Lassa fever

Japanese: ラッサ熱 - ラッサねつ（英語表記）Lassa fever

What kind of infection is it?

In 1969, a patient with a hemorrhagic fever-like illness broke out at a hospital in Lassa village in northeastern Nigeria (Lassa General Hospital), and medical staff at the hospital also died of the same illness. The virus that was first isolated at that time was the Lassa virus. It was named Lassa fever because the name of the village was Lassa.

Lassa fever is endemic in West Africa, where hundreds of thousands of people are infected with the virus every year, and although the exact number is unknown, many are believed to have died. To date, more than 20 people have contracted Lassa fever in areas other than the endemic area. Most of these people are in Europe, but imported cases of Lassa fever have also been confirmed in the United States and Japan.

Lassa virus Host ( Shuck ) is called Mastomys rodent ( Ghastly ) (A member of the rat or squirrel family). Mastomys infected with the virus continuously excrete the virus in bodily fluids such as urine, and if a human becomes infected with the virus, they will develop Lassa fever. The virus is not transmitted through the air.

If you are staying in West Africa, it is important to prevent infection with the Lassa virus by maintaining a hygienic environment and preventing rats and other insects from entering your living area.

How symptoms manifest

The incubation period is 5 to 21 days. Symptoms include fever, Fatigue ( Health test ) , muscle pain, abdominal pain, vomiting, diarrhea, Pharyngitis ( Introductory ) Symptoms, Sternal back pain ( Today's Animals ) , cough ( cough ) , conjunctivitis ( Ketsumakuen ) Symptoms include facial edema, purpura, and impaired consciousness. Hearing loss ( What a ) Although the exact morbidity and mortality rates among infected individuals are unknown, it is estimated that approximately 80% of infected individuals develop mild Lassa fever, and 20% develop severe Lassa fever.

Testing and diagnosis

It is difficult to diagnose viral hemorrhagic fevers based on clinical symptoms alone, and diagnosis is based on virological tests that detect viral antigens and specific antibodies against the virus.

Treatment methods

Treatment is primarily symptomatic (maintenance of cardio-respiratory dynamics, fluid and blood transfusions, electrolyte correction, etc.), but it has been experimentally confirmed that ribavirin, an antiviral drug, can suppress the proliferation of the Lassa virus, and if this drug is administered early in the onset of the disease, it can be expected to be effective.

Under Japan's Infectious Diseases Control Act, Lassa fever is classified as a Class 1 infectious disease, and patients are treated in special isolation rooms.

Masayuki Saijo

Source: Houken “Sixth Edition Family Medicine Encyclopedia” Information about the Sixth Edition Family Medicine Encyclopedia

Japanese:

どんな感染症か

　1969年にナイジェリア北東部のラッサ村の病院（ラッサ総合病院）で、出血熱様疾患の患者が発生し、その病院の医療従事者も同様の疾患にかかって死亡しました。その時にはじめて分離されたウイルスがラッサウイルスです。この村の名前がラッサ村であったことから、ラッサ熱と命名されました。

　ラッサ熱の流行地は西アフリカで、そこでは毎年数十万人の人がラッサウイルスに感染し、正確な数は不明ですが多くの人が死亡していると考えられています。また、現在までに20人を越える人が流行地以外の地域でラッサ熱を発症しています。その地域の多くはヨーロッパですが、米国や日本でも輸入感染例としてのラッサ熱患者の発生が確認されています。

　ラッサウイルスの宿主(しゅくしゅ)はマストミスと呼ばれる齧歯類(げっしるい)（ネズミやリスの仲間）です。ウイルスに感染しているマストミスは、ウイルスを持続的に尿などの体液に排出し続け、そのウイルスにヒトが感染するとラッサ熱を発症します。空気感染はしません。

　西アフリカに滞在する場合には、ネズミなどが生活圏に入り込まないように衛生環境を整えることが、ラッサウイルス感染を予防するうえで大切です。

症状の現れ方

　潜伏期間は5～21日です。症状は、発熱、倦怠感(けんたいかん)、筋肉痛、腹痛、嘔吐、下痢、咽頭炎(いんとうえん)症状、胸骨背部痛(きょうこつはいぶつう)、咳(せき)、結膜炎(けつまくえん)症状、顔面浮腫、紫斑、意識障害で、後遺症として難聴(なんちょう)を残すこともあります。感染者での正確な発症率や死亡率は明らかではありませんが、感染者のおよそ80％が軽症のラッサ熱を、20％が重症のラッサ熱を発症すると推定されています。