"earlier-tick-activity-northward-range-expansion" . "5.2"^^ . "Ticks capable of carrying the bacteria that cause Lyme disease and other pathogens will show earlier seasonal activity and a generally northward expansion in response to increasing temperatures associated with climate change [Likely, High Confidence]. Longer seasonal activity and expanding geographic range of these ticks will increase the risk of human exposure to ticks [Likely, Medium Confidence]."^^ . . . "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."^^ . "There is strong evidence that temperature affects the geographical distribution of ticks, the timing of host-seeking activity of ticks, and even the timing of Lyme disease case occurrence. However, the abundance of ticks infected with Lyme disease spirochetes, which is considered a better predictor of human risk for Lyme disease compared with nymphal density alone, has rarely been found to be strongly associated with meteorological variables. Studies aimed at identifying meteorological variables associated with the geographical distribution of human Lyme disease vary in their support for demonstrating positive associations between temperature and Lyme disease."^^ . "Based on the evidence, there is high confidence that climate change, especially temperature change, is likely to cause shifts in the geographical distribution of ticks capable of carrying B. burgdorferi to more northern latitudes, the timing of host-seeking activity of ticks, and the timing of Lyme disease case occurrence. While these changes are 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 the risk of human exposure to ticks carrying B. burgdorferi."^^ . "While the effects of temperature, precipitation, and humidity on the spatial distribution of ticks and the timing of their host-seeking activity have been clearly established in both the eastern and western regions of the United States, where Lyme disease is common, the degree to which climate change will alter Lyme disease incidence remains uncertain. The observation that meteorological variables play a lesser role than other variables in predicting the density of nymphs infected with Lyme disease bacteria raises uncertainty in how climate change will affect the distribution and magnitude of Lyme disease incidence. This uncertainty is reflected in results from models aiming to associate meteorological variables with Lyme disease incidence that yielded inconsistent findings."^^ . . . . . . . . . . . . . . . . . . . . . . . . . .