Range Expansion of Tick Disease Vectors in North America: The Spread of Tick-Borne Disease

By Maryann Makosiej


Artwork by Reese Green

Lions and tigers and…ticks, oh my? It’s not Oz, but we live in a world where ticks, external parasites that attach to the skin of animals and suck blood, are growing increasingly common. These arthropods are responsible for nearly 95% of vector-borne diseases in the United States and facilitate the transmission of many diseases (e.g. Lyme Disease, Rocky Mountain Spotted Fever, Tick-borne Encephalities). In recent decades, ticks have expanded their geographic ranges due to climate change, increasing their population and placing a new threat to humans, livestock, and companion animals. In this article, we will examine the range expansion and public health implications of three ticks: the American Dog Tick, the Lone Star Tick, and the Black-Legged Tick.


The American Dog Tick is primarily responsible for carrying the bacteria that causes certain dangerous medical conditions, such as Rocky Mountain Spotted Fever in humans and companion animals. Colloquially known as the “ambush” tick because of its tendency to cling to woodland vegetation and roadsides, it is most commonly carried by meadow voles and mice. American Dog Ticks have expanded their range into southern Canada (including Ontario and Saskatchewan), but it is unknown if these arthropods can definitively survive over the winter in climates that remain below 0 °C for a sustained period of time. Generally, that includes areas north of Southern Ohio and Northern New Jersey. If current climate change trends continue, models predict that suitable host areas will increase by 50%, resulting in northward expansion throughout most of Canada and firmly placing Burlington, VT as an epicenter for tick abundance.


The Lone Star Tick is responsible for the spread of human monocytic ehrlichiosis, an acute bacterial disease. It is known as a “hunter” tick, crawling rapidly for many meters in response to host odors. While an American Dog Tick will wait for a passing host, Lone Star Ticks will actively search for one, considerably increasingly their geographic range. Beginning in Texas, these ticks have now been documented as far north as Michigan, South Dakota, and in most counties in New England. As extensive range expansion continues, so does rapid genetic change. Lone Star Ticks, depending on climate, are genetically disparate and are thought to potentially transmit different disease-causing agents, raising alarm for public health experts and proper medical diagnostics.


The Black-Legged Tick is responsible for carrying the greatest number of tick-borne diseases in North America. Since the 1970s, this arthropod’s range has increased substantially due to warming winter temperatures and the reintroduction of white-tailed deer. It can now be found throughout the eastern United States (including here in Burlington) and southern Canada . In Quebec, the number of ticks collected has increased more than four-fold over the six-year period from 2008 to 2014. The Black-Legged Tick is best suited to deciduous forests with ample ground cover, allowing for humid microenvironments.


As a result of climate change, the geographic ranges of ticks are expanding at incredible rates to areas that were previously considered inhospitable. With them, they bring genetic mutations and host geographically new diseases to humans, livestock, and companion animals.


We do not live in a vacuum, and as we continue to interact with our environment, we must remember the extent to which our environment interacts with us.


References:

Sonenshine, D. (2018). Range Expansion of Tick Disease Vectors in North America: Implications for Spread of Tick-Borne Disease. International Journal of Environmental Research and Public Health,15(3), 478. doi:10.3390/ijerph15030478

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