Chris Smith, University of Cambridge
This week weíve seen reports from West Africa of the worst outbreak of the ebola virus since the disease was first discovered in the 1970s. So far over 700 people have died in Sierra Leone, Guinea and Liberia. Governments internationally have been holding emergency meetings to discuss the threat. Ginny Smith put your questions to Virologist Chris Smith...
Ginny - But what exactly is Ebola? Where did it come from and what can we do to stop it? Chris, you are a virologist. In fact, weíve already had a question in from Twitter (@chainG) wants to know what causes Ebola.
Chris - Ebola Ginny, is a virus. Itís what we call a filovirus and down a microscope, you see this very thin, they look almost like little straws or tent pegs because they often bend over and tangle themselves up or sometimes even wire themselves up into sort of figure of 8 shape. They're about 18 nanometres. So, 80 millionth of a millimetre across and up to about a thousandth of a millimetre long. When they spread which they do via body fluids of an infected case, or sometimes even via the air possibly which is interesting because weíve had a tweet here from Collin Parrington (13:15) who says, ďWhy do healthcare workers cover their noses with a mask if Ebola is not airborne? Do they think itís potentially airborne?Ē Yes, we do. And if a person has Ebola then any part of their body is infectious. When they're injured or a needle goes into them to take a sample or when they give fluids or if they're sick or they have diarrhoea, all of these body fluids are infectious and can go up into the air, and a person can get those particles landing on their eyes or in their mouth, and it can infect them.
Ginny - What makes Ebola so deadly? Why are so many people dying from it?
Chris - Well, itís not a human infection, and itís naturally an infection of fruit bats. Weíve found this since 2005 when a scientist called Eric Leroy did a big trapping exercise in Africa and went and trapped all the animals that he could around areas where there were outbreaks of Ebola actually affecting great apes because itís not just humans who succumb. And they found that when they tested the bats that they caught for antibodies to Ebola and also the genetic material of Ebola, they were positive of both proving that they were both infected and carrying the Ebola virus which is what you would expect of a carrier. And so, it looks like itís bats passing it into other animals and then into people or even directly into people and then you get an outbreak in humans.
Ginny - So, does that mean itís not quite as deadly for the bats.
Chris - Yes and that's why itís nasty for people because the viruses evolve to live in a bat and itís not very good if you kill your host too quickly because you can't pass yourself onto others. You want to maintain a state where your host is infectious in carrying you, but not killing you. But a batís immune system and a batís body is very different to a human. Weíre both mammals, but weíre quite distinct from each other. The viruses evolved to outwit the immune system of the bat, but when it gets into a human, itís a massive case of overkill and the virus goes into actually our immune system itself. It attacks cells called dendritic cells, grows in those, but at the same time, triggers the release of huge numbers, or huge amounts, of immune signalling chemicals that drive the immune system absolutely haywire. And at the same time, cause lots of our first line of defence Ė our lymphocytes Ė which are the white blood cells that fight off infection. It drives them to commit suicide. And so, you end up with a very, very poorly functioning immune system and the release of lots of inflammatory chemicals that cause your body to go into a sort of shock.
Ginny - So, itís almost turning our own bodies against themselves. Are there any treatments for it?
Chris - At the moment, no and this is the big problem. The only thing we can offer people is supportive therapy. That means that basically, you prop up their failing organs using whatever means you can, making sure people have enough fluids, making sure they have calories going into them, making sure their blood pressure stays up. And also, dealing with the coagulation problem because the shock state that people go into means that they consume all of their owm clotting factors. As a result, there's a high risk of bleeding. One of the characteristics of late phase Ebola is people bleed from every orifice pretty much. Even their tears can be full of blood. So, making sure that doesnít happen by supportive management is the mainstay and ultimately we would hope we can get a vaccine.
Ginny - That was going to be my next question. I've heard talks of a vaccine. Are we far away from that?
Chris - There have been experiments done and scientists in a number of countries including in the States have done various studies where they have taken certain coat proteins, the outer coat of Ebola. They've inserted the gene for that into another harmless virus, an adenovirus that normally causes the common cold. The idea being that you could infect someone with that that when the common cold virus was multiplying, it would also show the immune system what Ebola looks like and you would therefore safely make antibodies against Ebola. So, if you did then catch Ebola, you'd have antibodies that could defend you and protect you.
Ginny - And how far is that away from being able to actually help people?
Chris - Well, it hasnít really been a research priority because until now, Ebola hasnít been a big threat to countries that have the money or the will to want to make a vaccine. This latest outbreak is the largest weíve ever seen in the four decades since Ebola was first discovered in 1976. The fact that now, more than 700 people have died, weíve got more than 1200 cases and itís affecting people who are going into airports and potentially, within striking distance of western countries. Suddenly the minds of western countries have been focused and itís been made a research priority now to try to develop a vaccine that might work.
Ginny - And how likely do you think it is that it might spread and affect say, us here in the UK?
Chris - Well, I think at the moment, the risk is really small, luckily. I don't think we have to worry straightaway. But the fact is that there are millions of airplane flights happening and people travelling via airplanes all the time. And as a result, you've got very rapid transit between countries and the incubation period of Ebola can be up to 3 weeks. So, itís perfectly feasible for someone to leave a country incubating, but not symptomatic with Ebola, arrive in another country like a western country and then go out, but go about their business becoming infectious and potentially infecting people before we actually know what they've got and therefore, we could get an outbreak. That's why governments have been meeting to discuss various strategies to stop it if that does happen.
I heard a suggestion that the Ebola virus sheds a lot of loose virus coat protein into the bloodstream. Antibodies attack the loose protein instead of the protein forming the virus coat, which diverts the immune response.