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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 3 2013: I wonder if it is a side effect of globalization? Maybe it will subside as defenses come about?
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      Jun 3 2013: Absolutely globalization influences the transmission of infectious disease. The more contact rate between people the higher the probability of transmission. This paper looks like it describes the models they use for disease transmission pretty clearly http://www.sciencedirect.com/science/article/pii/S0169534701021449. If you look at the disease threshold model there are several factors that are involved. A high contact rate, a high infection rate and mortality rates will all determine how the disease is spread through a population.
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      Jun 4 2013: In addition to globalization, population growth and urbanization by themselves are also hugely important factors. More people equal more possible contacts with diseased animals and urbanization means its easier for a disease to spread from person to person.
      I don't know if the emergence of infectious diseases will ever really subside. Some of this increase in emergence is almost certainly due to increased reporting and awareness of disease, but much of the increase is certainly a 'real' increase, as we humans are changing out interactions with our environments and global warming permits the spread of some diseases to new locations. (See the Slate article I posted a link to above, about Dengue fever in the US: http://www.slate.com/articles/health_and_science/pandemics/2012/12/dengue_fever_in_united_states_breakbone_fever_outbreaks_florida_texas_and.html
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        Jun 4 2013: I'm glad you pointed out how the human factors, like urbanization and changing interactions with the environment, are critical to consider. This article (http://link.springer.com/article/10.1007/s10393-005-8961-3) uses the term "biocomplexity" to encompass the interactions among physical, chemical, biological and social dimensions that all come together to influence the earth's systems.
        • Jun 4 2013: Here is an article by a law professor on behalf of the CDC that explores what measures are taken within a country as well as international laws that are in place to limit the exposure/spreading to infectious diseases:
          http://wwwnc.cdc.gov/eid/article/9/3/02-0336_article.htm

          I found it particularly interesting that some of the recommendations are considered to be "soft-norms" or recommendations by the World Health Organization as a way to give guidance to countries on guidelines, practices or policies a country should consider to enact.
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        Jun 4 2013: Along similar lines, this paper on "Engineering Responses to Pandemics" (written by folks at MIT) has a lot of really interesting information about social adaptations and behaviors that are used by people to avoid contracting an infectious disease:

        http://esd.mit.edu/staging/WPS/2009/esd-wp-2009-14.pdf

        It also discusses in detail how these "soft" responses affect the R_0, "reproductive number," of the infection and goes through quite a bit of the math, if anyone is interested.
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      Jun 4 2013: Although globalization is an element, one thing that needs to be done (in the case of hunting and the transfer of diseases between hunters and their prey) is the education of hunters. From my experience with Ivorian and Liberian hunters, many are not aware of the inherent dangers of the unsanitary conditions of handling meat. Since we currently cannot prevent outbreaks through medication, educating hunters and consumers of wild meat would be the simplest and most cost effective approach currently.
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        Jun 4 2013: I completely agree! The hope would be that once some of the hunters that are educated on the consequences of unsanitary or diseased meat would eventually spread their knowledge to others. It wouldn't solve the problem of disease transfer but it would be a help a great deal.

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