Babesiosis, a tick-borne disease that can be fatal in rare cases, is becoming more prevalent in the Northeast, the Centers for Disease Control and Prevention said in a report released on Thursday.

The findings show that among the 10 states that reported babesiosis cases between 2011 and 2019, eight saw their numbers increase, while only two, Minnesota and Wisconsin, saw decreases.

Additionally, babesiosis is now considered endemic in three new states: Maine, New Hampshire, and Vermont. Previously, the disease was considered endemic only in Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, and Wisconsin.

«Nine years of data show [an] increase in tick-borne diseases in parts of the US that previously had few cases,» said Megan Swanson, an epidemiologist in CDC’s Division of Parasitic Diseases and Malaria, a co-author of the report.

Symptoms of babesiosis include fever, chills, sweating, headaches, body aches, nausea, fatigue, or muscle and joint pain. The disease has an overall mortality rate of about 1% to 2%, according to Dr. Peter Krause, a senior research scientist at the Yale School of Public Health, who was not involved in the CDC study.

Up to 20% of adult cases and 50% of pediatric cases are asymptomatic. Older or immunocompromised people are more vulnerable to serious outcomes such as low platelet counts, kidney failure, or acute respiratory distress syndrome, in which fluid builds up in the lungs.

The report highlights «an unfortunate milestone in the rise of babesiosis in the United States,» Krause said. “More cases mean more disease, and in fact, some people die.”

Babesiosis may be more serious than Lyme disease

Humans acquire babesiosis largely from deer ticks, whose bites can transmit babesia parasites that infect red blood cells.

Most of the transmission occurs from late May to early September. The researchers believe that as climate change brings longer periods of wetness, it creates more hospitable environments for ticks.

«Ticks survive better in the winter, so next spring there will be more ticks to bite more people,» said Edouard Vannier, an assistant professor who studies babesiosis at Tufts Medical Center in Boston and was not involved in the report. .

The new data shows that the number of babesiosis cases increased 17-fold in Vermont and more than 34-fold in Maine between 2011 and 2019.

Babesiosis can sometimes be confused with Lyme disease, another tick-borne disease that causes fever and muscle aches. While Lyme disease has one defining feature, a rash at the site of the tick bite, Krause said there’s no obvious symptom of babesiosis. It is usually diagnosed through a blood test.

«Sometimes the patient will have been feeling fatigued and not quite right, maybe with a low temperature for a week or two, and then all of a sudden it’s worse,» Krause said. «That’s not usually the case with Lyme — you get it and then, bingo, you get the rash and so on.»

Babesiosis tends to be more serious than Lyme disease, although Lyme disease is much more common. The CDC records about 30,000 cases of Lyme disease each year, while between 2011 and 2019 there were about 16,500 total cases of babesiosis.

People can get both diseases at the same time, Vannier said. He estimated that half the people with babesiosis also have Lyme disease.

An increase in tick-borne diseases

Scientists identified the first human case of babesiosis in the US in 1969. Its increasing prevalence has coincided with a general increase in tick-borne diseases, which pink by 25% from 2011 to 2019. From 1999 to 2019, confirmed cases of Lyme disease pink by 44%.

The researchers attribute the trend to a few factors. For one thing, deer populations have expanded, giving ticks more opportunities to feed and reproduce. People are also increasingly traveling to forested areas and building their homes.

On top of that, rising global temperatures have resulted in longer summers and shorter wintersand ticks thrive in hot, humid climates.

Krause also noted that older people have come to represent a larger portion of the population, saying they are more vulnerable to severe babesiosis and therefore more likely to receive an official diagnosis.

“It tends to be the most serious cases, the ones that are admitted to the hospital, the ones that are reported,” he said.

The CDC report recommended that people who spend time outdoors in babesiosis-endemic states wear long pants, use tick repellent, and avoid brush and long grass.

The researchers said babesiosis is probably more common than the CDC count suggests, taking into account asymptomatic infections and because not all doctors report cases to state health departments and not all states report cases. to the CDC.

“Babesia is a much bigger problem than the general public recognizes and can be fatal, in up to 20%, in people who have HIV/AIDS or severe cancer with chemotherapy or people who don’t have a spleen,” Krause said.