Skip Navigation LinksBabesiosis


What is bab​es​​​​​​​​​iosis?

Babesiosis is infection of red blood cells by a parasite called Babesia. People who get sick with babesiosis may have fever, chills, muscle pain, and fatigue. Most infections are acquired in the northeastern United States (U.S.) and are due to a kind of Babesia called Babesia microti. Cases of babesiosis caused by B. microti in California have been diagnosed in people returning from the northeastern U.S. Additionally, rare cases of babesiosis have occurred in California since 1993 caused by a different Babesia called Babesia duncani.

How do you get babe​s​​iosis?

People get infected with the Babesia parasite when a tick infected with Babesia bites them. An infected tick must be attached and feeding for at least 24 hours before it can transmit the organism. In the U.S., B. microti is transmitted by the bite of female deer ticks. These ticks do not occur in California. It is unknown what kind of tick carries the Babesia duncani. Rarely, people can get babesiosis when they are given blood taken from people infected with the Babesia parasite.

How are Bab​​esia parasites mai​​ntained in nature?

The white-footed mouse is the most important animal in maintaining B. microti in nature. Babesia microti has also been detected in the meadow vole, the eastern chipmunk, the Norway rat, the cottontail rabbit, and the short-tailed shrew. The animal reservoir for the Babesia duncani is unknown.

What are the sympto​ms of babesiosis?

Symptoms of babesiosis vary. Most people infected with Babesia never feel ill. Severe and fatal cases usually occur in patients who have a weakened immune system, in older individuals or those without a spleen. Patients have flu-like symptoms such as fatigue, fever, sweats, and muscle aches, typically within one to four weeks following a tick bite. Symptoms of nausea, vomiting, headache, shaking chills, and bloody urine, can also occur.

How is babesiosis diag​nosed?

Babesia infects red blood cells. As such, a decrease of red blood cells may be detected in severely affected patients. A reduction of clotting cells (platelets) is also typical in severe babesiosis. Babesia organisms can sometimes be observed in red blood cells under a microscope. Specific blood tests for babesiosis can also help a physician make a diagnosis.

How is babesiosis tr​eated?

Drugs used to treat babesiosis are similar to those used to treat malaria. Patients who have a significant reduction in red blood cells may need a blood transfusion.

How do I keep from getting babesi​​osis?

The best way to keep from getting babes​​iosis, or any other disease from ticks, is to avoid areas where ticks are found. Stay on trails away from tall grasses where ticks may occur. Wear light-colored long pants and long-sleeved shirts when outside. Apply tick repellents to your clothes and skin. Most importantly, if you have been in an area where ticks may occur, thoroughly check your body immediately after returning indoors and promptly remove any ticks you find.

Where can I find more informa​​tion on babesiosis?

The U.S. Centers for Disease Control and Prevention (CDC) has information available on their babesiosis webpage. ​ ​​
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