Ebola

The Ebola virus was “discovered” in 1976 causing trouble for people living near the Ebola River in the Democratic Republic of Congo (DRC). Since then it has popped up several times in the DRC, Sudan and Uganda. The current outbreak is the first to involve Guinea, Liberia and Sierra Leone.

The virus itself is a filovirus, a group of long filamentous RNA viruses that are surrounded by a lipid envelope. It causes a severe disease in people characterised by vomiting, abdominal pain, fever, headache and bleeding. Symptoms usually appear eight to 10 days after infection but this can range from two to 21 days. Mortality rates can be as high as 90%. Unlike influenza, people tend not to be infectious until they are symptomatic.

The virus is spread via direct contact with blood and body fluids, although there was a publication indicating airborne spread between pigs and monkeys (Weingartl et al 2012). Although not in direct contact the two groups of animals were caged only eight inches apart. According to a second report it appears that the Ebola virus causes a different disease in pigs compared with primates (http://www.vox.com/2014/8/10/5980553/ebola-outbreak-virus-aerosol-airborne-pigs-monkeys/in/5712456). The virus hits the lungs of pigs, whereas the liver is the main target organ in primates. Therefore, while pigs can cough and sneeze out viral particles, primates tend to shed large numbers of virus in the blood and faeces, making airborne transmission unlikely. This is borne out by the current situation. If the Ebola virus was as contagious as the influenza virus we would all be drowning in our own blood by now. Instead the outbreak has remained relatively localised.

The main reservoir of Ebola virus is unknown although, as with most emerging diseases nowadays, bats have been fingered as the main culprit. Ebola has been found in gorillas, chimpanzees and duikers but, as they also develop clinical disease and die, they are unlikely to be a reservoir. However, as they are part of the bush meat cycle they represent a great way for the virus to spread to people.

The virus itself is not particularly hardy. It can survive for several days at room temperature but is destroyed by boiling for five minutes, and common disinfectants such as bleach, phenolics, glutaraldehyde, formaldehyde and 3% acetic acid (vinegar is 4-8% acetic acid). Alcohol hand wipes and washing with soap and water are also effective at killing the virus.

Unfortunately there is no vaccine and no treatment. ZMapp, a drug made of monoclonal antibodies, has been used experimentally but, oddly, there appears to be some debate over the ethics of using this unlicensed drug on people. I know that if I was infected with Ebola and someone waved a drug at me that might or might not work, I would certainly risk it.

The biggest problem in controlling the current epidemic is a lack of infrastructure and knowledge. I can imagine that it is not easy to convince people with very little or no education that a thing that is far too small to see is killing off your family, friends and community. And no, it is not us, the aid workers, who are bringing it in. And yes, you really should stop eating bush meat, even though it is a centuries old tradition. And no, if someone dies don’t wash the body by hand. And yes, we really need you tell us if you, or someone you know, is feeling sick so we can stop them spreading the virus to other people. Please don’t hide them at home. With early medical care they do stand a chance of recovery. Previous Ebola outbreaks had mortality rates of 90%. This one is running at 60%. So it is possible to survive an Ebola infection.

As an interesting aside to the Ebola issue, in 1989 shipments of monkeys were imported into a holding facility in Reston in the US from the Philippines. Those monkeys died with symptoms similar to those caused by an Ebola virus infection. It turned out they were full of a related filovirus subsequently named Reston virus. Interestingly, 14% of the people who had contact with the monkeys had filovirus antibodies, indicating they had also been exposed to the virus. It was just lucky that this, closely related virus, does not appear to cause disease in people. It is amazing that such a small change in viral structure can turn a harmless virus into a lethal one.

Dr. F. Bunny

Reference

Weingartl H.M., C. Embury-Hyatt, C. Nfon, A. Leung, G. Smith, and G. Kobinger. 2012. Transmission of Ebola virus from pigs to non-human primates. Scientific Reports 2, 811; DOI:10.1038/srep00811.

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