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Deer ticks showing signs of three disease-carrying organisms, including Lyme

Approximately one-third of blacklegged ticks (also called deer ticks) tested during recent years in Minnesota were positive for disease-causing organisms, say state health officials. Blacklegged ticks carry Lyme disease, human anaplasmosis (HA), and babesiosis, three illnesses which can lead to serious complications.

Between 2005 and 2008, staff members at the Minnesota Department of Health (MDH) collected blacklegged ticks from regions of Minnesota where Lyme disease and other tick-borne diseases are commonly reported. The MDH Public Health Laboratory tested these ticks for the presence of disease-causing organisms.

"Overall, about one out of every three adult blacklegged ticks was positive for the bacteria that cause Lyme disease. In many parts of Minnesota, this means that there is a good chance that any blacklegged tick you encounter is carrying the Lyme disease bacteria," Melissa Kemperman, an epidemiologist specializing in tick-transmitted diseases at MDH, said.

Nymphs, the immature stage of tick, were also tested. Just over 10 percent of nymphal blacklegged ticks were positive for the Lyme disease bacteria. Although fewer nymphs than adults were positive for the Lyme disease bacteria, their small size makes them more dangerous.

Lyme disease is not the only disease that can follow bites from infected ticks. Overall, nearly 10 percent of adult blacklegged ticks and about 5 percent of nymphs were positive for the organisms that cause HA or babesiosis.

Bites from blacklegged ticks have led to record numbers of tick-borne disease cases in Minnesota in recent years. The ticks are typically active from April through October, but mid-May through mid-July represents the period of greatest activity for the nymph stage of the tick and therefore the highest risk time for disease transmission to people.

Precautions are most important during the late spring, early summer, and fall, when blacklegged ticks are active. When spending time in wooded or brushy areas, it is crucial to use tick repellents containing DEET or permethrin. Repellents containing up to 30 percent DEET can be used on the skin or clothing. Permethrin-based products, which are only applied to clothing, are highly effective and can last through several washings.

More information is available at or by calling MDH at 651-201-5414.