Powassan virus causes tick-borne encephalitis (TBE)is a flavivirus transmitted by ticks, found in North America and in the Russian Far East. It is named after the town of Powassan, Ontario, where it was identified in a young boy who would died from it.
The Powassan Virus is an RNA virus split into two separate lineages, Lineage I, labeled as the “prototype” lineage, and Lineage II, the deer tick virus (DTV) lineage. Lineage II has the most genetic variation, which indicates that it is most likely the ancestral lineage that split as a result of positive natural selection. DTV is very closely related to Powassan virus and a sequence analysis showed that the two viruses diverged about 200 years ago. Even though lineage II has been predominant in POWV positive tick pools, both lineages have had confirmed cases of human disease in North America and Russia. The lineages share 84% nucleotide sequences and 94% amino acid sequence identity. Cross-neutralization occurs among flaviviruses due to the conservation of the envelope protein; this is what contributes to the fact that the two lineages are “serologically indistinguishable”. As a result, the lineages are part of the same viral species.
Many people who become infected with Powassan (POW) virus do not develop any symptoms. The incubation period (time from tick bite to onset of illness) ranges from about 1 week to 1 month.POW virus can infect the central nervous system and cause encephalitis (inflammation of the brain) and meningitis (inflammation of the membranes that surround the brain and spinal cord).
Symptoms can include fever, headache, vomiting, weakness, confusion, loss of coordination, speech difficulties, and seizures.
Approximately half of survivors have permanent neurological symptoms, such as recurrent headaches, muscle wasting and memory problems. Approximately 10% of POW virus encephalitis cases are fatal. Symptoms may include fever, convulsions, headache, disorientation, lethargy, partial coma and paralysis. Ten percent of patients die and survivors may have permanent damage.
There are no vaccines or medications to treat or prevent POW virus infection.If you think you or a family member may have POW virus disease, see your health care provider for evaluation and diagnosis.Persons with severe POW illnesses often need to be hospitalized. Treatment may include respiratory support, intravenous fluids, and medications to reduce swelling in the brain.
You need to remove the tick as soon as possible. Call your doctor if you are unable to remove the entire tick from your skin.
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