Ver.1.0 (140908-23:47)

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＜SMC発サイエンス・アラート＞

西アフリカにおけるエボラ出血熱のアウトブレイクについて

西アフリカでは、今年の2月よりエボラ出血熱の流行が拡大し続けています。7月31日、WHO（世界保健機関）は、ギニア、シエラレオネ、リベリア、ナイジェリアの4カ国で死者が計729人に上ったと発表し、警戒を呼びかけています。こうした事態について、海外の専門家のコメントを紹介します。

参考＞エボラ出血熱とは（国立感染症研究所HP）

http://idsc.nih.go.jp/idwr/kansen/k02_g2/k02_32/k02_32.html

 Andrew Easton 教授

Professor of Virology, University of Warwick School of Life Sciences

エボラ出血熱は1976年に西アフリカで発見され、当時の致死率は約62％でした。その後、24回の大規模な流行（アウトブレイク）が起き、死亡率は25〜90％と高いままです。このことは、対処が不完全であることを示しています。すでに診断ツールがあるにもかかわらず、経済的な理由で使われておらず、予防や治療の面でも状況が改善されていません。

【コメント原文】

“The first Ebola outbreak was in late 1976 and since then the advance in our knowledge and progress has been mixed. To date, including the current outbreak, there have been 3647 cases of infection in 24 separate incidents and 2262 deaths as a result of the infection – an overall fatality rate of 62%. The current outbreak with over 1200 cases is the largest seen and far exceeds the previous largest outbreak that involved 425 cases.  The mortality within outbreaks is very variable and has ranged from 25% (37 of 149 cases) to 90% (128 of 143 cases). The current toll of the West Africa outbreak is 672, though the number of cases and associated deaths continues to rise.  The consistently high mortality associated with Ebola virus disease reflects our lack of successful interventions with only supportive treatments being available.

 

“However, there have been some advances in Ebola virus research. We now fully understand the genetic makeup of the virus strains that have been associated with human infection. Five distinct strains have been identified, of which three have been associated with large outbreaks of Ebola virus disease. Modern diagnostic tools are available to rapidly identify Ebola virus, though access to these in the isolated rural areas of Africa remains problematic for financial and practical reasons. This is unfortunate because rapid diagnosis early in an outbreak is likely to reduce the impact of the infection.

 

“In terms of treatment there have been no significant advances at all. Our greater understanding of the route of transmission of the virus between people – through close contact with body secretions and infected blood – means that healthcare staff can take measures to reduce the risk of infection from the patients they are treating and family members can be alerted to the risks.

 

“Of particular note is the discovery that Ebola virus can persist for several weeks in patients who have recovered and are not presenting with any symptoms of disease. This provided a mechanism for the virus to reappear after an outbreak was apparently declining.

 

“Finally, we have a greater, but not complete, understanding of the natural animal host in which Ebola virus resides and from which it is introduced into human populations. While Ebola can infect many wild animal species fruit bats are the most likely source of transfer to humans. This knowledge led to the banning of sales of bats in markets in Guinea.

 

“The overall picture is that while we know a great deal about the virus we have a long way to go in providing effective and accessible prevention and treatment for those at risk.”

Tom Solomon教授 

Director NIHR Health Protection Research Unit in Emerging and Zoonotic Infections, and Professor at Institute of Infection and Global Health, University of Liverpool

Q:エボラ出血熱は治療することができますか？

A:エボラ出血熱の抗ウイルス薬もワクチンもありません。経口および静脈からの水分補給などの対処療法しか行えません。

Q:ブタインフルエンザのように広がるとお考えでしょうか？

A:今回の流行が、以前の流行よりも拡大している点は憂慮すべきです。ただし、エボラウイルスは空気感染しないので（血液や体液を介する）、インフルエンザでおきるようなパンデミックにはならないと考えます。

Q:今回の流行がこれまでと異なる点は？

A:第1に、流行の規模が大きいという点。第2に、地理的に離れた地域に流行が広がっているようにみえる点です。

Q:ウイルスが「感染しやすい型」に変異しているのでしょうか？

A:現在までのところ、そのような証拠は出ていません。

Q:感染拡大を食い止めるために何をすべきでしょうか？

A:医療従事者がガウン、手袋、ゴーグル、マスクを使い、患者の血液や汚物を確実に処理することです。遺体は専門家チームによって速やかに火葬する必要があります。

【コメント原文】

Q1.  What is Ebola?

A1. “Ebola is a disease caused by Ebola virus.”

 

Q2. What are the symptoms?

