Infectious disease? No Worries. Let's domesticate those germs!

Over the last few decades, when thinking of addressing harmful infectious diseases such as Cholera, we often turn to pharmaceutical drugs to solve the problem. However, in recent times, researchers have started to question the effectiveness of this method in combatting infectious diseases.  This is because while drugs can help our body combat and recover from diseases, they can be extremely costly to design and produce. Additionally, drugs can potentially facilitate the emergence of drug-resistant strains of infectious diseases, as my fellow contributor Nkemji Nweke points out in her blog post. In other words, our reliance upon drugs are in fact making these harmful infectious diseases hardier in the long run. This is fundamentally problematic!

In light of this issue, evolutionary biologist, Dr. Paul Ewald started to wonder: Instead of using drugs that can potentially make these bacteria more harmful over time, how can we use the theory of evolution via natural selection to make these harmful organisms more benign instead? In other words, how can we introduce a selection pressure that selects against the more toxic strains of the harmful organisms?

To answer his question, Dr. Ewald turned to investigating whether we can introduce a selection pressure against the more toxic strains of Vibrio Cholerae, which is the bacteria that causes Cholera. Cholera is an infection of the small intestines that often lead to diarrhea.

Cholera can spread via three ways.

1. Person to Person contact.
2. Person to Food to Person.
3. Transmitted through the infected water systems.

Change in Toxicity of V. cholerae in the three
Latin American Countries (Source: TED Talk)

The key difference between these three methods is that the third method does not require the infected individual to be mobile. Since mobility of the infected is not required to spread the disease, studies have found that bacteria strains that spread through water tend to be more toxic and harmful.

Based on this understanding, Dr. Ewald hypothesized that one way to introduce a selection pressure against the more toxic strains of Cholera is to remove the bacteria’s ability to spread via water. This can be done by introducing clean water ways where people would have access to not only clean water, but also stay protected from unsanitary sewage.  With the introduction of clean water systems, the only way in which Cholera can spread is through either method 1 or 2, where each requires the bacteria to be less toxic so the infected individual is able to remain mobile.

To test his hypothesis, Dr. Ewald looked at three countries in Latin America that were affected by the 1991 Cholera epidemic (Peru, Chile, and Ecuador). In this research, Dr. Ewald wanted to see if the standard of the water system in each of the countries influenced how the Cholera bacteria evolved. The results of his study yielded very interesting results. The bacteria strains in Chile, home to one of the most well protected water ways in Latin American, evolved to be much milder in a few years.  On the other hand, the bacteria strains in Ecuador, which has one of the least protected water ways, actually evolved to become much more toxic. Peru, being in the middle in terms of its water systems, saw no change in the bacteria’s toxicity.

In another similar study, Dr. Ewald once again compared the toxicity of the Cholera bacteria strains that were found in different places. Sure enough, the results were similar. The greater the proportion of the population having access to clean portable water regions, the less toxic the Cholera bacteria strains were.

Toxigenicity against Access of population to portable water (%) (Source: Ewald, P. et al. 1998)

All in all, the results from Dr. Ewald’s studies tell us one thing: we actually have the ability to “domesticate” harmful diseases by changing our living conditions so that the new conditions actually select against the more harmful strains of the infectious bacteria! This finding is not only highly fascinating, but also very important. This is because Dr. Ewald has demonstrated that sometimes using natural selection as a force to tackling infectious diseases might be a much better way than traditional drug research!

Perhaps it is time we start re-evaluating the ways we combat infectious diseases. Perhaps it is time we start “domesticating” germs.

By: Ben Ong (685 Words)

References

Ewald, P. 1994. Evolution of Infectious Diseases. Oxford University Press

Ewald, P. et al. 1998. Evolutionary Control of Infectious Disease: Prospects for Vectorborne and Waterborne Pathogens. Mem Inst Oswaldo Cruz, Rio de Janeiro. 93(5): 567-576

Ewald, P. 2002. Plague Time: The New Germ Theory of Disease. Knopf Doubleday Publishing Group.

Faruque, S. M., Albert, M. J. and Mekalanos, J. J. 1998. Epidemiology, Genetics, and Ecology of Toxigenic Vibio cholerae. Microbiol Mol Biol Rev. 62(4): 1301–1314. 

TED Talks: Paul Ewald asks, Can we domesticate germs? 2008. TED Conferences, LLC. http://www.ted.com/talks/paul_ewald_asks_can_we_domesticate_germs.html. Accessed 21 Feb 2013.