June 29, 2011
Minnesota records first death from tick-borne Powassan virus
State health officials emphasize the importance of preventing tick bites
A woman in her 60s from northern Minnesota has died from a brain infection due to Powassan (POW) virus. This is the first death in the state attributed to the disease. One other likely POW case has been identified this year in Minnesota, in an Anoka County man in his 60s who was hospitalized with a brain infection and is now recovering at home. POW virus is transmitted through the bite of an infected tick.
Both 2011 cases became ill in May after spending time outdoors and noticing tick bites. The fatal case was likely exposed to ticks near her home. The case from Anoka County might have been exposed near his home or at a cabin in northern Minnesota.
Health officials say this death serves as a reminder of the vital importance of preventing tick bites. “Although Powassan cases are rarely identified, it is a severe disease which is fatal in about 10 percent of cases nationwide, and survivors may have long-term neurological problems” said Dr. Ruth Lynfield, state epidemiologist with the Minnesota Department of Health (MDH).
“Powassan disease is caused by a virus and is not treatable with antibiotics, so preventing tick bites is crucial.”
In Minnesota, POW virus can be transmitted by the blacklegged tick (also called the deer tick), which can also carry Lyme disease, anaplasmosis, and babesiosis. The blacklegged tick is abundant during our warm weather months in hardwood and mixed-hardwood forests of Minnesota. When a tick infected with POW virus attaches to a person, it might take only minutes of tick attachment for the virus to be transmitted.
POW was first detected in Minnesota in 2008, in a Cass County child who was exposed near home. In 2009-2010, five additional POW cases were identified in Minnesota. These cases were likely exposed to infected ticks in north-central or east-central counties (Cass, Carlton, Hubbard, Itasca, or Kanabec). In addition to these human cases, MDH has found POW-infected ticks in northern counties (Cass, Clearwater, and Pine) and in southeastern Minnesota (Houston County).
POW virus was first described in 1958 in Powassan, Ontario. Since then, about 60 cases have been identified in North America. Most of these cases were from eastern Canada and the northeastern U.S. until the last decade, when cases began to be reported from Michigan, Wisconsin, and now Minnesota.
POW virus is related to West Nile virus (WNV). Like WNV, POW virus can cause severe disease of the central nervous system, involving inflammation of the brain (encephalitis) or the lining of the brain and spinal cord (meningitis). People with POW may have fever, headache, vomiting, weakness, confusion, loss of coordination, speech difficulties, and memory loss. Signs and symptoms occur within one to five weeks of an infectious tick bite.
To prevent tick-borne diseases, always use tick repellents containing DEET (up to 30 percent concentration) or permethrin when spending time in tick habitat. Products with 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 and wearings. Also, wear long pants and light-colored clothing to help detect and remove ticks before they’ve had time to bite. People with homes or cabins near the woods can also use landscape management and targeted pesticide applications to reduce exposure to disease-carrying ticks.
After returning from outdoors, check your body carefully for ticks and promptly remove any you find. The process of bathing or showering shortly after returning indoors can help remove ticks before they bite or before they’ve been attached for long.
The back end of the adult female blacklegged tick is reddish-orange in appearance and teardrop-shaped. The nymph, or immature, stage of the blacklegged tick is about the size of a poppy seed and dark-colored. It is so small that it often goes unnoticed. When the nymph is noticed, it is easily mistaken for a speck of dirt or small freckle on people’s skin. Blacklegged ticks are smaller and darker in color than American dog ticks (also known as wood ticks). They also lack the dog tick’s characteristic white markings. To remove a tick, use tweezers to grasp it by its head close to the skin and pull it out gently and steadily.
More information about Minnesota’s tick-borne diseases, including details on tick-borne disease prevention and pictures of ticks, is available on the MDH Web site at www.health.state.mn.us/divs/idepc/dtopics/tickborne/index.html or by calling MDH at 651-201-5414.