About Babesiosis

Key points

  • Babesiosis is a disease caused by a parasite that infects red blood cells.
  • It spreads through tick bites, primarily by blacklegged (deer) ticks.
  • Some people show no symptoms, others have flu-like symptoms.
  • Babesiosis is preventable and treatable.
Tick that spreads the parasite that causes babesiosis.


Babesiosis is a disease caused by microscopic parasites that infect red blood cells. A parasite is an organism (living thing) that lives on or inside another organism. Although there are many different species (types) of Babesia parasite found in animals, only a few infect people. The most common species to infect people in the United States is Babesia microti.

Signs and symptoms

Many people with Babesiosis do not feel sick and have no symptoms. However, some people might get flu-like symptoms, such as:

  • Fever
  • Chills
  • Sweats
  • Headache
  • Body aches
  • Loss of appetite
  • Nausea
  • Fatigue

Since the parasites attack red blood cells, babesiosis can lead to hemolytic anemia. Hemolytic anemia occurs when your red blood cells are destroyed faster than they can be replaced. Babesiosis can become a serious, even life-threatening illness for certain people, especially those who:

  • Do not have a spleen
  • Have a weak immune system for other reasons such as cancer, lymphoma, or HIV
  • Have serious health issues such as liver or kidney disease
  • Are older (> 50 years old)

Symptoms, if they appear, may start around a week after infection, but usually develop over a few weeks or months, or longer.

How it spreads

In the U.S. most Babesia infections are from blacklegged or deer tick (Ixodes scapularis) bites. Ticks are typically found in wooded, brushy, or grassy areas. Currently, most babesiosis cases occur in the Northeast and upper Midwest.

Other less common ways of getting infected with Babesia include:

  • Getting a blood transfusion that has the parasite in it.
  • If a mother has babesiosis, she might pass it to her baby during pregnancy or when the baby is born.

Babesia parasites do not spread from person-to-person like the flu or the common cold.


To reduce your risk of babesiosis, avoid outdoor areas infested with ticks. If you are in these areas, use tick repellents, wear socks, long-sleeved shirts, and pants, and check yourself and pets for ticks before going inside.

Keep Reading: Preventing Babesiosis


A healthcare provider can diagnose babesiosis by examining a small sample of your blood under a microscope. This lab test can confirm the presence of the Babesia parasites in your red blood cells.

Another way your healthcare provider can diagnose babesiosis is by sending your blood samples to a special lab, such as the CDC or a health department, for testing.


If you have babesiosis, there is effective treatment. You usually do not need treatment if you have no symptoms or signs of babesiosis. Talk with your healthcare provider for more information.