Likely Geographic Distributional Shifts among Medically Important Tick Species and Tick-Associated Diseases under Climate Change in North America: A Review

Simple Summary North America is considered as an area likely to be significantly affected by global warming, with climate change causing markedly warmer winter temperatures in the United States in recent decades. Ticks are sensitive to changes in ambient abiotic conditions and, therefore, climate: they are poikilothermic, with the life stages of each species requiring specific sets of environmental conditions for successful development and survival. Our review focuses on (1) identifying and exploring suitable areas for the eight medically important vector tick species in North America; (2) exploring whether and how species' distributions are likely to shift in coming decades in response to climate change, and in what ways; (3) and providing a picture on the status of the tick-associated diseases in North America from the present to the future. Ticks rank high among arthropod vectors in terms of numbers of infectious agents that they transmit to humans, including Lyme disease, Rocky Mountain spotted fever, Colorado tick fever, human monocytic ehrlichiosis, tularemia, and human granulocytic anaplasmosis. Increasing temperature is suspected to affect tick biting rates and pathogen developmental rates, thereby potentially increasing risk for disease incidence. Tick distributions respond to climate change, but how their geographic ranges will shift in future decades and how those shifts may translate into changes in disease incidence remain unclear. In this study, we have assembled correlative ecological niche models for eight tick species of medical or veterinary importance in North America (Ixodes scapularis, I. pacificus, I. cookei, Dermacentor variabilis, D. andersoni, Amblyomma americanum, A. maculatum, and Rhipicephalus sanguineus), assessing the distributional potential of each under both present and future climatic conditions. Our goal was to assess whether and how species' distributions will likely shift in coming decades in response to climate change. We interpret these patterns in terms of likely implications for tick-associated diseases in North America.