Powassan is a genus of viruses from the family Flaviviridae. The West Nile virus, dengue virus, tick-borne encephalitis virus, yellow fever virus, and Zika virus, among others, are viruses in this class. The Powassan virus was initially discovered in Powassan, Ontario, Canada in 1958. It does not have a cure.
In North America, scientists have discovered two kinds of Powassan. These are called lineage 1 and lineage 2 Powassan viruses. Lineage 2 is known also as the deer tick virus. For humans, infected ticks are the transmission culprits of the Powassan virus. Approximately 75 cases of the disease have been reported in the US in the last decade, and most have originated in the Great Lakes and northeast regions of the country.
The virus is not carried by all ticks. Moreover, not everyone who is bitten will become ill. Usually, a tick must be in physical contact with a human in order to generate the illness. The contact time required for the Powassan virus is not known, although many believe that the time frame is less than the amount of time required for other tick borne diseases.
One Powassan virus, the second lineage, is carried by deer ticks. These ticks also spread Lyme disease. They often are found in wooded areas where they inhabit the ground, or in areas that have heavy brush. The ticks seek out people and animals – hosts – near the ground by grabbing onto them. Ticks do not fly or fall from bush or trees.
The ecology of Powassan has modified. It is only recently, relatively speaking, that the deer tick has begun to carry the virus. Previously, the virus was only transmitted by a tick species that usually doesn't bite humans. But that changed a few decades back. Now, human cases of Powassan are more common. This change has raised concerns among public health officials.
Symptoms and Diagnosis
Many infected with Powassan are asymptomatic. The virus may not be diagnosed by clinicians if there are no symptoms. It can take anywhere from one week to one month from a tick bite to the actual illness. The virus has potential to affect the central nervous system and cause brain inflammation, or inflame membranes that surround the brain and spinal cord. Among the symptoms are: nausea, weakness, high fever, seizures, difficulty speaking, and general confusion.
Diagnosing Powassan involves determining when a patient might have been in the vicinity of black-legged ticks or tick environments. Then, the patient must undergo a physical examination. Next, lab tests involving blood or spinal fluid will be assessed to ascertain a specific diagnosis.
The Powassan virus is neither preventable nor treatable. No therapeutics or vaccines exist. Those who contract severe Powassan illnesses are usually hospitalized and receive respiratory support, IV fluids, and therapies that lessen brain swelling. In about 50% of cases, neurological issues will persist, such as memory challenges, loss of muscle, and recurring headaches. In about 10% of cases, patients will die.
A greater number of deer ticks is helping the Powassan virus to spread. Moreover, since transmission of the disease through deer ticks is now more pervasive, instances of the disease are being reported in geographic areas where they had not been reported previously, such as along the east coast of the US, in Pennsylvania, New Jersey, and New York. In addition, cases of the virus are growing in number in the New England area of the US. Cases are also occurring in the upper mid-west region of the country. Moreover, as Lyme disease expands geographically, Powassan will expand as well.
Since techniques and methodologies do not exist for controlling the spread of deer ticks or Lyme disease, strategies for controlling Powassan are also lacking. As the disease evolves into new areas, the number of human cases will increase as more people are bitten by infected ticks.
Some conjecture that with a greater number of infected ticks and more human cases of the virus, Powassan might reach epidemic stages, as did Lyme disease. And because Powassan does not have a cure, it actually could become a greater public health threat than Lyme disease.
Reviewed by Catherine Shaffer, M.Sc.