Powassan Virus Encephalitis in Children: Two Infant Case Reports

Powassan virus encephalitis is a rare but serious tick-borne infection that can lead to severe neurologic disease. Although most reported cases occur in adults, Powassan virus in children has been documented, including infants who develop encephalitis after tick exposure. Although uncommon, Powassan virus infection can be life-threatening and has been associated with fatal encephalitis in the medical literature.

In this report, the authors describe Powassan virus infection in children involving two infants who developed Powassan virus encephalitis following tick exposure. The cases highlight two important concerns: Powassan virus can be transmitted rapidly after a tick bite, and infants may be exposed when ticks are unknowingly brought into the home by adults or pets.

Powassan virus encephalitis in two infants

The first case involved a 5-month-old infant hospitalized after two days of fever, vomiting, and facial twitching that progressed to seizures. Approximately two weeks before the illness began, a tick had been removed from the child’s forehead. Laboratory testing confirmed Powassan virus infection.

The second case involved a 2-month-old infant who presented with fever and increasing listlessness for one day.

According to the authors, the infant then developed “left-sided focal seizures (rhythmic left arm twitching, facial deviation to the left, and tongue thrusting with lip smacking).”

A tick had been removed from the infant’s arm roughly two weeks before hospitalization. The family suspected that the tick had been carried indoors after a walk outside by the father or the family dog. The tick was not engorged and likely had not fed for more than 24 hours.

READ MORE: Can Powassan virus cause encephalitis or other neurologic damage?

The infection was confirmed when testing showed a positive plaque reduction neutralization test (PRNT) in both serum and cerebrospinal fluid.

Powassan virus infection is notable for the severity of illness it can produce. The authors note that approximately half of patients may experience long-term neurologic complications including hemiplegia, muscle wasting, personality changes, and chronic headaches.

How infants may become exposed to infected ticks

Infants rarely spend time in tick-infested environments on their own. Instead, exposure often occurs when ticks are unknowingly brought into the home.

In these cases, the investigators believe the parents inadvertently carried ticks indoors after outdoor activities.

In one instance, the father had brushed multiple ticks off his clothing after walking in the woods and may have carried one into the home. In the second case, the father had been walking outdoors with the family dog, and the tick may have entered the house on either the parent or the pet.

These cases illustrate an important prevention message: tick exposure in children can occur even when they have not been outdoors.

Tick prevention measures for parents

Parents and caregivers can reduce the risk of tick exposure in children by following several preventive measures:

1. Protective outdoor clothing may limit skin exposure, but ticks may remain on clothing and detach indoors when body heat drops, such as after removing a jacket.
2. Tick checks should be performed more than once after outdoor exposure because ticks may crawl on the body before attaching.
3. Outdoor clothing can be treated with permethrin, which kills ticks on contact.
4. Dogs and other pets should be inspected for ticks after outdoor activity since they can carry ticks into the home.
5. Many pet tick preventives kill ticks only after attachment, although some collars containing permethrin or similar agents may repel ticks.

Editor’s Note: Although the authors did not discuss treatment of the two infants, both recovered from their infections.

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