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Christine O'Connor

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Can we control the emergence of zoonotic infectious disease?

Seventy five percent of the world’s emerging infectious diseases are zoonotic, or animal, in origin. Familiar examples include HIV/AIDS, Ebola, SARS, Lyme disease and West Nile Virus.

Humans play a big part in the emergence and spread of these and other infectious diseases. Our ever-expanding encroachment on forests – due to deforestation and increases in bushmeat hunting – increases the potential for disease transmission from animals to humans. Urbanization and global travel more easily allow for the spread of a disease from person to person and across the globe. These factors combine to greatly increase the probability of successful emergence and spread of an infectious disease.

Despite the clear importance understanding and controlling zoonotic diseases we have not had much success eradicating them, or even limiting their spread. It is hard to eradicate what we can’t find. Fore example, despite many years of study, researchers still are not sure where Ebola comes from. Outbreaks can be traced to handling of dead chimpanzees and gorillas, but neither appears to be the reservoir host (a species that is a source of infection but not affected by the disease) for Ebola.

What should be done to stop or control the emergence and spread of these diseases before they become global pandemics? Should we try and limit close contact with wild animals, perhaps via habitat preservation? Should we better control the bushmeat trade and/or educate hunters and consumers of bushmeat and other types of wild animal markets of the risks involved with such meat? Or, is a more proactive approach possible? Is there a way to pre-emptively identify such emerging diseases, via monitoring of wild animals and those who regularly have close contact with them?

Souce: Spillover by David Quammen

Also see: Q&A on swine flue with virus hunter Nathan Wolfe "We've created the perfect storm for viruses" http://blog.ted.com/2009/04/28/qa_with_virus_h/


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    Jun 4 2013: An important approach to limiting the spread of zoonotic diseases could be providing villagers that depend on bushmeat for a source of food and income with alternative sources of protein. People need to eat, and if there are not other options they are likely to continue extracting wild meat even if it poses a health threat. The Wildlife Conservation Society posted an article about developing snail farms in Nigeria to help alleviate some of the hunting pressure on Gorillas. Apparently, they are a good source of protein and fetch a nice price at the market, providing a possible source of income as well as food.


    More programs like this, that provide a reliable source of food, could be successful in reducing the take from the forest,and reducing transmissions between humans in animals. However, I'm not sure if there are any negative impacts of snail farming or diseases associated with them?? .
    • Jun 4 2013: From what it sounds like in your link, they want to utilize the African giant snail, which - if it is what I think it is (Achatina fulica) - is actually considered an invasive species! Although a great idea to help alleviate hunting pressures on gorillas and other primates for protein. I also found an article on one of the other species the author of your WCS article may be discussing, Archatina marginata, that did a study on school-aged children and their mothers preferences with "snail pie". Basically, the children and mothers were given a beef pie and a pie made of the edible parts of the snail. Both the parents AND kids enjoyed the snail pie; it topped beef for texture, appearance, taste and flavor. It also was higher in protein and iron. I got a good laugh from that. But in all seriousness, it would be interesting to explore alternative sources of protein and iron, like snails, as a replacement for bushmeat. As long as there is no snail-human transmission of another zoonotic infectious disease. Plus, the snail farm seems relatively cheap to maintain (WCS article: $87 per year) and like you said Sandra, could be a source of income!

      Invasive species: http://www.invasivespeciesinfo.gov/animals/africansnail.shtml
      "Snail pie": http://www.inderscience.com/info/inarticle.php?artid=29278
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        Jun 5 2013: Shelby-- huh, snail pie, that's a new one to me! I was so surprised, I looked to see if there were any diseases associated with the giant African snail, and it turns out they act as a vector for a parasitic nematode worm that can cause a form of meningitis in humans!...they actually act as a host and can pass it from rats to humans.


