Prime tick season is approaching, and those creepy little arachnids are carrying all sorts of diseases, including a rare one that’s becoming more prominent: Annual reported cases of babesiosis—a tick-borne disease that can trigger flu-like symptoms, and lead to life-threatening complications in vulnerable people—doubled in the United States between 2011 and 2019, and the true number of infections is probably much higher, according to a recent report from the Centers for Disease Control and Prevention (CDC). 

Babesiosis is now endemic—meaning it occurs regularly but is contained to specific regions—in at least 10 states in the Northeast and Midwest, but the disease has been detected in many others. Babesiosis is not nearly as common as Lyme disease, the most common tick-borne disease in the country; 16,456 cases of babesiosis were reported to the CDC between 2011 and 2019, while roughly 30,000 cases of Lyme are reported to the CDC each year. Both diseases are likely underdiagnosed and underreported: Lyme is believed to affect up to 476,000 people in the U.S. each year, and the true burden of babesiosis remains unclear, as it’s not required to be reported in all states.

While it’s still somewhat rare, it’s not exactly great news that babesiosis is gaining traction. Lyme disease is caused by Borrelia burgdorferi bacteria, which are “loosely related to syphilis,” Thomas Russo, MD, an infectious disease expert at the University of Buffalo Jacobs School of Medicine and Biomedical Sciences, tells SELF. The pathogen that causes babesiosis, Babesia, “is a parasite that invades red blood cells. It’s a completely different beast.”

Curious about what that means? Here’s what you should know about babesiosis, including where it’s stirring up the most trouble so far, the symptoms it can set off, and how to protect yourself from tick bites as you enjoy the warmer weather.

Where is babesiosis spreading?

Babesiosis is mainly transmitted through the bite of an infected blacklegged tick (aka a deer tick), which is also known to carry Lyme-causing bacteria, among other harmful pathogens. Most human Babesia infections are caused by the microscopic parasite Babesia microti.

Because these parasites infect red blood cells, babesiosis can also spread via blood transfusions, during organ transplants from infected donors, or from an infected pregnant person to a fetus. “The expansion of babesiosis risk could have implications for the blood supply,” the CDC report notes. “[People] who acquire babesiosis through contaminated blood have been shown to have significantly worse health outcomes and a higher risk for death than do those who acquire the disease from a tick bite.” (Note: the Food and Drug Administration recommends blood donation screening for babesiosis in 14 states and D.C.)

Babesiosis is considered endemic in the following states: Connecticut; Massachusetts; Minnesota; New Jersey; New York; Rhode Island; Wisconsin; Maine; New Hampshire; and Vermont.

Vermont, Maine, and New Hampshire are recent additions to this list due to “significantly increasing incidences” of the disease in these states, the CDC notes. Connecticut, Massachusetts, New Jersey, New York, and Rhode Island also saw significant increases.

The report didn’t explore why babesiosis is expanding its reach, but Dr. Russo points out that one big factor scientists have been researching is climate change’s potential influence on tick populations, especially when studying the growing prevalence of Lyme. Warmer temperatures may help ticks thrive in areas where they historically couldn’t: “The tick is able to spread to new geographic zones and it brings these pathogens with it,” Dr. Russo says.

Where are the most common babesiosis symptoms?

Here’s where things get a bit tricky: Some people with babesiosis feel perfectly fine and don’t have any symptoms, while others come down with a flu-like illness,  Dr. Russo says. 

People who develop symptoms may have a fever; chills; sweats; headache or body aches; loss of appetite; nausea; and fatigue, per the CDC. “Most people have a mild illness,” William Schaffner, MD, an infectious disease specialist and professor of medicine at the Vanderbilt University School of Medicine in Nashville, tells SELF.

However, babesiosis can cause severe, life-threatening disease in people who don’t have a spleen; have a weakened immune system; have certain underlying health conditions (like liver or kidney disease); or are elderly. Potential complications include low blood pressure, severe hemolytic anemia, a low blood platelet count, and organ malfunction, among others.

How is babesiosis diagnosed and treated?

To accurately diagnose babesiosis, your doctor should order a blood test; a lab technician will examine your blood under a microscope to confirm if the Babesia parasites have invaded the red blood cells. 

This blood test is different from ones used to detect other tick-borne illnesses, including Lyme, which is why it’s important for health care providers to be aware of babesiosis in endemic states, as well as neighboring areas, Dr. Russo says. “If there is any question that you may have had a tick bite or you know that you had a tick exposure and you have symptoms, tell your doctor,” he urges. 

If the test is positive, the good news is there are medications available—usually a combination of antiparasitic and antibacterial drugs, which are generally prescribed for a week to 10 days—to clear the infection. 

How to protect yourself from ticks

The biggest takeaway: Tick bites can be gnarly, and babesiosis—while still rare—is not something you want to mess with. In general, avoiding a tick bite can help reduce your chances of catching any tick-borne illness that’s more prevalent in your immediate area.

To make yourself less appealing to these arachnids, the National Institutes of Health and CDC recommend taking small-but-simple steps before you head outdoors—especially if you’re hanging out where ticks thrive, like wooded areas and brushy or grassy landscapes:

  • Use an insect repellent that contains DEET or picaridin. Consider treating your clothing or gear with a permethrin-based repellent.
  • Wear light-colored clothing that covers your arms and legs when possible. (Light colors will help you see a tick more easily.)
  • Tuck pant legs into socks if you’re in a known tick zone.
  • Check yourself, your kids, and your pets daily for ticks, especially right after you’ve been outside, and carefully remove any from the skin if you do find them.


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