Babesiosis Fact Sheet

• Introduction
• What is babesiosis?
• How do people get infected with Babesia?
• Where do most of the cases of babesiosis occur in the United States?
• What are the symptoms and signs of Babesia infection?
• How soon after the exposure do symptoms develop?
• What should I do if I think I might have babesiosis?
• How is babesiosis diagnosed in people who have symptoms of the infection?
• Can babesiosis be treated?
• Can babesiosis be prevented?

Introduction

Babesiosis [ba-BEE-see-OH-sis] is caused by microscopic parasites that infect red blood cells. Most human cases of Babesia infection in the United States are caused by the parasite Babesia microti. Occasional cases caused by other species (types) of Babesia have been detected. Babesia microti is spread in nature by Ixodes scapularis ticks (also called blacklegged ticks or deer ticks). Tickborne transmission is most common in particular regions and seasons: it mainly occurs in parts of the Northeast and upper Midwest; and it usually peaks during the warm months. Babesia infection can range in severity from asymptomatic to life threatening. The infection is both treatable and preventable.

What is babesiosis?

Babesiosis is caused by microscopic parasites that infect red blood cells. Many different species (types) of Babesia parasites have been found in animals, only a few of which have been found in people. Babesia microti—which usually infects white-footed mice and other small mammals—is the main species that has been found in people in the United States. Occasional cases caused by other Babesia species have been detected.

How do people get infected with Babesia?

The main way is through the bite of an infected tick:

• Babesia microti is spread by Ixodes scapularis ticks, which are commonly called blacklegged ticks or deer ticks. (Although white-tailed deer are the most important food source for the adult stage of the tick, deer are not infected with B. microti.)
• The parasite typically is spread by the young nymph stage of the tick. Nymphs are most apt to be found during warm months in areas with woods, brush, or grass.
• Infected people might not recall a tick bite because I. scapularis nymphs are very small (about the size of a poppy seed).

Other possible ways of becoming infected with Babesia include:

• receipt of a contaminated blood transfusion (no tests have been licensed yet for donor screening); or
• transmission from an infected mother to her baby during pregnancy or delivery.

Where do most of the cases of babesiosis occur in the United States?

Tickborne transmission of B. microti primarily occurs in the Northeast and upper Midwest, particularly in parts of New England, New York State, New Jersey, Wisconsin, and Minnesota. In the Northeast, babesiosis occurs in both inland and coastal areas, including off-shore islands such as Nantucket and Martha’s Vineyard (Massachusetts); Block Island (Rhode Island); and Shelter Island, Fire Island, and eastern Long Island (New York State).

What are the symptoms and signs of Babesia infection?

Many people who are infected with Babesia microti feel fine and do not have any symptoms. Some people develop flu-like symptoms, such as fever, chills, sweats, headache, body aches, loss of appetite, nausea, or fatigue. Because Babesia parasites infect red blood cells, babesiosis can cause hemolytic anemia (from destruction of red blood cells).

Babesiosis can be a severe, life-threatening disease, particularly in people who:

• do not have a spleen or whose spleen does not function normally;
• have a weak immune system for other reasons (such as cancer, lymphoma, or AIDS);
• have other serious health conditions (such as liver or kidney disease); or
• are elderly.

How soon after the exposure do symptoms develop?

Symptoms, if any, can start within a week or so. They usually develop within a few weeks or months, sometimes longer.

What should I do if I think I might have babesiosis?

See your health care provider.

How is babesiosis diagnosed in people who have symptoms of the infection?

In symptomatic people, babesiosis usually is diagnosed by examining blood under a microscope and seeing Babesia parasites inside red blood cells. To be sure the diagnosis is correct, your health care provider might have specimens of your blood tested by a specialized reference laboratory (such as at CDC or a health department). In addition, your health care provider might decide to have your blood tested for other possible causes of your symptoms, including other tickborne infections, such as Lyme disease and anaplasmosis. See CDC’s Tickborne Rickettsial Diseases website.

Can babesiosis be treated?

Yes. Effective treatments are available, and most people respond well. People who do not have symptoms or signs of babesiosis usually do not need to be treated. Your health care provider may talk with CDC staff about whether to treat your case of babesiosis, what type of therapy to use, and how long to treat. The first step is to make sure the diagnosis is correct.

Can babesiosis be prevented?

Yes. You can take steps to prevent babesiosis and other tickborne infections. The use of prevention measures is particularly important for people at increased risk for severe babesiosis (for example, people who do not have a spleen). If possible, areas infested with ticks should be avoided, especially during warm months. If such areas cannot be avoided, use protective measures during outdoor activities. See the Tickborne Rickettsial Diseases' Prevention and Control webpage for tips, including the importance of checking yourself daily for ticks. The tiny I. scapularis ticks that spread B. microti usually must stay attached to a person for more than 24-36 hours to be able to transmit the parasite.

No vaccine is available to protect people against babesiosis.

This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the disease described above or think that you may have a parasitic infection, consult a health care provider.