The northeastern states have reportedly seen cases of a tick-borne disease, called babesiosis, more than double in the past eight years.

The findings were reported on Thursday by researchers from the Centers for Disease Control and Prevention (CDC).

Babesiosis is caused by parasites that generally infect mice and other rodents. Called deer ticks or black-legged ticks, these insects can transmit Lyme disease and also spread babesiosis to humans after feasting on infected mice.

Babesiosis usually manifests as an asymptomatic condition in people, but some do develop flu-like symptoms, including fevers, chills, sweats, and muscle aches. The disease can turn fatal in people with compromised immune systems or other risk factors.

Unfortunately, the disease, which was considered extremely rare in the United States for decades, is now endemic in 10 states in the northeast and the midwest, as per the agency.

Experts suspect the increase may be driven by rising temperatures and the growing population of deer. The ticks thrive in warm, wet conditions.

“I think this is an unfortunate milestone,” said Dr. Peter Krause, a babesiosis expert at the Yale School of Public Health, who was not involved in the study, the New York Times reported.

In the study, more than 16,000 babesiosis cases reported in 10 states between 2011 and 2019 were analyzed. It was found that in 2019, the states witnessed more than 2,300 cases, which was more than twice the cases reported in 2011.

In two midwestern states--Minnesota and Wisconsin--the number of annual cases remained more or less constant, the study found. On the flip side, in eight northeastern states, the number of cases increased dramatically over the same time period. The most increase was seen in Vermont, Maine, New Hampshire, and Connecticut.

Concerningly, In three of the highest scoring states--Maine, New Hampshire, and Vermont--babesiosis was not considered an endemic before this study.

“The disease is going north,” said Edouard Vannier, a babesiosis expert at Tufts Medical Center in Boston who was not involved in the new study, as per the outlet. “And it’s probably due to climate change.”

Moreover, a growing deer population is also being blamed for the rise in babesiosis. Deer are not carriers of the parasites that cause babesiosis, but they are the preferred food source for adult ticks.

“That greatly amplifies the number of ticks,” Dr. Krause said. “A lot more survive, a lot more females lay eggs.”

It remains unclear why the midwestern states do have the same pattern of rising cases. “I don’t have an explanation for it,” Dr. Vannier said.

Treatment of babesiosis consists of antimicrobial drugs. The disease can be prevented by eschewing tall grass and underbrush, and protecting oneself by wearing long pants and tick repellent, especially in areas where the disease is endemic.