海外専門家コメント
WHO、アメリカ大陸のジカウイルス感染者が最大で400万人に達するとの予測発表
・これは、2016年1月29日にジャーナリスト向けに発行したサイエンス・アラートです。
・記事の引用は自由ですが、末尾の注意書きもご覧下さい。
＜海外SMC発サイエンス・アラート＞
WHO、アメリカ大陸のジカウイルス感染者が最大で400万人に達するとの予測発表：海外専門家コメント
中南米とカリブ諸国において感染が拡大しているジカウイルス（*）について、WHO（世界保健機関）は1月28日、アメリカ大陸での感染者が最大で400万人に達する恐れがあると発表し、2月1日にジュネーブで緊急委員会を招集することを決めました。すでにお伝えしたように、流行国の一つであるブラジルでは先天性小頭症（**）が急増しており、母親が妊娠中にジカウイルスに感染したこととの関連解明が急がれています。この件についての海外専門家コメントをお送りします。
*ジカウイルス
フラビウイルス科に分類され、遺伝子として1本鎖のRNAをもつウイルス。デング熱も同じグループに属するが、ジカウイルスによる症状でみられる発熱、頭痛、発疹などは、デング熱よりも軽いとされる。
**先天性小頭症
頭蓋骨が十分に成長せず、脳が異常に小さくなる病気
翻訳は迅速さを優先しております。ご利用の際には必ず原文をご確認ください。
【参考リンク】
WHOによる報告（WHOのHP）
ジカ熱について（厚生労働省HP）
http://www.mhlw.go.jp/stf/seisakunitsuite/bunya/0000109881.html
Dr Grant Hill-Cawthorne
Medical Virologist and Senior Lecturer in Communicable Disease Epidemiology at the Marie Bashir Institute, University of Sydney
ジカウイルスのタイプとして、アフリカ系統とアジア系統の２つが知られています。今回の南アメリカでの流行は、アジア系統によるものだとわかっています。今のところ、このジカウイルスに感染しても約80%の人には何の症状も見られず、残りの20%に軽い頭痛、発疹、微熱、関節痛、結膜炎などがみられる程度で、死亡の報告はありません。
ただし、合併しておきると考えられる2種の疾患が問題視されています。一つは、フランス領ポリネシアでみられたギラン・バレー症候群(GBS)です。73例と比較的まれといえますが、GBSを合併した患者の25％が筋力低下によって呼吸困難に陥り、人工呼吸器を必要としました。もう一つは、現在のブラジルで急増している先天性小頭症です。ブラジルでの先天性小頭症発生は年間150例ほどですが、ジカ熱が流行した昨年は3000～4000例に増えています。
原文
"There are two types, or lineages, of Zika virus – the African and the Asian lineages. Recent genetic studies have shown that the one currently causing a panic in South America belongs to the Asian lineage.
Around 80% of people infected with the virus do not experience any symptoms. However for the rest it typically presents with a mild headache, followed by a rash, mild fever, joint pains and conjunctivitis (pink eye). It is usually mild and there have been no reported deaths.
However, there have been two concerning aspects that have appeared in the recent outbreaks. In French Polynesia there were 73 cases of a relatively rare condition called Guillain-Barré syndrome. This is a rapidly progressive muscle weakness due to damage to the peripheral nervous system. A quarter of people affected by GBS go on to experience weakness of their breathing muscles and need artificial ventilation.
The other, even more concerning, aspect is a significant increase in cases of microcephaly in Brazil. Microcephaly means “small head” and can stem from a number of conditions that cause abnormal growth of the brain. Children affected often have impaired intellectual development and may have neurological defects and seizures. Brazil usually sees 150 cases per year, but has recently reported 3000–4000 cases in the past year, occurring in the same timeframe as the spike in Zika virus cases.
What is the risk in Australia?
The Aedes group of mosquitoes can transmit the virus. The most efficient transmitter is the day-biting mosquito Aedes aegypti, which exists in Australia in tropical areas such as far north Queensland. The global distribution of this virus is increasing due to global trade and travel and climate change.
In 2009 there was a case of an infected biologist passing on Zika virus to his wife via sexual transmission. In 2015 Zika virus genetic material has been detected in the amniotic fluid and placenta of infected mothers, suggesting that mother-to-child infection could occur. There have been a number of travellers returning to Australia infected with the virus over the last few years. In theory it could be transmitted via the A. aegypti mosquitoes present in Australia in the same way that limited outbreaks of dengue virus are seen in Queensland. Therefore it is important to continue with mosquito-control problems in far north Queensland to prevent this possibility.
