Climate Change Threatens Health: Infectious Diseases

Infectious Diseases: Dengue Fever, West Nile Virus, and Lyme Disease

While many infectious diseases were once all but eliminated from the United States, there's evidence that climate change is a factor that could help them expand their range and make a comeback.

Mosquitoes capable of carrying and transmitting diseases like Dengue Fever, for example, now live in at least 28 states. As temperatures increase and rainfall patterns change - and summers become longer - these insects can remain active for longer seasons and in wider areas, greatly increasing the risk for people who live there.

The same is true on a global scale: increases in heat, precipitation, and humidity can allow tropical and subtropical insects to move from regions where infectious diseases thrive into new places. This, coupled with increased international travel to and from all 50 states, means that the U.S. is increasingly at risk for becoming home to these new diseases.

Nearly 4,000 cases of imported and locally-transmitted Dengue Fever were reported in the U.S. between 1995 and 2005, and that number rises to 10,000 when cases in the Texas-Mexico border region are included. In Florida, 28 locally-transmitted cases were reported in a 2009-2010 outbreak, the first there in more than 40 years. Dengue Fever, also known as "Breakbone Fever", is characterized by high fever, headaches, bone and joint aches, and a rash. Recurrent infection can lead to bleeding, seizures, and death.

Lyme disease - transmitted primarily through bites from certain tick species - could expand throughout the United States and northward into Canada, as temperatures warm, allowing ticks to move into new regions.

West Nile virus, which first entered the U.S. in 1999, expanded rapidly westward across the country. By 2005, over 16,000 cases had been reported. Warmer temperatures, heavy rainfall and high humidity have reportedly increased the rate of human infection.

Communities across the nation must educate themselves about the risks from climate change and spreading infectious diseases and learn how to protect their most vulnerable residents.

Eleven states and several local governments have developed preparedness measures to address the spread of infectious diseases associated with climate change. The most frequent recommendation is improving statewide surveillance for vectors such as mosquitoes, and the presence of vector-borne diseases.

How are states addressing the threat of infectious diseases?

  • Alaska's climate preparedness strategy for infectious diseases focuses on increased disease surveillance and monitoring. Find out more >>
  • California's plan includes a measure to identify vulnerabilities to the spread of infectious diseases with climate change, such as Valley Fever. Find out more >>
  • Florida's plan includes measures to research and assess increased health threats from infectious diseases due to climate change. Find out more >>
  • Maryland's plan includes measures to identify, track, prevent, and respond to vector-borne and infectious diseases. Find out more >>
  • Michigan's plan identifies the spread of infectious diseases as a threat due to climate change, but it does not include specific measures to address this threat. Find out more >>
  • New York's plan acknowledges better integration of environmental and health data/analysis is needed for vector-borne disease forecasting. Find out more >>
  • New Hampshire's and the city of Keene's plans include measures to improve infectious disease forecasting and surveillance. Find out more >>
  • Oregon's plan includes monitoring, detection, and control measures for insects that can carry climate change-related illnesses, and wildlife diseases that can also affect humans, and increased outreach and community education about disease prevention. Find out more >>
  • Washington's plan increases the overall efficiency and sensitivity of its current surveillance systems to monitor and respond to disease events. King County's plan includes measures to research infectious disease threats and improve response protocols. Find out more >>
  • Wisconsin's plan includes measures to study the relationship between climate and the spread of infectious diseases. Find out more >>
  • Virginia's plan includes measures to better track diseases that may be related to climate change. The city of Alexandria's plan includes measures to reduce mosquito vectors and to improve response plans for disease outbreaks. Find out more >>

Map Methods

For NRDC's 2009 issue paper, Fever Pitch: Mosquito-Borne Dengue Fever Threat Spreading in the Americas, we created an online Appendix that describes the method we used to create the map of dengue fever vulnerability you're viewing now.

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