A2. “The first symptoms of the disease are fever, severe headache, muscle aches, and abdominal pains. There are often small vesicle lesions in the mouth and at the back of the throat, which are associated with a very sore throat, and maybe pain down the throat and into the chest. The whites of the eyes may become red (called conjunctival injection), and patients may have diarrhoea and a skin rash. This is followed by bleeding (haemorrhage) which may occur from the mouth and other body orifices, for example bloody vomiting and bloody diarrhoea. This leads to a low blood pressure (known as shock) and the body’s clotting becomes completely disarrayed, and patient’s metabolism goes awry and they become acidotic. The brain can also be involved to cause convulsions and coma.  Deaths occur around the tenth day of illness. Death is usually caused by multiple organ failure, caused by dehydration, the abnormal metabolism and acidosis, rather than due to blood loss.”

 

Q3. How bad is it? (What does it do and what proportion of people die?)

A3. “Ebola is worrying because:-

a. it is not completely clear how humans become infected in the first place at the start of an outbreak

b. it can spread from human to human, as described above

c. The death rate depends on the subtype of Ebola virus; but it can be up to 90%, making it one of the most severe infections of humans”

 

Q4. How does it spread?

A4. “Research suggests the virus exists naturally in some fruit bats, and that humans can become infected directly from the bats (perhaps through exposure to bat blood, or other bodily fluids excreta – faeces and urine).  Humans may also become infected by contact with blood or bodily fluids of moneys, or “bush meat”; i.e killing, butchering, and eating the meat of bush animals, that had presumably become infected from the bats.

Once the first person has become infected, then others are at risk, because the virus is excreted in a patient’s blood and other bodily fluids. Family members and health care workers looking after patients are especially at risk. In the early outbreaks the lack of precautionary and protective measures and the reuse of non-sterilised needles contributed to the rapid spread.  Some traditional burial customs, whereby all mourners touch the body, also causes the virus to spread, because the virus may be on the skin.”

 

Q5. What can we do to treat it?

A5. “There is no antivirus drug to treat Ebola. However, if we can keep people alive through replacing lost fluids etc, by oral or intravenous rehydration, then this gives their body the best chance of fighting the infection itself. There is no vaccine to protect people.”

 

Q6. Should we be concerned that it’s going to spread like the swine flu pandemic?

A6. “The fact that this Ebola outbreak has spread more than any previous ones is worrying, and we are doing research to try and understand why this is. However, because it does not spread via the respiratory route (i.e. people coughing and sneezing on each other) it is unlikely to cause a pandemic like flu.”

 

Q7. Are people infectious before they show symptoms? How long are they infectious for?

A7. “Typically people are infected for 4-10 days before they start to show symptoms, though it can be as little as 2 days, and as much as 3 weeks. However, as far as we know they are unlikely to spread the virus until they start having the symptoms of bleeding, etc. If people survive the acute stages they may remain infectious for up to 2 months.”

 

Q8. Is this outbreak different to others and if so, how?

A8. “This outbreak is different to others in several respects. Firstly, it is larger than previous outbreaks. More than 670 people have died. Secondly, it appears to be spreading between different geographical places more easily than other outbreaks. So far it has spread from Guinea to Sierra Leon, Liberia, and now Nigeria.”

 

Q9. How can we detect whether someone has Ebola?

A9. “If someone has symptoms suggestive of Ebola, then we can test their blood for the virus, by detecting the virus itself, or looking for antibodies to the virus.”

 

Q10. How likely is it that Ebola will mutate into something that can spread more easily?

A10. “There is nothing to suggest this so far. The current outbreak is caused by Ebola Zaire strain, which is the most dangerous strain of the virus.”

 

Q11. What do people need to do to stop it spreading?

A11. “The risk of spread is reduced by people wearing protective clothing (barrier nursing) when they are looking after patients. The use of gowns, gloves, goggles and masks greatly reduce the chance of someone becoming infected. The risk of spread is greatest later in the disease when patients are bleeding. Diarrhoea, vomit, and blood from patients need to be decontaminated. The risk of respiratory spread, whereby virus is spread from one person breathing, coughing or sneezing on another is thought to be very low. When patients die they should be buried promptly, or cremated by specialist teams, to avoid the risk of virus being transmitted to mourners.”

 

Q12. What are researchers in the UK doing to protect us?

A12. “I lead the NIHR Health Protection Research Unit in Emerging and Zoonotic Infections which was established by the UK Government in April 2014 to help protect us from infections like Ebola. It is a collaboration between researchers from the University of Liverpool’s Institute of Infection and Global Health, the Liverpool School of Tropical Medicine, and Public Health England.  Members of the Health Protection Research Unit are currently helping to fight the Ebola outbreak in Africa, as well as doing research to try and better understand why this outbreak is especially bad. The Health Protection Research Unit’s virologists are doing research to understand what makes particular strains of Ebola more severe. The Unit’s epidemiologists and modelers are working together to understand the factors involved in its spread, and the risks to the UK.”

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