Tick talk: avoiding these pests and the diseases they can carry

By Russell C. Johnson, Ph.D.

When summer arrives and Minnesotans flock outside, they share the scenery with several species of ticks. Although some ticks can carry diseases that can be transmitted to humans, with just a bit of precaution Minnesotans can enjoy their beautiful state even during peak tick season.

One type of tick, the deer tick, can carry and transmit Lyme disease, as well as two lesser known diseases, human anaplasmosis and babesiosis. These three diseases are increasing in Minnesota; in 2006, 914 cases of Lyme disease, 177 cases of human anaplasmosis, and 18 cases of babesiosis were reported statewide. A specific microorganism causes each of these diseases; a deer tick infected with one of these microorganisms can transmit the disease to a human through a bite. The wood tick, a common species that is much larger than the deer tick, does not transmit these microorganisms.

Lyme disease cases are concentrated geographically, particularly in Minnesota, Wisconsin, and the northeastern United States. Lyme disease cases have been reported in several eastern and central Minnesota counties and western Wisconsin, although the distribution is expanding. The greatest risk for exposure to Lyme disease exists in the warmer months, from mid-May to mid-July. Although infected deer ticks are active in the spring and fall, fewer cases of Lyme disease occur then in part because people tend to be wearing more protective clothing.

If you find and remove a deer tick while it is still flat (meaning it has not yet eaten), the chances of being infected with Lyme disease from the bite are minimal. A deer tick must be attached for 36 hours to transmit Lyme disease, although human anaplasmosis may be transmitted more quickly. Symptoms of Lyme disease usually include a red, expanding rash at the bite site that develops after 7-10 days and a fever and headache that develop up to 30 days later. If these symptoms occur following a tick bite, contact your physician. Lyme disease is treated with antibiotics and responds well to early treatment. If left untreated, Lyme disease can lead to nerve or joint damage. There is no current Lyme disease vaccine for humans.

University of Minnesota researchers were the first to characterize the bacterium that causes Lyme disease and to patent a vaccine for dogs. University of Minnesota scientists are currently studying the ecology of Lyme disease and human anaplasmosis, tracking the movement of infected deer ticks throughout areas around the Twin Cities and identifying high-risk areas.

Not all deer ticks carry Lyme disease, and a bite from an infected tick will not necessarily transmit Lyme disease. To protect against tick-borne illnesses:

• Avoid tick habitats. Stay in the middle of the path when walking in brushy, grassy, or wooded areas.
  
  
• Use personal protection. Wear long pants tucked into your socks and use a DEET-containing insect repellent when going into high-risk tick areas.
  
  
• Perform a daily full body tick check after being outdoors and, for children, pay special attention to the hair, scalp, and ears. Deer ticks are tiny--approximately the size of a poppyseed. Visit www.health.state.mn.us/divs/idepc/dtopics/tickborne/ticks.html to see photos of ticks.

Russell C. Johnson, Ph.D., is professor of microbiology at the University of Minnesota Medical School.

Health Talk & You is an educational service of the University of Minnesota. Advice presented here should not take the place of an examination by a health-care professional. For more health-related information, go to http://www.healthtalk.umn.edu.