Deer ticks, common carriers of Lyme disease, have seen an increase in habitat due to climate change and, with current trajectories, will continue to do so.
By Zoe E. Quin, undergraduate researcher
Lurking within the tall grasses of many backyards and forests is a dangerous little critter who is out to drink your blood. These real-life vampires can locate you by sensing your breath. And if you come close enough, they can latch on without you ever knowing. Sometimes they may even leave you with an unpleasant parting gift.
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Ixodes scapularis (deer tick). James Gathany, Centers for Disease Control and Prevention |
Lyme disease has been highly prevalent within northeastern United States and just recently has become more apparent with in southern Canada. It was previously believed that the climate of Canada was uninhabitable for deer ticks because of its cold winters. The colder temperatures would kill off tick populations, inhibiting them from feeding on new animal hosts. However, climate change has altered overall temperatures, the lengths of winter, and the tick’s host populations. All of which, have led to a northward growth of tick habitat into Canada and colder parts of the United States; potentially giving rise to more cases of Lyme disease.
Within their lifetime, deer ticks will latch onto an animal and drink their blood three separate times. Once when they are a larva, once when they are a nymph, and then again when they are an adult.
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| Visual representation of Ixodes scapularis at different life stages (not to scale). Unfed adults are 2-6 millimeters in length; Adult males are often smaller than the adult females and misidentified as nymphs. Unfed nymphs are about 1.5 mm, and larva are less than 1 mm long, about the size of a poppy seed. |
The animals that ticks feed on usually depend upon their current life stage and the availability of hosts. Larva and nymphs are usually found feeding from small rodents and birds, while adults are found on medium to large mammals such as white-tailed deer and humans. Generally, the smaller tick hosts like the white-footed mouse, will acquire B. burgdorferi and readily infect other ticks more than their larger host counterparts; This may be due to body size, but it is overall unclear why. The infectivity of white-footed mice and other small mammals makes nymphal ticks much more dangerous to humans because they are more likely to acquire B. burgdorferi from their prior host and they are much harder to see.
With current climate change trajectories warming cold climates, white-footed mice have been predicted to have a 186-mile shift north within the next forty years. This suggests that there will be an increase of hosts that can infect larval and nymphal ticks with the bacteria causing Lyme disease. These ticks can then grow into an adult to feed on another host, such as a white-tailed deer or humans. Over the last half of the 20th century, white-tailed deer populations have had an 88% increase in probability of white-tailed deer presence by area due to climate change and land use. The white-tailed deer acts as vehicles to transport pregnant deer ticks to new destinations where they lay their eggs, thus expanding the area where larval and nymphal ticks are found. Within northern Alberta Canada alone, there is a predicted 50,268 square mile increase in white-tail deer range size.
As temperatures continue to rise due to climate change so do populations of deer ticks and their hosts. This brings humans closer in contact with B. burgdorferi thus increasing their risk of contracting Lyme disease. Researchers have yet to determine the extent that climate change will affect Lyme disease cases. Despite this, citizens need to be informed about where ticks are most likely to be found, how to prevent getting bitten by a tick, and what to do when bitten by a tick.
To protect yourself against tick bites, you should know that they are commonly found in areas that are grassy and wooded. If you are hiking in these areas, be sure to stay in the middle of the trail to avoid brushing up against plants that may have ticks on them. You should use Environmental Protection Agency (EPA) registered insect repellent and even treat your clothing with products that contain 0.5% permethrin. After being outdoors you should check your body, clothing, gear, and pets that came with you.
If you find a tick attached to your skin, you should remove it as soon as possible. To do this, you should use a set of fine-tipped tweezers and position them as close to the skin as possible. Then clamp the tweezers down and steadily pull the tick away from your body without twisting. If the mouth part of the tick stays embedded in your skin, remove it if possible. Afterwards, you should clean the wound and dispose of the tick in an escape-proof container.
Other than individual tick safety practices, areas at risk from the range expansion of ticks could implement integrated tick management, consisting of host population removal which has been seen to positively reduce the number of nymphs looking for blood meals. By reducing host population or attempting to alter our climate change trajectory, we may be able to prevent many new cases of Lyme disease.
In conclusion, while the expansion of deer ticks and the successive spread of Lyme disease due to current climate change predictions should be expected, preparative measures can be taken to minimize tick bite risk.
To learn more about tick bite prevention and tick removal head to the CDC’s website:
https://www.cdc.gov/ticks/index.html
To learn more about tick and host migration, here are the following articles explored:
Brunner, Jesse L, et al. “Estimating Reservoir Competence of BorreliaBurgdorferi Hosts: Prevalence and Infectivity, Sensitivity, and Specificity.” Validate User, 1 Jan. 2008, academic.oup.com/jme/article/45/1/139/874411.
Dawe, Kimbery L., and Stan Boutin. 2016. “Climate change is the primary driver of white-tailed deer (Odocoileus virginianus) range expansion at the northern extent of its range; land use is secondary.” Ecology and Evolution 6, no. 18. https://doi.org/10.1002/ece3.2316
Dumic, Igor, and Edson Severnini. 2018. “‘Ticking Bomb’: The Impact of Climate Change on the Incidence of Lyme Disease.” Canadian Journal of Infectious Diseases and Medical Microbiology. Hindawi. October 24. https://www.hindawi.com/journals/cjidmm/2018/5719081/.
Ebi, Kristie L., Ogden, Nicholas H., Semenza, Jan C., and Woodward Alistar. 2017. “Detecting and Attributing Health Burdens to Climate Change.” Environmental Health Perspectives 125, no. 8. https://doi.org/10.1289/EH
Gandy, Sara Louise (2020) “The impacts of host community composition on Lyme disease risk in Scotland”. PhD thesis, University of Glasgow. http://theses.gla.ac.uk/81708/
Little, Eliza, Scott C. Williams, Kirby C. Stafford III, Megand A. Linske, and Gourdarz Molaei. “Evaluating the effectiveness of an integrated tick management approach on multiple pathogen infection in Ixodes scapularis questing nymphs and larvae parasitizing white-footed mice”. Experimental and Applied Acarology 80 (2020): 127-136 . https://doi.org/10.1007/s10493-019-00452-7
Myers, Philip, Barabara L. Lundrigan, Susan M. G. Hoffman, Allison Poor Haraminac, and Stephanie H. Seto. “Climate-induced changes in the small mammal communities of the Northern Great Lakes Region.” Global Change Biology 15, no. 6 (2009). https://doi.org/10.1111/j.1365-2486.2009.01846.x
Roy-Dufresne, Emilie, Logan, Travis, Simon, Julie A., Chmura, Gail L., and Virginie Millien. 2013. “Poleward Expansion of the White-Footed Mouse (Peromyscus leucopus) under Climate Change: Implications for the Spread of Lyme Disease” PLoS One 8(11). Doi: 10.1371/journal.pone.0080724
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