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California Environmental Health Tracking Program

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Last Edited: 4/15/2014

Vector-Borne Disease and Climate Change

Vector-borne diseases (VBD) are infectious diseases that are transmitted to humans by animals, also called vectors, such as mosquitoes, ticks, fleas, lice, and rodents.  Climate change can cause vectors or the diseases they carry to multiply or spread out more rapidly.  When vectors spread to new areas where people live, work, or play, more people may be at risk of contracting VBD.  This is particularly true when vectors move into places that they have never inhabited before, or conversely, when people move into areas where vectors exist.

 

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How does climate change affect vector-borne disease?

The ecology of Vector-Borne Diseases (VBD) is complex, and climate is a major factor that may influence disease transmission cycles and disease occurrence.  Changes in temperature and humidity can affect where vectors proliferate.  These changes can also affect the life-cycles of the pathogens they carry.

  • Drought and heat
    • West Nile virus activity often appears to be greatest during La Niña conditions of drought and hot summer temperatures
  • Wet conditions
    • A prolonged rainy season could make California more at risk for the introduction and establishment of exotic vectors, such as those that carry dengue and yellow fever

Climate change may impact the distribution of vectors- depending on whether drier or wetter habitats are more suitable for any particular vector- and may allow them to exist where they previously did not.

 

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How do vector-borne diseases impact health?

 Human Hantavirus Cardiopulmonary Syndrome (HCPS), Lyme disease, and West Nile virus are three VBD that climate change may impact in California.  As climate conditions change to alter the ecology of vectors, it is possible for human exposure to these diseases to increase significantly.  For example:

  • Human Hantavirus Cardiopulmonary Syndrome

    • Although HCPS infections have remained rare in California, more common flooding or heavy precipitation cycles could increase deer mice populations, which can carry the virus.  People at risk for infection include those exposed to rodent-infested dwellings.  This is particularly true in undeveloped areas where deer mice are abundant, such as poorly maintained mountain cabins or long-vacant cabins. 

  • Lyme Disease

    • Climate change may impact the distribution of the tick that transmits Lyme disease.  As wet, humid areas become drier they will be less suitable tick habitat, while some dry areas may become wetter, allowing for the tick to exist where it previously did not.

Indirect health effects of VBD may include pesticide-related health effects.  Use of pesticides might increase in response to growing populations of disease vectors.  Human exposures to pesticides may cause a wide variety of health effects, depending on the pesticide used and the amount of exposure.  For more information on pesticide health and safety issues, see EHIB's webpage on pesticides.

 

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Resources on climate change and vector-borne diseases

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1. Public Health Climate Change Adaptation Strategy (Draft). 12/18/2008. p. 15-16; www.climatechange.ca.gov/adaptation/publichealth/index.html