A blood parasite spread by deer ticks is on the rise across New England, and most of the existing treatments for it don’t work well in people who are immunocompromised.
But a researcher at the University of Vermont has isolated a few drugs he thinks could change that, and this summer secured a $150,000 grant from the Bay Area Lyme Foundation to test them in mice, in hopes of developing the first-ever therapy created specifically to treat the condition babesiosis.
“In the last decade, since we’ve been monitoring this, the incidence of babesiosis has actually increased 1,600%,” said Dr. Peter Hyson, who secured the grant. He’s a researcher and professor of infectious disease at the Larner School of Medicine.
Babesiosis is a blood infection caused by the parasite babesia microti. It’s spread to humans by ticks who get it from white-footed mice.
Once in the blood stream, the parasite makes its home inside its host’s red blood cells.
“They get nutrition from the contents of the red blood cells, and that’s also where they replicate,” Hyson said. “And when they replicate themselves, they actually burst out of the red blood cell, which effectively destroys it.”
Many people who contract the parasite clear the infection on their own, never having symptoms or getting a mild flu-like illness with a fever, fatigue, chills or night sweats.
But the infection can cause very severe illness and even death in infants, older people and people who are immunocompromised, especially those without a spleen. It can also make otherwise healthy people anemic if the parasite kills too many red blood cells.
Right now, Hyson says the standard treatment for babesiosis is to dose people with some combination of anti-malarial medication and standard antibiotics until a provider lands on a cocktail that kills the infection.
But often, those treatments don’t work for the people who need them most.
In severe cases, where patients are facing complications like pulmonary edema, multiple-organ failure or liver failure, doctors sometimes prescribe blood transfusions in an effort to manually reduce the number of infected cells in a patient’s bloodstream. But even that isn’t always effective.
“So you treat the person for babesiosis, and then the parasites come back. And sometimes this happens over and over again, and sometimes the parasites actually get resistant to the drugs we have. And my theory on this is that this is because the drugs we have really aren't very effective against the parasites.”
Hyson has isolated several compounds that disrupt the way the parasite creates new proteins, and he’s looking to test them on animals – a first step towards someday advancing them to the first-ever clinical trial for a babesiosis specific drug.
UVM is one of just a few institutions in the country where researchers are looking for a cure.
Babesiosis rates are on the rise in Vermont. Along with Lyme disease and anaplasmosis, it’s one of the top three most common tickborne illnesses in the state. Roughly 70% of babesiosis cases in Vermont occur in older people, who are more likely to get very sick, said Natalie Kwit, Vermont’s public health veterinarian.
“We had a very active tickborne illness year in 2025, where I think all of our top three reportable tickborne conditions saw the highest numbers ever reported,” said Kwit.
This year has also been an above average year for ticks in the state, and a banner year for tickborne illness nationwide.
“My hope is, as we do go on, there will be more and more tools available for preventing infections in humans, but also perhaps interventions at the tick environmental level, which there hasn't been many tools available yet,” Kwit said.
In the meantime, Hyson says rises in tickborne illness in New England are a perfect example of how climate change and development patterns are exposing humans to more disease.
“With babesiosis, we're seeing kind of the malaria of developed New England,” Hyson said. “It's just kind of the vector-borne disease that we've paved the way for.”
