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Arthropod-borne virus encephalitis
Published in Avindra Nath, Joseph R. Berger, Clinical Neurovirology, 2020
Powassan virus appears to produce a multifocal and diffuse gray matter infection of all levels of the central nervous system so that no one presentation is characteristic. The incubation period ranges from 8 to 34 days. Fever may be absent at the beginning, but is a consistent finding thereafter. Signs of CNS involvement can be diffuse with headache, obtundation and vomiting. Focal or generalized seizures can occur. Motor weakness can manifest as a monoparesis, hemiparesis, or quadriparesis and be of the upper or lower motor type. Gait ataxia has also been observed. POWV shares with its TBE counterparts the capacity to produce acute spinal cord clinical disorders, followed by muscular atrophy. A case has been reported resembling herpes simplex encephalitis [93]. Ophthalmoplegia has been documented [91].
Powassan Virus
Published in Sunit K. Singh, Daniel Růžek, Neuroviral Infections, 2013
Laura D. Kramer, Alan P. Dupuis, Norma P. Tavakoli
Powassan virus (POWV; family Flaviviridae, genus Flavivirus) is a member of the mammalian tick-borne virus group (Grard et al. 2007). The virus appears to be widely distributed in its enzootic hosts in North America and Far East Asia (Mandl et al. 1993). Remarkable disease is rare (Hoang Johnson et al. 2010), but encephalitis in humans may be associated with significant neurologic sequelae. The first case was identified in 1958 in Powassan, Ontario, Canada (McLean and Donahue 1959). The virus appears to be increasing in prevalence in the United States, possibly as a consequence of improved diagnostics leading to increased detection, but equally likely as a consequence of the proliferation of vector tick populations or increased contact between infected ticks and humans due to lifestyle changes. An increased incidence of the closely related TBEV has also been noted in Europe, more likely due to socioeconomic factors than climate warming (Godfrey and Randolph 2011). POWV is comprised of two lineages, lineage I (POWV) and II (Deer tick virus; DTV), with distinct transmission cycles (Ebel et al. 2001). It has been speculated that DTV may lead to milder cases (Ebel et al. 1999); however, at least two recent cases of DTV that were fatal (Tavakoli et al. 2009) (and unpublished data) demonstrate this virus has the potential to be virulent. This chapter will address the biology, epidemiology and ecology, pathology, and diagnostics of these two viruses.
Novel Case of Multifocal Choroiditis following Powassan Virus Infection
Published in Ocular Immunology and Inflammation, 2022
Jamie M. Nord, Naomi R. Goldberg
Powassan virus is a tick-borne, RNA virus of the Flaviviridae family with rare but slowly increasing incidence in the Northeast United States. Powassan virus has been increasingly identified as the etiology for encephalitis since it was first isolated in the United States in 1958.1,2 There have been 133 cases of Powassan virus infections reported to the United States Center for Disease Control and Prevention from 2009 to 2018.3 Humans are infected with Powassan virus by the bite of an infected tick, typically of which belongs in the genus, Ixodes. Cases have been reported in eastern Canada, northeastern and north-central United States,4 making Powassan virus the only tick-borne encephalitis group of flaviviruses causing disease in North America. The incidence of Powassan virus has been increasing in recent decades, with a 671% rise in cases in the last 18 years compared to the previous 40 years, possibly due to the rising surveillance and/or emergence of the disease.5 In humans, Powassan virus causes severe neuroinvasive diseases, most commonly presented as encephalitis, meningoencephalitis, and aseptic meningitis. The incubation period has been described as 1–5 weeks with a subsequent prodromal phase consisting of fatigue, headache, and disorientation. In the encephalitic phase, vomiting, fever, difficulty speaking, and seizures can occur. Ten percent of Powassan virus encephalitis cases are fatal, and 50% of survivors experience neurological sequelae.6 Ocular symptoms such as ophthalmoplegia, nystagmus, optic disc edema, and retinal vein tortuosity have been reported.7 Here, we report novel retinal changes following systemic infection with Powassan virus.