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  • Kris Sundberg

Tick Borne Disease - Fall Season Begins

In Minnesota, there are about a dozen different types of ticks. Not all of them spread disease. Three types that people may come across in Minnesota are the blacklegged tick (aka deer tick), the American dog tick (aka wood tick), and the lone star tick. The blacklegged tick causes by far the most tickborne disease in Minnesota. People in Minnesota are often bitten by American dog ticks but they rarely spread diseases. American dog ticks may spread Rocky Mountain spotted fever and tularemia. Lone star ticks are rarely found in Minnesota but can spread diseases such as ehrlichiosis and tularemia.

Blacklegged Tick Life Cycle

Blacklegged ticks live for about two to three years. Most of their life is spent out in the environment rather than on a host or in a host’s nest. During their entire lifetime, they will only have up to three blood meals. The picture to the left shows that the life cycle begins when the female lays eggs. As the egg matures, it develops into a larva (right-middle), then a nymph (top-middle) and finally, an adult male or female (bottom-right).

The blacklegged tick, shown in the lower right, is much smaller than the American dog tick, shown in the upper right. The lone star tick is shown in the upper left of this photo and is a little smaller than the American dog tick but larger than the blacklegged tick.

In Minnesota, adult ticks will usually emerge right after the snow melts and reach peak spring-time activity during the month of May. The adult ticks will typically stay active throughout June. Adults will also become active again in the fall, usually by the end of September and through October, until temperatures drop below freezing or snow covers the ground. Blacklegged tick nymphs start to become active in mid-May and reach peak activity at the end of May through the month of June. Nymph activity tapers off slowly, and they are much less active by the end of July. Larvae are typically most active in June.

This map, from the Minnesota Department of Health, depicts the risk of contracting Lyme disease or anaplasmosis (another tick-borne illness) by county, the darker the color, the higher the risk.

In the spring of their first year, eggs hatch into larvae. Larvae prefer to feed on blood from small mammals, like mice and birds. Larvae have one feeding then molt into nymphs and rest until the next spring. During this first meal, the larva may pick up a disease agent (like the bacteria that causes Lyme disease) while feeding on a small mammal, such as a white-footed mouse.

Late in the spring of their second year, nymphs take their second feeding. Nymphs aren’t as picky with their choice of host and will feed on blood from small or large mammals, such as white-tailed deer or humans. At this time, if the nymph is infected with a disease agent, then it could spread the disease agent to a human or animal that it feeds on.

In the fall of their second year, nymphs that have had a blood meal will molt into an adult male or female tick. Adults prefer to feed on large mammals, such as white-tailed deer or humans. The females find a host to feed, mate with an adult male tick, lay hundreds to thousands of eggs, and then die. The males attach to a host to find a female mate and then die. Some adults who do not feed or mate in the fall will survive through the winter and then come out to feed and/or mate the following spring. If there is little to no snow cover and temperatures rise above freezing, it is possible to find an active adult tick searching for a host on a warm winter day.

Lyme Disease Statistics

In 2021, 1,033 confirmed Lyme disease cases (18 cases per 100,000 population) were reported in Minnesota. In addition, 869 probable cases (physician-diagnosed cases that did not meet clinical evidence criteria for a confirmed case but that had laboratory evidence of infection) were reported.

  • 642 (62%) confirmed cases were male

  • Median case age was 45 years (range, 2 to 94 years)

  • 697 (67%) cases had a physician-diagnosed erythema migrans rash (e.g., Bull’s eye rash)

  • 371 (36%) cases had one or more late manifestations of Lyme disease (e.g., arthritis or Bell’s Palsy) with confirmation by Western immunoblot laboratory testing (positive IgM ≤ 30 days post-onset or positive IgG).

  • Of the 934 cases with known illness onset dates, illness onsets peaked from June through August with 68% of erythema migrans rashes occurring in June or July.

Despite some yearly fluctuations, the number of reported cases of Lyme disease has been increasing over the years.

  • Median number of cases reported from 2000 to 2009 was 915 cases (range, 463 to 1,239).

  • Median number of cases reported from 2010 through 2019 was 1,190 cases (range, 896 to 1,431).

Source: MN Department of Health

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