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A reader asks: Does climate change trigger disease outbreaks?

Climate change has both direct and indirect effects on illness and disease, says UGA professor of environmental health

On Fridays, CNN answers one of our audience’s climate change questions as part of the Two Degrees series. Ask your question by filling out this online form. And sign up for the Two Degrees newsletter to learn more.

(CNN) —  

Erin Lipp is a professor of environmental health at the University of Georgia. She specializes in climate change and human health. She’s answering this week’s audience-generated climate change question as part of CNN’s Two Degrees series.

CNN reader Tiffany Dennis from Atlanta asks, could climate change lead to more disease outbreaks and infections?

The simple answer is yes, says Erin Lipp, professor of environmental health at the University of Georgia.

But the cause behind this increase is often more complex than other ways in which climate affects human health, Lipp says. For example, heat waves will result in more heat-related illnesses and deaths. This is a direct effect of climate change. Climate change has a more indirect effect on infectious diseases, with climate and shifts in weather patterns influencing the pathogens (bacteria, viruses, etc.) and their hosts (insects or other animals), and consequently how humans are exposed.

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Several diseases are sensitive to climate, among them diarrheal diseases and those transmitted by insect vectors.

For example, the tick that carries the bacterium responsible for Lyme disease has expanded its range northward in the United States and Canada over the past 20 years due to warming temperatures, according to a 2012 study published in the Journal of Applied Ecology.

Another example is the Vibrio bacterium. The pathogen is found naturally in warm marine waters and is responsible for diarrheal disease (and sometimes bloodstream poisoning) following consumption of raw oysters or wound infections after swimming in seawater. These bacteria also have expanded their range due to warming coastal waters.

The turn of this century saw Vibrio outbreaks extend as far north as New England and Alaska. Records from northern Europe also indicate that these bacteria are becoming more common. Vibrio infections are now considered to be an indicator of climate change by the U.S. Global Change Research Program.

In addition to temperature, changes in precipitation patterns can help to mobilize pathogens and increase the chances for transmission to humans. Intense rainfall events, flooding and drought – which are expected to increase with projected changes in climate – can affect the introduction of fecal contaminants to recreational waters or waters used for drinking.

For example, nearly 70% of waterborne disease outbreaks in the United States were preceded by heavy rainfall events (in the 80th percentile) from 1948 to 1994. These events can cause runoff from agriculture lands or overflows in sewage systems that can transport pathogens to water bodies.

Clearly there are many factors that ultimately affect infections and outbreaks, but climate change can add an additional level of risk.

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CNN’s Brandon Miller and Azadeh Ansari contributed to this report.