【解説】新型コロナウイルスの流行はどのくらい深刻なのか？

【パリＡＦＰ＝時事】中国・武漢で発生した新型コロナウイルスについて、深刻さや感染力の強さなど主な疑問についてまとめた。（写真は資料写真）

■どのくらい深刻なのか？
　２９日の時点で中国国内では６０００人近い感染者が確認されており、うち１３０人以上が死亡している。アジア諸国で合わせて約５０人の感染が確認されている他、オーストラリア、欧州、北米でも感染者が報告されている。
　これまでのところ死者は中国以外では出ていないが、２８日に確認されたドイツと日本の例は、人から人への感染だった。
　「２０１９─ｎＣｏＶ」と命名された新型ウイルスは、流行を引き起こし過去に多くの死者を出した二つの感染症と同じコロナウイルスの一種だ。一つは２００２～０３年に中国・北京から広がり、感染者８０９６人中７７４人が死亡した重症急性呼吸器症候群（ＳＡＲＳ）。もう一つは２０１２年に流行し、感染者２４９４人中８５８人が死亡した中東呼吸器症候群（ＭＥＲＳ）だ。この二つの流行での死亡率は大きく異なり、前者が９．５％、後者が３４．５％だった。
　今のところ、新型ウイルスによる死亡率は「５％未満」だと、パリ第７大学の感染症専門家、ヤズダン・ヤズダンパナ氏は言う。

■どんな症状が現れるのか？
　中国の研究者らが２４日に英医学誌ランセットに発表した４１の初期症例に基づいた報告によると、新型ウイルスの症状の一部はＳＡＲＳと似ている。
　患者は全員肺炎になり、多くは発熱し、観察例の４分の３でせき、半数以上で呼吸困難の症状がみられた。一方で、鼻水やくしゃみ、喉の痛みは少ないという「重要な違い」があるという。

■感染力はどの程度なのか？
　英インペリアル・カレッジ・ロンドンの研究者らは新型コロナウイルスの感染力について、患者一人当たりが２．６人に感染させると推計している。これは毎年流行するインフルエンザの感染力と同程度だ。
　中国国家衛生健康委員会の馬暁偉主任は、新型ウイルスの伝染が潜伏期に起きている可能性を指摘している。つまり、感染した人自身にまだ症状が現れていない段階で、他者に伝染する可能性があるということだ。ただし、この仮説はまだ完全には確認されていない。

■コウモリ由来のウイルスか？
　新型ウイルスは遺伝子構造の８０％が共通するＳＡＲＳウイルスと同様、コウモリに由来するのではないかと考えられている。だが、どの動物を通じて人へ感染したのかはまだ分かっていない。
　中国の研究チームは先週、中間宿主となったのがヘビである可能性を示唆したが、哺乳類が媒介となった可能性が高いと考える他の専門家らがすぐに反論した。ＳＡＲＳの場合は、ジャコウネコが中間宿主だった。ジャコウネコの肉は中国で人気が高い。

■予防策は？
　保健衛生当局や研究者らは、他のウイルス性疾患と同じ予防法を呼び掛けている。つまり頻繁に手を洗うこと、せきをする際には口を覆うこと、顔を手で触らないことなどだ。また感染が確認された場合は、隔離措置が必要だという。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/01/30-08:54）

How serious is the coronavirus outbreak? What are its symptoms and how contagious is it? Experts studying the new virus, still have key questions to answer before they can assess its danger.
- The toll so far -
As of Tuesday, more than 4,500 cases have been confirmed in China, its country of origin, of which 106 have been fatal. Several cases have been detected in Asian countries, as well as a few in Australia, France and the United States.
So far, no-one outside China has died, but both Germany and Japan on Tuesday confirmed cases of human-to-human transmission of the disease.
2019-nCoV, as it has been named, is part of the coronavirus virus family, the source of two previous fatal epidemics.
The 2002/03 SARS outbreak (Severe Acute Respiratory Syndrome) started in Beijing and killed 774 people out of a total 8,096 infected.
The 2012 MERS outbreak (Middle East respiratory syndrome) killed 858 people out of the 2,494 infected.
So those outbreaks had significantly different mortality rates of 9.5 percent and 34.5 percent respectively.
In general however, those hit by the new virus are in a less serious condition than with SARS, said Yazdan Yazdanpanah, head of infectious diseases at Paris Diderot University.
For the moment, the mortality rate is less than five percent, he added.
- Symptoms -
Chinese scientists reported in The Lancet Friday that, based on a study of 41 early-detected cases, some of the new virus's symptoms resemble those of SARS.
All patients had pneumonia, most had a fever, three-quarters of them were coughing and more than half had trouble breathing.
Despite this, lead author Bin Lao added: there are some important differences, such as a lack of runny noses, sneezing or sore throats.
The average age of the 41 patients studied was 49, most of them having visited Wuhan market, identified as the source of the outbreak. Nearly a third of them had serious breathing difficulties and six of them died.
All this gives a preliminary sketch of the new virus, even if one has to be cautious about drawing conclusions based on such a small sample.
The study is all the more important because a current epidemic of flu, which has similar symptoms, has made isolating patients of the new virus difficult.
- Contagion -
Scientists at Britain's Imperial College estimate that each coronavirus patient infects on average 2.6 others -- making it roughly as infectious as annual influenza outbreaks.
Ma Xiaowei, head of China's National Health Commission, said that transmission of coronavirus was possible during the disease's incubation period.
That means that someone who is sick with coronavirus would be able to pass it on to someone else even if they aren't yet displaying any symptoms.
This working hypothesis is yet to be fully confirmed, however.
In my view it is premature to conclude, on the basis of the evidence currently available, that the new virus can be transmitted before symptoms appear, said Mark Woolhouse, professor of Infectious Disease Epidemiology, University of Edinburgh.
- Origins -
Researchers think the new virus probably came from bats, as the SARS virus did, with which it shares 80 percent of its genetic makeup.
But we still don't know which animal passed it on to humans. Last week a Chinese team suggested it could be a snake, but that was immediately challenged by other experts, who think a mammal is the more likely culprit.
Identifying which animal it was could help fight the outbreak.
With SARS, it turned out to be a civet, whose meat is very popular in China.
Banning the consumption of civet and closing their breeding farms helped stop SARS from making a comeback, says Arnaud Fontanet of the Pasteur Institute in Paris.
On the other hand, one reason it was harder to stem the MERS outbreak is because it came from dromedary camels, a widely used working animal.
- Precautions -
Health authorities and scientists say the same precautions against other viral illnesses can be used: wash your hands frequently, cover up your coughs, try not to touch your face.
And anyone who does come down with the virus should be placed in isolation.
Considering that substantial numbers of patients with SARS and MERS were infected in health-care settings, precautions need to be taken to prevent that happening again, the Chinese team warned in The Lancet.