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Babesiosis is an infectious tick-borne disease that comes from protozoa, which are microorganisms. There are over 100 species of Babesia, common in animals like deer, mice, horses, cats, and dogs. Only two strains of Babesia are known to infect humans. Recently, cases of babesiosis have more than doubled in some Northeastern states between 2011 and 2019. Many people who develop babesiosis are asymptomatic, while others experience flu-like symptoms (chills, sweats, and muscle aches). People with compromised immune systems or other risk factors are at risk of having severe or fatal cases. The disease was rare for decades in the United States but is now endemic in 10 states in the Northeast and the Midwest. Experts are trying to determine why cases are climbing.