finding 6.1 : seasonal-geographic-changes-waternborne-illness-risk

Increases in water temperatures associated with climate change will alter the seasonal windows of growth and the geographic range of suitable habitat for freshwater toxin-producing harmful algae [Very Likely, High Confidence], certain naturally occurring Vibrio bacteria [Very Likely, Medium Confidence], and marine toxin-producing harmful algae [Likely, Medium Confidence]. These changes will increase the risk of exposure to waterborne pathogens and algal toxins that can cause a variety of illnesses [Medium Confidence].



This finding is from chapter 6 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. 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.

Many water-related illnesses are of critical importance globally, such as cholera and hepatitis E virus, and they affect U.S. interests abroad, but the focus of this chapter is to address climate impacts on water-related illnesses of primary importance to human health within the United States. In addition, although climate change has the potential to impact national as well as global seafood supplies, this chapter does not cover these types of impacts because the peer-reviewed literature is not yet robust enough to make connections to human health outcomes in the United States. Even with those constraints, the impacts of climate on water-related illness are regionally or locally specific and may include increased risks as well as benefits. For example, the projected geographic range shifts of some Gambieridiscus species to more northern latitudes may mean that dominant ciguatera fish poisoning toxins enter the marine food web through different species, with increases of toxins in new areas where waters are warming and potential decreases in areas such as the Yucatan and eastern Caribbean Sea.1dfd14e0-eae8-46d9-9c3e-0fa3f0c37da4

Description of evidence base: Vibrio, a genus of naturally occurring waterborne pathogens, thrives in water temperatures above a 15¡C/59¡F threshold.8640a3db-35fa-4089-8fb5-d52dc8b35c71 2b04b041-511c-4b3f-9e44-70d0cfae3052 7965c0b9-f4c0-43c4-8c4c-8e918935f88e 918354f7-f16e-4cad-9289-20d41305abb8 Rising sea surface temperatures have contributed to an expanded geographic and seasonal range in outbreaks of human illness associated with Vibrio in shellfish.dcfc6226-3871-4225-86f7-948f7db208fb 2b04b041-511c-4b3f-9e44-70d0cfae3052 84bc6e97-2f18-4ebd-b36a-a576fa710edd 7965c0b9-f4c0-43c4-8c4c-8e918935f88e 9cef4119-4454-439b-829a-bdb8f458dd15 In recreational waters, projected increases in sea surface temperatures are expected to lengthen the seasonal window of growth and expand geographic range of Vibrio.dcfc6226-3871-4225-86f7-948f7db208fb 8640a3db-35fa-4089-8fb5-d52dc8b35c71 Like other heterotrophic bacteria, growth of Vibrio is ultimately limited by availability of carbon substrate, though the coastal areas where Vibrio exposure is most likely, either through recreation or consumption of shellfish, generally have sufficient dissolved organic carbon.e3dacc9e-e7ee-4513-b8e1-f867412428f5 Reported rates of all Vibrio infections have tripled since 1996 in the United States, with V. alginolyticus infections having increased by 40-fold.59b468e2-b673-4b43-9daf-6b01b4084163 Increasing sea surface temperatures, changes in precipitation and freshwater delivery to coastal waters, and sea level rise will continue to affect Vibrio growth and are expected to increase human exposure.dcfc6226-3871-4225-86f7-948f7db208fb 226d31a2-0831-48a5-b8fd-f1093c62db54 2b04b041-511c-4b3f-9e44-70d0cfae3052 918354f7-f16e-4cad-9289-20d41305abb8

