Transmission of Powassan Virus

Key points

  • Powassan virus is a tickborne flavivirus.
  • It is maintained in the environment between Ixodes species ticks and small rodents.
  • Humans are dead-end hosts but can rarely transmit the virus through blood transfusions.
adult tick walking on a blade of grass towards warm source

Virus

  • Powassan virus disease is caused by a tickborne flavivirus (genus Flavivirus, family Flaviviridae).
  • There are two lineages of Powassan virus, specifically Lineage 1 - Powassan virus and Lineage 2 - deer tick virus.
  • Powassan virus has been identified in North America and isolated locations of Russia.
  • It is related to tick-borne encephalitis virus that occurs in Europe and Asia.

Transmission

Powassan virus is spread to people by the bite of an infected tick. Ticks become infected when they feed on groundhogs, squirrels, mice, or other rodents that have the virus in their blood. Infected ticks can then spread Powassan virus to people and other animals by biting them. People do not develop high enough levels of the virus in their blood to infect biting ticks. As a result, people are considered "dead-end" hosts for Powassan virus.

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Image of Powassan virus transmission cycle. A woodchuck and squirrel are shown on opposite sides of a circle to a tick with arrows connecting them to represent how Powassan virus cycles between ticks and small mammals. Woodchucks, squirrels, and other small mammals are considered amplifying hosts. Another arrow outside of the circle connects the tick to a human adult and child to show how ticks infect humans with the virus. The human is a dead-end host because it does not pass on the virus.
Powassan virus transmission cycle

The virus is not transmitted from person to person, except in rare instances by blood transfusion. Because the virus can be transmitted through blood, persons who were recently diagnosed with Powassan virus infection should not donate blood or bone marrow for 120 days following infection.

Three types of ticks spread Powassan virus and are primarily found in the eastern half of the United States.

  • Ixodes cookei (groundhog tick),
  • Ixodes marxi (squirrel tick), and
  • Ixodes scapularis (blacklegged or deer tick).

The groundhog tick and the squirrel tick rarely bite people. The blacklegged, or deer tick, which feeds mainly on white-footed mice and deer, often bites people. These bites can result in several types of diseases (e.g., Lyme disease).

Ticks can attach to any part of the body but are often found in hard-to-see areas such as the groin, armpits, and scalp.

Prevent getting sick with Powassan virus by preventing tick bites.

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Content Source:
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)