Ask The Entomologist

Tick diseases in Montana

Spring has sprung, and our first ticks are out and about.
When folks start talking about illnesses transmitted by ticks, the first to come up almost always seems to be Lyme Disease. While Lyme Disease is the most common tick-borne disease among Montanans, you don’t need to worry about picking it up around here – it tends to be something folks pick up on vacation.

The Black-Legged Tick, also known as the deer tick, is the primary culprit responsible for transmitting Lyme Disease. Black-legged ticks are not found in Montana – they are, however, found all across the eastern half of North America. A related tick on the west coast, the Western Black-Legged Tick, is a less-effective vector of Lyme Disease.

A black-legged tick feeding on you isn’t a guarantee of disease – to transmit the disease, the tick first needs to feed on a small mammal (usually a White-Footed Deer Mouse) which is infected with the bacterial agent responsible for the disease… Because these ticks eat blood meals only once per life stage (once each as a larva, nymph, and an adult), you’re most likely to get the disease from a black-legged tick nymph. The adults prefer deer to us humans, anyways.

The lifecycle of the Black-Legged Tick, sometimes known as the Deer Tick.
The common hosts for each life stage are pictured as well.
The CDC’s helpful graphic on the black-legged tick lifecycle.

Our northwestern corner of Montana is untroubled by tick-vectored disease. That said, if you venture into the southern portions of the state, we do have four tick-borne illnesses you could contract.

Rocky Mountain Spotted Fever
-About 6 cases reported in MT per year.
-This disease is potentially deadly, moreso than Lyme Disease. Symptoms include achiness and fatigue, as well as a distinctive mottled rash.
-This disease is vectored by larger ticks, the Rocky Mountain Wood Tick and the American Dog Tick, both of which should be easier to spot.

Tularemia
-About 4 cases reported in MT per year.
-Sudden high fever, swollen lymph nodes, and pervasive weakness.
-Tularemia can be vectored by the same two ticks that transmit Rocky Mountain Spotted Fever. However, more people catch it from contact with blood from infected rodents and especially rabbits. Something to keep in mind if you’re fond of skinning.

Colorado Tick Fever
-1 to 2 cases reported in MT per year.
-This feels much like flu – aching, fever, chills, fatigue – which makes sense, as flu and Colorado Tick Fever are both are caused by viruses. Not too dangerous, usually goes away after 1-3 days.
-Like the previous two diseases, this one is transmitted by both the Rocky Mountain Wood Tick and the American Dog Tick.

Tick-Borne Relapsing Fever
-Extremely rare, but it does occur in MT.
-Fever rapidly develops after the initial infection, but then subsides, and reocurs in cycles about four days long.
-Transmitted by soft-bodied ticks that specialize on chipmunks and pine squirrels – avoid contact with small woodland mammals and sleeping in dilapidated cabins and you should be okay.

I would strongly advocate wearing clothes treated with permethrin if you’ll be in good tick habitat for a while – especially if you’re someplace with more interesting tick-borne diseases, like Red Meat Allergy, in the American southeast.

The ticks you’re most likely to find here in Montana are these two… but if you come across something odd, there’s the CDC’s tick ID page, and beyond that I’d be more than happy to take a look at any bugs you might have for me!

A poster from the MT Department of Health & Human Services
Communicable Disease Epidemiology Program

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