The Pennsylvania Department of Environmental Protection (DEP) has confirmed higher than expected rates of Powassan (POW) virus in ticks located in multiple Pennsylvania counties during the 2021 surveillance season including Clearfield, Centre, Wyoming, Bradford and Schuylkill counties.
POW virus is spread to people through the bite of an infected deer tick, and although no human POW virus cases were reported in Pennsylvania in 2021, ten cases of POW virus have been reported since surveillance started in 2011.
While the state Powassan infection rate for the fall 2020/winter 2021 deer tick collections were consistent with previous findings at 0.6%, Powassan hot spots with higher than expected rates were found in the following counties: Wyoming (67%), Clearfield (48%), Centre (40%), Bradford (11%) and Schuylkill (4%). While tickborne diseases such as Lyme require an infected deer tick be attached for over 24 hours to transmit the disease, studies have shown significantly less time may be needed to transmit POW virus.
POW virus is transmitted by the bite of an infected tick. More than 150 cases have been documented in
the United States, mostly in the northeast and Great Lakes regions. The deer tick (Ixodes scapularis),
also known as the blacklegged tick, is capable of being infected with and transmitting POW virus. This
tick species is also the primary vector of Lyme disease and several other tickborne pathogens, and
deer ticks can be found throughout Pennsylvania.
Most people infected with POW virus are asymptomatic. Illness, if it develops, appears one week to
one month after the tick bite. Symptoms are typical of neuroinvasive arboviral disease and include (but
are not limited to) fever, headache, vomiting, weakness, altered mental status, loss of coordination,
speech difficulties, memory loss, encephalitis and meningitis. Non- neuroinvasive POW virus disease
has been documented and manifests as a febrile flu-like illness. Infection can be fatal in about 10% of
There is no specific treatment, such as antivirals, for POW virus disease and supportive care is
appropriate. The best way to prevent POW virus disease is to prevent tick bites.