Powassan is rare but kills 10% of those who get it and leaves half of its victims with lasting neurological problems. It's viral and related to West Nile Virus.

Deer Tick
Deer Tick

Ticks that Carry It

Powassan is carried by deer ticks and found where Lyme disease occurs.


Between Jan. 2018 and Jan. 2023, 144 cases of Powassan were reported, with most cases occurring in the northeast and Great Lakes regions.

Powassan incidence map
Source: Centers for Disease Control and Prevention, National Notifiable Diseases Surveillance System


Solomon, I. H. et al. JAMA Neurology Fatal Powassan Encephalitis (Deer Tick Virus, Lineage II) in a Patient With Fever and Orchitis Receiving Rituximab Jun, 2018 Powassan virus is a rare but increasingly recognized cause of severe neurological disease. It can cause severe neuroinvasive illness with 50 percent of survivors displaying long-term neurological sequelae.

Bogaty, C. Canadian Medical Association Journal Powassan virus - an emerging public health concern Apr 16, 2018 POWV is emerging as an important pathogen … [It] is transmitted by the blacklegged tick  Ticks harboring POWV have been detected in Nova Scotia, Ontario and Manitoba, with expansion of the tick across eastern and central Canada

Corrinet, T. et al. Zoonosis and Public Health Powassan virus, a scoping review of the global evidence Jun 17, 2019 Powassan virus (POWV…causes sporadic but severe cases of encephalitis. 178 articles are included. The majority of the studies were conducted in North America (88.2%) between 1958 and 2017.  To date, POWV has been reported in 147 humans in North America. The virus has also been isolated from five tick species, and several animals have tested positive for exposure to the virus.

Kemenesi, G. et al. Clinical Microbiology Reviews Tick-Borne Flaviviruses, with a Focus on Powassan Virus. Dec, 2018 Despite the low disease incidence, the approximately 10% to 15% case fatality rate of neuroinvasive Powassan virus infection and the temporary or prolonged sequelae in >50% of survivors make Powassan virus a medical concern. NJ Newton NJ Man Dies With Rare Scary Tick Disease; Another Seriously Ill June 8, 2019 The potentially deadly Powassan tick-borne virus has been confirmed in two Sussex County residents, one of whom died last month…. The Powassan virus is spread by the deer tick. The illness is rarer than Lyme disease, which is also spread by the tick, but 10% of people who contract the illness die from it.

Robich, R. M. et al. The American Journal of Tropical Medicine and Hygiene Prevalence and Genetic Characterization of Deer Tick Virus (Powassan Virus, Lineage II) in Ixodes scapularis Ticks Collected in Maine. June 17, 2019 The number of reported human cases with neuroinvasive disease has increased substantially … indicating that POWV may be of increasing public health importance. … These results are the first reported infection rates and sequences for POWV in questing ticks collected in Maine.

Fatmi S. S. et al. Frontiers in Public Health Powassan Virus – A New Emerging Tick-borne Disease Dec 12, 2019  

  • Powassan virus (POWV) can cause encephalitis and meningitis
  • The fatality rate is 10%. 50% of survivors who develop neurological symptoms have long term sequelae.
  • Reported cases have increased by 671% since 2004, compared to the previous 40 years.
  • Deer ticks (Ixodes scapularis) are the primary vector on the East Coast of US and Ixodes cookei in the Midwest and Canada.
  • Infection in humans has been rare. Comparative prevalence is less than other diseases but incidence in endemic areas may be much higher than originally believed.
  • Powassan causes a rapidly progressing, neurological disease. Prevention of infection is a priority. Use of repellents and wearing long, light clothing when in wooded or grassy areas is important in decreasing tick contact.
  • Cases presenting to medical authorities, with neurological symptoms of unknown origin in a tick infested area, should always have Powassan encephalitis as a differential diagnosis. With the neurovirulent nature of the virus, any delays in diagnosis can leave long-lasting neurological sequels.