Most harmful algae, including freshwater cyanobacteria that can contaminate drinking water and marine dinoflagellate species that can contaminate fish and shellfish with natural toxins, thrive during the warm summer season or when water temperatures are higher than usual. As the climate continues to warm, water temperatures will rise above thresholds that promote bloom development earlier in the spring and will persist longer into the fall and expand into higher latitudes. This will result in a longer seasonal window and expanded geographic range for human exposure into higher latitudes.1dd93561-606a-43ea-a054-c2626750c5f0 1fd644a4-c88d-4a0f-9353-bdb018ed2ccf 204a45ba-2f11-48f2-82e0-8075379b0a7d 3cfcb05a-9a2a-4fb1-89be-6377ea83e5d0 0ccd902c-2e71-4609-a8e8-67d8370f0042 b4b8411d-3670-43ec-a0a0-506018d910bd be655d0c-74e0-4fb4-afa3-2f4a0770dc38 3325ef64-347b-4c33-9289-9e05e905dcbe db612cfb-eafa-45fc-8083-1606aa5c5801 69d04f03-5ba1-46a6-a7e3-fa449d448bea d8dfdb53-b50a-49f5-b1e1-4886738b1297 Climate change, especially continued warming, will increase the burden of some marine HAB-related diseases, particularly ciguatera fish poisoning, in some regions of the United States.

New information and remaining uncertainties: Uncertainty remains regarding the relative importance of additional factors that may also act on naturally occurring pathogens and harmful algae at local or regional levels to influence their growth, distribution, and toxicity. In many cases, it is uncertain how these multiple factors may interact with each other to influence the seasonal windows and geographic range for pathogens and harmful algae, especially in dynamic coastal marine environments. For example, changes in salinity, competition with other plankton, and presence of viruses or other organisms that consume plankton or bacteria can affect abundance.d0d412e3-c46b-45a3-b4e5-c3e54c896c36 cb3ad7db-a5a1-473e-bda9-ff18f5f06b6f Changing distribution patterns for some marine species of harmful algae is not well understood and some regions may become too warm for certain species of harmful algae to grow, shifting (without changing in total size) or even shrinking their geographic range.

Additionally, there are limited studies on projections for changes in illness rates due to naturally occurring waterborne pathogens and harmful algae. Uncertainty remains regarding appropriate methods for projecting changes in illness rates, including how to integrate considerations of human behavior into modeling (current methods to assess exposure risk assume similar human behavior across time scales and geography). Methodological challenges are related to 1) underreporting and underdiagnosis of cases that affect the accuracy of baseline estimates of illness, 2) ability to project changes in strain virulence, 3) accounting for the effects of potential adaptation strategies/public health interventions (for example, public service announcements on how to avoid exposure), and 4) accounting for changes in public healthcare infrastructure and access that can reduce the risk of exposure or illness/death if exposed.

Assessment of confidence based on evidence: Based on the evidence, there is medium confidence that, with changing climate, the annual seasonal and the geographic range for Vibrio and certain marine harmful algae will expand. The assessment of medium confidence is due to less certainty from modeling results regarding the magnitude of projected changes in abundance. The conclusions were deemed very likely to occur for Vibrio and likely for marine harmful algae based on good levels of agreement found in the published quantitative modeling projections for both Vibrio and marine harmful algae (Alexandrium and Gambieridiscus) cited above. This conclusion takes into consideration that for some marine algae (for example, Gambieridiscus), lower latitudes may become too warm and risk may decline in those areas as it increases at higher latitudes. For freshwater harmful algae, there is high confidence that annual season and geographic range will expand with changing climate, which will also prolong the time for exposure and the potential for public health impacts. Consistent and high-quality evidence from a limited number of laboratory studies, modeling efforts, field surveys, and comparisons of historic and contemporary conditions support this assessment. The conclusion was deemed very likely to occur for freshwater harmful algae with high confidence based on laboratory studies and field observations, as well as a greater fundamental understanding of inland hydrodynamics and bloom ecology as indicated in the literature cited in the chapter. There is medium confidence regarding increased risk to human health from a longer potential time for exposure to waterborne pathogens and algal toxins and potential exposure for a wider (or novel) population. This confidence level was chosen due to less certainty stemming from a relative lack of quantitative data and projections for future illness rates in the peer-reviewed literature.

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