Powassan virus

Powassan virus (POWV) is a flavivirus named after the town of Powassan, Ontario, Canada, where it was identified in a five-year-old boy, Lincoln Byers, who died from encephalitis in 1958. The ICTV species name for the Powassan Virus is Orthoflavivirus powassanense. The virus exists in North America and causes long-term neurological sequelae. The first human case in the United States was found in 1970 in New Jersey and the first in Russia in 1978. Powassan virus is also found in the warm climate across Eurasia, where it is part of the tick-borne encephalitis virus complex. It is found in the Russian Far East (Primorsky Krai) and appears to have been introduced there 70 years ago. ==Evolution==

Powassan virus is an RNA virus split into two separate lineages: Lineage I, the "prototype" lineage; and Lineage II, the deer tick virus (DTV) lineage. 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. The value is compatible with that of tick-borne encephalitis virus (TBEV) and louping-ill virus (LIV) (1.0 × 10−5–2.2 × 10−5 for TBEV and 5.7 × 10−6–3.9 × 10−5 for LIV). The most recent common ancestor of modern POWV split into two independent genetic lineages between 2,600 and 6,030 years ago, probably as a result of the Beringia flood, about 11,700 years ago. == Vectors ==

The virus can be transmitted with bites from six known species of ticks: four species of Ixodes ticks, Ixodes cookei, Ixodes scapularis, Ixodes marxi and Ixodes spinipalpis, and the ticks Dermacentor andersoni and Dermacentor variabilis. In North America, the POWV's lineages are maintained in three main enzootic cycles Once the POWV reaches humans it cannot be transmitted to a feeding tick, so humans are considered "dead-end" hosts. ==Signs and symptoms==

Powassan virus infection is rarely diagnosed as a cause of encephalitis, but when it is, Powassan encephalitis is severe, and neurologic sequelae are common. No medications or approved vaccines treat or prevent the POWV. People affected by the Powassan virus generally first show symptoms 1 to 3 weeks after infection. On October 28, 2019, former U.S. Senator Kay Hagan died after contracting the Powassan virus in 2016. She was 66 years old. In 2022, the Connecticut Department of Public Health confirmed that a man aged in his 50s contracted the Powassan virus in the state during March and was hospitalized with severe neurological symptoms. He was discharged to recover at home. In 2023, the Maine Center for Disease Control and Prevention reported that a 58-year-old man from Sagadahoc County died from Powassan virus. On June 3, 2024, artist, author, and musician MaryAnn Harris, spouse and longtime collaborator of Charles de Lint, died after a long struggle with Powassan virus, at age 71. Harris contracted the virus in 2021 and was subsequently paralyzed. She spent much of the rest of her life in the hospital and other care facilities. == Epidemiology ==

Powassan Virus (POWV) is the only tick-borne flavivirus endemic in North America. It has two distinct lineages. POWV lineage I is transmitted by the Ixodes cookei, which is endemic in the Great Lakes region. Ixodes ticks have three life stages that require a host: larva, nymph, and adult. Each stage requires a blood meal to progress to the next life stage. Nymphs frequently bite humans, which is when I. scapularis is most likely to infect a human host with a pathogen. The most common reservoirs (hosts) for I. scapularis are white-footed mice and white-tail deer. The most common reservoirs for I. cookei are skunks, woodchucks, and squirrels. In the U.S., the highest incidence of POWV is in Minnesota and Wisconsin, with Massachusetts and New York also having higher incidence than other states in the Great Lakes or Northeast region. Since its discovery in 1958, there have been 150 reported human illnesses caused by POWV. These tests for POWV can only be done at a state lab or the CDC. The CDC's diagnostic criteria are: resides in an endemic area, reported tick exposure, and presented with fever, altered mental status, seizures and focal neurological deficits and blood, tissue or cerebrospinal fluid (CSF) are positive on Powassan IgM or Powassan PRNT tests. ==Research==

Scientists at the Vaccine and Immunotherapy Center at The Wistar Institute have designed and tested the first-of-its-kind synthetic DNA vaccine candidate against Powassan virus (POWV), targeting portions of the virus envelope protein. == References ==