Massachusetts has not had any reported cases of Bourbon virus, a rare, incurable tick-borne disease discovered in 2014 that killed a Missouri woman last month.
But the state is seeing an increase in the number of people contracting Powassan virus, another serious illness transmitted by the black-legged or deer tick, commonly thought of as a carrier of Lyme disease.
Powassan virus is more dangerous than Lyme, which is a bacterial disease that can be treated successfully with antibiotics if caught early.
There is, however, no treatment for Powassan virus.
The disease is also transmitted by the groundhog, or woodchuck, tick. Symptoms include headache, fever, vomiting, weakness, confusion, memory loss, seizures and long-term neurological problems. The most dangerous form of the illness can lead to encephalitis, meningitis and death.
The virus was first diagnosed in 1958 in Powassan, Ontario, in a 5-year-old boy who died from encephalitis. The first case reported in the U.S. was in a New Jersey woman in 1972. It was 2005 when the Centers for Disease Control and Prevention required clinicians to report cases of Powassan to the CDC via state health departments.
Between 2006 and 2015, the CDC received reports of 68 cases of neuroinvasive Powassan, mostly in Wisconsin, Minnesota, New York and Massachusetts. Eight of those cases resulted in death.
Since 2013, 15 cases of the potentially deadly virus, including two this year, have been reported in Massachusetts, according to the state Department of Public Health. The DPH said the Powassan cases were reported in Barnstable, Essex, Middlesex and Norfolk counties. They did not say if any of the cases were fatal.
Sam R. Telford III, an expert on tick-borne diseases and a professor in the department of infectious diseases and global health at the Cummings School of Veterinary Medicine at Tufts University in Grafton, said Bourbon virus and other tick-borne illnesses found in other parts of the country should not be a concern for residents of Massachusetts, although they may be a problem in the future.
Ticks that carry Bourbon virus have been found in the southern part of the state – including Cape Cod and some of the islands – and they are slowly creeping farther north. Since they are new in the state, it could be several years before they actually carry the virus, he said.
“Ten years from now, sure,” Mr. Telford said about when ticks may carry Bourbon virus. “That’s all the more reason to manage our deer better.”
“There are undoubtedly things we don’t know about yet and people like me – virus hunters – are hunting strongly for,” he said. People don’t realize that there are well over a dozen different infectious transmitters and we only look for a third or half of them routinely,” he said.
One of the problems, he said, is the rising population of deer, a main blood meal source for ticks and mosquitoes needed by them to reproduce. Every deer has as many as 300 ticks that feed on it before they drop off into vegetation to lay as many as 2,000 eggs each.
Mr. Telford said hunting in Central Massachusetts has kept the deer population in line. But the dying sport and less hunting in the eastern part of the state has led to an overpopulation of deer.
“We’re not saying that deer should be extinct. We’re saying make it more like what your grandfather saw in New England when it was a treat to see a deer. Now, we see so many deer that when you see one, it’s like ‘so what?’ “
On the other hand, Mr. Telford, who has helped discover some tick-borne diseases, said the number of Lyme cases might not be as high this year as some had predicted. Pest control experts who began seeing ticks in early February attributed the prediction to a warm winter and an abundance of acorns that caused a hardy population of white-footed mice that carry Lyme. When ticks in the nymph stage attach to the carrier they become infected and pass the infection on to humans and other animals.
Mr. Telford said the abundance of rain in the past two months could work in a number of ways to influence the final Lyme disease case count. Fewer people spend significant amount of time outside when it rains. And ticks don’t look for hosts in the rain. With the relatively cool summer so far, and the rain, the nymphal deer ticks – more likely to go unnoticed on a person because of their size – could last longer.
“I and others believe that if we see a typical July (warm and very dry), the nymphal ticks will disappear because the dryness kills them,” Mr. Telford said.
He emphasized that the best way to stay free of tick- and mosquito-borne disease is to prevent bites. Recommendations include avoiding areas with tall, thick vegetation, walking in the center of trails when hiking, and using a repellent that contains 20 percent or more DEET on exposed skin.
“One of the things that would really help is having kids grow up reaching for the repellent as they reach for the bicycle helmet to go outside,” Mr. Telford said.