Posts Tagged Chimpanzee
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
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.
Recently I watched a TED talk by Suzana Herculano-Houzel (http://www.suzanaherculanohouzel.com/lab) entitled, “What is so special about the human brain?” (http://www.ted.com/talks/suzana_herculano_houzel_what_is_so_special_about_the_human_brain.html). In this presentation she makes the intriguing assertion that our brain is as large as it is, at least in part, because we cook our food.
Size, as in brain size, is not as important as neuron number when it comes to intelligence. Although the elephant brain is three times as large as the human brain it contains 23 billion neurons, compared with 86 billion in the human brain (http://en.wikipedia.org/wiki/List_of_animals_by_number_of_neurons).
Unfortunately the human brain is incredibly expensive to run, 25% of the energy consumed daily goes to fuel the brain. It costs around 6 kCal to run one billion neurons per day. Despite great apes being physically larger than us, their brains are smaller. Herculano-Houzel proposes that this is because they cannot consume enough calories on a daily basis to run a bigger brain. They do have a fairly low energy diet consisting predominantly of high fibre plant material with a few fruits and, in the chimpanzee’s case, some meat. This may be why the chimpanzee can afford to run 5.5 to 6.2 billion cerebral cortical neurons compared with the gorilla’s 4.3 billion.
However, humans maintain between 19 and 23 billion cerebral cortical neurons. Herculano-Houzel believes we can feed this number because of cooking, which effectively predigests our food releasing more energy and allowing us to more completely absorb our food. She depicts a graph, which correlates the increase in brain size of our ancestors with the invention of cooking.
Paradoxically we are now moving away from cooking and processing back to a more unprocessed diet because we appear to have overdone it, consuming too many calories and becoming extremely obese in the process. If we could only divert all those extra calories to our brains instead of our bodies imagine how incredibly intelligent we could become.
Dr. F. Bunny
If I was hungry and my family was hungry and a tasty looking antelope skipped past it would be hard to resist the temptation to stuff it into the pot for dinner just because my government or a foreign NGO told me not to. Family comes first after all and, while I appreciate the need to conserve biodiversity and protect endangered species, I also appreciate the need to put a bit of protein on the table.
In many ways I don’t have a problem with this subsistence approach to bush meat harvesting. People need to eat and why shouldn’t they avail themselves of their country’s natural resources? It becomes a problem when the meat is taken, not for local subsistence, but for a wealthy foreigner who wants to eat it because it’s a bit different and a status symbol he can show off to his friends.
The global bush meat trade is now estimated to be at least $1 billion annually (http://www2.macleans.ca/2013/04/15/gorillas-in-our-midst/). As much as 25 million kilograms of meat is smuggled into the US each year, 30% of it primate, while 11,000 tons find their way into the UK (http://www.independent.co.uk/life-style/health-and-families/health-news/african-monkey-meat-that-could-be-behind-the-next-hiv-7786152.html). That’s a lot of illegal, probably endangered, meat. The irony is that because bush meat has now become a luxury food item that fetches high prices internationally (hundreds of pounds per kilogram of gorilla and chimpanzee meat in the UK, apparently) the very people who used to hunt it for subsistence can no longer afford it.
Primate meat in particular also carries with it a significant disease risk. Simian Immunodeficiency Virus (SIV) is closely related to HIV and one theory is that SIV passed to humans where it mutated into HIV because of the close contact that occurs during hunting. Numerous outbreaks of Ebola virus infections are also likely connected to the harvesting of wild primates, as are Simian Foamy Virus infections and yellow fever. The potential is certainly there for these diseases to leave their African homes and pop up in other countries via smuggled meat. “Outbreak” here we come.
Of course, it is not just meat that is the problem. Smuggled wildlife destined for the pet trade can be just as dangerous, as shown by the 2003 outbreak of monkeypox in the US, courtesy of some infected prairie dogs who caught it from imported Gambian giant rats (http://www.cdc.gov/ncidod/monkeypox/qa.htm).
Unfortunately as long as we continue to desire the exotic, and are prepared to pay for it, and keep moving species around the world without adequate controls some sort of global pandemic is a very real possibility, not just a science fiction scenario.
Dr. F. Bunny