Not as well known as Lyme disease but more dangerous, babesiosis — carried by the same tick as Lyme — has been increasing in Connecticut in the last decade.

Babesiosis is caused by a microscopic parasite, Babesia microti, not by a bacterium, as Lyme disease is. But someone bitten by a blacklegged, or deer, tick can get both diseases, which may be why someone treated for Lyme may continue to feel ill, according to Dr. Peter Krause, a specialist in vector-borne diseases at the Yale School of Public Health.

“Lyme disease is the easiest one to diagnose because that gives you the red rash in about 80 percent of cases,” Krause said. “Adults don’t get fever very often, kids more so, but if there’s a fever there are more possibilities.” In addition to babesiosis, anaplasmosis and, more rarely, Powassan virus can be transmitted by the deer tick.

According to the state Department of Public Health, cases have risen from 85 in 2009 and 107 in 2012, rising to a recorded high of 324 confirmed and probable cases in 2019. But Krause said that number is probably underreported.

While not as common as Lyme, with 1,752 confirmed or probable cases in Connecticut in 2019, and not a major health threat for most people, it can be serious and even fatal in people with compromised immune systems. “Even with treatment, they can either die or they have prolonged infection lasting two or three years,” Krause said.

That includes “people with cancer, people who have HIV/AIDS, people who are in the extremes of age — newborn infants and people who are 60 and over — and people who are on immunosuppressant drugs,” as well as people who have had their spleen removed, he said. “It’s a danger for them,” he said.

About one in five people with babesiosis will have no symptoms, but “this disease can also be transmitted through the blood supply,” he said.

Krause led a committee that revised guidelines for treatment of babesiosis, issued by the Infectious Diseases Society of America. They were last issued in 2006, before the disease became as prevalent as it is today.

Now is the season for deer tick nymphs, which are only as big as a poppy seed, making it easy to miss them if they bite. They usually contract diseases as larvae the previous summer from an infected animal such as a white-footed mouse.

A problem with babesiosis is that when someone is bitten by a tick, their doctor often will prescribe doxycycline, which is a standard treatment for Lyme disease, “in hopes it will prevent Lyme disease, but it won’t prevent babesiosis,” Krause said. That requires two antibiotics: atovaquone and azithromycin, he said, although an older alternative is clindamycin plus quinine. Quinine, however, can cause buzzing in the ears, gastrointestinal upset and hearing loss in up to 75 percent of patients, Krause said.

Symptoms of babesiosis include fever, sweats, chills, fatigue, headache and nausea, among others, according to the Centers for Disease Control and Prevention.

“The good news is, for both babesiosis and anaplasmosis, the blood tests are very helpful,” Krause said. A blood smear or polymerase chain reaction test will determine whether a patient has either disease, while an antibody test isn’t useful because antibodies don’t appear for two or three weeks, he said.

“Lyme disease is sort of the flip side of that,” Krause said. “You can tell from a clinical diagnosis, the red rash.” That can then be confirmed with an antibody test.

First found in Connecticut in 1989, babesiosis is fairly spread out throughout Connecticut, with the fewest cases in Middlesex, Windham and Tolland counties, according to the state health department.

“It’s never been really, really high, although a lot of cases are probably undiagnosed, so we don’t know what the real incidence is or have a good handle on it,” said Kirby Stafford, the state entomologist at the Connecticut Agricultural Experiment Station in New Haven.

Stafford said 3,517 ticks were submitted for testing in 2019, with 9.4 percent of adults and nymphs positive for Babesia microti alone and 5.1 percent positive for babesia and Borrelia burgdorferi, the Lyme bacteria.

The experiment station began an active tick-surveillance program in 2019, with 40 sites statewide, Stafford said. In 2020, 8.6 percent of female adult ticks and 6.8 percent of nymphs tested positive for babesia, he said.

“Obviously, the risk goes up as you get older,” he said. “For most people it’s self-limiting and that’s the irony of babesiosis. It ranges from no symptoms at all to some people have died from it.”

Connecticut Media Group