Here come the ticks: is global warming leading to an increase in Lyme disease?

This is the last of 16 student posts, guest-authored by Jessica Waters. 

Climatologists have been warning us about the ongoing and impending consequences of global warming for years. But the results of climate change affect more than just polar bears and penguins  - if you live anywhere in the northeastern, north-central or west coast states of the U.S.., you could be at a greater risk for contracting Lyme Disease.

Lyme disease is an infection of the Borrelia burgdorferi bacterium that is spread through black legged ticks (otherwise known as deer ticks) who feed on the white footed mouse species, also known as the wood mouse, which carries the bacteria.  The symptoms of the disease itself include fever, headache, fatigue, and a telltale “bulls eye” rash near the site of the tick-bite. Left untreated, Lyme disease can spread to affect the joints (causing arthritis), heart, and nervous system – often causing irritability and mood swings.

Lyme disease transmission occurs in a Reservoir à Vector à Host cycle.  A Reservoir is the habitat in which an infectious agent normally lives, grows and multiplies – in this case, it is the white-footed mouse. A disease vector is a carrier animal (usually an arthropod) that transfers an infective agent from one host to another- i.e. the blacklegged tick.  And the host in this scenario is an organism that harbors an infective agent – us, our pets, and other animals.

Lyme disease is transmitted when a nymphal (young) tick feeds on a B. burgdorferi carrying white-footed mouse. The contaminated bloodmeal that it ingests allows the bacterium to live on in the tick (the vector), and the infected tick can then transmit the bacteria to its next host – a dog, your child, you, or any other animal roaming around in a wooded area.

Nearly a quarter of all Lyme disease cases are in children, as they play near to the ground, where host-seeking ticks are often waiting.  The CDC reports that pet owners and outdoorsy types are also at higher risk, as dogs and people traipsing through thick brush can easily pick up a tick or two without realizing it.

So how does climate change factor into this? According to ecologist Rick Osfeldt, a small mammal expert in Millbrook , New York, it all comes down to acorns.

“ Acorn abundance gives rodents a jump start on breeding. By the next summer, mice numbers are through the roof”.

This phenomenon gave rise to a “mouse-boom” in 2010, a low-acorn year in 2011, and what promises to be a busy summer for public health officials in 2012.  As the theory goes, as nymphal ticks wake up to a low mouse count (from 2011), they will feed on the existing mice and then turn to the next best thing – humans.

While the exact science behind what causes oak trees to produce more acorns is not yet identified, studies suggest that plants in warmer climates produce more seeds.

More acorns means a bumper crop for hungry mice, and milder winters mean higher breeding rates and higher survival rates for the B. burdorferi carrying rodents.

Maria Diuk-Wasser, an assistant professor of epidemiology at the Yale school of public health also attributes an increase in Lyme disease to higher average temperatures, but for a different reason.

“One possible way in which temperature may limit tick populations is by increasing the length of their life cycle from two to three years in the north, where it is colder.”  As average temperatures increase, climate change could be reverting the normal temperature pattern and increasing the production Lyme disease carrying ticks.

If both hypothesis prove to be true (and so far, CDC reported cases of Lyme disease have increased from 15,000 in the mid 1990s to over 40,000 today), an increase in both mouse and tick populations could indicate an increased prevalence of Lyme disease in years to come.

It may also be that the number of (geographically) susceptible people will increase as well. Nick Ogden, a zoonoses  researcher with the Public Health agency of Canada recently published a paper suggesting that the tick-inhabitable regions of North America may be increasing – in Eastern Canada, the tick inhabitable region will expend from 18% to over 80% by 2020, while the average temperatures in Canada have simultaneously increased by 2.5 degrees Fahrenheit over the past 60 years.

While some measures can be taken to prevent infection of Lyme disease once a tick has made a meal of you, cautionary measures are the best way to prevent you and your loved ones from becoming hosts.

The CDC recommends using insect repellant, applying pesticides, reducing tick habitat (i.e. cutting down heavy brush areas in your yard), and wearing long sleeves and pants when in wooded areas.  Prompt removal of ticks is also necessary, so continually check exposed skin areas when you are outdoors  -the backs of your legs, the back of your neck, the ears of your dog, etc.

One creepy-but-saving grace in tick removal may be that once a tick has landed on you, it will not immediately attach, instead crawling around for up to three hours to find an ideal location to feed. While not pleasant to imagine, it may give you enough time to jump in a hot shower after time outdoors and wash off any unattached ticks. Even attached ticks still require 24 to 36 hours to spread the B. burgorferi bacteria into your blood – if you remove a tick within 24 hours, you are greatly reducing your chances of getting Lyme disease.   Attached ticks  should be removed gently with tweezers.

