An unusually warm, dry spring and summer may have contributed to a substantial drop in cases of disease caused by ticks in 2012 in Minnesota, but the decline doesn't mean the risk of illness from tick bites in 2013 will be any less than in most previous years, state health officials reported today.
The three main tick-borne diseases carried by blacklegged ticks (also called deer ticks) in Minnesota - Lyme disease, human anaplasmosis and babesiosis - were all down in 2012. There were 911 confirmed cases of Lyme disease, down from 1,201 in 2011 and the lowest since 2003. There were 503 cases of human anaplasmosis in 2012, down from 782 in 2011 and 40 cases of babesiosis in 2012, down from 72 in 2011.
Pinpointing a cause for decline in case numbers is difficult, said David Neitzel, tick-borne disease specialist with the Minnesota Department of Health. Despite an early warm-up in spring that led to an earlier than normal start to tick activity, continued hot, dry weather may have reduced blacklegged tick feeding activity, thus lowering disease risk. Blacklegged ticks do thrive in humid conditions, however.
Besides the three commonly reported diseases, blacklegged ticks carry the agents for Powassan disease and a new form of human ehrlichiosis. American dog ticks ("wood ticks"), which are very common in spring and early summer throughout Minnesota, can carry Rocky Mountain spotted fever (RMSF). While RMSF is most common in the southern United States, a small number of RMSF cases have occurred in Minnesotans who did not travel outside the state.
The best way to prevent tick bites is to avoid tick habitat during warm weather months:
- Wooded or brushy areas for the blacklegged tick.
- Grassy or wooded areas for the American dog tick.
- If you can't avoid tick habitat, use repellent to reduce the risk of disease:
- DEET-based repellents (up to 30 percent DEET), which can be applied to clothing or skin for temporary protection.
- Permethrin-based repellents, which are used to pre-treat fabric and can protect against tick bites for at least two weeks without reapplication.
- People who live on heavily wooded property, or visit cabins, often encounter ticks on a daily basis. Since daily repellent use can be more challenging for these people, they should consider the following landscape management techniques:
To make your yard less attractive to ticks:
- Keep lawns mowed short.
- Remove leaves and brush.
- Create a landscape barrier of wood chips or rocks between mowed lawns and woods.
- To reduce tick numbers at your yard-woods interface:
- Apply pesticide treatments in the spring or early summer along the edges of wooded yards and trails; follow pesticide label instructions carefully.
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Early detection of tick-borne illness is important to prevent potentially severe complications, so people should seek medical care if they develop symptoms suggestive of a tick-borne disease after spending time in tick habitat. Signs and symptoms of the various tick-borne diseases can include, but are not limited to, rash, fever, headache, fatigue, muscle aches, and joint pain or swelling. These symptoms can be associated with other diseases, so it is important for patients to mention possible tick exposures or time spent in tick habitat to their medical provider. Except for Powassan disease, which is caused by a virus, all of Minnesota's tick-borne diseases are treatable with antibiotics.