Babesiosis is caused by microscopic parasites that infect red blood cells and are spread by certain ticks. In the United States, tickborne transmission is most common in particular regions and seasons: it mainly occurs in parts of the Northeast and upper Midwest and usually peaks during the warm months.
Although many people who are infected with Babesia do not have symptoms, for those who do effective treatment is available. Babesiosis is preventable, if simple steps are taken to reduce exposure to ticks.
People can get infected with Babesia parasites in several ways:
- The main way is through the bite of an infected tick—during outdoor activities in areas where babesiosis is found (see below).
- A less common way is by getting a transfusion from a blood donor who has a Babesia infection but does not have any symptoms. (No tests have been licensed yet for screening blood donors for Babesia.)
- Rare cases of congenital transmission—from an infected mother to her baby (during pregnancy or delivery)—have been reported.
Babesia parasites are not transmitted from person-to-person like the flu or the common cold.
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 (sporadic) cases of babesiosis caused by other Babesia species have been detected.
Babesia microti is transmitted in nature by Ixodes scapularis ticks (also called blacklegged ticks or deer ticks).
- Tickborne transmission primarily occurs in the Northeast and upper Midwest, especially in parts of New England, New York state, New Jersey, Wisconsin, and Minnesota.
- The parasite typically is spread by the young nymph stage of the tick, which is most apt to be found (seeking or “questing” for a blood meal) during warm months (spring and summer), in areas with woods, brush, or grass.
- Infected people might not recall a tick bite because I. scapularisnymphs are very small (about the size of a poppy seed).
n symptomatic people, babesiosis usually is diagnosed by examining blood specimens 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).
Effective treatments are available. People who do not have any symptoms or signs of babesiosis usually do not need to be treated.
Before considering treatment, the first step is to make sure the diagnosis is correct.
For more information, people should talk to their health care provider.