Powassan Encephalitis: Young Boy Develops It After Camping Trip

Powassan encephalitis can be transmitted within 15 minutes of tick attachment and carries a 10-15% fatality rate with up to 50% of survivors experiencing long-term neurologic damage. A 9-year-old boy developed life-threatening Powassan encephalitis one week after returning from a camping trip in northern Ontario, presenting with fever, neck stiffness, and severe headache that rapidly progressed to nonverbal unresponsiveness requiring ICU transfer. With no treatment available for Powassan virus and cases rising across North America, this tick-borne infection represents an emerging threat that can progress from initial symptoms to critical illness within days, emphasizing why tick prevention during outdoor activities is essential.

For an overview, see Powassan virus.

Rising Cases Across North America

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.

The geographic spread and increasing frequency of cases indicate Powassan virus is an emerging threat, not a rare curiosity. Cases are being reported across the northeastern United States and Canada, wherever blacklegged ticks are found.

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.

This 15-minute transmission timeline is critical. Lyme disease typically requires 24-48 hours of tick attachment for transmission, giving time for tick checks and removal to prevent infection. Powassan virus has no such grace period — by the time you find and remove the tick, transmission may have already occurred.

Symptoms and Neurologic Complications

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.

This asymptomatic presentation is particularly concerning. Many infected individuals never know they had Powassan virus, but those who develop neuroinvasive disease face devastating complications. The unpredictability — most have no symptoms, some develop fatal encephalitis — makes it impossible to predict outcomes.

Powassan 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.

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.”

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.

These statistics are sobering. A 10-15% chance of death and 50% chance of permanent neurologic damage means most patients with neuroinvasive Powassan disease will either die or have lifelong disability. Unlike Lyme disease, which is treatable with antibiotics, there is no treatment for Powassan virus.

No Treatment Available

There is no treatment for the Powassan virus.

This bears repeating: there is no antiviral medication, no immunotherapy, no cure. Treatment is purely supportive — IV fluids, respiratory support, seizure management, monitoring. Doctors can only support patients through the acute illness and hope their immune system clears the virus before irreversible brain damage occurs.

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.”

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.

The one-week incubation period is typical for Powassan virus. Symptoms appear 7-10 days after tick bite, initially resembling viral meningitis or other infections.

Initial Treatment for Presumed Bacterial Meningitis

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.”

Rapid Deterioration to ICU

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.”

Diagnostic Findings

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, CSF testing was negative for autoimmune encephalitis.

Treatment Attempt With IVIG

“Given concern for potential autoimmune encephalitis, the patient received intravenous immunoglobulin…”

Age and Mortality Risk

New research indicates that the Powassan virus may be more deadly in older patients…

The Need for Clinical Awareness

“Increased awareness of Powassan virus…”

Clinical Perspective

This case highlights the diagnostic challenges and clinical urgency of Powassan encephalitis in children…

Frequently Asked Questions

---

Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention