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The Bizarre Chain of Events That Led to an Unusual Number of Ticks This Summer

Ticks can carry Lyme disease and other pathogens, so be extra cautious.
Image: spex/Flickr

If you live anywhere east of the Mississippi (and even some places west of it), you've probably heard this is a bad year for ticks. But why exactly are these little disease-carrying pests so prolific this year? Turns out, you can blame the oak trees.

Every two to five years, oak trees have what's called a "mast" season, meaning they drop way more acorns on the ground. Scientists aren't 100 percent surewhat causes mast years, but they know that in 2015, we had one. This had a ripple effect: last summer, all those acorns provided a bumper crop of food for white-footed mice in many tick-prone areas. And these mice are a major reservoir for the bacteria that causes Lyme disease, an infection that can cause chronic issues if left untreated. Lyme disease infections have been on the rise in recent years and this trickle down from the oak mast means this summer could be particularly risky.


Scientists around the East coast all noted a spike in white-footed mice populations last summer, with some areas seeing more mice than they'd seen in almost thirty years. In turn, those mice have provided plenty of feeding (and disease swapping) opportunities for ticks, causing the tick population to surge.

A Lyme-disease-carrying mouse can infect as much as 95 percent of the ticks that feeds on it, and one mouse can have up to 100 ticks on its body. The mice also don't really mind the ticks, so they spend plenty of time together, unlike some other species that are more fastidious groomers and remove the pests. Researchers have found that a spike in rodent populations correlates to a spike in Lyme disease infections in humans the following year, which is why the tick population is causing so much concern.

In Ontario, some public health agencies have seen the number of ticks submitted to check for Lyme disease double over this time last year. And tick season is just beginning.

What's worse is that climate change is expanding the time of year and areas where ticks thrive, putting more and more people at risk of getting a disease—and increasing the rate of Lyme disease:

Spread of Lyme disease in the US. Image: Centers for Disease Control

Ticks can also carry other dangerous pathogens like Rocky Mountain spotted fever, which can be deadly.

Experts say your best bet is to be extra vigilant with the normal precautions during tick season. Avoid long grass, wear long sleeves and bug spray, and if you're spending any time in the outdoors, do a thorough tick check when you get back inside.

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