Babesiosis, a tick-borne disease that can be deadly in rare cases, is becoming more common in the Northeast, according to a report released Thursday by the Centers for Disease Control and Prevention.
The findings show that of the 10 states that reported babesiosis cases from 2011 to 2019, eight saw their numbers rise, while only two – Minnesota and Wisconsin – saw a decline.
In addition, 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.
Showing nine years of data [an] increase in tick-borne diseases in parts of the U.S. that previously had few cases,” said Megan Swanson, an epidemiologist in the CDC’s Division of Parasitic Diseases and Malaria, who co-authored the report.
Symptoms of babesiosis include fever, chills, sweating, headache, 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 researcher at the Yale School of Public Health, who was not involved in the CDC study.
Up to 20% of cases in adults and 50% of cases in children are asymptomatic. Older or immunocompromised people are most vulnerable to serious consequences such as low platelet counts, kidney failure or acute respiratory distress syndrome, where 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 means more disease, and some people are even dying.”
Babesiosis can be more serious than Lyme disease
Humans get babesiosis largely from deer ticks, whose bites can be transmitted Babesia parasites that infect red blood cells.
Most transmission occurs from late May to early September. Researchers think that if climate change brings longer periods of humidity, it will make for more hospitable environments for ticks.
“The ticks survive better in the winter, so next spring you have more ticks to bite more people,” said Edouard Vannier, an assistant professor who studies babesiosis at Tufts Medical Center and was not involved in the report.
The new data shows that between 2011 and 2019, babesiosis cases increased 17 times in Vermont and more than 34 times in Maine.
Babesiosis can sometimes be confused with Lyme disease, another tick-borne illness that causes fever and muscle aches. While Lyme disease has a defining feature — a rash at the site of the tick bite — Krause said there’s no clear symptom of babesiosis. It is usually diagnosed through a blood test.
“Sometimes the patient just feels fatigued and not quite right, maybe a low temperature for a week or two, and then all of a sudden they get worse,” Krause said. “That’s usually not the case with Lyme — you get it and then, bingo, you have a rash and so on.”
Babesiosis is usually more serious than Lyme disease, although Lyme is much more common. The CDC records about 30,000 cases of Lyme disease each year, while a total of about 16,500 cases of babesiosis were recorded between 2011 and 2019.
People can get both diseases at the same time, Vannier said. He estimated that about half of people with babesiosis also have Lyme disease.
An increase in tick-borne diseases
Scientists identified the first human babesiosis case in the US in 1969. Its increasing prevalence coincided with a general increase in tick-borne diseases, which increased by 25% between 2011 and 2019. %.
Researchers attribute the trend to a number of factors. First, deer populations have expanded, giving ticks more opportunities to feed and reproduce. People are also increasingly traveling to and building homes in wooded areas.
In addition, rising global temperatures have led to longer summers and shorter winters, and ticks thrive in warm, humid climates.
Krause also noted that older people have become a larger portion of the population, and they are more vulnerable to severe babesiosis, making them more likely to receive an official diagnosis.
“It’s usually the more serious cases, the ones that get to the hospital, that get reported,” he said.
The CDC report recommended that people who spend time outdoors in states where babesiosis is endemic wear long pants, use tick repellent, and avoid undergrowth and long grass.
Researchers said babesiosis is likely more common than the CDC count suggests given asymptomatic infections and that not all physicians 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 — up to 20% — in people who have HIV/AIDS or serious cancer with chemotherapy, or individuals who don’t have a spleen,” Krause said.