Babesiosis is a parasite infection passed through the bite of a tick. It damages red blood cells and makes it hard for them to carry oxygen to the body.
Babesiosis is caused by a parasite found in some ticks. An infected tick passes the parasite to humans.
The parasite can also be passed through a blood transfusion from an infected donor. This is not common.
Things that may raise the risk of this infection are:
Some people will not have symptoms. Others may not have them until a few days or weeks after the bite. They are often flu-like symptoms such as:
A severe infection can be deadly. It can make it hard to breathe and lead to problems with the heart, liver, or kidney.
You will be asked about your symptoms and health history. You may be asked if you have spent time in places where there are ticks. A physical exam will be done.
Blood tests will be done to look for signs of the infection.
A person without symptoms may not need to be treated. The immune system will clear the parasite from the body.
An infection that causes symptoms will need to be treated with antibiotics and antiparasitic medicines.
To lower the chance of this infection:
Centers for Disease Control and Prevention
Family Doctor—American Academy of Family Physicians
Public Health Agency of Canada
Babesiosis. Centers for Disease Control and Prevention website. Available at:
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Updated April 11, 2018. Accessed November 20, 2019.
Babesiosis. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/babesiosis. Updated July 9, 2018. Accessed November 20, 2019.
Vannier E, Krause PJ. Human babesiosis. N Engl J Med. 2012 Jun 21;366(25):2397-407.
Last reviewed September 2019 by
EBSCO Medical Review Board
James P. Cornell, MD
Last Updated: 5/27/2020