What Is Powassan Virus? Symptoms, Transmission, and Treatment
Rare tick-borne viral infection
Rapid transmission from infected blacklegged ticks
Early recognition and supportive care are essential
Powassan virus is a rare but potentially serious virus spread by infected blacklegged (deer) ticks. Although many infections are believed to be asymptomatic or cause only a mild febrile illness, some individuals develop meningitis or encephalitis. Unlike Lyme disease, which is caused by bacteria, Powassan virus is a viral infection with no specific antiviral treatment. Severe neuroinvasive disease has been associated with approximately a 10% mortality rate, and many survivors experience lasting neurologic complications.
In their article “Underrecognized Tickborne Illnesses: Borrelia Miyamotoi and Powassan Virus,” Della-Giustina and colleagues explain why Powassan virus deserves increased attention. “We chose to review the Powassan virus because it only requires 15 min. of tick attachment for transmission, and the sequelae of the neurologic disease are devastating, in addition to a 10% mortality rate.”1
What is Powassan virus?
Powassan virus (POW) is a tick-borne flavivirus related to several other important viruses, including dengue virus, yellow fever virus, West Nile virus, and the tick-borne encephalitis viruses found primarily in Europe and Asia.
“Flaviviruses are a group of single stranded RNA viruses that cause severe endemic infection and epidemics on a global scale.”2
Other emerging tick-borne viruses identified in North America include the Heartland virus (a phlebovirus) and the Bourbon virus (a thogotovirus).
Powassan virus consists of two closely related lineages: the prototype Powassan virus (lineage I) and deer tick virus (lineage II). Although genetically distinct, they cause clinically indistinguishable disease and are collectively referred to as Powassan virus infection.
How was Powassan virus discovered?
Powassan virus was first identified in the brain tissue of a young child.
“Powassan virus is named for the Ontario, Canada, town where it was first isolated from the brain of a 5-year-old boy who died of severe encephalitis in 1958,” the authors write.
Where is Powassan virus found?
The second recognized human case was reported in New Jersey in 1970, followed by another in eastern Russia in 1978.
Today, most reported U.S. cases occur in the Northeast and upper Midwest, particularly New York, Massachusetts, Minnesota, Wisconsin, Maine, Connecticut, New Jersey, and Pennsylvania. The geographic range continues to expand as blacklegged ticks spread into new areas. Cases have also been reported in Canada and eastern Russia.
Powassan virus can be transmitted much more rapidly than Lyme disease and may cause severe neurologic complications, including permanent disability or death.
How is Powassan virus transmitted?
Powassan virus is transmitted primarily by Ixodes scapularis, commonly known as the blacklegged tick or deer tick. This is the same tick responsible for transmitting Lyme disease, babesiosis, anaplasmosis, and several other tick-borne infections.
Unlike many other flaviviruses, Powassan virus is not transmitted by mosquitoes.
“Although many flaviviruses have mosquitos as competent vectors, there is no evidence of human POW virus disease transmitted by mosquitos,” the authors point out.
How quickly can Powassan virus be transmitted?
Experimental animal studies have demonstrated Powassan virus transmission within approximately 15 minutes of Ixodes scapularis attachment. This appears to occur substantially faster than transmission of Lyme disease bacteria.
This rapid transmission occurs because the virus is already present in the tick’s salivary glands. In contrast, Borrelia burgdorferi, the bacterium responsible for Lyme disease, generally resides in the tick’s midgut and typically requires a longer period of attachment before transmission occurs.
What is the incubation period for Powassan virus?
Symptoms generally develop between 1 and 4 weeks after the bite of an infected tick, although longer incubation periods have occasionally been reported. Many infected individuals never become ill, while those who develop neuroinvasive disease may deteriorate rapidly once symptoms begin.
What are the symptoms of Powassan virus?
“Few people who become infected with the POW virus have clinically significant disease,” the authors write.
When illness develops, early symptoms commonly include fever, headache, vomiting, weakness, malaise, and fatigue. Patients who develop neuroinvasive disease may progress to meningitis or encephalitis.
According to the authors, Powassan infection can lead to disorientation, headache, neck stiffness, fever up to 40°C, clonus, ocular and other motor palsies, obtundation, and convulsions. Severe cases may resemble herpes simplex encephalitis.
Can Powassan virus be serious?
Yes. Powassan virus can cause severe encephalitis with significant long-term neurologic complications.
Approximately half of survivors of severe neuroinvasive disease experience persistent neurologic deficits, including weakness, cognitive impairment, or paralysis.
Approximately 10% of recognized neuroinvasive cases are fatal, although reported mortality varies among published case series.
What are the long-term effects of Powassan virus?
Persistent neurologic complications may include paralysis, weakness, cognitive impairment, memory loss, ataxia, cranial nerve dysfunction, speech disorders, muscle wasting, difficulty walking, and chronic headaches. Recovery often requires prolonged rehabilitation, and some deficits may be permanent.
Are there tests for Powassan virus?
Diagnosing Powassan virus infection requires a high degree of clinical suspicion because routine commercial testing is limited.
