Global warming is spreading insect-borne diseases

Global warming is spreading insect-borne diseases

By Dana Nuccitelli, CCL Science Policy Network Team

People often don’t realize that climate change is already impacting us in adverse ways. As a result, we tend to underestimate the urgency of the problem and consider it a low priority. Thus, it’s important to convey the ways we’re already feeling the effects of global warming, and that those impacts will only worsen until we succeed in curbing climate change. Vector-borne diseases are a good example that many people can relate to—a threat exacerbated by climate change that will only get worse as the planet keeps warming.

Recently, a report from the Centers for Disease Control and Prevention (CDC) made headlines for its finding that diseases spread by ticks, mosquitoes, and fleas more than tripled in the U.S. from 2004 to 2016. A story from the New York Times mentioned that warmer temperatures are one contributing factor, but that the CDC report didn’t make a connection to global warming or climate change. That’s because the CDC report focused on factors causing these diseases to spread; the causes of warmer temperatures are outside its scope. The Washington Post story about the CDC report was more thorough, making note of several climate change connections:

  • Mosquitoes and ticks thrive in hotter temperatures caused by global warming.
  • Warmer temperatures tend to make mosquitoes get infected faster and be more infectious.
  • Higher temperatures allow ticks to spread into new areas farther north.
  • When the tick season is longer, people are exposed over longer periods.

However, there are some important caveats. For example, various factors contributed to the rise in vector-borne diseases, like a growing deer (and deer tick) population in New England. Also, the headline “tripling” of vector-borne disease outbreaks can be traced back to an outbreak of Zika virus in Puerto Rico in 2016. It would be more accurate to say that vector-borne diseases approximately doubled in the U.S. between 2004 and 2016, and 2016 was a particularly bad year due to the Zika outbreak in Puerto Rico.

Most of the long-term increase is due to a rise in Lyme disease spread by ticks, which accounts for about 63% of all reported vector-borne diseases in the US. The number of reported Lyme disease cases is increasing by more than 1,000 per year, but far more go unreported. The CDC notes that Lyme disease infects approximately 300,000 Americans yearly, which is about tenfold the number reported (those who seek care for the disease).

Reported cases of tickborne disease in U.S. states and territories, 2004–2016.  Sources: CDC, National Notifiable Diseases Surveillance System, 2016 Annual Tables of Infectious Disease Data.

These vector-borne diseases are an example of how climate change is already impacting American health today.  Higher temperatures caused by global warming allow ticks and mosquitoes to thrive, have longer seasons, expand to new areas, and in some cases, carry more of the disease. These adverse outcomes will only get worse as temperatures continue to rise.

Dana Nuccitelli is an Environmental Scientist and writes about climate change for The Guardian and Skeptical Science.

The Science Policy Network is a team of CCL leaders and supporters with a diverse background in the field of climate science. These network contributors write regular guest posts, offering thorough insight into topics that fall within their expertise. This post and other resources are available in the form of white papers on CCL Community.

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