infectious diseases
Other Arbovirus Infections
Powassan virus
In the United States, Tick-borne encephalitis is caused mainly by Powassan virus, a flavivirus that is antigenically related to In the United States, there are 2 types of Powassan virus, both linked to human disease: Lineage 1 Powassan virus: Associated withIxodes cookeiorIxodes marxiticks ticks, the same tick that spreads Lyme Disease , Lineage 2 Powassan virus infection is more likely than lineage 1 infection becauseI. cookeiticks rarely bite people. The time an infected tick must be attached to transmit Powassan virus is probably much shorter (15 minutes) than that needed for Lyme Disease (24 to 48 hours) ( Although rare, Powassan virus encephalitis appears to be increasing since 2009. A total of 202 cases of Powassan virus disease infection have been reported in the United States from 2012 to 2021, ranging from 7 to 43 cases per year; most (189) were neurologic disease, resulting in 24 deaths. Cases occur in the late spring to mid-fall, when ticks are most active ( Arbovirus references ). In the reported cases of Powassan virus infection, neurologic sequelae were common, and the case-fatality rate was high (up to 10 to 15%). This high morbidity and mortality may result from reporting bias because seropositivity in endemic regions is known to be much more common than reported cases, suggesting that there are higher rates of asymptomatic infection. Powassan virus infection should be considered in patients with Encephalitis , especially when the patient has a history of tick bite or spends a lot of time outdoors and lives in or has recently traveled to an endemic area. Diagnosis is similar to that of tick-borne encephalitis, with serologic tests to detect Powassan virus–specific IgM antibody in serum or cerebrospinal fluid and confirmed by neutralizing antibody testing of acute- and convalescent-phase serum specimens at a state public health laboratory or the CDC. There is no vaccine for Powassan virus infection; the vaccine for tick-borne encephalitis is directed against different flaviviruses and, when one of these tick-borne encephalitis vaccines was tested in mice, it did not prove to be protective against Powassan virus. People at risk should use personal protective measures to Prevention . 