What Is Babesiosis? Tickborne Disease on the Rise in the Northeast, CDC Says

By Brian Mastroianni  Published on March 27, 2023

Fact checked by Nick Blackmer

• Babesiosis, a tickborne disease, is on the rise in the U.S., and is newly considered endemic to three states.
• Cases of babesiosis have risen significantly in eight states in the Northeast over the course of a decade: Connecticut, Massachusetts, New Jersey, New York, Rhode Island, Maine, New Hampshire, and Vermont.
• Though many people with babesiosis don’t experience symptoms, the disease can be fatal for others.

ROBERTAX/GETTY IMAGES

Babesiosis, an emerging tickborne disease, is on the rise in multiple states across the U.S., including three states where it is newly considered endemic, new research shows.

Overall, the U.S. has seen a 25% increase in tickborne diseases over the past decade, rising from 40,795 cases reported in 2011 to 50,856 reported in 2019. Babesiosis cases are part of that spike, according to the new report from the Centers for Disease Control and Prevention.¹

During the same time period—from 2011 to 2019—cases of babesiosis rose significantly in five states with endemic transmission: Connecticut, Massachusetts, New Jersey, New York, Rhode Island. The data also showed that some neighboring states without endemic disease—Maine, New Hampshire, and Vermont—showed case counts comparable to or higher than those five states.

Meanwhile, babesiosis cases in Minnesota and Wisconsin—also considered states with endemic disease—actually decreased between 2011 and 2019.

Though still considered generally rare across the U.S., experts say the growing number of babesiosis cases is a serious health concern—particularly for people who live in or travel to states where the disease is endemic. Here’s what to know about babesiosis, including common symptoms and how to protect yourself. What Is Heartland Virus? Tickborne Disease May Be Expanding Its Reach Across the U.S.

What Is Babesiosis and Why Are Cases Rising in the US?

Babesiosis is a disease caused by microscopic parasites—specifically, Babesia parasites—that infect red blood cells in the body. In the U.S., most cases of babesiosis are caused by Babesia microti, a parasite spread by blacklegged or deer ticks.²

Though tick bites are the most common mode of transmission for B. microti, transmission can also occur through blood transfusions, organ transplants, or from a pregnant person to their fetus.

Until recently, babesiosis was considered endemic in seven U.S. states, most of which are in the Northeast or upper Midwest: Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, and Wisconsin. The new CDC report, however, added three more states to the list: Maine, New Hampshire, and Vermont.

According to Griffin Dill, PhD, manager of the Tick Lab within the Diagnostic and Research Laboratory at the University of Maine, the increasing spread of babesiosis is directly related to the increasing population size and geographic range of the blacklegged tick.

“This tick species, which is also responsible for transmitting the causative agents of Lyme disease, anaplasmosis, and several other pathogens, has become widespread throughout the eastern United states and around the Great Lakes,” Dill told Health.

“There are a variety of factors including land use change, climate change, changes in wildlife populations, and changes in human behavior that have contributed to the blacklegged tick’s ability to spread into new regions,” added Dill, “which it turn has allowed babesiosis and other tickborne illnesses to spread.”

What Are the Symptoms of Babesiosis?

Many people who contract a Babesia infection don’t show symptoms; in those who do begin to feel ill from babesiosis, symptoms can seem flu-like and include:²

• Fever, chills, and sweats
• Headache
• Body aches
• Loss of appetite
• Nausea
• Fatigue
  

For some people, however, babesiosis can be severe. Because Babesia parasites infect red blood cells, infections can cause what’s known as hemolytic anemia, or a lack of healthy red blood cells in the body.

“The pathogen that causes babesiosis infects red blood cells which can lead to anemia and related symptoms like jaundice and dark urine,” Dill said.

