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.
General Information
Babesiosis 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.
Epidemiology & Risk Factors

Babesia parasites are not transmitted from person-to-person like the flu or the common cold. 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 of becoming infected is by getting a transfusion from a blood donor who has a silent Babesia infection. (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.

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, 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).

Biology
Causal Agents:
Babesiosis is caused by apicomplexan parasites of the genus Babesia. Although more than 100 Babesia species have been reported, relatively few have caused documented cases of human infection; these include (but are not limited to) B. microti, B. divergens, B. duncani, and a currently unnamed agent designated MO1.
Disease
Many people who are infected with Babesia microti feel fine and do not have any symptoms. Some people develop nonspecific flu-like symptoms, such as fever, chills, sweats, headache, body aches, loss of appetite, nausea, or fatigue.
Because Babesia parasites infect and destroy red blood cells, babesiosis can cause a special type of anemia called hemolytic anemia. This type of anemia can lead to jaundice and dark urine.
Babesiosis can be a severe, life-threatening disease, particularly in people who:

• do not have a spleen;
• 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.

Complications of babesiosis can include:

• a low and unstable blood pressure;
• severe hemolytic anemia (hemolysis);
• a very low platelet count (thrombocytopenia);
• disseminated intravascular coagulation (also known as “DIC” or consumptive coagulopathy), which can lead to blood clots and bleeding;
• malfunction of vital organs (such as the kidneys, lungs, and liver); or
• death.

Diagnosis
In symptomatic people, babesiosis usually is diagnosed by examining blood specimens under a microscope and seeing Babesia parasites inside red blood cells.
If babesiosis is being considered, examination of blood smears should be specifically requested. Multiple smears may need to be examined to detect low levels of parasites.
Sometimes it is hard to distinguish Babesia from malaria parasites by blood-smear examination. Also, some Babesia species (such as B. microti and B. duncani) look identical: they cannot be distinguished from each other by microscopy. To be sure the diagnosis/species is correct, consider having a reference laboratory confirm the diagnosis—by blood-smear examination and, if indicated, by other means (for example, by serologic and molecular methods).
Treatment
Before considering treatment, the first step is to make sure the diagnosis is correct.
Effective treatments are available, and most people who are infected with Babesia microti respond well. People who do not have any symptoms or signs of babesiosis usually do not need to be treated.
For more information, patients should consult their health care provider.
Prevention & Control
Steps can be taken to reduce the risk for babesiosis and other tickborne infections. The use of prevention measures is especially important for people at increased risk for severe babesiosis (for example, people who do not have a spleen). Avoiding exposure to tick habitats is the best defense.
Babesia microti is spread by Ixodes scapularis ticks, which are most apt to be found in wooded, brushy, or grassy areas, in certain regions and seasons. No vaccine is available to protect people against babesiosis. However, people who live, work, or travel in tick-infested areas can take simple steps to help protect themselves against tick bites and tickborne infections.
During outdoor activities in tick habitats, take precautions to keep ticks off the skin.

• Walk on cleared trails and stay in the center of the trail, to minimize contact with leaf litter, brush, and overgrown grasses, where ticks are most apt to be found.
• Minimize the amount of exposed skin, by wearing socks, long pants, and a long-sleeved shirt. Tuck the pant legs into the socks, so ticks cannot crawl up the inside of the pants. Wear light-colored clothing, to make it easier to see and remove ticks before they attach to skin.
• Apply repellents to skin and clothing. Follow the instructions on the product label.
• Products that contain DEET (N,N-diethylmetatoluamide) can be directly applied to exposed skin and to clothing, to help keep ticks away (by repelling them). The product label includes details about how and where to apply the repellent, how often to reapply it, and how to use it safely on children.
• Permethrin products can be applied to clothing/boots (not to skin), actually kill ticks that come in contact with the treated clothing, and usually stay effective through several washings.

After the outdoor activities, conduct daily tick checks and promptly remove any ticks that are found. Thorough, daily tick checks are very important. The I. scapularis nymphs that typically spread B. microti are so small (about the size of a poppy seed) that they are easily overlooked. But they usually must stay attached to a person for more than 36-48 hours to be able to transmit the parasite.

• Remove ticks from clothing and pets before going indoors.
• Conduct a full-body exam for ticks. Use a hand-held or full-length mirror to view all parts of the body. Be sure to check behind the knees, between the legs (groin/thighs), between the toes, under the arms (armpits), around the waist, inside the belly button, the back of the neck, behind and in the ears, as well as in and around the scalp, hairline, and hair. Remember to check children and pets, too.

Remove ticks that are attached to the skin as soon as possible, preferably by using pointed (fine-tipped) tweezers. Grab the tick’s mouth parts close to the skin, and slowly pull the tick straight out (with steady outward pressure), until the tick lets go.