Feder et al.
Powassan virus encephalitis following brief attachment of Connecticut deer ticks.
Clin Infect Dis. 2021;73(7): e2350-4. doi:10.1093/cid/ciaa1183

Powassan virus (POW virus) is a flavivirus belonging to the tick-borne encephalitis complex and has been reported from North America (New England States and Midwestern USA) and Eastern Russia (see also Snapshot week 25/2021). POW virus can cause severe encephalitis with a case-fatality rate of about 10%, and long-term sequelae are common in survivors (approx. 50%).

Recently, two POW virus encephalitis cases have been reported in infants indicating that the virus can be quickly transmitted following a tick bite.

Case 1
Two weeks before a 5-month-old male was hospitalized, a deer tick had been found on the body of the infant and the infant’s father had been outside hunting in the Connecticut woods, and while outside, he had brushed multiple ticks off clothing. The infant’s mother was convinced that the tick was attached for no more than three hours. POW virus infection was diagnosed by IgM ELISA testing and by a specific neutralization test. The infant was severely ill, but by the age of 15 months, the patient’s growth and development became normal.

Case 2
13 days before hospitalization, a tick had been removed from the body of a 2-month-old male child. The tick was found not more than six hours after the child’s bath. The family thought most likely that either the father or the dog had brought the tick into the house following a walk. As in case 1, this infant was severely ill and infection by POW virus was verified by positive IgM ELISA and neutralization test. In the tick removed from the infant, POW virus could be detected by RT-PCR.

POW virus – like TBE virus – invades tick salivary glands very rapidly after infection and persists there in unfed ticks for at least 120 days. Both reported cases appear to have been rapidly infected by the bite of infected deer ticks. The authors suggest that parents should be educated about the need to treat outdoor clothing with permethrin, about the possibility that dogs could bring ticks into homes, and that these animals should be inspected after every outdoor exposure.

In this context, one may also take notice of:
Hassett EM, Thangamani S. Ecology of Powassan Virus in the United States. Microorganisms. 2021;9(11):2317. https://doi.org/10.3390/microorganisms9112317

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