People who are most at-risk for severe disease or complications from babesiosis—which can include thrombocytopenia, renal failure, and acute respiratory distress syndrome—are those who:²

• Do not have a spleen
• Have a weakened immune system or are immunocompromised.
• Have another serious health condition
• Are elderly

According to the CDC, symptoms of babesiosis can show up within a week of a tick bite, and can further develop over the course of a few weeks to a few months. First Lyme Disease Vaccine in 20 Years Begins Final Clinical Trial—What You Need to Know

How Is Babesiosis Diagnosed and Treated?

To diagnose a case of babesiosis in a symptomatic person, a blood sample is analyzed for the presence of Babesia parasites in the person’s red blood cells. A healthcare provider may then double check this by having more blood tested by a special reference laboratory, like those that would be found at a major health department, according to the CDC.

After a diagnosis is made, babesiosis is treated with a combination of anti-parasitic and antibiotic medications, Dill said. In more severe cases, people may need supportive care, which can include blood transfusions, dialysis, or mechanical ventilation.³

Although “preventative doses of antibiotics are frequently prescribed following a tick bite to help prevent the development of Lyme disease, this is not done as a preventative measure against babesiosis,” Dill said.

How to Prevent Babesiosis

For those who live in areas where tickborne illnesses are common, Dill said that people should be aware of the risks and take personal protective measures. That said, the threat of babesiosis or any other tickborne illness should not prevent anyone from enjoying the outdoors, he added.

In fact, many cases of tickborne illness don’t result from large outdoor outings, but rather from everyday activities.

“While we often think about hiking and camping as particularly risky in regard to ticks, the majority of those bitten by ticks actually encounter them around the home landscape,” Megan Swanson, MPH, an epidemiologist with the CDC’s Division of Parasitic Diseases and Malaria and co-author of the CDC’s new report, told Health.

“When going outside, even just to check the mail or take the dog for a walk, we should be wearing protective clothing and an EPA-recommended insect repellent like DEET, picaridin, or permethrin,” Swanson added. “After spending time outdoors, it is important to check ourselves, our children, and our pets carefully for ticks.”

It may also be a good idea to bathe or shower as soon as possible after being outside, which could help you find ticks more easily. “It’s important to remember when you are checking for ticks that they can be as small as a poppyseed,” Swanson said.

What the Rising Cases of Babesiosis May Mean for the Future

According to Dill, the upward trend of both reported babesiosis cases and the geographic range of the illness are likely to continue.

“While Lyme disease cases have begun to plateau in some states, case rates are continuing to rise in many regions, including northern New England,” Dill said. “We have yet to see any indication of babesiosis cases leveling out.”

According to the new CDC report, rising babesiosis cases are also a threat to the blood supply in the U.S. Babesia infections are transmissible through blood transfusions, and people who acquire babesiosis through contaminated blood often have worse health outcomes and are more likely to die from the disease compared to people are infected via tick bite. Currently, the FDA recommends blood donation screening for babesiosis in 14 states plus the District of Columbia.¹

Because there are no vaccines for tickborne diseases, public education has become the “primary mitigation strategy” to control the disease, Dill said.

“This includes providing information on tick identification and removal, how to avoid tick habitat, and the use of repellents. Surveillance efforts are also increasing in intensity and importance in order to help identify trends and inform prevention strategies,” he added. “Regular monitoring of human cases and of tick populations can help identify areas of high risk and inform targeted interventions.”

In any given year, however, the number of ticks found in a specific area will vary region to region, state to state, and even county to county, Swanson said.

“[The] CDC, working with state and local health departments where the disease is reportable, will continue to track cases of babesiosis,” she said, “so we can promote tick prevention and awareness in places where people are at risk.”

From her perspective, Swanson said that predicting the number of tickborne diseases moving forward is complicated. In a given year, the number of ticks found in a specific area will vary, region to region, state to state, “and even county to county.”

“[The] CDC, working with state and local health departments where the disease is reportable, will continue to track cases of babesiosis so we can promote tick prevention and awareness in places where people are at risk,” she said.