JOURNAL OF THE LOUISIANA STATE MEDICAL SOCIETY
Unlike theOldWorldTBEVs, Powassanencephalitis is uncommon, with only 31 confirmed cases reported by the CDC from 1958- 2001. 3 Powassan virus disease (POWV) can be transmitted to humans by blood-feeding ixodid ticks in as little as 15 minutes and mimics other arthropod-borne viral encephlaitides, such as LaCrosse encephalitis and West Nile virus neuroinvasive disease, in clinical presentation. 5 The CFR can be as high as 10%, and permanent neurologic sequelae are common. 5 Therefore, clinicians should include POWV in their differential diagnosis of encephalitis in endemic regions, such as New England and the upper Midwest, during the mosquito-borne encephalitis season and also obtain serological tests for POWV on cerebrospinal fluid samples (POWV-specific neutralizing IgM antibody titers). 4,5 Unlike the prolonged attachment time required for the transmissionof Lymedisease, theshort attachment time required for transmission of POWV underscores the critical importance of personal protective measures, such as repellents and clothing, in preventing tick-transmitted infectious diseases. 4,5 The deer tick virus is closely related to Powassan virus and is also transmitted by ixodid ticks in the same endemic regions of New England. 6 It also causes a meningoencephalitis syndrome with a high CFR. 6
The NewWorld TBEVs Powassan Encephalitis in the US
Powassan encephalitis, first isolated in 1958, typifies a NewWorld TBEV with an initially highly confined regional distribution in the New England states (especially Connecticut, Massachusetts, and New York) and Eastern Canada, several ixodid tick vectors, primarily Ixodes spp., an extensive wild animal reservoir in rodents and medium-sized mammals, especially woodchucks and skunks, and a seasonal occurrence. 3 Cases occur from May- December and peak during June to September, when ticks and humans are most active outdoors. 3 Since 2008, Powassan encephalitis cases historically confined to the Northeastern U.S. and Canada have been increasingly confirmed farther westward in Minnesota and Wisconsin, with fatal cases reported in the elderly. 4 Patients with Powassan encephalitis present with somnolence, headache, confusion, high fever, weakness, ataxia, and CSF lymphocytosis. 3 Transient improvement may be followed by neurologic deterioration, evidence of ischemia or demyelination on magnetic resonance imaging, and slow recovery, often with permanent deficits including memory loss, weakness, ophthalmoplegia, and lower extremity paraparesis. 3-5
TABLE 2
VIRUS NAME
FAMILY TAXONOMY
GEOGRAPHIC DISTRIBUTION
TICK VECTORS
ZOONOTIC RESERVOIRS
Alkhurma hemorrhagic fever virus
Flaviviridae
Saudi Arabia
Camels, sheep
Ornithodoros savignyi (suspected) Dermacentor reticulatus, Ixodes apronophorus
Omsk hemorrhagic fever Flaviviridae
Western Siberia
Mammals - rodents, especially muskrats, water voles Mammals - especially monkeys, domestic livestock (cattle, goats, sheep), rodents, insectivores Mammals - rodents, skunks, other medium-sized mammals Mammals - many domestic animals (buffalo, camels, cattle, goats, sheep), rabbits, rodents (hedgehogs), birds Mammals - many domestic animals (buffalo, camels, cattle, goats, sheep), rabbits, rodents (hedgehogs), birds
Kyasanur Forest disease Flaviviridae
Western India
Haemaphysalis spinigera
Heartland virus
Bunyaviridae
Missouri, Kansas, Tennessee Asia, Easter Europe, Africa, Middle East
Amblyomma americanum
Crimean-Congo hemorrhagic fever (CCHF)
Bunyaviridae
Hyalomma marginatum, Hyalomma anatolicum
Severe fever with thrombocytopenia virus (SFTV)
Bunyaviridae
China (mostly), Japan, Korea
Haemaphysalis spp., especially H. longicornis > H. concinna
Orthomyxoviridae Missouri, Kansas, Oklahoma
Unknown
Unknown
Bourbon virus
Table 2: The Tickborne Hemorrhagic Fever Viruses
J La State Med Soc VOL 170 MARCH/APRIL 2018 49
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