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Arthropod-borne virus encephalitis
Published in Avindra Nath, Joseph R. Berger, Clinical Neurovirology, 2020
Powassan virus (POWV) was first isolated from the brain of a five-year-old boy from Powassan, Ontario, Canada, who died from acute encephalitis in September 1958 [88]. By 1998, 27 cases of POW encephalitis had been reported from the U.S. and Canada, 7 of which were from Ontario, and 10 of which were from New York State [89]. In 2001, it was added to the U.S. nationally notifiable disease list and neuroinvasive disease was added in 2004 [90]. In the 11-year period from 2006 through 2016, 89 neuroinvasive cases and 10 non-neuroinvasive cases were reported to the Centers for Disease Control [90]. The disease remains rare with an average annual incidence of Powassan encephalitis is 0.0025/100/000 persons. The majority of affected persons are male with a median age of 62 years (range 3 months to 87 years) [90]. Transmitted by four tick species in North America, the principal vectors are Ixodes ticks. The primary hosts are medium sized mammals, particularly woodchucks, but household pets can also carry Powassan infected ticks. Infections have occurred from May to December but peak from June to September [91]. Several strains of POWV exist, including a recently described deer tick virus, which separate into two phylogenetic lineages, each of which can cause disease in humans [92].
Ticks
Published in Gail Miriam Moraru, Jerome Goddard, The Goddard Guide to Arthropods of Medical Importance, Seventh Edition, 2019
Gail Miriam Moraru, Jerome Goddard
Powassan encephalitis (POW)—also in the TBE serocomplex—is a rare infection of humans that mostly occurs in the northeastern United States, adjacent regions of Canada, and parts of Russia. Characteristically, there is a sudden onset of fever with temperature up to 40°C along with convulsions. Also, accompanying encephalitis is usually severe, characterized by vomiting, respiratory distress, and prolonged, sustained fever. Only a few dozen cases of POW have been reported in North America,86,87 although its reported incidence is increasing.18 Recognized cases have occurred in children and adults, with a case fatality rate of approximately 50%. POW is transmitted in an enzootic cycle among ticks (primarily Ixodes cookei) and rodents and carnivores. Ixodes cookei only occasionally bites people; this may explain the low case numbers. Antibody prevalence to POW in residents of affected areas is less than 1%, indicating that human exposure to the virus life cycle is a rare event.
Ticks
Published in Jerome Goddard, Public Health Entomology, 2022
Viruses associated with ticks. Tick-borne encephalitis (TBE) is a disease complex encompassing at least three syndromes caused by closely related viruses spanning from the British Isles (Louping ill), across Europe (Central European tick-borne encephalitis), to far-eastern Russia [Russian spring-summer encephalitis (RSSE)] (Figure 10.12). In Central Europe the typical case has a biphasic course with an early, viremic, flulike stage, followed about a week later by the appearance of signs of meningoencephalitis.15 Central nervous system (CNS) disease is relatively mild, but occasional severe motor dysfunction and permanent disability occur. Powassan encephalitis (POW)—also in the TBE subgroup—is a relatively rare infection of humans that mostly occurs in the northeastern United States and adjacent regions of Canada. Characteristically, there is sudden onset of fever with temperature up to 40°C along with convulsions. Also, accompanying encephalitis is usually severe, characterized by vomiting, respiratory distress, and prolonged, sustained fever. Cases of POW are still relatively rare in North America, although its reported incidence is increasing.4,16 There were 21 cases reported in 2018.4 Colorado tick fever is a moderate, self-limiting febrile tick-borne illness occurring in the Rocky Mountain region of the United States and Canada. The primary vector is Dermacentor andersoni. Small mammals such as ground squirrels and the ticks themselves serve as reservoirs of the virus. Crimean-Congo hemorrhagic fever is a rather serious tick-borne illness occurring in many countries in central and eastern Europe, Russia, China, India, Pakistan, the Middle East, and parts of Africa. Transmission is mainly by Hyalomma marginatum and other closely related species. Rabbits, cattle, and goats are believed to be the reservoir hosts. Kyasanur forest disease, transmitted primarily by Haemaphysalis spinigera and related species, occurs in southern India. The disease is believed to be contracted by people working in/near the Kyasanur forest or cattle grazing at the forest edge. In the last decade, several new tick-borne viruses have been identified. Heartland virus (a Phlebovirus) is associated with the Lone Star tick, Amblyomma americanum and has been recognized in Missouri, Oklahoma, Kentucky, and Tennessee.17,18 Only about 50 cases of Heartland virus have been identified. A couple of cases of a new Thogotovirus called Bourbon virus have been identified in the Midwest and southern United States with an unknown tick vector.19 Evidence suggests the lone star tick may be a potential vector.20
Novel Case of Multifocal Choroiditis following Powassan Virus Infection
Published in Ocular Immunology and Inflammation, 2022
Jamie M. Nord, Naomi R. Goldberg
A 51-year-old man with a 7-year history of chronic bilateral noninfectious anterior and intermittent uveitis with secondary macular edema had been treated with mycophenolate mofetil and adalimumab, with the disease quiescence. Uveitis workup had been unrevealing for any secondary rheumatologic or infectious conditions. Funduscopic examination had remained unremarkable over years of follow-up (Figure 1a), and the patient was also managed for concomitant glaucoma and cataract at that time. In May 2017, the patient developed an acute altered mental status and a fever of 104 degrees Fahrenheit following a recent tick bite in New Jersey. The patient was admitted to the hospital for 3 weeks for management of encephalitis, and an extensive encephalitis workup was performed, including serologies for Lyme and West Nile virus, which were negative. Lumbar puncture revealed the presence of Powassan virus-specific IgM and neutralizing IgG antibodies. One year following inpatient management and recovery of Powassan encephalitis, the patient returned for ophthalmology follow-up, off all systemic immunomodulatory treatment. Best-corrected vision was 20/40 in the right eye and 20/50 in the left eye, and there was new disease activity with increased anterior chamber and vitreous cells. Fundus examination revealed new chorioretinal lesions in a linear streak-like distribution, as shown in Figures 1b, 2, 3. Fundus autofluorescence highlighted the presence of hypo-autofluorescent streaks, and fluorescein angiography further revealed the extent of the multifocal choroidal inflammation. The patient had no other lesions elsewhere in the body. Treatment was resumed with oral and topical corticosteroids with quiescence of cellular activity, but persistent multifocal choroiditis changes.