Connecticut Reports its First Human Case of Powassan Virus

There are several tick-borne diseases that infect those living in the United States, the most common of which is Lyme disease, according to the Centers for Disease Control and Prevention (CDC). Now, another tick-borne disease is emerging in the United States and the effect appears to be quite debilitating.

In the most recent Morbidity and Mortality Weekly Report (MMWR), researchers described a case of a 5-month-old infant from Connecticut who was diagnosed with Powassan virus (POWV) in November of last year.

“Powassan virus is a tick-borne flavivirus that was first discovered in Ontario in 1956… It’s a relatively newly discovered virus, and so we don’t know exactly how prevalent it is in humans in the United States,” Holly Frost, MD, pediatrics physician scientist at the Marshfield Clinical Research Foundation, in Minocqua, Wisconsin, told Contagion^® at ID Week 2016.

The MMWR reports that from 2006 to 2015, an average of 7 cases of POWV were reported each year in the United States. Although the virus is mostly found in the Northeast region of the United States, some states outside of this area have been reporting their first cases. According to the study, “it is not known whether this represents spread of the virus within the local tick population, or increased testing and recognition of the virus as a cause of human disease.”

The Connecticut infant was a “previously healthy male” who presented with fever, vomiting, facial twitching, and seizures “that included rightward eye deviation and right arm stiffening.” According to the field notes, the infant was hospitalized for his seizures. The parents reported that a tick had bitten the infant 2 weeks prior to symptom onset, and that the tick was attached for less than 3 hours. This is important since, according to the CDC, a tick must be attached for 36 to 48 hours, and sometimes more, for it to transmit Lyme disease.

At the hospital, the patient underwent several tests, including a magnetic resonance imaging (MRI) scan of the brain. The MRI “showed a symmetric pattern of restricted diffusion (suggestive of cellular edema) involving the basal ganglia, rostral thalami, and left pulvinar, consistent with encephalitis.” The doctors treating the patient also performed a “white blood cell count in the cerebrospinal fluid (CSF), which was found to be 125/μL (81% lymphocytes) (reference range = 0—15 cells/μL).”

These and other clinical findings along with the reported tick bite, led the infectious disease specialist treating the infant to request the CDC to test for POWV. According to the MMWR, “The cerebrospinal fluid sample obtained on admission (4 days after illness onset) was positive for POWV immunoglobulin M, with a POWV-specific neutralizing antibody titer of 32.”

After receiving therapy to control his seizures, the infant was released from the hospital; nonetheless, one month after initial symptom onset, the parents reported that the child “could no longer sit up unaided, a milestone that he had met prior to the illness.” At 10 months old, the child regained motor and verbal abilities, such as “crawling, walking with a walker, and babbling;” however, “a second MRI performed 4 months after the first revealed gliosis and encephalomalacia in the thalami and basal ganglia bilaterally, with volume loss and evidence of early mineralization in the left basal ganglia.”

This is the first report of a POWV disease in Connecticut. The researchers believe that this “highlights the importance of considering POWV disease in persons with a clinically compatible illness and obtaining a comprehensive exposure history.” It is recommended that healthcare providers in areas known to be endemic for ticks, test patients who present with encephalitis for POWV disease.