Babesiosis, another disease spread by ticks, is on the rise

The tick-borne illness babesiosis is one of the next most common after Lyme. And it is on the rise, especially in the Northeast, according to a 2023 report by the Centers for Disease Control and Prevention.

“Babesiosis is less common than Lyme disease but tracks in the same areas,” said Paul Auwaerter, a professor of medicine and clinical director of the division of infectious diseases at the Johns Hopkins University School of Medicine in Baltimore. And it’s worth knowing about because it can be serious, especially for people who are immunocompromised, he said.

Here’s what you should know about babesiosis.

Another tick-borne disease

Many of the illnesses spread by ticks, including Lyme disease, ehrlichiosis and anaplasmosis, are bacterial. Ticks can also spread viral illnesses, including Powassan virus, Heartland virus, and Colorado tick fever.

Unlike these, babesiosis is a parasitic illness, spread by Babesia microti parasites, which can live inside blacklegged ticks. It’s similar to malaria, a parasitic disease that’s spread by mosquitoes, said Maria Diuk-Wasser, a professor in the department of ecology, evolution and environmental biology at Columbia University. Once they enter the bloodstream of a human or certain other mammals, Babesia microti parasites infect red blood cells, which can cause anemia and other symptoms.

And while cases are on the rise now, babesiosis is not a new illness by any means. It has been known to infect cattle since 1888, and the first human case was described in 1957, with the first U.S. case documented in 1968 — before Lyme was even identified.

The symptoms

Babesiosis infections can range from asymptomatic to severe. Many people don’t feel any symptoms, but those who do may have some flu-like symptoms, including fever, chills, body aches, nausea and fatigue, according to the CDC. The destruction of red blood cells by parasites can also cause anemia.

The symptoms may appear in the weeks or months after a tick bite. Even without treatment, most adults clear the infection on their own within a year, according to Evan Bloch, an associate professor of pathology and associate director of transfusion medicine at the Johns Hopkins University School of Medicine.

But babesiosis can be life-threatening for people who don’t have a spleen, have a weakened immune system, have other serious health conditions or are elderly, according to the CDC.

If you feel sick and there’s reason to suspect babesiosis or another tick-borne disease, a doctor can order a tick-borne disease panel that looks for all possible infections, Auwaerter said. Some infections can be missed, especially if a test is run early in the course of an illness — and be wary of tests not ordered by your doctor, because some might not be credible indicators of a current infection. However, babesiosis in particular is easy to identify because the parasites are visible in blood samples when examined under a microscope.

Late spring and early summer are typically when these types of infections are most common, Auwaerter said, though they can happen in fall or anytime ticks are active.

How is babesiosis treated?

Fortunately, there are effective treatments for babesiosis.

Asymptomatic cases don’t necessarily need to be treated, but doctors will order treatment for asymptomatic people who continue to have evidence of parasites in their blood for over a month, according to Wolters Kluwer’s UpToDate, a decision-making tool for doctors.

People with mild to moderate disease can be treated with a seven-to-10-day oral course of azithromycin, an antibiotic, and atovaquone, an antifungal and anti-parasitic drug.

Severe cases require hospitalization. Patients are treated with the same medications but may also require blood transfusions.

Immunocompromised patients with mild to moderate disease can still receive outpatient treatment but with regular monitoring of their blood counts every two to three days.

In a study that began in June, researchers are testing whether adding the anti-malaria drug tafenoquine to the standard treatment regimen helps hospitalized patients clear the parasite from their systems more effectively and safely.

How common is it?

After Lyme, babesiosis or the bacterial disease anaplasmosis tends to be the next most common tick-borne illness, depending on the state, Diuk-Wasser said.

But while babesiosis is on the rise, documented cases are still not common. Between 2011 and 2019, 16,456 cases were reported to the CDC from 37 states, according to the 2023 CDC study, with the vast majority of cases coming from 10 states. New York reported the most cases, about 526 per year, followed by Massachusetts and Connecticut. As with most tick-borne illnesses, many cases go unreported, Auwaerter said. But reports can show trends, including when a disease is becoming more common, he said.

CDC surveillance data from 2011 to 2019 indicates that babesiosis is now endemic in 10 states: Connecticut, Maine, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Rhode Island, Vermont and Wisconsin. That’s up from seven states in previous years. To prevent the illness from spreading through the blood supply, the Food and Drug Administration recommends that donated blood be screened for the parasites in those 10 states plus Delaware, Maryland, Pennsylvania, Virginia and D.C.

Babesiosis is probably spreading for many of the same reasons that Lyme spreads, Auwaerter said, including the large populations of deer and mice that help spread blacklegged ticks across neighborhoods and state lines.

Infected mice can transmit the parasites to their pups, so pups can be born infected, which provides opportunities for the illness to spread, especially because more mice may be surviving warmer winters, Diuk-Wasser said. Plus, while more research is needed to understand this interaction, co-infection with Lyme disease seems to increase the likelihood that babesiosis spreads. One potential explanation for this could be that the immune system may be less able to fight off a babesia infection if it’s simultaneously trying to respond to the borrelia bacteria that transmit Lyme, she said.

Is donated blood a risk?

Historically, babesiosis was one of the leading risks of blood transfusions, with hundreds of cases transmitted that way, according to Bloch. But in 2019, the FDA instituted mandatory babesiosis screening for donated blood in 14 states where the disease is most common and D.C., the first such screening strategy that was specific to certain regions.

Since then, there have been only a couple of breakthrough cases, Bloch said. That could happen if, for example, someone donates blood in their home state after traveling to a state where babesiosis is endemic.

How to protect yourself

To protect yourself against babesiosis, you’ll want to use the same basic tick prevention strategies you’d use to protect yourself against Lyme or any other tick-borne disease.

Wear long sleeves and long pants when in wooded or grassy areas. Tuck your shirt into your pants, and tuck your pants into your socks. Consider treating your clothes and shoes with permethrin to keep ticks away, and apply an effective insect repellent to exposed skin. Take a shower after you’ve spent time outside, and perform a thorough tick check when you do.

It takes time for a tick to transmit babesia parasites — usually a tick has to be embedded for 36 to 48 hours to do so, according to the CDC. So if you do find a tick on you, use fine-tipped tweezers to grasp the tick as close to your skin as you can, and then pull it steadily out, trying not to jerk or twist the tweezers.

Diuk-Wasser said that people who want to help researchers better understand how ticks are spreading can use the Tick App, a citizen science project coordinated by researchers from four universities (including Diuk-Wasser’s team at Columbia) to report tick encounters.

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