Powassan Virus

Powassan virus disease is a rare but serious illness caused by the bite of an infected tick. Three species of ticks found in Vermont can transmit the virus, but only one of these species  the blacklegged tick  commonly bites humans.

The last reported case of Powassan virus infection in a Vermont resident occurred in 1999. This disease can be difficult to diagnosis and is likely underreported. The Health Department is working with health care providers to test and identify cases of Powassan virus disease in Vermont residents.

Symptoms

Many people who get infected with Powassan virus do not develop symptoms. People who do get sick with a Powassan virus infection may develop a fever, headache, sore muscles, weakness, vomiting, loss of coordination, difficulty speaking and seizures.

Powassan virus can also infect the central nervous system and cause meningitis or encephalitis. Even after recovering from a Powassan virus infection, many people may have permanent neurological symptoms.  In a smaller number of cases, Powassan virus can also be fatal.

Diagnosis

A Powassan virus infection can only be diagnosed through laboratory testing. Commercial and hospital laboratories cannot test for this disease, but under certain circumstances testing is available through the Vermont Department of Health and CDC.

Health care providers who are interested in testing a patient for Powassan virus should follow the instructions in the Health Care Providers section of this page.

Treatment

There is no specific treatment for a Powassan virus infection. Supportive care is often given to patients to help treat the symptoms of a Powassan infection.

Transmission

People get infected with Powassan virus following the bite of an infected tick. Three types of ticks have been shown to carry Powassan virus: the squirrel tick (Ixodes marxi), the woodchuck tick (Ixodes cookei) and the blacklegged tick (Ixodes scapularis).

Vermont is home to all three species of ticks, but squirrel and woodchuck ticks rarely bite humans. The blacklegged tick will bite humans and is the same tick responsible for transmitting anaplasmosis, babesiosis, Borrelia miyamotoi and Lyme disease.

Powassan virus can be transmitted more quickly than other tickborne diseases. One study has shown that blacklegged ticks transmitted Powassan virus to mice in as little as 15 minutes.

Prevention

The best way to prevent a Powassan virus infection is to prevent tick bites. Get more information on how to Be Tick Smart.

Powassan Virus in Vermont

Powassan virus can be found throughout the upper Midwest and northeastern portions of the United States, including Vermont.

The only reported case of Powassan virus in a Vermont resident occurred in 1999. Some cases probably go unreported.

Powassan virus has also been found in blacklegged ticks collected in Vermont. In 2016, the Vermont Agency of Agriculture, Food and Markets tested approximately 250 ticks collected from across the state. Around 1% of these blacklegged ticks were positive for Powassan virus.

Information for Health Care Providers

Powassan virus testing is not available through clinical or commercial laboratories, but the Health Department can help providers test for this disease free of charge. Patients who are eligible for Powassan virus testing through the Health Department should:

  • Be hospitalized with meningitis or encephalitis
  • Have a presumed infectious cause of illness
  • Be negative or concurrently tested for more common causes of meningitis and encephalitis such as West Nile virus, Lyme disease, herpes and varicella.

Providers who wish to order testing should follow these instructions:

  1. Contact the Infectious Disease Epidemiology Program at the Health Department by calling 802-863-7240.
  2. Provide patient information (name, address, date of birth and sex), information about their illness (date of onset, clinical presentation) and any recent travel history.
  3. Collect the appropriate specimens. 1.0 mL of serum and/or 2.0 mL of cerebrospinal fluid should be collected 3-10 days after the patient’s illness onset. Keep the specimens cold or frozen.
  4. Complete the Clinical Test Order Form. Skip the Billing Information section, but be sure to complete the rest of the form. On the back page under Laboratory Examination Requested, check “Other” under Serology and write “Powassan”.
  5. Ship the specimens to: 
    Vermont Department of Health Laboratory 
    359 South Park Drive
    Colchester VT 05446.