It already has come to Australia in returning travellers but there have not yet been any reports of transmission within the country. This is a possibility in areas that see limited outbreaks of dengue virus, for example, and so it is important for everyone to be vigilant and take precautions against mosquito bites in at-risk areas."
Prof Michael Bonsall
Professor of Mathematical Biology,University of Oxford
WHOの推定値は妥当だと思いますが、急ぐべきなのはジカウイルスを媒介する蚊の駆逐でしょう。航空機で運ばれないようにすることも重要です。媒介蚊の一つであるネッタイシマカは熱帯・亜熱帯性なので、英国で生息できる確率は非常に低いと思います。WHOは一般的なヤブカ（ヒトスジシマカなど）もウイルスを伝播するとし、イエカについては現時点では媒介を疑う証拠がないとしていますが、私もそのとおりだと思います。
原文
“WHO have estimated there may be 3-4 million cases of Zika in the Americas over the next 12 months, but I think we would need to see the model details before being able to be clear on the predictions. WHO’s estimate was based on previous dengue outbreaks – the epidemiology of Zika is different from dengue but because transmission is by the same Aedes vector the estimate is probably sensible. Fast and effective vector control will be absolutely essential here. Aedes aegypti is day-flying and urban-dwelling so appropriate vector controls to prevent ‘explosive spread’ are paramount.
“Regarding questions from the media about whether Culex mosquitoes could be involved with this Zika outbreak, I agree with WHO that Aedes aegypti is quite enough to be responsible for the rate of infection we are seeing (Aedes aegypti is urban and likes humid places, hence why Recifie is at such high risk).
“Aedes aegypti is the mosquito implicated in the current epidemic in Brazil. It is very unlikely that these mosquitoes could live in the UK because they are a tropical and subtropical beast. There are around 30 other species of mosquitoes in the UK of which about 1/2 are in the Aedes genus (group) but are different sepcies. Species of Culex mosquito can be easily mis-identified as Aedes.”
Prof Paul Reiter
Consultant on mosquitoes and mosquito-borne diseases and Professor of Medical Entomology, Pasteur Institute
WHOの流行予測は不確実性が高いと考えます。なぜなら、感染しても症状の出ない不顕性感染も多いと思われるからです。つまり、400万人というと極めて多いように思えますが、不顕性感染を含めると過少な推定値なのかもしれないということです。
原文
“There are many uncertainties with WHO’s estimate of the number of Zika virus infections there may be in the Americas. An important one is the ratio of asymptomatic to symptomatic cases. This can be very high (many more asymptomatic than symptomatic cases), and may vary with the strain.
“Four million clinical cases may sound a lot but may well be an underestimate. For comparison, in one dengue epidemic that we investigated in Guayaquil, Ecuador, we estimated 405,000 cases in about four months. That city had 2 million people so was smaller than many urban areas in the Americas and in Asia.
“Regarding Culex mosquitoes and Zika, I totally agree with the WHO – there is no evidence in the field or in the laboratory that Zika or closely related viruses (e.g. dengue, yellow fever) can replicate in any species other than the urban Aedes (Aedes aegypti and Aedes albopictus) that are implicated in all outbreaks. The hyper-abundance of Aeges aegypti (which we already know is implicated in this Zika outbreak) is more than enough to sustain the very high incidence of Zika virus that we are seeing. So there’s nothing to suggest that any Culex species are involved.
“Aedes aegypti has never been established in Britain. It has no diapause or cold-hardiness and so is unable to survive our climate. Moreover, it is an urban species, closely associated with human habitation—that is why it is such a good vector in cities throughout the tropics—and is never found in the countryside.”
Prof Jonathan Ball
Professor of Molecular Virology, University of Nottingham
現在の流行はジカウイルスに暴露されたことのない地域でみられており、驚くべき現象とはいえません。今後も散発的な大流行がおきるでしょうが、女児が出産適齢期を迎える前に感染して免疫を得ることは悪いことではないと思います。WHOによる予測シナリオはあり得ると思いますが、これまでのジカ熱は風土病であり、世界規模でどう流行するかはよくわかりません。私たちの周りにいるヤブカについては警戒すべきです。
原文
“The numbers likely to be infected by Zika in the current Americas outbreak are immense, but not so surprising. The virus has been unleashed in an area where its insect vector is widespread and the human population has never been exposed in the past – they don’t have any immunity and so the mosquito can pass the virus from person to person unhindered.
