comes down to the recognition or awareness and efforts of the nation, local community, and individuals regarding infectious diseases.

Previously, the prevention and treatment of infectious diseases was governed by the Infectious Diseases Prevention Law, which came into force in 1897 (Meiji 30). However, as it contained provisions that were outdated with the times, such as the compulsory isolation of infected persons, the blocking of traffic to infected areas, and compulsory disinfection, this law was abolished in 1999 (Heisei 11) and replaced by the Infectious Diseases Prevention and Medical Care Act (Infectious Diseases Act).

[Noriaki Yanagishita]

"Medical Science Selection: Epidemiology" by Yukiomi Shimizu and Masamitsu Kae (1997, Interzoo) " "How Humankind Conquered Infectious Diseases" by Harry Fillmore Dowling, translated by Yoshifumi Takeda (Kodansha Academic Library)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

病原体が宿主から宿主へと次々に感染を伝播(でんぱ)する疾患の総称で、しばしば感染症と同義に用いられるが、感染症のほうがより広義なものといえる。すなわち伝染病は、たとえば赤痢やインフルエンザなどのように人から人へと伝染して流行性におこりうる感染症を意味しており、破傷風や敗血症などのように人から人へ伝染することのない非伝染性感染症は含めないのが普通である。また回虫や肺吸虫など細菌やウイルスよりは高等な生物による感染症も、一般に寄生虫症として別に扱われる。なお、伝染病と似た用語に疫病があるが、これは伝染病のなかでもとくに全身的な症状を示して急性な経過をとり、集団的な発生、つまり流行するものをさす古い呼称であるが、伝染病と同義に解してもよい。

［柳下徳雄］

分類

伝染病は種々の観点から分類される。すなわち、発病や経過の緩急による分類、おもに侵される部位からの分類、感染経路による分類、病原体の微生物学的観点による分類をはじめ、感染症予防・医療法（感染症法）が指定している1類～5類感染症・新型インフルエンザ等感染症・指定感染症・新感染症、検疫法が指定している検疫感染症、学校保健安全法が指定している学校感染症などの法律的な分類もある。

　なお、これらとは別に国際伝染病という行政上の名称もある。これはラッサ熱、マールブルグ熱、エボラ出血熱などをいい、いずれも国内には常在せず、予防法や治療法も確立されていないため、致命率が高くて感染力も強いので、患者や検体の取扱いには特殊な施設を必要とする特定の伝染病である。また、最近注目されているものとしては、エイズ（AIDS）やB型肝炎、C型肝炎がある。

［柳下徳雄］

入院と治療

伝染病は、病気そのものの治療ばかりでなく、周囲へ広がるのを防ぐために伝染源となるおそれのある患者、疑似患者、保菌者や接触者などを一般社会生活環境からしばらく切り離して生活させる必要がある。とくに感染症予防・医療法において、1類、2類感染症、新型インフルエンザ等感染症および新感染症に分類される感染症の患者は、特定の設備がある感染症指定医療機関への入院が必要となる。検疫感染症の病毒に感染した者およびそのおそれのある接触者は、観察のために一定期間隔離されるが、これは停留とよばれる。なお、3類、4類、5類感染症の患者は自宅治療または一般の医療機関で治療してもよい。

　伝染病にかかるのは個人的な不注意にもよるが不可抗力的な場合も多く、また入院して治療を受けることは、なかば本人の治療のためであるが、なかばは周囲への感染を防ぐために個人的な不便、すなわち感染症指定医療機関では外出や退院が個人の自由にならないなどに耐えることでもある。したがって、これらの入院料や治療費が一部無料であり、国や市町村が負担して患者の負担をごく少額ですむように配慮されているのも、このへんの事情による。

［柳下徳雄］

治療の進歩とその影響

1930年代から1940年代にかけてサルファ剤や抗生物質などの化学療法剤が出現し、細菌性やリケッチア性の伝染病に対する治療が飛躍的に進歩し、病苦は速やかに軽減して致命率も著しく減少した。たとえば細菌性赤痢の場合、化学療法剤出現以前では普通1週間前後も頻回の下痢と腹痛に苦しめられ、死亡の危険が10～20％程度と大きかったが、化学療法剤が用いられるようになってからは、治療開始後1～2日で主要症状が消失して急速に回復し、致命率も1％以下に激減した。しょうこう熱、腸チフス、発疹(はっしん)チフス、流行性髄膜炎などについても同様である。しかし、この結果、ともすれば病気を軽視しがちで、こうした風潮が生じたことは予防上、困った問題となっている。

［柳下徳雄］

予防と対策

伝染病を予防するには、(1)外来伝染病から国全体を守ること、(2)国内に常在する伝染病の流行を防ぐこと、(3)個人レベルで感染を予防すること、以上の3点がもっとも重要である。そのためには、それぞれ、(1)検疫を完璧(かんぺき)に行うこと、(2)感染源となる患者や保菌者の早期発見と入院治療のほか、排出物・衣類・寝具などの消毒、病原体を媒介する昆虫類の駆除、上下水道などの環境整備、予防接種などを適宜実施すること、(3)感染の機会を避けるとともに個人衛生を守り、身体の抵抗力を増強するほか、予防接種も必要に応じて受けることが望まれるわけで、結局、国家―地域社会―個人の伝染病に対する認識または自覚と努力に還元される。

　従来、伝染病の予防、治療については、1897年（明治30）に施行された伝染病予防法によっていたが、感染者の強制隔離や感染地域の交通遮断、強制消毒など、時代の変化にあわない内容を含んでいたため、同法は1999年（平成11）廃止、かわって感染症予防・医療法（感染症法）が施行された。

［柳下徳雄］

『清水悠紀臣・鹿江雅光著『Medical Science選書　伝染病学』（1997・インターズー）』▽『ハリー・フィルモア・ダウリング著、竹田美文訳『人類は伝染病をいかにして征服したか』（講談社学術文庫）』