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The Impact of Environmental Changes on Zoonotic Diseases

ttruong's picture

The Impact of Environmental Changes on Zoonotic Diseases


Defined as an infectious disease that can be transmitted from non-humans vertebrates to humans, a zoonotic disease can be as deadly as ebola, which kills up to 88% of its victims, or as benign as ringworm.  For a pathogen to be successful, it must be able to chronically infect its host, remaining alive without killing its host. Most modern human pathogens began as animal pathogens that were non-lethal to the animals. At times when humans become the "accidental" hosts, human hosts are killed so swiftly that the virus quickly die out along with its host before spreading. Humans are sometimes the dead end hosts of different pathogens' evolutionary inertia.

Recently scientist have become increasingly aware of the linkage between emergence of outbreaks in zoonotic diseases and the destruction of natural habitat of animal hosts, climatic changes due to global warming, and other environmental changes caused by humans. Efforts are being made to develop a surveillance system in which outbreaks can be quickly identified and contain, or even prevented by the prediction of possible future outbreaks.


Transmission of Ebola


        Fruit Bats                            --------->                Gorillas and Chimpanzees                ------>         Humans

   Nonpathogenic                                                          Extremely Pathogenic                               Extremely Pathogenic

(natural reservoirs) 


What are zoonotic diseases?

Connection between human-induced environmental changes and outbreaks.

Connection between similar water resource and outbreaks.

Preventing and limiting transmission between animals and humans.

Predicting of new emergence.


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RachelBrady's picture

When discussing the how the

When discussing the how the actions of a small number of people can generate significant adverse effects for the larger population and the use of intervention here, a question kept plaguing me; who is responsible for this intervention? From what I've found it seem that much of the responsibility concerning zoonotic diseases has fallen to the emerging field of conservation medicine which integrates human and veterinary medicine and environmental science. Now I'm 100% in favor of any field of study that promotes conversation between academic concentrations, but I can't help but notice the absence of the public element. From what we discussed in class, it seems that what really needs attention is the understanding of zoonotic diseases and the behaviors that promote the spread of these diseases. This emerging field of study appears to be focusing on dealing with these diseases once they are upon us instead of identifying and educating people on the behaviors that facilitate their spread.

ttruong's picture

Individual and collective decision making

During the discussion we talked about how the decisions of a small number of people can generate significant adverse effects for the large number of people, even though that small group benefit more from such decisions than they suffer.

One current example that was recently in the news is the meeting between and China regarding efforts to reduce pollution. (In this situation, however, the problems are between an individual governing state and a collection of governments) While many developed countries have implemented strategies to reduce gas emission, some developing countries, are not as committed to the green cause due to extensive costs. China makes the argument that it is unfair that the developed countries were once the primary culprits of pollution and now they have only began reaping the economic benefits of industrialization unhindered by environmental laws that the developed countries received in their early development. This argument is similar to an argument someone made during regarding water irrigation. Though I still believe actions should be taken to reduce emission, I can disregard the fairness of China's argument to the developed countries.


Paul Grobstein's picture

looping, animal viruses, the environment, and research practice

Lots of intriguing ideas here.  Among them is a specific example of the general phenomena of "looping," the notion that causal relationships are bidirectional rather than unidirectional: we are both influences on and influenced by things around us  (the "environment," which includes pathogenic organisms and the circumstances in which they do or do not thrive).  A particularly interesting notion along these lines is that we may be ourselves increasing the problem of viruses moving from other hosts to humans.  Both the frequency of jumps and their pathogenicity may well be increasing because of both globalization and environmental instability. 

A second intriguing idea related to this is an alternative to "tree hugging" as a style of encouragement for people to pay more attention to the environment.  The key point here is not that people should learn that the environment is "good" and should be protected but that people should learn more about the extent to which we live in interaction with the environment, and that rapid environmental change disturbs complex patterns of human/environment interaction. 

Here too we run into a matter not only of science education but of research practice as well.  To the extent scientists are preoccupied with "isolating variables" so as to make possible clear demonstrations of cause/effect relations, their work will tend to encourage belief in simple undirectional cause/effect relationships.  There is a serious challenge here to conceive new forms of research practice, not less "rigorous" but more aware of the complexity of causal relations (and the significance of some degree of randomness). 


ttruong's picture

Unobservable results

I think another issue with trying to use isolating variables and clear cut cause/effects relations to study zoonotic diseases is that the effects take a considerable amount of time before they even surface. For example, some studies suggests that the earliest cases of HIV in humans appeared in 1930s, yet the disease went undetected until the 1980s. Trying to prevent and contain zoonotic diseases that have high mortality rates is much easier than lentiviral diseases which attack the immune system and take a long time to produce adverse effects.

Lisa B.'s picture

Transmission of Influenza

The information below is from a Bryn Mawr College biochemistry lecture on “Attachment of Helicobacter pylori to Human Gastric Epithelium Mediated by Blood Group Antigens” (Borén et al.): 


Influence of viral tropism on transmission and virulence of influenza.


Seasonal influenza viruses bind exclusively to α-2,6 sialyl linked sequences in the upper respiratory tract, which is why human-to-human transmission is spread through coughing and sneezing. Also, human-to-human transmission is unlikely in some influenza epidemics since sialyl glycan receptors vary in tissue distribution in different species. For example, the avian flu binds to α-2,3 linkages in the intestinal tract and the lower respiratory tract in humans. As a result human-to-human transmission is uncommon in humans, since influenza is spread through coughing and sneezing, and common in birds.