Babesiosis, a tick-borne disease that can be fatal in rare cases, is becoming more prevalent in the Northeast, according to a report released Thursday by the Centers for Disease Control and Prevention.
The results show that of the 10 states that reported babesiosis cases from 2011 to 2019, eight saw their numbers increase, while only two – Minnesota and Wisconsin – saw declines.
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 United States that previously had few cases,” said Megan Swanson, epidemiologist in the CDC’s Division of Parasitic Diseases and Malaria, co-author of 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, principal investigator 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 most vulnerable to serious outcomes such as low blood platelet counts, kidney failure, or acute respiratory distress syndrome, in which fluid builds up in the lungs.
The report highlights “an unfortunate step in the emergence of babesiosis in the United States,” Krause said. “More cases means more disease, and in fact some people are dying.”
Babesiosis may be more serious than Lyme disease
Humans largely contract babesiosis from deer ticks, whose bites can transmit Babesia parasites that infect red blood cells.
Most transmissions occur from late May to early September. Researchers believe that climate change is leading to longer periods of humidity, which creates more hospitable environments for ticks.
“Ticks survive better in the winter, and so the following 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 the number of babesiosis cases increased 17-fold in Vermont and more than 34-fold in Maine from 2011 to 2019.
Babesiosis can sometimes be confused with Lyme disease, another tick-borne illness that causes fever and muscle aches. While Lyme disease has one defining characteristic – a rash at the site of the tick bite – Krause said there were no obvious symptoms of babesiosis. It is usually diagnosed by a blood test.
“Sometimes the patient just feels tired and not quite well, maybe a low temperature for a week or two, and then all of a sudden it gets 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 is much more common. The CDC records about 30,000 cases of Lyme disease each year, while about 16,500 total cases of babesiosis were recorded from 2011 to 2019.
People can get both diseases at once, 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 case of babesiosis in the United States in 1969. Its rising prevalence has coincided with an overall increase in tick-borne diseases, which increased by 25% from 2011 to 2019. From 1999 to 2019, confirmed cases of Lyme disease increased by 44%.
The researchers attribute this trend to a few factors. For one thing, deer populations have increased, giving ticks more opportunities to feed and reproduce. Increasingly, people are traveling and building homes in forested areas.
On top of that, rising global temperatures have resulted in longer summers and shorter winters, and ticks thrive in hot, humid climates.
Krause also noted that older people now make up a larger portion of the population and are more vulnerable to severe babesiosis, thus more likely to get an official diagnosis.
“It’s usually the most serious cases, the ones that enter the hospital, that get reported,” he said.
The CDC report recommends people who spend time outdoors in states where babesiosis is endemic wear long pants, use tick repellent, and avoid undergrowth and tall grass.
The researchers said babesiosis is likely more prevalent than the CDC tally suggests, given asymptomatic infections and not all doctors report cases to state health departments and not all states report cases. case at the CDC.
“Babesia is much more of a problem than the general public recognizes and can be fatal – up to 20% – in people with HIV/AIDS or severe cancer with chemotherapy, or in people who have no no spleen,” Krause said.