Madison Area Lyme Support Group

Although the Powassan virus is considered to be a rare tick-borne illness, the number of cases is rising, and at an alarming rate. A recent survey found, a 4-fold rise in the number of Powassan virus cases in the US from 2014 to 2023 (compared with 2004 to 2013). [3]

This summer, a 9-year-old boy in Canada developed Powassan virus encephalitis, a life-threatening condition. In Pennsylvania, another young child was hospitalized with the virus. And, in April, an older man from Massachusetts was infected. Meanwhile, last year, a Maryland resident died from Powassan encephalitis after contracting it in Canada.

Powassan virus – transmitted in 15 minutes

The Powassan virus, which is transmitted through the bite of an infected blacklegged tick, can be deadly. And, most concerning, as cases are rising, the infection can be contracted within 15 minutes of a tick attachment.

The virus can cause fever, headache, vomiting, loss of coordination and memory and speech problems. It can also cause encephalitis (inflammation of the brain) and meningitis (inflammation of the membranes surrounding the brain and spinal cord.)

However, it often does not present with any symptoms, according to the CDC.

POWV encephalitis can be deadly

From 2004 to 2022, the US reported 288 cases of Powassan virus infection. Of these cases, 72 (25%) occurred in children, 264 patients (92%) required hospitalization, and 36 patients (13%) died.¹

Patients infected with the virus have a “10% risk of developing fatal encephalitis and up to 50% of infected patients have long-term neurologic damage.”²

Up to 50% of patients have long-term neurologic complications.

The prognosis for individuals with Powassan virus neuroinvasive disease is poor. The case fatality rate is 10%–15%, and survivors have about a 50% probability of persistent neurologic deficits, including headaches, altered mental status, and cognitive difficulties.¹

There is no treatment for the Powassan virus.

Case Report: 9-year-old boy

In July, a 9-year-old boy, residing in Canada, was hospitalized with Powassan encephalitis, after returning from a camping trip in northern Ontario.

Blatman and colleagues describe the case in their article, “Powassan virus encephalitis in a 9-year-old.”¹

The young boy was admitted to the hospital with a fever, neck stiffness and headache, which began 1 week after returning from his camping trip.

Initially, he was treated with ceftriaxone and vancomycin for suspected meningitis.

PCR testing of the CSF for viral causes of meningitis or encephalitis, however, was negative. Bacterial culture and Gram stain of the CSF sample was also negative. And, an MRI of the brain was unremarkable.

The patient had no known tick bites or rashes.

“Over the next 48 hours, blood cultures showed no growth,” the authors state. However, “The patient remained persistently febrile with ongoing severe headache.”

After 3 days in the hospital, the boy’s condition worsened and he was transferred to the ICU. At this point, he was nonverbal and nonresponsive to commands, according to the authors.

Testing for Lyme disease was negative.

“Tick-borne Powassan virus encephalitis is associated with high mortality and a risk of long-term neurologic sequelae in survivors.”

Repeat EEG showed generalized slowing of brain activity. Meanwhile, a repeat MRI of the patient’s brain and full spine showed subtle bilateral basal ganglia and substantia nigra.

However, CFS testing was negative for autoimmune encephalitis.

“Given concern for potential autoimmune encephalitis, the patient received intravenous immunoglobulin at a dosage of 1 g/ kg for 2 days, with notable improvement in his level of consciousness within 24–48 hour,” the authors state.

Within 2 months, the boy had made a complete recovery.

New research indicates that the Powassan virus may be more deadly in older patients. “… only minimal infectious doses of the virus were highly lethal in older mice and that lethality increased >10-fold with age,” states Mackow.²

“Increased awareness of Powassan virus among clinicians in Canada will likely lead to increased identification of Powassan virus and other arthropod-borne infections, which should always be reported,” the authors state.