Diseases from ticks rise to record levels in Minnesota
Bites from blacklegged ticks (also called deer ticks) led to a record number of tick-borne disease cases in Minnesota during 2007, say state health officials. Blacklegged ticks carry Lyme disease, human anaplasmosis, and babesiosis, three illnesses that can all lead to serious complications.
To prevent these diseases, it is critical for people who spend time outdoors in many areas of east-central, north-central and southeast Minnesota to take precautions against tick bites.
"Minnesota continues to be one of the highest-risk states for diseases from blacklegged ticks," said Melissa Kemperman, an epidemiologist at the Minnesota Department of Health (MDH). "If you visit or live in forested parts of Minnesota during late spring and early summer, you must protect yourself from tick bites to avoid developing Lyme disease or other tick-borne illnesses."
Record tick-borne disease numbers suggest that many Minnesotans aren't taking the simple steps necessary to protect themselves from tick bites. In 2007, record totals of 1,239 Lyme disease cases, 322 human anaplasmosis cases, and 24 babesiosis cases were reported to MDH. These numbers were greater than the previous records of 1,023 Lyme disease cases reported in 2004, 186 human anaplasmosis cases reported in 2005, and 18 babesiosis cases reported in 2006.
Precautions are most important during the late spring, early summer, and fall, when blacklegged ticks are active.
"It is important to check yourself for ticks, but these ticks are so difficult to see that you should also strive to prevent bites in the first place," said Kemperman. "When spending time in wooded or brushy areas, it is crucial to use tick repellents containing DEET or permethrin. Also, wear long pants and light-colored clothing and stay to the center of trails. Keep these steps in mind when hiking, camping, biking, hunting, working, or doing other activities in forested areas."
Repellents containing up to 30 percent DEET can be used on the skin or clothing. Permethrin-based products, which are applied to clothing only, are highly effective and can last through several washings. Since ticks climb up from the ground, focus repellent use below the knees.
Minnesotans who live in or near the woods can also be exposed to blacklegged ticks during yardwork or other outdoor activities at home. Maintaining a yard free of brush and leaves, constructing a wood chip barrier between the lawn and woods and keeping children's play areas in sunny areas of the yard will help limit exposure to disease-carrying ticks. Under certain conditions, using a carefully applied pesticide targeted towards ticks may also help reduce tick numbers in wooded yards.
The prime season for tick-borne disease begins in May. This puts Minnesotans in some parts of the state at risk for tick-borne diseases as they begin to enjoy outdoor activities in forested areas of the state. Although blacklegged ticks are typically active from April through October, mid-May through mid-July represents the period of greatest activity for the nymph stage of the tick. Nymphs are most likely to spread disease because they are very small and can feed without being detected.
Minnesota's recent snowy winter will not likely reduce overall disease risk from tick-borne diseases.
"A thick blanket of snow actually could have helped insulate ticks as they overwintered on the forest floor," Kemperman said. "We've already observed typical numbers of adult blacklegged ticks out and feeding this spring." Kemperman adds that milder winters predicted by some climate change models could support even greater numbers of blacklegged ticks in the future.
Blacklegged ticks, often called "deer ticks," are smaller and darker in color than the common wood ticks that people may also encounter this time of year. They also lack the wood tick's characteristic white markings, and the back end of the female blacklegged tick is reddish in appearance.
Blacklegged ticks are found in wooded, brushy areas in central and southeast Minnesota. Over the past few years, they have appeared to expand their range into parts of west-central, northwest, and northeast Minnesota. The ticks are also common in wooded areas of Wisconsin and northeastern states.
Not all blacklegged ticks carry the organisms that cause disease and prompt removal of infected ticks can prevent disease transmission. If an infected deer tick bites you, it needs to be attached at least 12-24 hours to transmit human anaplasmosis bacteria and 24-48 hours to transmit Lyme disease bacteria. Not every person who is infected with these organisms will develop symptoms.
Signs and symptoms of Lyme disease can include an expanding rash, fever, headache, chills, muscle pain, joint pain, and fatigue. The rash, one of the earliest symptoms, typically appears between three and 30 days after an infectious tick bite. Not everyone with Lyme disease develops the rash. Untreated Lyme disease can develop into joint swelling, nervous system problems, or heart problems.
More information about Minnesota's tick-borne diseases is available at www.health.state.mn.us/divs/idepc/dtopics/tickborne/index.html or by calling MDH at (651) 201-5414.