8) A型肝炎

Hepatitis A

A型肝炎は，A型肝炎ウイルス(HAV)の経口感染により引き起こされる伝染性疾患である．患者の排泄物や汚染された飲食物が感染源となる．一般に予後良好な疾病ではあるが，数か月間の療養を必要とし，社会的・経済的損失は大きい．本邦では，衛生環境の改善に伴いA型肝炎の大規模な集団発生はみられなくなった。近年の患者報告数は年間200人程度である．感染機会の減少に伴い，HAV防御抗体をもたない感受性者が増加し，全人口の88％に及ぶ．A型肝炎はワクチンで予防できる疾病である．A型肝炎ワクチンは効果・安全性ともに高い．A型肝炎の予防は衛生管理，ワクチン接種，もしくはガンマグロブリンの投与が有効である．

Hepatitis A is a self-limited disease which results in fulminant hepatitis and death in only a small proportion of patients.　However, it is a significant cause of morbidity and socio-economic losses in many parts of the world.

Hepatitis A is caused by the hepatitis A virus (HAV).　Transmission of HAV is typically due to the fecal-oral route.

In Japan, with improved sanitation and hygiene, cases of HAV infection have decreased (200 cases annually) and, consequently, the number of persons susceptible to the disease has increased.　The latest ratio of the susceptible population is 88%.

Hepatitis A is a vaccine preventable disease.　Hepatitis A vaccine is safe and the efficacy is long lasting.　Vaccination, good hygiene practice and the administration of HAV immune globulin are effective hepatitis A preventive measures.