The podcast of the University of Colorado Consortium for Climate Change and Health
Episode 9: Climate Change and Water-Borne Disease
In this episode, Jake and Cam interview Dr. Beth Carlton, who teaches them how climate change influences diarrheal diseases.
Dr. Beth Carlton earned her PhD in Environmental Health Science from UC Berkeley and her MPH from Columbia University. She is an assistant professor in the Department of Environmental and Occupational Health at the Colorado School of Public Health, a recent recipient of several grants to study infectious diseases as well as climate change, and a member of the University of Colorado Consortium for Climate Change and Health.
Before we dive in, check out the definitions for a few terms we use in this episode:
In the context of climate change, vulnerability refers to a person’s or community’s predisposition to be adversely affected by climate change and its health effects. Vulnerability encompasses three elements: exposure, sensitivity (or susceptibility to harm), and the capacity to adapt. These three components of vulnerability are illustrated below in a scheme from Dr. Carlton’s Climate Change and Health course in the Colorado School of Public Health.
Diarrheal disease is a category of illnesses caused by a variety of infectious agents, which can lead to severe gastrointestinal symptoms, dehydration, and malnutrition. Worldwide, diarrheal diseases are one of the leading killers of children under the age of 5, according the IHME. A few examples of infectious pathogens that can cause diarrhea include Shigella genus bacteria (which cause dysentery), Vibrio cholerae (which cause cholera), E. coli bacteria, rotavirus, Giardia lamblia protozoa, Cryptosporidium genus parasites, and Schistosoma genus flatworms (which cause schistosomiasis).
Below, a simplified diagram of how diarrheal disease-causing pathogens are transmitted in the fecal-oral cycle.
Neglected Tropical Disease
Neglected tropical diseases refer to a diverse category of diseases (some of which are also diarrheal diseases) that prevail in tropical and sub-tropical regions throughout the world. They affect approximately one billion people worldwide, who tend to reside in low-income and disadvantaged populations. You can see a list of these diseases and learn more about them through the World Health Organization website, linked here. Below, a picture of a Schistosoma flatworm, which can cause schistosomiasis (considered both a neglected tropical tropical disease and a diarrheal disease).
To start us off, Dr. Carlton teaches us how, in general, climate change is facilitating the expansion of infectious diseases. To illustrate this phenomenon in the U.S., she mentions a climate-sensitive disease that often finds itself in the media spotlight: Lyme disease, which is transmitted by the Ixodes tick. While there are several factors implicated in the expansion of Lyme disease (which you can read more about in the vector-borne disease chapter of the U.S. Global Change Research Program’s Climate and Health Assessment), increased temperatures from climate change influence the disease-causing tick lifecycle and may increase human exposure to these ticks. The westward march of Lyme disease is pretty obvious in the maps below, available through the CDC.
Lyme disease is not a diarrheal disease, but it is a preeminent example of how the distribution of an infectious disease can shift with the changing climate (for more, be sure to check out our previous episode with Dr. Rosemary Rochford).
Unfortunately, climate change threatens to make diarrheal and neglected tropical diseases more rampant in communities that already experience them, and threatens to introduce them to new regions and new human populations. Below, a map from the Institute for Health Metrics and Evaluation showing global mortality from diarrheal diseases (the color scale on the bottom denotes number of deaths per 100,000 people). You can explore more of IHME’s global health visualization resources here.
Clearly, diarrheal diseases represent a significant global health problem–one that is slated to get worse with climate change. This is one reason why Dr. Carlton quoted a recent climate and health report from The Lancet:
Tackling climate change could be the greatest global health opportunity of the 21st century
With all this in mind, how do people contract diarrheal illness?
In simple terms, we can contract diarrheal illness by exposing ourselves to disease-causing pathogens (bacteria, viruses, parasites and protozoa) in feces.
A Deeper Dive
Below, a helpful diagram from the Water Engineering and Development Center at Loughborough University showing how fecal-oral transmission of diarrheal disease-causing pathogens can actually happen, and how we can protect ourselves from this transmission.
So how exactly does climate change interact with diarrheal disease? Dr. Carlton walks us through how increased temperatures and changes in rainfall can increase risk for contracting diarrheal illness.
Climate change will increase temperatures and change precipitation patterns around the world. In general, increased temperatures can accelerate the growth of diarrhea-causing bacteria. Increased heavy rainfall events can mobilize fecal films and cause sewage and drinking water sources to mix together, leading to increased exposure to diarrheal disease-causing pathogens.
A Deeper Dive
Below, a comprehensive overview of how climate change-related environmental factors can increase risk for diarrheal disease, adapted from a figure from Levy et al. (2016).
We know that climate change will increase extreme weather events in certain regions of the globe. Dr. Carlton explains that this can lead to increased diarrheal disease by disrupting infrastructure. How does this work, and how can we protect ourselves?
Extreme weather events (like the 2013 floods in Boulder, pictured above in an image from the Boulder Daily Camera) can disrupt the infrastructure that keeps our water clean. Without ways to sanitize our drinking water, we are at much higher risk for diarrheal disease.
A Deeper Dive
In another comprehensive figure from Levy et al. (2016), we can see how flooding from extreme weather events can increase risk for diarrheal disease, and where we can intervene during such events to reduce this risks. For those interested in reading more about water sanitation in disaster settings, the World Health Organization has excellent resources available here.
To close out this episode, we chat with Dr. Carlton about how we can slow global climate change, and how many mitigation strategies have immediate health co-benefits. In the interview, Dr. Carlton explained co-benefits using electric vehicles as an example. With widespread adoption of electric vehicles and reduction of fossil fuel-burning cars on the road, we would expect less tailpipe pollution and improved air quality. This would result in immediate benefits for health, such as reduced asthma exacerbations in kids and heart disease in adults. The figure below from the British Medical Journal illustrates many other health co-benefits that can arise from efforts to mitigate climate change.
background readings and resources for the interested listener: