finding 5.3 : changing-mosquitoborne-disease-dynamics

Rising temperatures, changing precipitation patterns, and a higher frequency of some extreme weather events associated with climate change will influence the distribution, abundance, and prevalence of infection in the mosquitoes that transmit West Nile virus and other pathogens by altering habitat availability and mosquito and viral reproduction rates [Very Likely, High Confidence]. Alterations in the distribution, abundance, and infection rate of mosquitoes will influence human exposure to bites from infected mosquitoes, which is expected to alter risk for human disease [Very Likely, Medium Confidence].

This finding is from chapter 5 of The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment.

Process for developing key messages: The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at several workshops, teleconferences, and email exchanges. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, and Federal agencies. For additional information on the overall report process, see Appendices 2 and 3.

The approach and organization of this chapter was decided after conducting a comprehensive literature review. Two case studies, Lyme disease and West Nile virus, were chosen as representative examples of vector-borne diseases in the United States for this chapter because of their high incidence rates and the body of literature available on the association between climatic and meteorological variables and occurrence of these diseases.

Regarding human outcomes related to vector-borne diseases, there is a much greater volume of published literature available on meteorological and climatic influences on vectors. As a result, our certainty in how climate change is likely to influence the vectors far exceeds our certainty in how changing climatic conditions are likely to affect when, where, and how many cases of vector-borne diseases are likely to occur.

Although the topic of zoonotic diseases was included in the original prospectus, it was later removed due to space constraints. Additionally, since both West Nile virus infection and Lyme disease are zoonotic diseases, these case studies address concepts that are common to both vector-borne and zoonotic diseases.

Description of evidence base: Higher temperatures affect the West Nile virus (WNV) system by accelerating mosquito development6cb63356-47f7-4ba2-aa75-dbc7517b5399 8fdde45b-cdd1-49de-b74f-966c15770b2d and virus reproduction rates,c3fa0d45-e602-4539-b0d8-98516bcee406 8c5c5e1d-4d05-4c0e-8587-95895e42c7f3 133275d2-6318-44fd-b5be-2e3ab47b5d2b 2a946904-7173-4d32-8f15-db4f8f45f5f5 increasing egg-laying and biting frequency,fe14b0e8-c6e8-4e81-bd63-955c7d780308 and affecting mosquito survival.6cb63356-47f7-4ba2-aa75-dbc7517b5399 b18cdaac-0f7f-48ef-a9b9-ec3e27006924 Increased WNV activity has been associated with warm temperatures, mild winters, and drought.c3fa0d45-e602-4539-b0d8-98516bcee406 5bd8de26-58f4-44b9-9919-885bb217bfb1 945868ae-7a42-4c03-aecf-42d9f4b39a65 Very few studies have used climate variables to predict the occurrence of human WNV cases in the United States in response to climate change (for example, Harrigan et al. 2014),132133f3-1705-42ed-b505-8ccbaa497968 but available results suggest that areas of WNV transmission will expand in the northern latitudes and higher elevations driven by increasing temperature, while WNV transmission may decrease in the South if increasing temperatures reduce mosquito survival or limit availability of surface water, such as that provided by agricultural irrigation.

New information and remaining uncertainties: While the influence of temperature and precipitation on mosquito and WNV biology are fairly well-understood, these relationships vary across the United States depending on the local mosquito vector species, land use, and human activity.8a6987a1-ec6c-4027-9a29-315c7bfdbdd2 56d62d2b-1544-45fa-9336-aaf3708df8d0 For mosquitoes in urban areas, droughts may lead to stagnation of water and increased mosquito populations that enhance WNV transmission,5bd8de26-58f4-44b9-9919-885bb217bfb1 6c4943e6-2a76-4989-b80e-8b4d9bacd78a while in rural or agricultural areas, droughts may reduce mosquito populations by reducing available mosquito habitat for breeding,c3fa0d45-e602-4539-b0d8-98516bcee406 except when irrigation compensates for drought conditions.56d62d2b-1544-45fa-9336-aaf3708df8d0 Long-term projections of human WNV risk under climate change scenarios are still in the early stages of development and are impeded by the complexities of the disease transmission cycle. Evolution of the virus, improvements in mosquito control, and the potential for long-term changes in human behavior that may affect exposure to WNV are key sources of uncertainty. For this reason, short-term, seasonal forecasts of WNV may be more fruitful in the near term and may provide information for seasonal resource allocation and public health planning.

Assessment of confidence based on evidence: Based on the evidence, there is high confidence that climate change is very likely to influence mosquito distribution, abundance, and infection prevalence by altering habitat availability and mosquito and viral reproduction rates. While this is very likely to influence human disease, due to the few sources with limited consistency, incomplete models with methods still emerging, and some competing schools of thought, there is medium confidence surrounding how, and how much, climate change will influence human incidence of disease.

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