Researchers discover novel bacteria linked to deadly fever in New England ticks (2025)

UMass Amherst researchers have discovered a new bacteria in Maine rabbit ticks linked to an infection that can be deadly for humans, the university announced Wednesday.

The researchers discovered the novel bacteria while testing ticks collected from the backyard of a Maine home for pathogens, UMass Amherst said in a press release. Though rabbit ticks can be found across North and South America, the scientists were surprised to encounter them at all, as they are uncommon in New England.

UMass Amherst microbiology Professor Guang Xu tested the ticks for bacteria that can cause Rocky Mountain spotted fever — which has a death rate of 20 to 30% when untreated — and discovered they were infected, the university said. The professor then sequenced the bacteria’s DNA and found that, though it was unlike any other strain previously identified, it was similar to one identified in California a few years ago that has caused severe cases of Rocky Mountain spotted fever.

The University of Maine soon sent Xu more ticks to test. He ultimately found that just over 6% of the nearly 300 rabbit ticks that were collected from nine Maine counties tested positive for the new bacteria, UMass Amherst said.

“This wasn’t a needle in a haystack. It looks like lots of the rabbit ticks there have this pathogen,” UMass Amherst microbiology Professor Stephen Rich said in the release.

Cases of Rocky Mountain spotted fever have climbed in recent years, from 495 in 2002 to a peak of 6,248 in 2017, though most of these cases occurred in the South and Midwest, according to UMass Amherst. Dog ticks are the usual vector for bacteria that can cause the infection, but despite the fact that the bacteria has yet to be found in New England dog ticks, the region has still had a few cases of Rocky Mountain spotted fever.

“It was a mystery. Why are there some cases of Rocky Mountain spotted fever in New England?” Xu said in the release. “This finding may solve part of the puzzle. Maybe the rabbit ticks are the vector.”

Rabbit ticks typically don’t feed on humans, but there are other ticks common in New England that feed on both rabbits and humans, Rich explained in the release. The researchers posit that the rabbit ticks may be infecting the rabbits, who then pass the bacteria on when a different tick feeds on them, and that that tick could then infect a human when it feeds on them.

Rich plans to collaborate with rabbit hunters in Massachusetts to collect more rabbit ticks from the region, UMass Amherst said. The hope is that this will advance scientists’ understanding of the bacteria’s impact on public health.

“While these rabbit ticks don’t feed on people very often, there’s a possibility that they could spill over into systems where people could get exposed. We’re interested in figuring out the nature of this environmental risk,” Rich said in the release.