        You're right, it sounds like they reek havoc as an invasive species in other areas, and interestingly are used in skin creams.
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      Jun 4 2013: I'm interested in discussing the morality and theoretical sustainability of bushmeat hunting versus current large-scale commercial livestock practices. It is my personal opinion that we may be like the pot calling the kettle black, since the land cover change associated with agriculture is one of the largest causes of global extinctions. I am not convinced that we should be calling for native Africans to curtail their traditional hunting practices until after we control our own appetite for excessive consumption. In addition, conventional livestock operations are, in my opinion, callous and inhumane industries that have reduced the value of a life to abstract cellophane packages of meat.
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        Jun 4 2013: The rainforest ecosystems need to be treated differently. It's one thing to use grasslands in the U.S. for livestock, but to clear rainforest is sort of counterproductive. It's a difficult problem to tackle because human populations are increasing around forested habitats, and we obviously want to shift them away from relying on the forest for its meat while also preserving the forest. Many of the villages suffer from poor access to urban areas, so meat transportation is very difficult. If this were too improve, it'd be much easier to provide rural areas with protein from areas that did not require the destruction of rainforests. Ultimately, better access to sustainable resources, and a reduction in the human population will alleviate much of the strain on the environment, which will also minimize contact between humans and disease carrying wild animals.
        • Jun 4 2013: Ryan, I think that yes ideally that if there was greater access to sustainable resources that some of the strain on the environment would be eliminated, however what kind of policy do you think would help minimize the contact between humans and disease carrying wild animals that isn't a complete change of norms for these people?

          Here is an article review of game meat safety: http://www.ojvr.org/index.php/ojvr/article/view/422
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        Jun 4 2013: Okay, let me first clarify, I am not by any means suggesting we start going and clearing large amounts of tropical rainforest to start growing beef and poultry. I personally have disengaged in supporting the livestock industry for a long period of time now for the same reason you listed above Gwynne, and additionally for the implications it has on excessive resource use CO2 emissions. Also, all the reading I did for our presentation suggested that livestock did not hold well in these areas anyways due to susceptibility of tropical diseases and other factors.

        However, if people in these areas are not able to limit their hunting they may push many local species to extinction. In lots of areas the hunters now have to travel long distances to find meat and ecologists are calling it the "empty forest" syndrome. If wild animals continue to be extracted at the same rate there may be none left for these people to depend on, and a new source of food will have to be implemented anyways. It does not have to be large scale production, other alternative might be finding vegetables or legumes that fair well in poor tropical soils, or start to research edible plants that grow naturally in the areas.

        Additionally, lots of people use bushmeat as a source of income in these areas because there is not many other options. If transportation of meat to these areas did improve they would still have to purchase it. If they cannot afford to purchase it, there is not much point in bringing it to them. Unless someone plans on subsidizing it.

        empty forest article
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          Jun 4 2013: True, the people in these areas may be over-harvesting the resource. I simply think that it is a minimal global impact compared to the impact that is attributable to our own lifestyles. I am wondering what is the best long-term solution for this? We cannot fix things with the same type of thinking that caused the problem in the first place. Better access to cities means that people living their traditional lifestyles will be more likely to begin adopting more Western practices - driving more, consuming more. If logging is one of the primary roots of the problem, then why don't we boycott unsustainably harvested tropical timber? Why don't we encourage higher income nations to not purchase bushmeat and trophies from wild animals? Perhaps what we need is not more restrictions upon the people trying to eke out a subsistence living, but more education and restrictions upon the populations of industrialized nations. I strongly believe that the change should start at home and we should be looking at ourselves before pointing fingers at others.

          This discussion reminds me of the TED Conversation that was up a couple weeks ago: "Why are YOU killing the planet?" (http://www.ted.com/conversations/18304/why_are_you_killing_the_planet.html)
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          Jun 5 2013: The problem basically lies in the increasing human population. Trying to limit hunting and deforestation is going to be problematic while the population continues to rise. Unless the people are provided jobs that do not involve utilizing the forest, providing them with an income that can pay for food transported in from long distances, limiting human growth is really the main challenge. If scientists are able to determine that certain amounts of forest can be cleared/utilized without much disturbance to the ecosystem, that could be an approach as well, but you still have to be cautious when populations continue to expand.
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      Jun 5 2013: I read this report of potential alternatives to bushmeat. I certainly don't claim to be an expert of the topic, but we cannot just say, "Remove a significant proportion of the protein in your diet because we say so."

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