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The Rise of Powassan Virus

April 20, 2015
by Michael Greenwood

A relatively unknown tick-borne disease has the potential to become a serious public health concern.

Professor Durland Fish of the Yale School of Public Health answers some important questions about an emerging tick-borne disease known as Powassan virus. The disease had been rare in humans, but ecological changes have resulted in the pathogen spreading to the common deer tick, the same insect responsible for Lyme disease. This change could result in many more human infections. Powassan virus differs from Lyme in that is can be transmitted from ticks to humans much more quickly and is much more likely to be fatal. Fish has studied the changing dynamics of Lyme and a of host other tick- and mosquito-borne diseases for decades at the Yale School of Public Health.

What is Powassan virus?

DF: It is a virus transmitted by tick-bite and was first discovered in Powassan, Ontario, in 1958. The virus is normally transmitted among wildlife (mammals) and humans get it when certain kinds of ticks become infected and later bite humans. It cannot be transmitted directly between humans as are many other diseases caused by viruses.

What kind of disease does it cause?

DF: Powassan virus attacks the nervous system and can infect the brain causing inflammation, a condition known as encephalitis. It can also infect the lining of the brain, causing meningitis. Symptoms of infection range widely from none to death. Serious infections can cause severe headache, muscle weakness, confusion and seizures within a week or more after infection. Long-term neurological effects may also result. Fatalities have been reported in 10 percent of cases with serious neurological disease. Fortunately, most infections appear not to cause serious illness.

Is there a treatment for Powassan virus?

DF: Like most other diseases caused by a virus, there is no specific treatment for illness caused by Powassan virus. In serious cases, supportive therapy may reduce the effects long enough for the immune system to resolve the infection and increase the chances of survival.

How do people get infected with this virus?

DF: People become infected when they are bitten by certain kinds of ticks, including the deer tick, which also transmits Lyme disease and is very common throughout many areas of the eastern United States. Unlike Lyme disease, infection with Powassan virus can occur within minutes after a tick attaches to the skin and all tick stages (larva, nymph and adult) are capable of transmitting the infection.

How can I prevent getting infected?

DF: Most methods recommend for Lyme disease prevention will also work for Powassan, but it is important to remember that infection can occur throughout the year and promptly finding and removing an attached tick is essential. Contact the local health department to determine if Powassan virus occurs in areas were you live or visit.

Where does it occur?

DF: Powassan virus most commonly occurs in the same areas where Lyme disease is prevalent, in the northeastern and upper mid-western states. But, it does not occur in the far western states where there is Lyme disease.

Why is there so much recent concern about it?

DF: There has been an important change in the ecology of Powassan virus in that the deer tick has recently become infected with the virus. Until a few decades ago, it was only transmitted by a tick species that does not commonly bite humans and human cases were extremely rare. This recent change in the ecology of Powassan virus has caused concern within the public health community.

Is the disease spreading?

DF: Powassan is spreading due to the expansion in the range of deer ticks. Because deer ticks can now transmit Powassan virus infection to humans, cases are being reported in areas where they have never occurred before. As the geographic range of Lyme disease expands, so will Powassan.

Can it be controlled?

DF: There are currently no practical methods to control the spread of deer ticks or Lyme disease and this is also true for Powassan virus. Nothing can be done to prevent it from expanding into new areas and human cases are expected to increase as more people become exposed to infected ticks.

Will it become an epidemic, like Lyme disease?

DF: Wildlife studies have shown that Powassan virus is increasing in the New England area and human case reports are increasing in the upper mid-west. As more ticks become infected with Powassan virus and more people become exposed to them, Powassan could become epidemic like Lyme disease. Because it can be a serious disease causing fatalities and there is no treatment for it, Powassan has the potential to become a greater of a public health threat than Lyme disease.

Submitted by Denise Meyer on April 20, 2015