Babesiosis is caused by Babesia parasites that infect red blood cells and are transmitted through tick bites. It is most common in the Northeast and Midwest U.S. during warm months. While many infected people do not show symptoms, some experience flu-like symptoms. It can be severe for those without a spleen or with weak immune systems. Effective treatment is available. To prevent babesiosis, simple steps can be taken to reduce tick exposure like walking on cleared trails, applying repellent, and conducting full-body tick checks after being outdoors.

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Babesiosis
Babesiosis is caused by microscopic parasites Babesia 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.
Babesia microti is transmitted by the bite of infected Ixodes scapularis ticks—typically, by the
nymph stage of the tick, which is about the size of a poppy seed. An Ixodes scapularis nymph is
shown on the face of a penny.
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 (yellowing of the
skin) 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);

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 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.
Epidemiology & Risk Factors
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.
Typically B. microti is transmitted by the nymphal stage of Ixodes scapularis ticks (about the
size of a poppy seed).
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.

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 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. scapularis nymphs are very small
(about the size of a poppy seed).
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.
Life Cycle:
The Babesia microti life cycle involves two hosts, which include a rodent, primarily the white-
footed mouse, Peromyscus leucopus, and a tick in the genus Ixodes. During a blood meal,
a Babesia-infected tick introduces sporozoites into the mouse host . Sporozoites enter
erythrocytes and undergo asexual reproduction (budding) . In the blood, some parasites
differentiate into male and female gametes, although these cannot be distinguished by light
microscopy . The definitive host is the tick. Once ingested by an appropriate tick , gametes unite
and undergo a sporogonic cycle resulting in sporozoites . Transovarial transmission (also known
as vertical, or hereditary, transmission) has been documented for "large" Babesia species but not
for the "small" Babesia, such as B. microti .
Humans enter the cycle when bitten by infected ticks. During a blood meal, a Babesia-infected
tick introduces sporozoites into the human host . Sporozoites enter erythrocytes and undergo
asexual replication (budding) . Multiplication of the blood-stage parasites is responsible for the
clinical manifestations of the disease. Humans usually are dead-end hosts. However, human-to-
human transmission is well recognized to occur via contaminated blood transfusions .

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Diagnosis
In 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).
Treatment
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.
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 mostly 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.
Apply repellents as a protective measure to reduce your risk for babesiosis.

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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 likely 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.
o 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.
o 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.