Babesia microti are tiny parasites, present on some ticks, that cause an infection known as babesiosis.

If a person receives a bite from a tick that is carrying Babesia microti (B.microti), they are at risk of a Babesia infection, or babesiosis. The infection can cause symptoms that range from a flu-like illness to severe problems with bleeding and organ failure.

Read on to learn more about Babesia infection, the symptoms and causes of babesiosis, and how doctors diagnose and treat the illness.

a tick crawling on skin which may infect with babesia if it bitesShare on Pinterest
A person may get a Babesia infection from a tick bite.

Babesia infections are usually due to one of three underlying causes:

Tick bite

The most common way of acquiring a Babesia infection is from a tick bite. Blacklegged (also known as deer) ticks are most likely to be carrying B.microti parasites.

These ticks are roughly the size of a poppy seed and are most common in the Northeastern and Midwestern United States.

Transmission from blood donor

In extremely rare cases, a person may get the Babesia infection from a blood donor who had no symptoms when they donated.

In 2018, the Food and Drug Administration (FDA) approved a test to detect B. microti antibodies in donated blood. The approval has the potential to make the U.S. blood supply safer.

Transmission from mother to fetus

A woman can transmit the Babesia infection to her baby during pregnancy or delivery, but this is very rare.

A person can have the signs of a Babesia infection a few weeks after exposure, but it can also be several months after exposure before the symptoms occur.

Some people may have mild to moderate symptoms. These include:

  • body aches
  • chills
  • fatigue
  • fever
  • weakness

Others may experience hemolytic anemia. This occurs when a person’s body cannot make red blood cells as fast as it destroys them. Hemolytic anemia can cause symptoms that include:

  • jaundice
  • liver enlargement
  • severe activity intolerance
  • shortness of breath
  • spleen enlargement

Severe cases of Babesia infections can be life threatening. In these instances, symptoms may include:

  • disseminated intravascular coagulation (DIC), a severe blood clotting disorder
  • heart attack
  • inability to maintain blood pressure
  • kidney failure
  • liver failure
  • respiratory distress

Certain individuals may be more at risk of severe infection than others, including:

  • those without a spleen
  • older adults
  • those with an underlying condition, such as liver or kidney disease
  • anyone with a compromised immune system

If a person experiences severe symptoms, they will require immediate medical attention.

Diagnosing a Babesia infection can be very difficult because symptoms will often mirror those of many other medical conditions. The illness is also rare, with an estimated 1,000–2,000 new cases reported annually in the U.S.

Doctors will often consider a diagnosis of babesiosis by exclusion or when a person does not have any other diagnosable condition.

If a person has risk factors, such as having spent time outdoors in areas where ticks carry the parasite or having received a blood transfusion, a doctor may request a blood sample.

That said, most medical laboratories are unable to test for the B.microti parasite. A doctor may have to send the specimen to a specialized laboratory, such as one at the Centers for Disease Control and Prevention (CDC).

Not all people with a Babesia infection will require treatment. Babesiosis can be asymptomatic (without symptoms), and usually, in these cases, doctors will not suggest treatment.

If a person does have symptoms or is asymptomatic but at risk of severe infection for other chronic health reasons, a doctor may recommend treatment.

Doctors will usually prescribe one of two medication combinations:

  • atovaquone plus azithromycin
  • clindamycin plus quinine (for very ill patients)

A person should take these for 7–10 days.

In addition to these medications to treat the infection, a doctor may prescribe supportive medications and therapies. Examples include:

  • blood transfusions
  • fever reducing medications
  • hemodialysis to filter the blood
  • drugs to increase blood pressure (vasopressors)

An individual with severe infection may require mechanical ventilation to support their breathing.

If a person has symptoms that are consistent with a Babesia infection, they should see their doctor. This is especially true if they have identified a previous tick bite or been outdoors in an area ticks commonly infest.

Taking steps to prevent tick bites when outdoors can help avoid Babesia infections. Ways to do this include:

  • Walking or hiking on cleared trails only: This helps to prevent brushing up against brush, overgrown grasses, and leaf piles where people find ticks.
  • Wearing long socks, long pants, and tucked in, long-sleeved t-shirts when outdoors: This minimizes the area a tick could bite.
  • Wearing light-colored clothing: This choice helps make identifying ticks on the clothing easier.
  • Carefully applying tick repellents to skin or clothing: Examples include permethrin and DEET-containing products. However, these are not always suitable for children.

A tick usually needs to remain on a person’s body for 36–48 hours before it can transmit the B.microti parasite. For this reason, people should conduct frequent tick checks on their bodies once they have been outside.

Tick bites mostly cause Babesia infections. Infection is rare and often asymptomatic in many people. However, some individuals can experience life threatening or fatal symptoms as a result of babesiosis.

If a person suspects they may have a Babesia infection, they should see a doctor or other healthcare provider.

If detected early, most infections are highly treatable.