Changes in the geographic distribution of the blacklegged tick, Ixodes scapularis, in the United States

History of the geographic distribution of the western blacklegged tick, Ixodes pacificus, in the United States

“…As noted by Eisen and Eisen (2023) , dramatic increases over the last century in the geographic distribution of I. scapularis in the northern part of the eastern US likely resulted in large part from processes of reforestation (following deforestation in the 1800s) and, especially, population recovery of the white-tailed deer, O. virginianus (following decimation of deer leading to historically low populations around 1900, including virtual absence of deer from many areas in the Upper Midwest, Ohio Valley region, and the Northeast). The scenario that played out for I. pacificus in the far western US over the last century appears to be different in several respects.…”

“…We speculate that deer have been abundant and widespread enough over the last 100 years to continuously support stable populations of I. pacificus across the tick’s present range in the far western US. This is in stark contrast to the northern part of the eastern US, where the decimation of white-tailed deer in the 1800s and early 1900s presumably led to the disappearance of I. scapularis from large parts of its previous range, and the subsequent reemergence of the white-tailed deer was followed by well documented spread and proliferation of I. scapularis across forested portions of the Upper Midwest and Northeast ( Eisen and Eisen, 2023 ).…”

“…It seems likely the tick was then documented successively from local areas with suitable habitat as surveillance efforts were initiated over time. In contrast to I. scapularis in the eastern US ( Eisen and Eisen, 2023 ), there is no clear evidence of range expansion for I. pacificus based on surveillance targeting questing ticks or from programs where ticks were recovered from wildlife, domestic animals, or humans. The density of nymphal or adult I. pacificus questing in a manner allowing for collection by drag/flag sampling (hereafter referred to simply as drag sampling) has been shown to vary between geographical areas as well as between habitat types (e.g., Eisen et al, 2006a , b ; Swei et al, 2011a ; Lane et al, 2013 ; MacDonald and Briggs, 2016 ).…”

“…In striking contrast to I. scapularis in the eastern US (see Eisen and Eisen, 2023 ), there has not been a dramatic change in the geographic distribution of I. pacificus over the last half-century ( Eisen et al, 2016a ). Collection records from 1893 to 1915 showed I. pacificus to be present in coastal and interior California and coastal Oregon, and extensive field surveys in the 1930s and 1940s documented the tick to occur along the Pacific Coast from southern California to northern Washington, as well as in the Sierra Nevada foothills of California and in western Utah (see Sections 3.2 - 3.5 ).…”

Estimating the Incidence and Economic Cost of Lyme Disease Cases in Canada in the 21st Century with Projected Climate Change

“…did, 18 because empirical data from the United States, showing continued increases in tick populations and LD incidence in southern parts of high-incidence states, does not support this idea. 55 …”