Powassan

Powassan is a rare, but often serious disease that is caused by a virus spread by infected ticks. Of the 75 cases of Powassan (POW) virus disease reported in the United States over the past 10 years, a few cases have been reported in southern New England in recent years. POW virus is one of a group of arthropod-borne viruses (arboviruses) that can cause inflammation of the brain (encephalitis).

At-Risk Populations

Anyone bitten by a tick in an area where the virus is commonly found can get infected with POW virus. The risk is highest for people who live, work or recreate in brushy or wooded areas, because of greater exposure to potentially infected ticks.

Symptoms

  • Many people who become infected with Powassan (POW) virus do not develop any symptoms.
  • The incubation period (time from tick bite to onset of illness) ranges from about 1 week to 1 month.
  • POW 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).
  • Symptoms can include fever, headache, vomiting, weakness, confusion, loss of coordination, speech difficulties, and seizures. 
  • Approximately half of survivors have permanent neurological symptoms, such as recurrent headaches, muscle wasting and memory problems. 
  • Approximately 10% of POW virus encephalitis cases are fatal.

How It Spreads

Powassan (POW) virus is an RNA virus that belongs to the genus Flavivirus. It is related to West Nile, St. Louis encephalitis, and Tick-borne encephalitis viruses.

Humans become infected with POW virus from the bite of an infected tick. Humans do not develop high enough concentrations of POW virus in their bloodstreams to infect feeding ticks. Humans are therefore considered to be “dead-end” hosts of the virus.

POW virus is maintained in a cycle between ticks and small-to-medium-sized rodents. In North America, three main enzootic cycles occur: Ixodes cookei and woodchucks, Ixodes marxi and squirrels, and Ixodes scapularis and white-footed mice. Ixodes cookei and Ixodes marxi rarely bite humans. Ixodes scapularis often bite humans and is the primary vector of Lyme disease.

There are two types of POW virus in the United States. The first type, often called lineage 1 POW virus, appears to be associated with Ixodes cookei or Ixodes marxi ticks. The other type, lineage 2 POW virus is sometimes called Deer tick virus, and is associated with Ixodes scapularis ticks. Both lineages have been linked to human disease.

Prevention

Reducing exposure to ticks is the best defense against Powassan virus disease, Lyme disease, Rocky Mountain spotted fever, and other tickborne infections. There is no vaccine for Powassan virus. There are several steps you and your family can take to prevent and control Powassan virus disease as demonstrated on the Lyme disease website.
Courtesy of the CDC Ticks website:

Testing & Diagnosis

Diagnosis is based on a combination of signs and symptoms and laboratory tests of blood or spinal fluid. These tests typically detect antibodies that the immune system makes against the viral infection.

Treatment

  • There are no medications to treat or prevent POW virus infection.
  • If you think you or a family member may have POW virus disease, see your health care provider for evaluation and diagnosis.
  • Persons with severe POW illnesses often need to be hospitalized. Treatment may include respiratory support, intravenous fluids, and medications to reduce swelling in the brain.