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Early warm weather means an early tick season


Fri, May 7th, 2010
Posted in The Great Outdoors

Warm early spring weather has brought out ticks earlier than usual in many regions of Minnesota. The Minnesota Department of Health (MDH) urges anyone heading outdoors in Minnesota this spring and early summer to use tick repellents and other measures to prevent Lyme disease and other serious diseases transmitted by ticks.

The most commonly reported tick-borne diseases in Minnesota are Lyme disease, anaplasmosis, and babesiosis. Several other tick-borne diseases are rare in Minnesota but have been detected in the state more frequently in recent years. These include Powassan disease, Rocky Mountain spotted fever (RMSF), ehrlichiosis, and tularemia. All of these diseases can be severe.

While the peak of the tick-transmitted disease season is typically from mid-May through mid-July, coinciding with the feeding of the tiny nymph stage of the blacklegged tick (also called deer tick), other ticks are feeding now and can also transmit disease.

"Tick repellent is the best defense for anyone spending time in wooded, brushy, or grassy parts of the state," urged Dave Neitzel, an epidemiologist specializing in tick-transmitted diseases at MDH.

Neitzel emphasized that it is important to use repellents containing one of the following active ingredients:

DEET: Repellents containing up to 30 percent DEET can be used on the skin or clothing. Lower concentrations can be used but might need to be applied more frequently.

Permethrin: These repellents are only applied to clothing, and are highly effective even after treated clothing has been washed.

Since ticks climb up from the ground, focus repellent use below the waistline. Also, wear long pants and light-colored clothing to spot ticks more easily, and walk in the center of trails. After returning from outdoor activities, check your body carefully for ticks and promptly remove any that are found. These precautions are most important during the late spring, early summer, and fall, when ticks are active.

Several tick species carry diseases in Minnesota. The biggest concern is the blacklegged tick, which can carry Lyme disease, anaplasmosis, babesiosis, and Powassan disease. Blacklegged ticks are most common in hardwood or mixed hardwood forests of east-central, north-central, and southeast Minnesota. Over the past few years, they have appeared to expand their range into forested parts of west-central, northwest, and northeast Minnesota. The ticks also are common in wooded areas of Wisconsin and northeastern states. Blacklegged ticks are most active from April through October.

"Adult blacklegged ticks started feeding as soon as the snow melted and temperatures were above freezing," said Neitzel.

Record numbers of disease cases from blacklegged ticks have been reported in Minnesota in recent years. Since 2004, an average of about 1,000 cases of Lyme disease have been reported to MDH each year, twice the average annual number from 1999 to 2003. Numbers of anaplasmosis and babesiosis cases are smaller but also have risen dramatically, to about 300 anaplasmosis and 30 babesiosis cases in each of the last three years. In addition, the first three cases of Powassan encephalitis ever reported in Minnesota occurred within the last 2 years.

A different tick species, the American dog tick (sometimes called "wood tick") can carry Rocky Mountain spotted fever and tularemia in Minnesota. American dog ticks, while usually just nuisance biters, can cause disease in Minnesota and are also active throughout the spring and early summer. These pests are found throughout the state in both wooded and grassy areas. American dog tick bites have led to only small numbers of Rocky Mountain spotted fever and tularemia cases in recent years in Minnesota, but both diseases can be very severe. Last summer, a Dakota County child with no history of travel outside Minnesota died from Rocky Mountain spotted fever.

In addition, very small numbers of Lone star ticks have been found in Minnesota in recent years. Lone star ticks are common in southern states, where they can carry ehrlichiosis (a disease related to anaplasmosis).

While it can be difficult to tell ticks apart, blacklegged ticks are smaller and darker in color than American dog ticks. They also lack the American dog tick's characteristic white markings, and the back end of the female blacklegged tick is reddish-orange in appearance. The adult female Lone star tick has a distinct white spot in the very middle of her back.

Tick-borne diseases of concern in Minnesota often have similar signs and symptoms. People who have these diseases might feel like they have "the flu" and experience symptoms such as fever, chills, headache, muscle aches, joint pain, or fatigue. These symptoms typically develop within a few days to a few weeks after the bite of an infected tick.

Some of these diseases also can involve a rash or skin sore. People with Lyme disease often notice a large, expanding red mark, which typically appears between 3 and 30 days after an infectious tick bite and often develops a "bulls-eye" appearance as it grows in size. Not everyone with Lyme disease develops this rash. In contrast, patients with Rocky Mountain spotted fever often have a rash appearing as tiny spots on the extremities and spreading to the rest of the body. Tularemia patients often have an ulcerated sore (usually at the site of the tick bite).

Other signs and symptoms can also be present. Untreated Lyme disease can develop into joint swelling, heart problems, or nervous system problems such as partial facial drooping. Severe infection with Powassan virus, which is related to West Nile virus, may lead to swelling of the brain or brain lining with signs of weakness, confusion, loss of coordination, speech difficulties, and memory loss. Any of these diseases can potentially be severe and result in hospitalization or, in some cases, death.

People who develop signs or symptoms of a tick-related illness after spending time in blacklegged tick habitat should see a physician right away, even if they don't remember getting a tick bite. Powassan disease has no specific treatment, but physicians can offer supportive care. The other tick-borne diseases of concern in Minnesota are treatable. Early diagnosis and treatment are important in preventing severe illness. Some people develop two or more of these diseases from the same tick bite.

More information about Minnesota's tick-borne diseases is available on the MDH Web site (http://www.health.state.mn.us/divs/idepc/dtopics/tickborne/index.html) or by calling MDH at 651-201-5414.

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