Gunner Quinn
Come spring, most hunters are acutely aware of ticks—those little arachnids that seemingly fall from the sky once the weather warms and the leaves green up. Out West, the common Rocky Mountain wood ticks aren’t much to worry about (though they do still carry and transmit disease), but Midwest and Eastern hunters are all too aware of the tiny blacklegged variety of ticks that can carry life-crippling Lyme disease.
Now, their range might be expanding. Last fall, a hunter in eastern Montana pulled a tick off his bird dog, but noticed it looked a little different than the area’s usual wood ticks. He packaged up the critter and sent it to researchers at Montana State University in Bozeman, who identified it as a blacklegged deer tick—the species known to carry Lyme.
The specimen didn’t have the disease, but it was the furthest west the species has ever been recorded, indicating that their range might be expanding, and with it, the potential for Lyme.
The disease itself is caused by a bacterium, Borrelia burgdorferi, that takes residency in small mammals like mice and voles. Ticks that suckle blood from infected rodents can then transmit the pathogen to humans, on whom the initial symptom is typically a “bullseye”-shaped rash around the bite site. If left untreated or undetected, the disease can ruin people’s lives with fatigue, joint inflammation, and even neurological problems like paralysis. It’s estimated that between 300,000 and half a million people contract the disease every year in the US, with most being in the Northeast and Great Lakes regions (there’s also a sub-species of blacklegged tick on the California coast that’s been known to carry Lyme, though infections are few and far between).
Over the last decade, researchers have noticed a slow western creep of black-legged deer ticks. The frontier was thought to stop on a transect stretching from central North Dakota to central Texas, but the new Montana case indicates a jump of several hundred miles westward.
Still, it’s unclear whether the sighting is an isolated incident or if it represents the tip of a proverbial iceberg. “It’s unknown whether blacklegged ticks can survive Montana’s winters, or if they need to rely on the movement of host animals to enter the state,” the researchers wrote in a press release. “However, wooded riparian corridors found along many of Montana’s rivers and streams may provide suitable habitat for this species, allowing it to migrate into the open plains.” Presumably, that holds true for other western states like Colorado, Wyoming, and Idaho as well.
In addition to an expansion in the range of Lyme, new research suggests that the disease may be increasing in prevalence for other reasons as well. In the United Kingdom, researchers recently found that ticks tend to carry Lyme at a higher frequency near pheasant-release sites.
Similar to management practices in the United States, pheasants in the UK are raised and released into the woods for hunters, with numbers ranging from several hundred to over 100,000 per release site. The same sites are used year after year, and many contain semi-permanent infrastructure like acclimation cages and food supplies.
Suspecting these release sites might be hot spots for Lyme, the UK researchers collected ticks in the release areas and in randomly selected “control” sites about a half mile to a mile away. They found that not only were ticks more abundant at the release sites, but they were also 2.5 times more likely to carry Lyme disease. At the pheasant release sites, 7.8% of ticks were infected with the Borrelia bacteria, versus only 3.2% at non-release sites. Those numbers are both relatively small, but could result in an increased risk of people contracting Lyme—especially if they spend a lot of time hunting and romping in the woods hunting pheasants.
However, the researchers note that more work is needed to determine the exact reasons for the discrepancy. A likely explanation is that pheasants, similar to rodents, can act as a localized host for Borrelia. Pheasants contract the bacteria from infected ticks and then pass it onto other ticks, who in turn infect other pheasants and even humans.
Should hunters be concerned about the increased prevalence of Lyme in these areas? Not necessarily, though more thorough tick-checks after a day of hunting might be prudent. Blacklegged ticks are significantly smaller than Rocky Mountain wood ticks, and can be difficult to find (which contributes to the high number of Lyme cases every year). But as most people who have contracted the disease could attest, it’s not something to be trifled with. Generally, it’s still a good idea to watch out for those little arachnids come spring and summer.
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