Powassan virus (POWV) is a Flavivirus transmitted by ticks, found in North America and in the Russian Far East.
It can cause encephalitis, inflammation of the brain.
No approved vaccine or antiviral drug exists.
Prevention of tick bites is the best precaution.
Powassan virus is a rare but serious tick-borne illness that has been gaining attention in recent years, particularly in the northeastern United States and Great Lakes region of North America.
Key facts about Powassan virus:
Transmitted primarily through the bite of infected ticks, mainly the blacklegged tick (Ixodes scapularis) and groundhog tick (Ixodes cookei).
While many tick-borne diseases require hours of attachment, Powassan virus can be transmitted in as little as 15 minutes after tick attachment.
Powassan virus belongs to the flavivirus family, related to West Nile virus.
Many infected people do. It develop symptoms, but when symptoms occur they typically appear 1-4 weeks after infection
Symptoms: Fever Headache Vomiting Weakness Memory problems Confusion -Seizures
In severe cases, it can cause encephalitis or meningitis.
Approximately 10-15% of cases with neurological involvement are fatal, and about half of survivors experience long-term neurological problems.
There are no specific treatments or vaccines for Powassan virus.
Management focuses on supportive care.
Prevention relies on avoiding tick bites through measures like using repellents, wearing protective clothing, checking for ticks, and controlling ticks in your environment.
The virus can be transmitted with bites from altogether six known species of ticks: four species of Ixodes ticks, Ixodes cookei, Ixodes scapularis, Ixodes marxi and Ixodes spinipalpus, and the ticks Dermacentor andersoni and Dermacentor variabilis.
People with POWV have been mostly confirmed as having one strain of POWV, the deer tick virus.
I. scapularis is an important vector for the deer tick virus, which plays a vital role in maintaining the POWV.
I. scapularis is also a primary vector for the agent of Lyme disease.
In Canada and the Northeastern United States Ixodes cookei is the predominant species.
I. scapularis is a significant vector in Minnesota and Wisconsin.
POWV is transmitted when an infected tick bites a human, the tick is typically I. scapularis.
The time interval for transmission of POWV is expected to be less than 12 hours.
Once the POWV reaches humans it cannot be transmitted to a feeding tick, therefore humans are considered dead-end hosts.
It is is rarely diagnosed as a cause of encephalitis; however, but when Powassan encephalitis is severe, and neurologic sequelae are common.
There are currently no medications or approved vaccines to treat or prevent the POWV.
People affected by Powassan virus generally first show symptoms 1 to 3 weeks after infection: initial symptoms include fever, headache, nausea, occasional confusion, and weakness.
With severe Powassan illnesses the victims should be hospitalized, because the symptoms do worsen, and could extend to meningoencephalitis, which may include: seizures, aphasia, cranial nerve palsies, paresis and altered mental status.
To treat POWV illnesses: use of medications to reduce brain swelling, respiratory support and intravenous fluids.
About 10% of POWV encephalitis cases are fatal and half the survivors have permanent symptoms that affect their brain.
Powassan Virus (POWV) is the only tick-borne flavivirus endemic in North America.
POWV human illnesses have been reported in the United States, Canada and Russia.
POWV has different genetic variations including deer tick virus (DTV) which is transmitted by the black-legged tick (aka deer tick), Ixodes scapularis.
POWV lineage I is transmitted by the Ixodes cookei which is endemic in the Great Lakes region of the United States.
POWV lineage II is transmitted by Ixodes scapularis which is endemic in the Northeast United States.
Humans can become infected in 15 to 30 minutes after tick attachment.
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.
The nymph stage frequently bites humans and is the stage in which I. scapularis is most likely to infect a human host with a pathogen.
The most common reservoir for I. scapularis are white-footed mouse and white-tail deer.
The most common reservoirs for I. cookei are skunks, woodchucks and squirrels.
Humans are incidental hosts which means the ticks do not need to feed on humans to survive, humans are merely the host they find at the time for their next blood meal.
In the US, the highest incidence of POWV is in Minnesota and Wisconsin.
Massachusetts and New York also having higher incidence than other states in the Great Lakes or Northeast region.
POWV is included in the list of nationally notifiable diseases to the U.S. Centers for Disease Control and Prevention (CDC).
The incidence rate of POWV in the United States was 1 case per year from 1958 to 2005, and has risen to an average of 10 cases per year since then.
Currently, POWV is detected with IgM antibody capture ELISA of an IgM immunofluorescence antibody (IFA) assay; plaque reduction neutralization test (PRNT); detection of virus-specific nucleic acids; isolation in culture, or a >4-fold increase in antibody titers from paired acute and convalescent sera.
Diagnosis of POWV infection is challenging due to the lack of pathognomonic findings and the need for specialized serologic tests, which are typically performed by state health departments or the CDC.
Diagnostic criteria: 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.
Human infection with POWV can lead to severe neuroinvasive disease, including encephalitis and meningoencephalitis.
The clinical presentation includes fever, headache, vomiting, and can progress to altered mental status, seizures, and localized neurological deficits.
The case fatality rate for neuroinvasive POWV infection is approximately 10%, and about 50% of survivors experience long-term neurological sequelae.
There are two recognized genetic lineages of POWV: lineage I (POWV) and lineage II (deer tick virus).
Imaging studies such as CT and MRI may show vascular insults similar to those seen in other tick-borne encephalitis viruses.
There is no specific antiviral treatment for POWV; management is primarily supportive.
Preventive measures include avoiding tick bites through the use of protective clothing, tick repellents, and prompt removal of attached ticks.