Powassan Virus: A Rare but Dangerous Tick-Borne Infection

Powassan virus is a rare but serious tick-borne infection that can cause severe neurologic disease, including encephalitis and meningitis. Unlike Lyme disease, which may require prolonged tick attachment, Powassan virus transmission can occur rapidly.

In their article “Underrecognized Tickborne Illnesses: Borrelia Miyamotoi and Powassan Virus”, Della-Giustina et al. explain why Powassan virus is raising concern. The authors note that transmission may occur within 15 minutes of tick attachment, and the neurologic complications can be devastating. Powassan virus infection is associated with an estimated 10% mortality rate.¹

What is Powassan virus?

The Powassan virus (POW) is a tick-borne flavivirus related to several other viruses including dengue, yellow fever, West Nile virus, and tick-borne encephalitis (primarily found in Europe).

“Flaviviruses are a group of single stranded RNA viruses that cause severe endemic infection and epidemics on a global scale.”²

In recent years, additional viruses transmitted by ticks have been identified including the Heartland virus (phlebovirus) and the Bourbon virus (thogotovirus).

Powassan virus is genetically similar to deer tick virus, and the clinical presentations are essentially identical.

How was Powassan virus discovered?

Powassan virus was first identified in 1958.

“Powassan virus is named for the Ontario, Canada, town where it was first isolated from the brain of a 5-year-old boy who died of severe encephalitis in 1958,” the authors write.

Where is Powassan virus found?

The second case was reported in New Jersey in 1970 and another case in eastern Russia in 1978. Although cases remain uncommon, the virus has been identified in a growing number of U.S. states.

In 2019, 13 U.S. states reported Powassan virus cases:

Connecticut, Indiana, Massachusetts, Maine, Minnesota, North Carolina, North Dakota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Wisconsin.

Ticks infected with Powassan virus can transmit the disease in as little as 15 minutes and may cause long-lasting neurologic complications in survivors.

How is Powassan virus transmitted?

Powassan virus is carried and transmitted by Ixodes scapularis ticks, also known as deer ticks or blacklegged ticks. These ticks can also transmit Borrelia burgdorferi, the bacteria which causes Lyme disease.

“Although many flaviviruses have mosquitoes as competent vectors, there is no evidence of human Powassan virus disease transmitted by mosquitoes,” the authors point out.

How fast can Powassan virus be transmitted?

Very fast. Experimental studies show that Powassan virus transmission can occur within 15 minutes of I. scapularis attachment.

This rapid transmission occurs because the virus is already present in the tick’s salivary glands. By contrast, many bacterial tick-borne pathogens reside in the tick’s mid-gut and require longer attachment before transmission occurs.

What are the symptoms of Powassan virus infection?

Many individuals infected with Powassan virus never develop symptoms. However, in some cases the infection can cause severe neurologic disease.

Symptoms may include:

• Fever
• Headache
• Neck stiffness
• Disorientation
• Seizures
• Motor weakness
• Paralysis
• Confusion or altered consciousness

Severe illness may resemble herpes simplex encephalitis.

Can Powassan virus cause long-term complications?

Yes. Powassan virus infection can lead to lasting neurologic damage.

“Approximately 50% of cases result in lasting hemiplegia, memory problems, and muscle wasting,” the authors explain.

Approximately 10% of cases are fatal.

How is Powassan virus diagnosed?

Diagnosis of Powassan virus infection can be challenging.

PCR testing may detect infection early in the illness. However, diagnosis more commonly relies on IgG antibody testing using enzyme-linked immunosorbent assay (ELISA). Confirmation typically requires specialized laboratory testing.

Why are co-infections important?

Individuals exposed to tick bites may also carry other tick-borne co-infections that are treatable.

The authors describe a patient with a combination of Powassan encephalitis, Lyme carditis, and Babesia.

Yoon and colleagues described the case of a 17-year-old young man who died waiting for a Powassan virus test.³ He was not treated for a Lyme disease co-infection. Autopsy revealed Borrelia spirochetes in his heart and liver, with PCR evidence of spirochetes in his brain and lungs.

What is the treatment for Powassan virus?

There is currently no specific treatment for Powassan virus infection. Care is supportive and focuses on managing neurologic complications.

Key Point

Powassan virus is a rare but potentially devastating tick-borne infection that can be transmitted within minutes of tick attachment and may lead to severe neurologic disease or death.

Clinical Insight

Powassan virus highlights an important principle in tick-borne disease care: a single tick bite can transmit multiple infections. Clinicians evaluating patients with suspected tick exposure should also consider treatable infections such as Lyme disease and other tick-borne co-infections.

Learn more in the Powassan virus hub and the tick-borne co-infections hub.