Cases of babesiosis, transmitted by tick bites, increase over the spring months with the majority of affected people falling ill in June or July. The seasonal rise in this parasitic disease in the United States is likely well underway.

Babesia microti/CDC
Babesia microti/CDC

Babesia microti, the species responsible for most cases, is a microscopic protozoan parasite that lives inside red blood cells. While many people are unaware they’ve been infected, others suffer severe and prolonged illness, sometimes ending in death. Babesiosis causes flu-like symptoms such as fatigue, headache, fever, poor appetite, and body aches. Over time, as the parasites destroy red blood cells, anemia sets in. Symptomatic cases of babesiosis typically strike older people with an average age of about 70 years.

Most people catch babesiosis from the bite of the blacklegged tick, Ixodes scapularis. In the spring, tiny young ticks emerge and can feed on wild animals, pets, and humans. At this stage they are very small and often go unnoticed when they bite but they transmit Babesia microti and other disease-causing organisms. An incubation period of up to two months means that babesia infections acquired in the spring become apparent in the summer months.

Ticks transmit babesiosis in the United States in Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, and Wisconsin, but infected people who have no symptoms can transmit it to others through blood donation. Pregnant women can pass the parasite on to the fetus.

Avoiding tick bites is the best way to prevent babesiosis, along with prompt removal of any tick that is found already attached to the skin. Those who live in places where blacklegged ticks transmit babesiosis should be vigilant about checking for ticks, and watchful for symptoms of infection.

For more information, visit the CDC website

Rosemary Drisdelle is the author of Parasites: Tales of Humanity’s Most Unwelcome Guests. She teaches clinical parasitology and writes about parasites from Nova Scotia, Canada. Her website is