I gave a presentation on parasites at a school a couple of weeks ago. After which a student asked me if I could help with an essay they were preparing on Ebola. I wrote up a rather long email to tackle some of those questions. Then realised that perhaps I could post it to this blog for those people who are interested. I'd just like to state now that I am not an Ebola expert, this was all information gathered from the web and is by no means exhaustive or complete. But perhaps it is of interest.
Response to student:
Although Ebola isn't my speciality at all (I'm all about the parasitic worm diseases) like everyone else I have been following the West African Ebola epidemic. This outbreak was so dramatic, it is fascinating to read about. The questions you are asking are exactly what scientists and public health organisations have been researching.
I'm sure you know that Ebola outbreaks have happened before, mainly in central African countries, particularly around the Gabon and Congo area. In fact the Ebola virus was named after the Ebola river in the Democratic Republic of Congo. But their spread was nowhere near as rapid and extensive as the latest West African one.
There are 5 identified species of the Ebola virus.
Four of them occur in Africa:
- Zaire ebolavirus,
- Sudan ebolavirus,
- Bundibugyo ebolavirus,
- Tai Forest ebolavirus)
The 5th is found in the Philippines (Reston ebolavirus). Up to now this 5th one in the Philippines has only caused disease in monkeys, not in humans. The 4 species found in Africa do cause disease in humans but the mortality rate is different. The Zaire ebolavirus has the highest mortality rate.
Ebola virus natural host:
These viruses naturally occur in bats and probably do not cause severe disease in these animals. Because the Ebola virus and the bat have been evolving together - the Ebola virus infecting the bat and the bat's immune system fighting the virus - for hundreds if not thousands of years, they have reached a sort of evolutionary equilibrium where the Ebola virus doesn't make the bat too sick thanks to the bats immune system and the bat transmits the Ebola virus to other bats during its life. (More on bats & disease here, very interesting! )
It is likely that humans came into contact with the Ebola virus by entering forests (to hunt or for wood or to build a new village etc) where infected bats lived and either got infected via bat fluids or by eating undercooked bushmeat. Because humans haven't evolved with Ebola it completely overcomes their immune system causing severe disease.
The disease is caused by the virus infecting human cells, replicating quickly till the cell burst and then each viral replicant then infects another human immune cell and continues. It spreads remarkably fast through the body and because it infects immune cells it can avoid and confuse the host's immune system so the immune system doesn't really have a chance to fight back. What's more, the Ebola virus manipulates the bodies immune system, using the blood system to travel around the body, it infects more cells and destroys them. The worst damage is in the liver, the gastro-intestinal tract and the adrenal gland (a gland near the kidneys); Ebola kills cells in the liver that provide important proteins and components of the blood system. In the gastrointestinal tract it damages so many cells leading to severe diarrhoea - this severely dehydrates the human host. And in the adrenal gland it destroys the cells that make a steroid used by the body to control blood pressure, this means that there is a sudden drop in blood pressure, the body can not circulate oxygen carrying blood which means that the organs are not receiving enough oxygen. All these combined is what kills people. Severely dehydrated, blood is too weak to carry oxygen, then blood pressure drops so dramatically that organs aren't receiving any. Ebola patients die of circulatory shock and multiple organ failure. Patients in hospitals do survive mainly because they receive both oral and intravenous rehydration to keep their blood pressure up and the blood flowing to the organs. It is also important that they receive food, warmth and general care, giving their bodies time to recover and the immune system time to fight back.
Ebola transmission is not airborne but through contact with bodily liquids such as blood, urine, vomit, mucous and breast milk. So a hunter killing an infected bat would get infected by the blood of the bat, either through a cut or a graze or rubbing his eyes. He may then infect his family by kissing his wife. Or If someone is taking care of an infected sick person, the sick person may accidentally cough droplets on their carers hand. Th carer may then rub their eyes or wipe their mouth. It is easy to see how Ebola can spread if people don't know about viral transmission.
