Ebola virus disease (EVD) kills up to 90% of those infected, making it one of the deadliest diseases known to affect humans. It is so dangerous that it is considered a Grade A bioterrorism agent – on par with anthrax, smallpox, and bubonic plague. Dr Derek Gatherer, a bioinformaticist at Lancaster University, has documented the latest Ebola outbreak since its beginning in December 2013, when the disease re-emerged for the first time since 2001. Gatherer has published an Insight Review about it in the Journal of General Virology.
The current outbreak of EVD has seen confirmed cases in Guinea, Liberia and Sierra Leone, countries in an area of West Africa where the disease has not previously occurred. There were also a handful of suspected cases in neighbouring Mali, but these patients were found to have other diseases. As of this week, over 400 suspected cases of EVD have been recorded, with the majority of them in Guinea. The outbreak has currently resulted in over 200 deaths. However, these figures may continue to rise as more patients die and as test results confirm whether they were infected with Ebola.
Quick… but not painless
In part, Ebola is devastating due to its highly unpredictable nature. During the incubation period, which can last from a day to several weeks, the Ebola virus operates similarly to HIV, weakening the body’s immune system and allowing the virus to spread around the body. The initial symptoms are similar to those observed in many tropical fevers such as malaria and include high fever, headaches and muscle pains. This means that early-stage EVD is often mistaken for more common tropical fevers, delaying quarantine measures.
Most patients then develop a final, and almost always deadly, haemorrhagic stage. Victims will suffer from bloody vomit, diarrhoea and rashes all over their body, and may bleed from all orifices. Blood loss is usually so severe that it leads to multiple organ failure within a very short period of time. The haemorrhagic stage is caused by a mechanism called a ‘cytokine storm’, during which the immune system overreacts to the presence of a disease. This overreaction results in a massive overproduction of antibodies that clogs up the bloodstream, destroying small blood vessels and causing heavy internal bleeding throughout the body.
Furthermore, both those who die of EVD and the few who survive remain highly contagious for up to 40 days after falling ill. All their bodily fluids are infectious – saliva, blood, semen, faeces, even tears. In the cash-strapped hospitals of West Africa, it is very difficult to effectively quarantine patients for such long periods of time, meaning that the risk of further infection is high. This is also why EVD outbreaks cannot be considered to be over until no new infections have occurred for two months.
Too deadly to spread?
The one ‘advantage’, such as it is, of EVD being so dangerous is that its very lethality limits its ability to spread. The speed with which the disease incapacitates and kills most patients makes it unlikely to be spread through contact with other people. Compare this to the common cold or influenza viruses: these spread around the world frequently because people can still leave the house when they’re ill, unintentionally infecting others. This self-limiting nature of EVD may help lower the likelihood that a large-scale epidemic could occur.
Nevertheless, new cases of EVD are still being diagnosed in rural Guinea, including in parts of the country that were previously unaffected. Those infected are suspected to have contracted the disease when an acquaintance who was killed by the virus was buried without due care. This shows that the difficulties in controlling Ebola are considerable even in rural, sparsely populated areas with poor transport links. The outbreak has also spread from Guinea into eastern Sierra Leone following that country’s decision not to close its land borders.
While the disease appeared to have been contained in April in the Guinean capital of Conakry, two new cases were diagnosed in late May. An epidemic in such a densely populated transport hub with long-distance transport links could have catastrophic consequences. To fully contain the disease, health workers need to track down every single person an infected patient has been in contact with, everyone that these secondary individuals have met and so on – before necessary quarantine, testing and treatment can take place.
A ray of hope?
An effective public health response to Ebola is also limited by the fact that no known vaccine or medication is currently available. As with many tropical diseases, large pharmaceutical companies simply have no incentive to research and develop an expensive new drug for a disease which affects very few individuals on a global scale: there would simply not be enough demand. Since its discovery in 1976, EVD has infected only around 2,500 people, killing 1,700 of them.
For now, treatment is purely symptomatic, meaning that symptoms are addressed without actually destroying the Ebola virus itself. However, a small American company is now on the brink of developing a successful drug for Ebola, offering a glimmer of hope for the future. The drug, currently named BCX4430, has successfully cured EVD – as well as related tropical fevers – in mice and guinea pigs, and also cured every single infected monkey in the next round of trials. The drug is likely to enter the human trial phase next year, and if it is found to be safe it could be tested for efficacy during the next Ebola outbreak.
Ebola is rare enough that we are still learning about it every time there is an outbreak. It is a terrifying disease by any measure, especially while we have no means to cure or prevent it. Credit must go to the health workers from around the world who are in West Africa working tirelessly to control the outbreak. Until an effective medication, and the means to distribute it are available, basic precautions, such as limiting physical contact and isolating patients are the only way to prevent the spread of this deadly virus.
Gatherer D (2014). The 2014 Ebola virus disease outbreak in west Africa. The Journal of General Virology DOI: 10.1099/vir.0.067199-0