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Ebola

Professor David Evans, Life Sciences

Published May 2015

The Ebola outbreak in West Africa which started in December 2013 has rapidly become the deadliest since the discovery of the virus. But what do we really know about this deadly disease? Virologist Professor David Evans explores a little of the history and biology of Ebola.
What is Ebola?

Ebola is a virus that doesn’t normally infect people, but transmits from animals to humans now and again. Unfortunately, once contracted, it causes pretty devastating symptoms, with a fatality rate from 50% – 90%. It was discovered in 1976 and since then it’s caused about around 14 outbreaks in the human population, usually in sub-Saharan Africa. It’s what’s called a level 4 pathogen, these are the most dangerous pathogens, and there’s only a small number of people and places which can work with them.

David Evans
Where does the virus come from?

We’re pretty sure bats are the hosts, or ‘reservoir’ for the virus, and bats are a major source of protein in some parts of Africa. When hunters butcher game, it’s possible they might cut their fingers, allowing the virus to transmit to humans. There are well established precedents for this type of transmission of other virus infection; for example, HIV has been transmitted from chimpanzees to humans at least three times via this route.

How have outbreaks been tackled in the past?

In every previous outbreak it’s been controlled using quarantine. Agencies such as the World Health Organisation or Médecins Sans Frontières‎ provide resources to tackle the outbreak – cases are identified and isolated, their contacts are traced and also monitored, supportive care is given to patients. This reduces transmission opportunities, and the virus dies out.

What was different about this outbreak?

In previous cases there’s been natural geographic isolation because outbreaks have generally occurred in isolated communities. Additionally, outbreaks have been tackled promptly before they have spread extensively. Although the index case in the recent West African outbreak was in a tiny village on the boarders of Guinea, Liberia and Sierra Leone, it very rapidly moved into big urban areas. Urbanisation coupled with economic devastation as a result of civil war in the affected parts of West Africa meant that while communication and transportation links helped spread the virus, the weakened governments and health services were unable to deal with the scale of the outbreak.

What does your work with viruses at Warwick entail?

I have spent my career working on the replication and evolution of viruses with ribonucleic acid (RNA) genomes. The RNA encodes the proteins that makes virus particles and contains signals that controls virus replication. The RNA changes as the virus evolves. It concerned me when the press were speculating that Ebola could “evolve” to become aerosol transmitted and I got involved in the debate. Ebola is transmitted directly via bodily fluids. To become aerosol transmitted (like ‘flu for example) would likely require extensive change in the virus lifecycle. Evolution works in incrementally small beneficial steps and it’s unlikely that sufficient would occur in the extremely acute infections that occur in humans. The virus occupies an environmental niche – probably in bats – and transmits perfectly adequately in its normal host, so there is no selection pressure to become aerosol transmitted. HIV has been in the human population for decades, infecting millions of people, without becoming aerosol transmitted.

What’s the future of Ebola treatment?

It’s more research and improved monitoring of potential outbreaks. Ebola effects a very small number of people in relation, for example, to malaria and it is important to retain a sense of proportion. The current outbreak has been devastating with more than 11,000 deaths. However, malaria kills about 1,500 people a day and more than a million people a year die of HIV in Africa. I expect we’re going to be able to protect people against Ebola, but developing something that’s effective, safe and economically viable is going to take time and require changes to the way we test and licence medicines. However, developments on Ebola treatment and prevention will also help us control the closely related Lassa and Marburg viruses, which cause annual outbreaks in Africa. I believe that the developed world has a moral and ethical obligation to research what are relatively obscure diseases to us, but potential devastating threats to developing communities. One promising approach is a therapeutic called Zmapp, a really neat technology which pits a cocktail of antibodies against the Ebola virus. Studies in non-human primates have been extremely promising and suggest it might be able to cure patients not only post-infection but also after the onset of disease. Finally, since prevention is better than cure, there are phase 2 trials of vaccines underway which are also showing considerable promise. So there is hope and we must persevere with our research.


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