Disease and the Environment –

Riley Herrmann

 

For the past few months, the Zika virus has caused panic as it has become an expanding epidemic. Transmitted by Aedes mosquitoes, Zika typically causes no or mild symptoms, however, the virus is known to cause birth defects in babies born to infected women.[1] According to the World Health Organization, Zika is “spreading explosively” in many parts of Latin America and millions in the Americas could be infected this year.[2] This rate of spread has caused panic in the past few months. With no cure, public health agencies are issuing warnings to several countries, advising citizens of infected countries to avoid getting pregnant.[3]

 

But why is Zika and diseases like it able to spread so successfully? What officials and scientists are finding is that what appears to be a public health issue is actually extremely linked to the environment.

 

To predict the spread of a disease like Zika, you have to look at the spread of its host. Zika spreads via Aedes mosquitoes, which tend to thrive best in warm, wet climates. This fact has scientists worried – future climate change could help mosquitos multiply and spread to new parts. As the world continues to warm, hosts of infectious disease will only continue to propagate and thrive. In the case of Zika, Climate change has allowed the Aedes mosquito to live in areas previously uninhabited by them. In recent years, the mosquito has been spotted as far north as Washington, DC and can survive year round in some parts of Arizona, Texas, and Florida.[4]

 

The executive director of the American Public Health Association called climate change “one of the most serious public health threats facing our nation.”[5] Global warming and vector-borne diseases like Zika have been associated for a long time. Kim Knowlton of the National Resource Defense Center says that as the Earth’s climate changes, Americans must learn more about diseases transmitted by insects.[6] Several incidences of disease within the last couple of decades are inextricably linked to climate change. In 1999, the West Nile virus spread from its origins in Uganda to New York City and killed seven people. Similarly, chikungunya (a mosquito-borne virus), came to the US in 2014 spreading to 46 states.[7] In both cases, the virus had never before been reported in theses places. One culprit? Global warming.

 

Global warming is changing the climate on earth in such a way that infectious diseases can spread ever more easily. Arthropods are the most common carriers of disease. Mosquitos, cold blooded arthropods, prefer warm, moist environments. Global warming has lengthened the warm seasons on earth and changed rain and weather patterns. With the temperature on earth rising each year,[8] we can expect that disease carrying mosquitoes will propagate and spread. This will occur for several reasons:

 

  1. With climate warming, mosquitoes will spread to new territories. As they expand their territory, if they carry disease, they can introduce them to new populations. For example, the Zika carrying mosquito has expanded its range in the past few decades. When the 2015 epidemic began, South America was experiencing it’s hottest year ever.[9] In another case, deer ticks which spread Lyme disease have expanded their range from Lyme, Connecticut in 1975 to every state except Hawaii due to warming weather.[10]

     

  2. Warmer air means viruses incubate faster. Viruses incubate inside mosquitos before the host becomes infectious. If mosquitos die, they will not spread the disease. With increasing temperatures on earth though, scientists believe that virus incubation periods will quicken – mosquitoes will be infectious for longer, giving them a chance to spread the disease.[11]

     

  3. Not only do viruses incubate more quickly inside the mosquito, but the eggs of mosquitoes themselves are incubating faster in warmer climates. Scientists found that most mosquitoes develop more quickly the closer temperatures get to around 86 degrees Fahrenheit.[12] This will result in a greater number of mosquitoes breeding and bearing more mosquitoes.[13]

     

The Washington Post reported that this “public health catastrophe” is yet another example of human changes to the environment that allow the propagation of diseases and the organisms that carry them.[14] Though obviously the environment is not the only contributor to the spread of disease, it is a huge player. If we continue to ignore our planet’s changing climate and do not attempt to combat global warming, we’re going to keep suffering from outbreaks of diseases like Zika. This is especially true for poorer, urban areas. These communities, dotted across the United States, present mosquitoes with an opportunity to access millions of citizens. Researchers believe that the people in these communities will be less prepared than wealthier areas to combat mosquito borne illnesses.[15] Durland Fish (professor of microbial diseases and environmental studies at Yale University) argues that we need to pay more attention to how our human projects that impact the environment change the habitats of virus carrying vectors.[16] As we urbanize and expand to new places, we create more waste, deforest, change habitats, etc., thus increasing a disease-spreading organism’s ability to spread as well as increase the likelihood of encountering these organisms.[17] When Fish looks at the problem, he sees mosquitos. “You have to do something about the mosquitos, and that’s strictly an environmental problem.”[18] To me, this makes sense. Looking at disease not only from a human and public health standpoint but also from an ecological and environmental standpoint will only increase our understanding of the issue. In turn, we will be better able to predict and prevent outbreaks of disease and protect our planet and human life.


[1] Zika virus infection (Zika) and pregnancy. (January 14, 2016). CDC. Retrieved from http://www.cdc.gov/zika/pregnancy/question-answers.html
[2] Desmond, Sally and Weaver, Matthew. (January 28, 2016). Zika virus spreading explosively, says World Health Organisation. TheGuardian. Retrieved from http://www.theguardian.com/world/2016/jan/28/zika-virus-spreading-explosively-says-world-health-organisation

[3] Zika: Peurto Rico the latest to warn against getting pregnant (January 28, 2016). AFP. Retrieved from http://news.yahoo.com/zika-puerto-rico-latest-warn-against-getting-pregnant-152626168.html

[4]Holthaus, Eric. (January 29, 2016). Could Climate Change Amplify the Zika Outbreak? Slate. Retrieved from http://www.slate.com/articles/technology/future_tense/2016/01/the_zika_virus_isn_t_coming_to_america_ignore_the_alarmists_who_say_it_is.html

[5] Knowlton, Kim. October 27, 2015. “Climate Changes Health: A Big Week Ahead in Chicago.” Available from https://www.nrdc.org/experts/kim-knowlton/cilmate-changes-health-big-week-ahead-chicago

[6] Ginty, Molly. “Climate Change Bites.” December 31, 2015; available from https://www.nrdc.org/stories/climate-change-bites

[7] Ginty, Molly.

[8] Dahlman, LuAnn. “Climate Change: Global Temperature.” January 26, 2016; available from https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature

[9] Ocko, Illissa. Environmental Devense Fund. February 16, 2016; available from https://www.edf.org/blog/2016/02/16/3-reasons-zika-outbreak-may-be-linked-climate-change

[10] Ginty, Molly. December 31, 2015.

[11] Ocko, Illissa. February 16, 2016.

[12] Worland, Justin. “How Climate Change Could Spread Diseases Like Zika.” January 30, 2016; available from http://time.com/4200851/climate-change-mosquitoes-zika/

[13] Ginty, Molly. December 31, 2015.

[14] Mooney, Chris. February 3, 2016. “The hidden environmental factors behind the spread of Zika and other devastating diseases.” available from https://www.washingtonpost.com/news/energy-environment/wp/2016/02/03/the-hidden-environmental-factors-behind-the-spread-of-zika-and-other-deadly-diseases/

[15] Worland, Justin. January 30, 2016.

[16] Mooney, Chris.

[17] Mooney, Chris.

[18] Mooney, Chris.

 

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