Lyme isn't the only tick-borne disease to worry about in the Northeast, says the C.D.C

Babesiosis, which can cause flu-like symptoms, could spread due to rising temperatures and a growing deer population.

Cases of a tick-borne disease called babesiosis more than doubled in some northeastern states between 2011 and 2019, Centers researchers reported Thursday. for Disease Control and Prevention.

Although many people with babesiosis are asymptomatic, others develop flu-like symptoms, including fever, chills, sweating and muscle aches. The disease can be serious and even fatal in people with weakened immune systems or other risk factors.

The disease, which for decades was extremely rare in the United States, is now endemic in 10 states in the Northeast and Midwest, the agency said. The increase may have been fueled by rising temperatures and a growing deer population, two factors that help ticks thrive, experts said.

"I think it's an unfortunate step," said Dr. Peter Krause, a babesiosis expert at the Yale School of Public Health, who was not involved in the study.

Babesiosis is caused by parasites that are usually made at home in mice and other rodents. Poppyseed-sized blacklegged ticks, also known as deer ticks and capable of transmitting Lyme disease, can transmit the disease to humans after feeding on infected mice.

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The first person known to be infected in the United States was reported in 1969 in Massachusetts. Today, most cases occur in the northeast and upper Midwest in the spring and summer. (The parasite can also be transmitted through blood transfusions, and the Food and Drug Administration recommends screening blood donations in some states.)

In the new study, the researchers analyzed 16,174 babesiosis cases reported in 10 states between 2011 and 2019. In 2019 alone, there were more than 2,300 cases, more than double the number in 2011. The disease was most common in New York, in Massachusetts and Connecticut, which typically had hundreds of cases per year.

But there were regional differences in trends. In two Midwestern states, Minnesota and Wisconsin, the number of annual cases has remained relatively stable. In contrast, in eight northeastern states, the number of cases increased significantly during this period, with the largest increases recorded in Vermont, Maine, New Hampshire and Connecticut.

< p class="css-at9mc1 evys1bk0">In three of these states - Maine, New Hampshire and Vermont - babesiosis was not previously considered endemic.

The increases in those states are particularly notable, said Edouard Vannier, a babesiosis expert at Tufts Medical Center in Boston who was not involved in the new study.

" The disease is spreading north," he said. "And that's probably due to climate change."

Ticks, which prefer warm, humid conditions, have indeed expanded their territory north. The findings underscore the need for expanded surveillance and screening for the disease, Dr. Vannier said.

A growing deer population could also fuel the rise in babesiosis. Although deer do not carry the parasites that cause babesiosis, they are the preferred food source for adult ticks.

"This greatly amplifies the number of ticks" , said Dr. Krause. . "A lot more survive, a lot more females lay eggs."

Building new housing in areas where ticks are present could also play a role, a- he added, because it could increase awareness, which could prompt more doctors to test patients for the disease.