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Powassan virus is a rare yet, often serious disease that is spread by the bite of infected ticks. Powassan virus is a virus that is related to West Nile, St. Louis encephalitis, and Tick-borne Encephalitis viruses. Within the previous 10 years, approximately 75 cases were reported in the United States. There has only been one reported case in Michigan to date. The signs and symptoms of Powassan virus range from no symptoms to encephalitis (inflammation of the brain) and meningitis (inflammation of the membranes that surround the brain and spinal cord). The best way to prevent infection is to protect yourself from tick bites.
In nature, Powassan virus is maintained in a cycle between ticks and small-to-medium-sized rodents. In North America, three cycles occur: Ixodes cookei and woodchucks, Ixodes marxi and squirrels, and Ixodes scapularis and white-footed mice. Both Ixodes cookei and Ixodes marxi rarely bite humans. However, Ixodes scapularis, which can also transmit Lyme disease, often bite humans.
The majority of Powassan virus cases have occurred during the late spring, early summer, and mid-fall when ticks are most active in the northeastern and Great Lakes regions of the United States. Anyone who is bitten by an infected Ixodes scapularis, Ixodes cookei, or Ixodes marxi tick, in an area where the virus is commonly found, can become infected. Individuals who live, work, or recreate in brushy or wooded habitats are at greater risk due to the increased chance of being bitten by an infected tick.
What are the signs and symptoms of Powassan virus?
After being bitten by an infected tick, the onset of illness can range from one week to one month. Many people who become infected with Powassan virus do not develop any signs or symptoms. However, others develop fever, headache, vomiting, weakness, confusion, loss of coordination, speech difficulties, and seizures. Powassan virus can infect the central nervous system and cause encephalitis (inflammation of the brain) and meningitis (inflammation of the membranes that surround the brain and spinal cord).
Approximately 10% of the Powassan virus encephalitis cases are fatal. Approximately half of the individuals who survive have permanent neurological systems, including recurrent headaches, muscle wasting, and/or memory problems.
How can Powassan virus be diagnosed?
Powassan virus is preliminarily diagnosed by a healthcare provider using a combination of signs and symptoms, places and dates of travel, activities performed, and epidemiologic history of the location where infection occurred. Laboratory tests of blood or spinal fluid are then ordered. Typically these tests detect antibodies that the immune system develops in response to the viral infection.
What should I do if I have a tick that I want to identify or test?
Knowing what kind of tick bit you may be important in knowing what your risk of disease is. The Michigan Department of Health and Human Services (MDHHS) provides tick identification at no charge to Michigan citizens. There are two ways to have a tick identified, 1) By submitting a photo of your tick, or, 2) by sending the tick to the MDHHS for microscopic identification. If you want to submit a photo of your tick, the MDHHS will make all attempts to identify the tick based on the condition of the tick and the condition of the photos. However, definitive tick identification may only be made by sending the tick for microscopic examination.
Ticks that are submitted from people to the MDHHS for microscopic identification and identified as blacklegged ticks (also known as deer tick) and are alive will be forwarded to the MDHHS Bureau of Laboratories for Lyme disease screening only, at no cost. Ticks that are dead when they are received or are from animals (dog, cat, horse, etc.) will not be tested however, they will be identified to species and life stage.
How can Powassan virus be treated?
There are no vaccines or medications that can be used to prevent or treat Powassan virus infection. Individuals with severe illness from Powassan virus typically require hospitalization. Hospital treatment may include respiratory support, intravenous fluids, and medications to help decrease brain swelling. See your health care provider if you think that you or a family member may have Powassan virus.
- CDC: What To Do After a Tick Bite
- CDC: Guidance for Clinicians: Recommendations for Patients After a Tick Bite