Powassan virus causes a rare, but often serious disease, and is spread by the bite of tiny, infected black-legged (deer) ticks. There are two types of Powassan virus in the United States. One type is found in ticks that normally feed on woodchucks (groundhogs); the second type is carried by black-legged ticks, the same ticks that can also carry the germs that cause Lyme disease, babesiosis and anaplasmosis.
Although approximately 100 cases of Powassan infection have been reported in the last 10 years in the United States, most of those cases have occurred in the Northeast and the Upper Midwest. There have been 16 cases of Powassan virus infection in Massachusetts in the last 10 years.
Powassan virus is spread by the bite of an infected tick. In Massachusetts, the black-legged tick is the type of tick most likely to carry this infection. While ticks must be attached for a certain length of time before they can spread most infections, there is some evidence that Powassan virus can spread from the tick into a person after only a short time of attachment.
Cases of Powassan virus disease can occur any time ticks are active. Young ticks (nymphs) are most active during the warm weather months between May and July. Adult ticks are most active during the fall and spring, but may also be out searching for a host any time that winter temperatures are above freezing.
Symptoms of disease usually begin between one week and one month after the bite of an infected tick.
Although most people who are exposed to Powassan virus likely never feel ill, others may become severely ill with meningitis (inflammation of the covering of the brain and spinal cord) or encephalitis (inflammation of the brain). Signs and symptoms include fever, headache, vomiting, weakness, confusion, loss of coordination, speech difficulties and seizures. Approximately 10% of people with this severe form of the disease will die and survivors may have long-term health problems.
There is no specific treatment once infection with Powassan virus has occurred. Treatment consists of supportive care, rest and fluids to prevent dehydration.