May also be called: Redwater Fever; Piroplasmosis

Babesiosis (buh-bee-zee-OH-sis) is a rare illness that happens when tiny parasites infect red blood cells, usually after a bite from an infected tick. Not all people who get infected have symptoms, but treatment is available for those who do.

What Happens With Babesiosis?

Babesiosis is caused by tiny parasites. The same ticks that spread Lyme disease can pick up the parasites by feeding on infected animals, like rodents. Then, they can pass the parasites to humans through a bite.

Babesiosis usually goes away on its own in 1–2 weeks and causes mild symptoms (such as fever, chills, sweats, headache, and tiredness), if any. To treat severe cases, doctors usually give antiparasitic medicines to ease symptoms and kill the parasites. People who get treatment often start feeling better within 48 hours of starting the medicines.

What Else Should I Know?

Cases of babesiosis are on the rise in some U.S. states, but it’s still rare, and most people who develop it don't need treatment.

All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.