Babesiosis is a tick-borne disease caused by microscopic parasites that infect red blood cells. It is transmitted primarily through the bite of infected deer ticks, but it can also spread via blood transfusions or from mother to baby during pregnancy. Symptoms range from mild flu-like signs, such as fever and chills, to more severe complications like anemia in individuals with weakened immune systems. Early diagnosis and treatment with specific antiparasitic medications are crucial to prevent serious outcomes.
What Is Babesiosis?
Babesiosis (pronounced buh-bee-zee-OH-sis) is a rare disease caused by tiny parasites that infect red blood cells, typically following a bite from an infected tick.
In the U.S., babesiosis cases linked to tick bites—also called Redwater fever or piroplasmosis—are most common in the Northeast and upper Midwest, especially during warmer months when ticks are active. Not everyone who gets infected shows symptoms, but treatment is available for those who do.
What Causes Babesiosis?
The disease is caused by Babesia microti parasites, which are too small to see without a microscope. The same ticks that carry Lyme disease (black-legged ticks, also known as Ixodes ticks or deer ticks) can also pick up Babesia parasites from infected animals, like rodents, and transmit them to humans through bites. It’s possible to have both Lyme disease and babesiosis simultaneously.
In rare cases, babesiosis can be transmitted through:
- Blood transfusions
- Pregnancy, from mother to fetus
However, babesiosis does not spread directly from person to person.
What Are the Signs & Symptoms of Babesiosis?
Once the parasites enter the bloodstream, they multiply within red blood cells, which can lead to:
- Flu-like symptoms: fever, chills, sweats, headache, body aches, appetite loss, nausea, and fatigue.
- Severe symptoms in people with weakened immune systems or serious health conditions, such as: anemia, low platelet counts, jaundice, organ malfunction, and in rare cases, death.
How Is Babesiosis Diagnosed?
Doctors diagnose babesiosis by reviewing symptoms and conducting blood tests to detect parasites in red blood cells. Additional tests may be done to confirm the infection.
How Is Babesiosis Treated?
Babesiosis often resolves on its own within 1–2 weeks with mild or no symptoms. However, severe cases may require antiparasitic medications to alleviate symptoms and eliminate the parasites. Patients receiving treatment generally start feeling better within 48 hours of beginning medication.
Can Babesiosis Be Prevented?
Currently, there is no vaccine for babesiosis. The best way to prevent the disease is by avoiding tick bites. To protect yourself and your family while outdoors:
- Stick to the center of trails, avoiding tall grass or wooded areas.
- Wear protective clothing: closed shoes or boots, long sleeves, and long pants with pant legs tucked into shoes or boots.
- Use insect repellent.
- Treat clothing and gear with permethrin to repel ticks. Permethrin is safe when used correctly but should not be applied to clothing or items that a child might chew on.
- Opt for light-colored clothing to spot ticks more easily.
- Shower and wash hair after spending time outdoors to remove unattached ticks.
- Check children and pets for ticks after outdoor activities.
If a tick is found, remove it promptly to minimize the risk of disease transmission.
What Else Should I Know?
While cases of babesiosis are increasing in some U.S. states, it remains relatively rare, and most infected individuals do not require treatment.