Until recently there was no known drug that could be used to kill the virus and stop the disease. This was part of the problem. The only thing doctors could do is make sure patients remained hydrated and blood pressure remained stable giving the body enough time to fight back. This is largely still the case. But there are some new drugs out now and work on a vaccine is being developed (now ready!). Hopefully this will help stop the disease. I really don't know much about the new treatment or the vaccine but will send you some resources (see below).
West Africa Epidemic
The current West African epidemic appears to be caused by the Zaire ebolavirus species. Why it has spread so quickly in West Africa is partly due to it's biology (it spreads rapidly through the human host) but also to do with human behaviour and local health infrastructures. People travel a lot more, especially to urban areas either to sell things in markets, to relocate and find jobs, to visit families. Transport in a lot of sub-Saharan African countries is often in large, packed groups. People don't own cars so they either use local buses or taxis which are packed since the more people in a bus the more money the bus driver makes. Get one infected person in their coughing and 4 other people are now infected. There is also a lack of understanding of transmission and hygiene in a lot of poverty-stricken areas, and it is particularly a problem in the slums of a city, which is densely populated, dirty and lacking in infrastructures like clean water, toilets etc.
Going to the doctor means a day away from work, which means less money for your family. People will generally only go when they are really ill. So they have probably already spread the disease to family members, friends, people at work, in buses etc.
As to the mortality rate - I have been to hospitals in poor rural and urban areas in numerous sub-Saharan countries - Hospitals are very poorly stocked and run, not the fault of the people working there but sadly of the socio-economic situation of the area. Often there are so many sick people, there's no room to put them anywhere so they sit in the corridors all together. There are no antibiotic hand gels or sprays. The equipment is old and often falling apart. There are regular power cuts so the hospitals have to operate without electricity. There are also water shortages so the hospital is without running water for an entire day, having to buy buckets of it from people bringing it from a far off well or pump. There is often a lack of availability of intravenous fluid and a lack of protective clothing for the staff.
You can see from the transmission and the disease why hospitals in West Africa have been in the centre of transmission and why there are so many deaths.
Finally there is such a huge stigma surrounding the disease that people are too scared to come forward if they are presenting symptoms.
A good public health infrastructure in these places would probably have prevented or at least delayed this epidemic and not quite so many people would have died. It is sad to think this epidemic could have been prevented and that there have been warnings from the scientific and health workers community about the dangers of ignoring the weak health infrastructures in developing countries. We like to think that problems in developing countries do not affect us here but we have been proven wrong about this sooooo many times. Supporting developing countries in health and education has global benefits not just local ones.
I think these are the main factors on why the West African Epidemic has spread so quickly and why it has such a high mortality rate. But I repeat that I am not an expert. So I have also included some links where you can find lots of useful info.
- World Health Organisation - http://www.who.int/csr/disease/ebola/en/
- London School of Hygiene and Tropical Medicine - http://www.lshtm.ac.uk/newsevents/features/2014/ebola_west_africa.html
- Ebola Response Anthropology Platform - http://www.ebola-anthropology.net/
- Science Journal - http://www.sciencemag.org/site/extra/ebola/
- European Centre for Disease Control and Prevention -http://www.ecdc.europa.eu/en/healthtopics/ebola_marburg_fevers/Pages/index.aspx
- Centre for Disease Control and Prevention - http://www.cdc.gov/vhf/ebola/
Media resources: You have to be careful with the media resources, they are not always based on fact. Some are pure scaremongering, others just misinterpret the science of the disease. But some are quite good and interesting:
- Great map and historical rep of disease here - http://www.nytimes.com/interactive/2014/12/30/science/history-of-ebola-in-24-outbreaks.html?_r=0
- Article on the identification of Ebola virus in 1976 http://www.bbc.co.uk/news/magazine-28262541
- start of the epidemic http://www.nytimes.com/2014/08/10/world/africa/tracing-ebolas-breakout-to-an-african-2-year-old.html?_r=0
- migration http://www.cidrap.umn.edu/news-perspective/2014/11/migrations-west-africa-seen-challenge-stopping-ebola