Powassan virus (POWV)

Powassan virus (POWV) is a rare tick-borne virus that primarily occurs where ticks are prevalent in the Midwest and Northeast United States. It is part of the Flavivirus family of positive-strand RNA viruses that includes such other pathogens as the West Nile, Yellow Fever, Dengue, and Zika viruses. Transmitted to humans through the bite of an infected tick, POWV can cause serious and even potentially fatal complications. In the most severe cases, it may lead to encephalitis or meningoencephalitis. Long-term problems such as recurrent headaches, muscular atrophy, and memory loss can also occur, though some infected individuals remain asymptomatic. Since there are no drugs capable of curing POWV, treatment for the condition is usually limited. There are also no available vaccines to prevent the condition, so the best way to avoid POWV is for individuals to take the necessary precautions to protect themselves from ticks when spending time outdoors.

Background

Ticks, a group of parasitic arachnids closely related to spiders and mites, spread POWV. Ticks are unique from other similar species in that they are the leading vectors of disease in animals and the second-most-frequent transmitters of human disease, behind only mosquitoes. This is because ticks harbor viruses, bacteria, and other pathogens that they can transmit to humans and wild and domesticated animals. Since some of the diseases they spread, like POWV and Lyme disease, can have serious health consequences, ticks are generally considered a dangerous organism that should be avoided whenever possible.

More than 800 distinct tick species have been identified around the world. These species are divided into three separate families, including the Ixodidae, Argasidae, and Nuttallellidae. The largest of the three families is the fourteen-genera Ixodidae, or the hard ticks. The hard ticks most commonly feed on humans and other animals. The Argasidae, or soft ticks, have only four different genera, while there is only one known Nuttalliellidae species in the world.

Ticks have a structured life cycle that progresses through egg, larva, nymph, and adult stages. At each stage, ticks must feed on a meal of blood to ensure proper development. They do this by locating and latching onto a host, from which they harvest the necessary amount of blood. In the process, ticks can become infected with pathogens from their hosts and then pass those pathogens on to future hosts. In this way, ticks regularly spread a number of diseases that can be potentially dangerous and even fatal to human or animal hosts.

Different types of ticks often spread diseases. The condition most commonly associated with ticks is Lyme disease. The main cause of Lyme disease is the bacterium Borrelia burgdorferi. It is a serious illness with symptoms that typically manifest in three stages and range from fever and headaches to immune system issues and widespread pain. The groundhog tick (Ixodes cookei), squirrel tick (Ixodes marxi), and blacklegged (deer) tick (Ixodes scapularis) are the specific vectors of POWV, which is much less common than Lyme disease. The blacklegged (deer) tick is primarily responsible for transmitting POWV to humans because the groundhog tick and squirrel tick rarely bite people.

Overview

POWV is a rare but serious tick-borne illness. It was first identified as a pathogen in 1958 following the death of a five-year-old boy in Powassan, Ontario, Canada. An autopsy performed on the child, whose immediate cause of death was encephalitis, revealed the presence of a never-before-seen Flavivirus. The newly discovered virus was subsequently named after the municipality where the original incidence of human infection was recorded.

There are two types of POWV, known as lineage 1 and lineage 2. Lineage 2 POWV is also commonly referred to as the deer tick virus because it is specifically spread by the blacklegged (deer) tick. This type of tick is also responsible for spreading diseases like Lyme disease, anaplasmosis, and babesiosis. They are widely distributed across the eastern United States, particularly in the Northeast, Upper Midwest, and mid-Atlantic regions. Blacklegged (deer) ticks usually live on the ground in wooded and bushy areas and generally latch onto hosts as they pass by. Lineage 1 POWV is much rarer than its lineage 2 counterpart because it is exclusively spread by groundhog and squirrel ticks, which do not normally bite humans.

The symptoms of POWV can vary significantly. Some people who become infected remain entirely asymptomatic. Others may begin to develop symptoms anywhere from a week to a month after being bitten. Mild first-stage symptoms can include fever, headache, weakness, or vomiting. Some cases of POWV may not worsen beyond this point, but approximately 30 percent of symptomatic adults contract a more serious form of the disease. In such cases, a patient with stage-one symptoms typically experiences a two- to three-week symptom-free period called quiescence. At some point after the quiescence, the patient will likely get a high fever that marks the beginning of stage-two POWV. Stage-two symptoms usually include nervous system problems in the form of confusion, loss of coordination, difficulty speaking, and seizures. Some patients may also develop a brain infection (encephalitis) or an infection of the membranes around the brain and spinal cord (meningoencephalitis). POWV that escalates to this point can be fatal. Around one in ten people who experience severe POWV symptoms ultimately dies. Those who survive may experience long-term health effects, including recurring headaches, memory problems, and muscular atrophy.

POWV is typically diagnosed based on the patient’s symptoms, their history of living in or visiting areas where ticks are present and POWV is known to circulate, their history of exposure to potentially infected ticks, and laboratory testing of blood or spinal fluid. Since there are no antiviral medications capable of curing POWV, treatment recommendations are usually limited to rest, appropriate fluid intake, and over-the-counter pain medicine. Patients with severe cases often require hospitalization for respiratory or hydration support. Some may also require treatment aimed at reducing swelling in the brain.

Aside from the young boy who was the virus’ first known victim, there is at least one other famous case of POWV. Kay Hagan, who represented the state of California in the US Senate from 2009 to 2015, became ill with a form of encephalitis while visiting Washington, DC, in December 2016. It was later determined that her illness was likely tied to POWV she may have gotten from a possible tick bite she experienced while on a hike earlier in the year. Hagan ultimately died of complications of POWV in 2019.

Bibliography

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“About Powassan Virus Disease.” Minnesota Department of Health, 2023, www.health.state.mn.us/diseases/powassan/basics.html. Accessed 31 Aug. 2023.

Kapoor, Andrew K. and Rebecca Zash. “Powassan Virus.” StatPearls (National Library of Medicine), 27 Mar. 2023, www.ncbi.nlm.nih.gov/books/NBK570599. Accessed 31 Aug. 2023.

Marcum, Lonnie. “Tick-Borne Powassan Virus Can Be Deadly.” LymeDisease.org, 2017, www.lymedisease.org/co-infections-tick-borne-powassan-virus-can-be-deadly. Accessed 31 Aug. 2023.

“Powassan.” State of Rhode Island Department of Health, 2023, health.ri.gov/diseases/ticks/?parm=150. Accessed 31 Aug. 2023.

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Yang, Xu, et. al. “Powassan Virus: A Tick Borne Flavivirus Infecting Humans.” Biosafety and Health, vol. 4, no. 1 (2022): pp. 30–37.