Experts warn of increases in tick-borne Powassan virus
Summer is nearly here, and it’s bringing fears of a rare tick-borne disease called Powassan. This potentially life-threatening virus is carried and transmitted by three types of ticks, including the deer tick that transmits Lyme disease.
Over the past decade, 75 cases have been reported in the northeastern states and the Great Lakes region, according to the US Centers for Disease Control and Prevention. Though no one can say how many infections will occur this year, warmer winters have led to an increased tick population, so experts predict rising tick-borne infections of many types.
Everyone is at risk for Powassan: Newborns, 20-somethings, the middle-aged, the elderly and the immunocompromised. Anyone bitten by an infected tick can get it, said Dr. Jennifer Lyons, chief of the Division of Neurological Infections and Inflammatory Diseases at Brigham and Women’s Hospital in Boston. Infections are most likely during late spring, early summer and mid-fall, when ticks are most active.
“About 15% of patients who are infected and have symptoms are not going survive,” said Lyons, who is also an assistant professor of neurology at Harvard Medical School. “Of the survivors, at least 50% will have long-term neurological damage that is not going to resolve.”
Although most infected people will never show symptoms, those who do become sick usually do so a few days to about a week after the tick bite, she said. The most common symptoms will be fever and headache.
“You basically feel nonspecific flu-like stuff,” Lyons said, including “muscle aches and pains; maybe you have a little rash on your skin, but almost certainly, you’ll have a fever and the headache.”
The unlucky few who develop a more serious illness will do so “very quickly over the next couple of days,” she said. “You start to develop difficulties with maintaining your consciousness and your cognition. … You may develop seizures. You may develop inability to breathe on your own.”
Just as there are no vaccines to prevent infection, there are also no treatments for Powassan.
“There are some experimental therapies we try when somebody comes in and they get here early enough and we get the therapy started early enough, but we have no idea if any of that works,” Lyons said.
Standard treatment includes intravenous fluids, though antiviral medications, systemic corticosteroids and other drugs have been tried in some patients.
Scientists also believe Powassan is on the rise based on studies that have identified an increasing number of infections in deer.
“So it does seem that there are more and more deer that they’re finding that have been infected with this virus,” Lyons said. “So we should expect it to increase in human disease incidence over the next few years.”
Similarly, Lyme is showing increasing numbers.
According to a recent tick summary report (PDF), 19% of deer ticks received and tested by the Connecticut Agricultural Experiment Station, a state-owned research facility, in 2012 were found to be infected with Lyme disease, and 29% of the deer ticks tested positive for the virus in 2016.
A bad tick season ahead
Goudarz Molaei, a research scientist at the Connecticut Agricultural Experiment Station, is predicting more new Lyme disease infections in the coming months due to larger numbers of ticks and higher infection rates among them. Each year, there are nearly 30,000 confirmed cases of Lyme disease across the United States, according to the CDC, though with unconfirmed cases, the total may be as high as 300,000.
Historically, in the winter, the station doesn’t receive many ticks for testing, he explained: one or two per month, maybe five at the most.
“This year so far, we’ve received hundreds of ticks,” Molaei said. “Since April 1, we’ve received nearly 1,000 ticks.” This greater abundance comes as a result of two consecutive warm winters, which the insects are better able to survive, and longer springs and summers.
Overall, 38% of these ticks have tested positive for Lyme disease, he said.
“In one day, 50% of ticks were infected,” he said. Peak season should be occurring around June or July.
“To make the matter more complicated, we are seeing greater number of ticks infected with other tick-associated pathogens, including babesiosis and anaplasmosis,” Molaei said. Both babesiosis and anaplasmosis usually don’t have symptoms, just like Powassan, though both may cause severe or even life-threatening illnesses.
“With ticks, it is no longer just Lyme disease,” Molaei said.
Prevention is the first step
The Powassan virus was first discovered in Ontario in 1958.
“A kid came down with an unspecified encephalitis,” or brain inflammation, Lyons explained. When the never-seen-before virus was identified, the scientists called it Powassan after the town where the child lived.
Only a couple of cases were seen each year from the 1950s to the early 2000s, when reports of cases in Canada and the US started to rise. A paper suggested that the virus might have been found in far eastern Russia as well.
Dr. Daniel Pastula, an assistant professor of neurology, medicine (infectious diseases) and epidemiology at University of Colorado Denver and Colorado School of Public Health, explains that of the three ticks that can carry Powassan — Ixodes cookei, Ixodes marxi and Ixodes scapularis — the third “likes to bite humans” the most.
Commonly known as a deer tick, Ixodes scapularis can also bite mice, Pastula explained.
“The thought is maybe that is where it gets Powassan from,” he said. The virus may enter the cycle between ticks and small and medium-size forest rodents that live up in the Great Lakes and Northeast, and “humans just happen to be occasionally involved in that cycle.”
“Unless you’re an entomologist, it’s very hard to identify ticks. They’re kind of small,” he said.
“The best thing people can do if they’re worried about Powassan or any other tick-borne virus is to prevent against all tick bites,” Pastula said.
This is best done by avoiding high brushy areas whenever you’re in the woods, wearing long sleeves and pants when feasible, using insect repellent and doing tick checks after being outdoors, he said.
“It has to be insect repellent that is actually shown to work. Things with DEET or picaridin or IR3535 are the recommended ones, according to the EPA and the CDC,” Pastula said.
“Essentially, you don’t need to worry about Powassan if you don’t get bit by a tick,” he said.