If diagnosed early, Lyme disease can be cured with antibiotics. If you find an attached tick, see a general practitioner. You may be offered a single dose of antibiotics if you were bitten by a Lyme disease carrying tick species and the tick has probably been attached for at least 36 hours.

So, perhaps most importantly, if you suspect that you may have been bitten by a tick or have symptoms of Lyme disease – get thee to a doctor, and consider saving the planet from further warming by riding your bike there.

Online Sources:

Patrick A. Leighton, Jules K. Koffi, Yann Pelcat, L. Robbin Lindsay, Nicholas H. Ogden. Predicting the speed of tick invasion: an empirical model of range expansion for the Lyme disease vector Ixodes scapularis in Canada.Journal of Applied Ecology, 2012; DOI: 10.1111/j.1365-2664.2012.02112.x



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Nice overview. A few comments are in order. 1. Ticks don't transmit a 'disease'. Instead, they may transmit the microbial agents (in this case Borrelia burgdorferi) that may cause disease in some hosts (such as human beings) but not in others (such as the white footed mouse). 2. The deer ticks (aka black-legged ticks), as well as the pathogens they transmit, have been spreading geographically for decades. Is it because of the abundance of acorns or foxes (another suggestion), warming climate or something else? Deer ticks travel from property to property on the backs of mice, between neighboring communities on the backs of deer, and to far more distant sites by the movements of birds. Deer abundance is the greatest factor responsible for the perpetuation of the deer tick population. 3. Finally, a practical note. Finding and promptly removing ticks (from a person or pet) can dramatically reduce risk of infection. Once the tick has been removed, have it identified. Only certain kinds of ticks can transmit the agents of Lyme disease, babesiosis and anaplasmosis. Other ticks may transmit other infections. The longer the tick is attached, the greater the risk of infection. Physical samples can be sent, or digital images uploaded, for a rapid, confidential, independent and expert evaluation. For more educational information and help with tick identification, visit

By Richard Pollack, PhD (not verified) on 23 Jun 2012 #permalink

" 1. Ticks don’t transmit a ‘disease’. Instead, they may transmit the microbial agents"

And cars don't transport people, the petrol burned in the engines cause the energy release which allows motion...

It's taken us 150 years to raise temps by .7°C. Just how hyper-sensitive are these ticks? Or is this just another piece where a "reporter" blindly parrots the line given to her by her betters?

By Mike Mangan (not verified) on 23 Jun 2012 #permalink

It's taken us 30 years for us to raise the temperature 0.5C.

Funny how you didn't mention that...

Global warming has already been blamed for everything bad. How could they have overlooked ticks?

By Jeff Morton (not verified) on 24 Jun 2012 #permalink

So you’re saying that people don’t die if its too cold?

Or that ticks are impervious to it?

There is actually no hard and fast minimum time for infection after a tick bite. 24 hours is often the minimum time but not always. You should get tested for lyme even if a tick is embedded for just a few minutes. Learn more at

I've been camping since I was an infant. Growing up I learned from my parents that we always check each other after being in water or dense brush. Ticks were luckily always removed before attachment. Later, camping with members of the opposite sex, this turned into grooming and helped with bonding. No kidding. It works.
I was told that if a tick became attached, a drop of gasoline or white gas would get it to let go. I have never needed to do it. Does it work? Oh, stay away from an open campfire, otherwise, the procedure consequences are far worse than the problem.


By Kenneth J Mareld (not verified) on 27 Jun 2012 #permalink

In re attachment time to infection; the spirochete resides at low levels in the tick midgut. It takes time for the bacteria to reproduce to high levels and time to move to the mouth parts as the tick returns excess fluid to the host victim. I don't have an academic literature citation at hand, but 24 hours is widely accepted as the minimum for potential infection.

Remember also that no study has cited prevalence even approaching 100%, more often 30%-50% is found.

A tick should be promptly removed using only fine tweezers.

By Doug Huffman (not verified) on 08 Jul 2012 #permalink

Same story here in the UK: our local ER department was getting up to 40 walk-ins a day for tick removal. My hound was regularly coming back from walks with a hanger-on or two. I used a fork-ended twister to get them out. Don't just grab and pull as you need the mouthparts out. Smearing them in Vaseline or tea tree oil kills them too and they drop off, mouthparts and all.

By Peter McGrath (not verified) on 29 Sep 2012 #permalink