PCR testing is most useful early in infection or in immunocompromised patients but becomes less sensitive once antibodies develop.
In most immunocompetent patients with neuroinvasive disease, diagnosis relies on detecting Powassan virus IgM antibodies in serum or cerebrospinal fluid, followed by confirmatory plaque reduction neutralization testing (PRNT). Specialized testing is typically performed through state public health laboratories or the Centers for Disease Control and Prevention (CDC).
Why are co-infections important?
Treatable tick-borne co-infections may occur alongside Powassan virus infection because blacklegged ticks can carry multiple pathogens simultaneously. Patients with suspected Powassan virus infection should also be evaluated for Lyme disease, babesiosis, anaplasmosis, or other treatable tick-borne infections when clinically appropriate.
The authors describe a patient with Powassan encephalitis, Lyme carditis, and babesiosis.
Yoon and colleagues described the case of a 17-year-old young man who died from Lyme carditis while clinicians awaited confirmation of Powassan virus infection.3 His autopsy demonstrated Borrelia spirochetes in the heart and liver, with PCR evidence of spirochetes in the brain and lungs.
What is the treatment for Powassan virus?
There is currently no specific antiviral treatment for Powassan virus infection.
Treatment is supportive and may include hospitalization, intravenous fluids, respiratory support, seizure management, treatment of increased intracranial pressure or brain swelling, and intensive rehabilitation for survivors with neurologic deficits.
Early recognition remains important because patients may have treatable bacterial tick-borne co-infections that require prompt antibiotic therapy.
How can Powassan virus be prevented?
Preventing tick bites remains the best way to reduce the risk of Powassan virus infection. Recommended measures include using EPA-registered tick repellents, wearing long sleeves and long pants in wooded or grassy areas, performing thorough tick checks after outdoor activities, and removing attached ticks promptly. Although Powassan virus may be transmitted much more rapidly than Lyme disease, early tick removal is still recommended because it can reduce the risk of Lyme disease, babesiosis, anaplasmosis, and other tick-borne infections.
Frequently Asked Questions
What are the first symptoms of Powassan virus?
Early symptoms often include fever, headache, vomiting, weakness, malaise, and fatigue. Some people remain asymptomatic or develop only a mild illness, while others progress to meningitis or encephalitis with confusion, seizures, weakness, or difficulty speaking and walking.
How quickly can Powassan virus be transmitted?
Experimental animal studies have shown Powassan virus transmission within approximately 15 minutes of tick attachment. Human transmission time cannot be measured directly, but the virus appears to be transmitted much more rapidly than Lyme disease because it is already present in the tick’s salivary glands.
Is Powassan virus curable?
There is currently no antiviral medication approved to treat Powassan virus infection. Management consists of supportive medical care while the body’s immune system clears the infection.
Which ticks carry Powassan virus?
In the United States, Powassan virus is transmitted primarily by the blacklegged tick (Ixodes scapularis). Less commonly, lineage I Powassan virus has also been associated with Ixodes cookei (groundhog tick) and Ixodes marxi (squirrel tick).
Can you get Lyme disease and Powassan virus from the same tick?
Yes. Blacklegged ticks can carry multiple pathogens simultaneously, making co-infections with Lyme disease, babesiosis, anaplasmosis, or other tick-borne diseases possible after a single tick bite.
Clinical Takeaway
Powassan virus is an uncommon but potentially devastating tick-borne infection that deserves increased awareness because it can be transmitted rapidly and may lead to severe neurologic disease. Although no specific antiviral treatment is available, prompt recognition, supportive care, and evaluation for treatable tick-borne co-infections remain important.
Anyone who develops fever, severe headache, confusion, weakness, seizures, or other neurologic symptoms after a tick bite should seek immediate medical evaluation.
Related Articles
Learn more about Powassan virus and other emerging tick-borne diseases:
Powassan virus in children
Fatal deer tick virus infection in Maine
Powassan virus causes polio-like illness
Tick-borne coinfections
Lyme disease symptoms guide
References:
- Della-Giustina D, Duke C, Goldflam K. Underrecognized Tickborne Illnesses: Borrelia Miyamotoi and Powassan Virus. Wilderness Environ Med. 2021;32(2):240-246.
- Chong HY, Leow CY, Abdul Majeed AB, Leow CH. Flavivirus infection—A review of immunopathogenesis, immunological response, and immunodiagnosis. Virus Res. 2019;274:197770.
- Yoon EC, Vail E, Kleinman G, et al. Lyme disease: A case report of a 17-year-old male with fatal Lyme carditis. Cardiovasc Pathol. 2015;24(5):317-321.
- Kakoullis L, Vaz VR, Kaur D, et al. Powassan Virus Infections: A Systematic Review of Published Cases. Trop Med Infect Dis. 2023;8(12):508.
- Klontz EH, Chowdhury N, Branda JA. Laboratory Testing for Powassan Virus: Past, Present, and Future. J Infect Dis. 2024;230(Suppl 1):S70-S75.
- Piantadosi A, Solomon IH. Powassan virus encephalitis. Infect Dis Clin North Am. 2022;36(3):671-688.
Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.
Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention
