There is a 10-15% fatality rate in reported cases of Powassan encephalitis, with many survivors suffering long-term neurological damage. Symptoms usually begin suddenly 7-14 days following infection, and include headache, fever, nausea and vomiting, stiff neck, and sleepiness. Later, breathing distress, tremors, confusion, seizures, coma, paralysis, and death can occur.
The illness was discovered in 1958 after a five year old boy from Powassan, Ontario died of severe encephalitis. Between 1958 and 2010 fewer than 60 cases of Powassan encephalitis were reported in North America. In 2011, there were 16 confirmed cases in the United States. Recently, the number of cases reported in upstate New York has increased dramatically.
Rick Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies said, “We’ve seen a rise in this rare but serious illness in parts of New York State that are hotspots for Lyme disease. And we suspected it was tied to an increase in black-legged ticks carrying deer tick virus, particularly on the east side of the Hudson River.”
Over the course of a five-year study, researchers assessed more than 13,500 ticks of seven species of ticks in seven counties and proved Mr. Ostfeld’s theory – there was an increase in the number of black-legged ticks carrying deer tick virus in counties east of the Hudson river.
Laura Kramer, a research scientist at the Wadsworth Center, said, “Our findings are consistent with deer tick virus infection rates in people revealed in clinical tests by the New York State Department of Health. Of fourteen individuals testing seropositive for deer tick virus, ten were residents of Westchester, Putnam, or Dutchess counties. Another two were from Albany and Suffolk counties, areas with burgeoning black-legged tick populations.”
Unlike Lyme disease, anaplasmosis, and babesiosis, which take feeding black-legged ticks hours to transmit, deer tick virus transmission can occur in just 15 minutes. This leaves very little “grace period” for removing ticks, and underscores the importance of vigilance in tick hotspots.
Ostfeld concludes, “When patients present with encephalitis symptoms in areas with high levels of Lyme disease, especially during the summer, physicians need to consider Powassan encephalitis. While rare, it’s associated with significant complications. There is no vaccine or specific antiviral therapy, the best strategy remains prevention.”
Knowledge of Powassan encephalitis has grown largely as a result of West Nile virus surveillance. Both are part of the flavivirus group of arboviruses. More extensive arbovirus testing may reveal that deer tick virus is more widespread than previously thought.