Powassan virus

• Powassan virus is spread to people by the bite of an infected tick.
• Although still rare, the number of reported cases of people sick from Powassan virus has increased in recent years.
• Most cases in the United States occur in the northeast and Great Lakes regions from late spring through mid-fall when ticks are most active.
• There are no vaccines to prevent or medicines to treat Powassan virus disease. Reduce your risk of infection from Powassan virus by avoiding ticks.

Naming

It is named after the town of Powassan, Ontario.

Epidemiology

• Powassan virus disease should be considered in any person with a febrile or acute neurologic illness who has had recent likely exposure to ticks (primarily Ixodes cookei, Ix. marxi, or Ix. scapularis) in Powassan virus endemic areas.

• In addition to other common causes of encephalitis and aseptic meningitis (e.g., herpes simplex virus and enteroviruses), other arboviruses (e.g., West Nile, St. Louis encephalitis, La Crosse, Jamestown canyon, eastern equine encephalitis viruses) should also be considered in the differential etiology of suspected Powassan virus disease.

• Powassan virus disease is a nationally notifiable condition in the United States.
• All cases should be reported to local public health authorities in a timely manner.
• Reporting can assist local, state, and national authorities to implement control measures to reduce future infections.

Clinical Signs & Symptoms

• The incubation period for Powassan virus disease ranges from 1–4 weeks. Initial symptoms include fever, headache, vomiting, and generalized weakness.
• The disease can progress to encephalitis, meningoencephalitis, or aseptic meningitis.

Symptoms of encephalitis may include altered mental status, seizures, speech problems (aphasia, dysarthria), paresis or paralysis, movement disorders, and cranial nerve palsies.

Clinical Evaluation

• Cerebrospinal fluid (CSF) findings include lymphocytic pleocytosis in the majority of patients with Powassan virus meningitis or encephalitis; neutrophils can predominate early in the disease.
• CSF protein is generally normal or mildly elevated, while glucose concentration is normal.
• Electroencephalography (EEG) in patients with Powassan virus encephalitis reveals generalized slow wave activity and results can resemble those seen in herpes simplex virus encephalitis.
• Magnetic resonance imaging (MRI) of the brain in patients with Powassan virus encephalitis can show hyperintensities in the superficial and deep white matter.

Outcomes

• Approximately 10% of Powassan virus neuroinvasive disease cases are fatal and about half of survivors have long-lasting neurologic deficits, such as headaches, muscle weakness, focal paralysis, or cognitive difficulties.

Diagnosis

• History of possible exposure to the ticks that can carry Powassan virus

Diagnostic Testing

• Preliminary diagnosis is based on the patient’s clinical signs and symptoms, location where infection likely occurred (including places and dates of travel), and activities leading to risk of possible exposure to Ixodes species ticks.

Antibody Testing

• Laboratory diagnosis is generally accomplished by testing of serum or cerebrospinal fluid (CSF) to detect Powassan virus-specific IgM and neutralizing antibodies.
• Immunoassays for Powassan virus IgM antibodies are available commercially and through state public health laboratories and CDC.
• Initial serological testing is performed using IgM capture enzyme-linked immunosorbent assay (ELISA).
• A positive Powassan virus IgM antibody test result should be confirmed by neutralizing antibody testing (plaque-reduction neutralization test [PRNT]) of serum specimens at a state public health laboratory or CDC.

Other Testing

• Molecular tests to detect viral RNA (e.g., reverse transcription-polymerase chain reaction [RT-PCR]) can be performed on serum, CSF, and tissue specimens that are collected early in the course of illness and, if positive, can confirm an infection.
• Immunohistochemistry (IHC) can detect Powassan virus antigen in formalin-fixed tissue. Negative results of these tests do not rule out Powassan virus infection.
• RT-PCR and IHC is performed at CDC and some state public health or reference laboratories.

Treatment

• There is no specific treatment for Powassan virus disease; clinical management is supportive.
• Patients with severe meningeal symptoms often require pain control for headaches and antiemetic therapy and rehydration for associated nausea and vomiting.
• Patients with encephalitis require close monitoring for the development of elevated intracranial pressure, seizures, and inability to protect their airway.

Transmission

• White-footed mouse
• White-footed mice can infect blacklegged ticks with Powassan virus.
• Blacklegged ticks often bite people.

• Powassan virus is spread to people by the bite of an infected tick.
• Ticks become infected when they feed on groundhogs, squirrels, mice, or other rodents that have the virus in their blood.
• Infected ticks can then spread Powassan virus to people and other animals by biting them.
• People do not develop high enough levels of the virus in their blood to infect biting ticks.
• As a result, people are considered “dead-end” hosts for Powassan virus.

Types of ticks

• Three types of ticks spread Powassan virus and are primarily found in the eastern half of the United States.

• Ixodes cookei (groundhog tick)
• Ixodes marxi (squirrel tick), and
• Ixodes scapularis (blacklegged or deer tick)
• The groundhog tick and the squirrel tick rarely bite people. The blacklegged, or deer tick, which feeds mainly on white-footed mice and deer, often bites people. These bites can result in several types of diseases (e.g., Lyme disease).

• Ticks can attach to any part of the body but are often found in hard-to-see areas such as the groin, armpits, and scalp.

Prevention

Prevent getting sick with Powassan virus by preventing tick bites.

External links

• Center for Disease Control (CDC): Preventing Ticks on Your Pets

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