Blacklegged Tick Populations in Michigan

 

Significant new information regarding the epidemiology of Lyme disease in Michigan has been discovered since 2002.   Numerous activities to characterize Lyme disease have been conducted for nearly 20 years in the state. Recently, Michigan State University (MSU) and Michigan Department of Community Health (MDCH) researchers have been conducting a long-term surveillance project for Ixodes scapularis (Black-Legged Tick), the vector species for Lyme disease, in western Lower Michigan and the western Upper Peninsula.  This project was initiated in 2001 based on environmental predictors that indicated Michigan has suitable habitat for invasion by this tick species, currently known to be present in Northern Indiana. This study has involved looking for the presence of the Black-Legged Tick, testing those ticks for infection with Borrelia burgdorferi, the bacterial cause of Lyme disease, and looking for evidence of infection in rodents and dogs in the area.    

Information being obtained from this ongoing study indicates an emerging presence of Black-Legged ticks in all counties along the western border of Michigan.  Many hundreds of these ticks have been tested for the Lyme disease bacteria, and up to 45 percent of the ticks have tested positive for Lyme disease.  Several rodents, including the white-footed mouse and the eastern chipmunk have also been found to be carrying the organism, but do not transmit the bacteria directly to people.  This data supports the identification of new endemic areas for Lyme disease in Michigan, in addition to previously recognized Menominee County in the Upper Peninsula.    As this is a region of the state that draws high numbers of tourists during the summer months, it is important to remind people to use personal protective measures when recreating in wooded areas, such as:

• Light colored clothing 
• Long pants tucked into socks and long sleeved shirt 
• Insect repellants that contain DEET (5% or lower concentration for children, and 30% or lower for adults) 
• Permethrin repellants can be used on clothing NOT on bare skin 
• Perform regular tick checks 

Below is a map of counties with defined blacklegged tick populations and counties determined "at risk" due to their proximity to the counties with known tick populations.  It is important to note that this map was updated as of May, 2009.  Tick populations will not remain static, and ongoing field research will continue to provide valuable information on the geographic extent of this species in Michigan.