“Eventually the outbreak is likely to burn itself out as people become exposed then immune. But it is unlikely to disappear completely. In future it will probably survive by causing sporadic outbreaks and by infecting people who haven’t been exposed to the virus, for example children. An infection of children wouldn’t be a bad thing as it would probably mean that they are immune to later infection, particularly when they are at a child-bearing age. So by a natural process we would hope that the really serious effects that Zika might be having on unborn children will dwindle in those areas where the virus does become endemic.
“But these are possible scenarios but until we know how the virus behaves, in this and in previous outbreaks, and where it is endemic, we won’t be able to make predictions with any degree of certainty.
“The viruses survive by infecting their human host and also the insect that spreads them. Maintaining an ability to infect both species puts a lot of genetic pressure on the virus to stay the same. So whilst not impossible the virus is unlikely to change its insect vector. And you have to ask, why would it anyway? There are enough Aedes mosquitos around to enable it to spread.”
Dr Anthony Wilson
Head of the Integrative Entomology group within the Vector-borne Viral Diseases Programme, The Pirbright Institute
WHOは現時点でイエカがジカウイルスを媒介している証拠はないとしていますが、そのとおりだと思います。媒介蚊であるネッタイシマカとヒトスジシマカのうち、前者はイギリスでは生息できませんが、より耐寒性をもつ後者は南欧の一部で発見されています。ただし南欧のヒトスジシマカからは、現時点でジカウイルスは検出されていません。
原文
“The WHO’s comments in response to questions about the vector responsible for the current Zika outbreak in Brazil, that we know Aedes aegypti is implicated and that there’s no reason to suspect Culex mosquitoes of being involved, is perfectly reasonable – other Aedes-borne arboviruses spread rapidly in the area and there is no reason to expect Culex to be involved based on the current pattern of spread. Other Aedes mosquitoes could plausibly be involved in the Brazilian outbreak, such as Aedes albopictus (the Asian tiger mosquito), which does also occur in parts of southern Europe (although not in the UK), although there is no evidence for that yet and there are no outbreaks of Zika in southern Europe.
“Aedes aegypti, the yellow fever mosquito, does not occur in the UK. It’s too cold for Aedes aegypti to establish in the UK, although in ideal summer conditions introduced individual mosquitoes might be able to survive for a few days; there was a small outbreak of yellow fever in Wales (Swansea) in 1861 which is believed to have been spread via mosquitoes that were inadvertently introduced on a ship returning from Cuba. It is plausible that a related species, Aedes albopictus (the Asian tiger mosquito) could be playing a role in the transmission of Zika virus in the Brazilian outbreak; it has been implicated during other Zika outbreaks. Aedes albopictus is more cold-tolerant and individuals introduced into Belgium and Netherlands have been detected in the past, although they have failed to establish in those locations. Aedes albopictus is found in parts of southern Europe, but Zika has not been seen there.”
記事のご利用にあたって
マスメディア、ウェブを問わず、科学の問題を社会で議論するために継続して
メディアを利用して活動されているジャーナリストの方、本情報をぜひご利用下さい。
「サイエンス・アラート」「ホット・トピック」のコンセプトに関してはコチラをご覧下さい。記事の更新や各種SMCからのお知らせをメール配信しています。
サイエンス・メディア・センターでは、このような情報をメールで直接お送りいたします。ご希望の方は、下記リンクからご登録ください。（登録は手動のため、反映に時間がかかります。また、上記下線条件に鑑み、広義の「ジャーナリスト」と考えられない方は、登録をお断りすることもありますが御了承下さい。ただし、今回の緊急時に際しては、このようにサイトでも全ての情報を公開していきます）【メディア関係者データベースへの登録】 http://smc-japan.org/?page_id=588
記事について
○ 私的／商業利用を問わず、記事の引用（二次利用）は自由です。ただし「ジャーナリストが社会に論を問うための情報ソース」であることを尊重してください（アフィリエイト目的の、記事丸ごとの転載などはお控え下さい）。
○ 二次利用の際にクレジットを入れて頂ける場合（任意）は、下記のいずれかの形式でお願いします：
・一般社団法人サイエンス・メディア・センター ・（社）サイエンス・メディア・センター
・（社）SMC ・SMC-Japan.org○ この情報は適宜訂正・更新を行います。ウェブで情報を掲載・利用する場合は、読者が最新情報を確認できるようにリンクをお願いします。
お問い合わせ先
○この記事についての問い合わせは「御意見・お問い合わせ」のフォーム、あるいは下記連絡先からお寄せ下さい：
一般社団法人 サイエンス・メディア・センター（日本） Tel/Fax: 03-3202-2514
