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
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This unwanted hitch hiker is called Ixodes scapularis, better
known as a deer or a black-legged tick. This tick can harbor a slew of
infectious bacteria in their gut that can be ‘gifted’ to you. One common
bacterium is Borrelia burgdorferi, which causes Lyme disease. The most common
symptoms of Lyme disease are fatigue, headache, chills, fever, and a bullseye
shaped rash called an erythema migrans. The current treatment for Lyme disease
is a course of antibiotics, but some people experience continued and worsening
symptoms after completing their medication. Unfortunately, recent research has
predicted the expansion of deer tick habitat due to climate change. They may
even be coming soon in a backyard near you!
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.
 |
| 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
