Powassan virus infection

Powassan virus infection

Description, Causes and Risk Factors:

A virus of the genus Flavivirus (family Flaviviridae), transmitted by ixodid ticks and causing Powassan encephalitis in children; also capable of producing meningoencephalomyelitis in rabbits and children.

Powassan virus infection is a rare tick-borne viral infection occurring in Wisconsin and other northern regions of North America. Powassan virus infection is caused by an arbovirus (similar to the mosquito-borne West Nile virus) but it is transmitted to humans by the bite of an infected tick instead of a mosquito bite. The virus is named for Powassan, Ontario where it was first discovered. Eleven reported cases of Powassan virus infection have been detected among Wisconsin residents during 2003 to 2011. At least 50 cases have been detected in the United States and Canada since 1958.

In Wisconsin, Ixodes scapularis (known as the blacklegged tick or deer tick) is capable of transmitting Powassan virus. In addition, several other tick species in North America can carry Powassan virus, including other Ixodes species and Dermacentor andersoni.

Everyone is susceptible to Powassan virus infection, but people who spend time outdoors in tick-infested environments are at an increased risk of exposure. In the upper Midwest, the risk of tick exposure is highest from late spring through autumn.


Symptoms usually begin 7-14 days following infection. Some people who are infected may experience mild illness or no symptoms. Symptoms of illness usually begin with acute onset of fever and may include headache, muscle weakness, nausea, vomiting, stiff neck, fatigue, confusion, paralysis, speech difficulties, and memory loss. Powassan virus infectioninfects the central nervous system and can cause encephalitis and meningitis. About 10-15% of persons infected with Powassan virus infectionwill experience severe illness and survivors may develop long-term neurological problems.


Laboratory diagnosis of arboviral infections is generally accomplished by testing of serum or CSF to detect virus-specific IgM and neutralizing antibodies. During an acute infection, certain viruses can be isolated through culture or detected by nucleic acid amplification.

In fatal cases, nucleic acid amplification, histopathology with immunohistochemistry and virus culture of autopsy tissues can also be useful. Laboratory tests for Powassan virus infection are not commercially available, but can be requested through laboratories for testing at CDC.


Currently, there are no medications available for the treatment of Powassan virus illness but supportive care can be used to manage and alleviate symptoms. No vaccine is available to prevent people from becoming infected with Powassan virus. Other precautions include wearing long pants and light-colored clothing, staying away from the brush and woods, and doing thorough tick checks after spending time in the woods. These precautions are most important from late spring until mid-summer, and again in the fall months, when blacklegged ticks are active.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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