Disease trackers in Massachusetts and Maine are investigating two apparent cases of a rare and severe tick-borne illness, providing new evidence of the suffering that can be inflicted by ticks and prompting warnings that the threat can persist into December.
Investigators suspect that the infections were caused by Powassan virus or a related virus, which can spawn headaches, vomiting, confusion, seizures, memory loss, and long-term neurological problems in those who survive the infection. The virus is believed to be fatal in 10 to 15 percent of those who are exposed.
Blood tests show that a Maine woman who died last week was infected with the virus. Health officials said it appears the woman, from mid-coast Maine, had not been traveling and probably was infected locally.
Massachusetts health authorities are investigating a suspected Powassan infection in a resident who became ill in October. Dr. Catherine Brown, state public health veterinarian, declined to identify the patient, or the county where the person lives, to protect confidentiality, but said the person survived.
Brown said the Massachusetts and Maine cases should serve as reminders to residents to continue checking themselves for ticks and tick bites, even during the winter.
Yet there are aspects of the recent cases that remain mysterious to investigators — most prominently, the type of tick responsible for the infections.
Powassan typically is spread by the woodchuck tick, but disease investigators are concerned that the more common deer tick may be the culprit in the Maine and Massachusetts cases, raising concerns because deer ticks are prevalent throughout the Northeast, already inflicting widespread misery as the major carrier of Lyme disease.
Sam Telford III, an infectious disease professor and tick specialist at the Cummings School of Veterinary Medicine at Tufts University, published a study in 1997 that identified a virus in Massachusetts ticks similar to Powassan, but spread by deer ticks. He called it deer tick virus.
Telford and colleagues then hunted for Massachusetts residents infected with that virus, but could not find any, and concluded it was perhaps not a risk to humans.
But about five years ago, another published study identified the case of a New York resident who died from a deer tick virus similar to Powassan.
Since then, health officials have been on the lookout for this Powassan-like variant spread by deer ticks. The hunt comes amid increasing reports of patients in several states, notably New Hampshire, New York, Minnesota, and Wisconsin, infected with Powassan virus. Roughly 50 cases of the virus have been reported to the US Centers for Disease Control and Prevention in the past decade. There is no treatment for the disease.
Maine’s last confirmed Powassan case was in 2004, but Dr. Sheila Pinette, director of Maine’s Center for Disease Control and Prevention, said state health officials were watching for the illness because of a reported case in New Hampshire in August.
She said Maine health care providers are not required to report suspected Powassan to the state, a rule that is likely to be changed to better track the illness. “If we know we have one, we recognize we may have others,” Pinette said, “so we need to track it to understand the prevalence and if it’s increasing in our state.”
A new rule in Massachusetts that became effective last week requires health care providers to report suspected Powassan cases to the Department of Public Health, Brown said.
“It’s not something that’s been on people’s radar, but we know that there is increasing awareness these days of diseases that could be introduced here,” she said.
The state had no documented Powassan cases in the past decade, but anecdotal reports suggest there may have been a handful in that period, she said.
Current testing methods to confirm Powassan illness, which look for signs of the virus in patients’ blood or spinal fluid, cannot distinguish whether the disease was caused by deer ticks or woodchuck ticks, Telford said. Consequently, researchers believe that some, if not many, of the reported Powassan cases have actually been deer tick virus, caused by the more common deer tick.
The only way to distinguish the two illnesses, he said, is to obtain tissue samples from a patient, then grow samples of the virus from that tissue and study the genetic components of that material.
Telford said he is expecting to receive tissue samples from the Maine patient to determine whether she died from Powassan, or from deer tick virus.
“I suspect it’s deer tick virus because there are no woodchuck ticks out this time of year,” he said. Woodchuck ticks are typically active from April through September, he said, but deer ticks are much hardier and known to be active into the winter.
Brown, the Massachusetts public health veterinarian, agrees. “We know that the adult deer ticks can be out and active if temperatures are above freezing,” she said.Kay Lazar can be reached at Kay.Lazar@globe.com Follow her on Twitter @GlobeKayLazar.