Powassan virus Agent Information Sheet

Boston University
Research Occupational Health Program (ROHP)
617-358-7647

Agent

A member of the genus Flavivirus, and Flaviviridae family, is an enveloped single stranded RNA virus with two distinct lineages of similar pathogenicity. Powassan Virus is related to other Tick-Borne Encephalitis viruses and may have a similar clinical manifestation to these viruses as well as to mosquito-borne encephalitis.

Disease/Infection

Powassan Virus is a viral infection that can progress to severe encephalitis and is fatal in approximately 10% of all infections. The viral course has an initial prodrome of 1 to 3 days with symptoms of fever, chills, malaise, somnolence, nausea and vomiting before progressing to meningoencephalitis – inflammation of the brain and/or spinal cord. Additional symptoms may include: headache, generalized weakness, altered mental status, seizures, aphasia and movement disorders. About half of all survivors have long-lasting neurologic deficits including but not limited to recurrent headaches, focal paralysis, muscle weakness and cognitive difficulties. While not all patients experience the prodrome or identifiable symptoms during the course of infection, symptoms can develop at any time during infection and should be monitored for.

Pathogenicity

Clinically, Powassan Virus may resemble mosquito-borne encephalitis with variable symptoms of asymptomatic or mild to severe and fatal. Infection, whether overt or unidentified clinically results in patient immunity.

Biosafety Information

Biosafety Level 3

Per the Biosafety in Microbiological & Biomedical Laboratories (6th Ed.) this is the recommended BSL.

Modes of Transmission

Powassan Virus is transmitted to humans from the saliva/bite of an infected tick. Early tick removal may not prevent transmission as the interval of attachment necessary for transmission of Powassan Virus is not known but is likely less than 12-24 hours and transmission in 15 minutes was confirmed in one trial. Of note, transmission can occur via blood transfusions–because of this, affected individuals should abstain from blood donation for at least 4 months after illness. Another potential mode of transmission includes consumption of raw milk from an infected animal.

Host Range/Reservoir

Outdoors in grassy/wooded areas: infected tick.

Host animals: Humans (dead-end reservoir), woodchucks, foxes, coyotes, racoons, skunks, domesticated cats and dogs.

Most cases in the United States occur in the Northeast and Great Lakes region.

Symptoms

Classic Powassan Virus presents 1 to 3 days of prodrome followed by symptoms of encephalitis and/or meningitis. Symptoms include: fever, chills, malaise, somnolence, nausea, vomiting, headache, generalized weakness, altered mental status, seizures, aphasia and movement disorders. About half of all survivors have long-lasting neurologic deficits including but not limited to recurrent headaches, focal paralysis, muscle weakness and cognitive difficulties.

Incubation Period

1 to 4 weeks post exposure, typically 7 to 14 days.

Viability

Inactivated by heat (50-60˚C for at least 30 min), 1% sodium hypochlorite, 2% glutaraldehyde, formaldehyde and 70% ethanol.

Survival Outside Host

Does not survive outside the host; however, transmission via blood transfusion and contaminated raw milk may be possible.

Information for Lab Workers

Laboratory PPE

Central European Subtype & All Other Subtypes
Biosafety Level 3 practices and facility are recommended for work involving Powassan Virus. Such practices should include respiratory protection if exposed to aerosolized virus/contaminated fluids, and eye protection must be used when there is a known or
potential risk for splash exposure.

Containment

BSL-3 facilities, equipment and operational practices for work involving infectious or potentially infectious materials, animals or cultures.

In Case of Exposure/Disease

• For injuries in the lab which are major medical emergencies (heart attacks, seizures, etc.…):
• Medical Campus: call or have a coworker call the Control Center at 617-358–4144.
• Charles River Campus: call or have a coworker call campus security at 617-353-2121.
  You will be referred to or transported to the appropriate health care location by the emergency response team.
• For lab exposures (needle sticks, bite, cut, scratch, splash, etc…) involving animals or infectious agents, or for unexplained symptoms or illness call the ROHP 24/7 hour number (1-617-358-ROHP (7647); or, 8-ROHP (7647) if calling from an on-campus location) to be connected with the BU Research Occupational Health Program (ROHP) medical officer. ROHP will refer you to the appropriate health care location.
• Under any of these scenarios, always inform the physician of your work in the laboratory and the agent(s) that you work with.
• Provide the wallet-size agent ID card to the physician.

Vaccination

No prevention is currently available for Powassan Virus.

Information for First Responders/Medical Personnel

Public Health Issues/PPE

Powassan Virus is not typically transmitted from person to person via casual contact without the intermediate tick vector. There have been reports of infections from blood transfusions with contaminated blood. Persons infected with Powassan should not donate blood for at least 4 months after infection.

After Exposure

Irrigate the area, call NIEDL Control and follow guidance provided.

In Case of (suspected) Illness

Call ROHP to discuss concerns.

Diagnosis/Surveillance

Monitor for symptoms. Clinicians should contact their state or local health department for assistance with diagnostic testing as they can assist with determining if samples should be sent to the CDC Arbovirus Diagnostic Laboratory for further testing. If diagnostic testing is warranted, samples need to be sent via the state health department. Of note, commercial testing for Powassan Virus is highly limited.

Infection is confirmed via virus-specific IgM antibodies in serum or CSF and samples may require plaque reduction neutralization tests to confirm diagnosis of Powassan as cross-reactivity with other flaviviruses (i.e. West Nile, Dengue, etc.) can occur.

First Aid/Post Exposure Prophylaxis

No current antiviral therapy exists.

Treatment

Treatment is supportive and symptomatic.

References

CDC: https://www.cdc.gov/powassan/diagnostic-testing.html

Biosafety in Microbiological and Biomedical Laboratories, 6th Edition: https://www.cdc.gov/labs/pdf/SF__19_308133-A_BMBL6_00-BOOK-WEB-final-3.pdf

UpToDate: March, 2023, Petersen, L. R., et al. https://www.uptodate.com/contents/arthropod-borne-encephalitides

Government of Canada, Pathogen Safety Data Sheets:
https://www.canada.ca/en/public-health/services/laboratory-biosafety-biosecurity/pathogen-safety-data-sheets-risk-assessment/powassan-encephalitis-virus.html