Babesia During Pregnancy: Two Infants With Congenital Babesiosis

Babesia can rarely pass from a pregnant mother to her baby
Symptoms may not appear until several weeks after birth
Congenital babesiosis can cause severe anemia and low blood cell counts

Babesia can rarely be transmitted from mother to baby during pregnancy. Two published cases describe infants who developed congenital babesiosis after their mothers had Lyme disease and unrecognized Babesia microti infection.

These cases were described by Saetre and colleagues in the Journal of the Pediatric Infectious Diseases Society.

What Is Babesiosis?

Babesiosis is caused by parasites that infect red blood cells. In the northeastern United States, most human cases are caused by Babesia microti and transmitted through the bite of an infected blacklegged tick.

Babesia is an important Lyme disease coinfection because the same type of tick can transmit both Borrelia burgdorferi, the bacterium responsible for Lyme disease, and Babesia microti.

Less commonly, Babesia can be transmitted through blood transfusions or from a pregnant mother to her baby. Maternal-to-infant transmission is known as congenital or vertical transmission.

Babesia may be detected through:

• Examination of a blood smear for parasites inside red blood cells
• PCR testing for Babesia genetic material
• Antibody testing for evidence of infection

No single test answers every clinical question. Test selection and interpretation depend on the timing of the illness, parasite level, symptoms, and other clinical findings.

First Infant With Congenital Babesiosis

The first mother lived in Westchester County, New York. At 32 weeks of pregnancy, she developed an erythema migrans rash and was diagnosed with Lyme disease. She was treated with amoxicillin.

Her son appeared healthy at birth and was initially sent home. At 4½ weeks of age, however, he returned with a fever of 101.7°F, sleepiness, and irritability.

The infant also had scleral icterus, or yellowing of the eyes consistent with jaundice. His spleen was enlarged, and a blood smear showed Babesia parasites in 2% of his red blood cells.

His blood counts dropped significantly:

• Hematocrit: 19.1%
• Platelets: 24,000 cells/mm³
• Absolute neutrophil count: 100 cells/mm³

These findings indicated severe anemia, thrombocytopenia, and neutropenia.

The infant was treated with azithromycin and atovaquone. His physicians selected this combination because they believed it would be better tolerated than clindamycin and quinine.

He was discharged after 10 days in the hospital and completed 14 days of treatment. According to the authors, he remained well following treatment.

Second Infant With Congenital Babesiosis

The second mother lived in Putnam County, New York. She experienced fever and muscle aches for two weeks before developing an erythema migrans rash at 37 weeks of pregnancy. She was treated with amoxicillin.

Her daughter was born one week later without perinatal complications. The infant tested positive for Babesia microti by PCR. Because she did not initially have symptoms, she was sent home without treatment.

At 18 days of age, the baby returned with malaise, tachycardia, and pallor. A blood smear showed Babesia parasites in 0.5% of her red blood cells.

Her hematocrit fell to 20.1%. She also developed neutropenia and thrombocytopenia.

The infant was treated with azithromycin and atovaquone. Because her anemia worsened and parasitemia persisted, clindamycin was added on the fourth day.

She also required a red blood cell transfusion because of worsening anemia, pallor, malaise, and tachycardia. The infant completed 14 days of combination therapy and recovered.

What Can We Learn From These Cases?

1. Babesia infection can occur during pregnancy without prominent maternal symptoms.
2. Babesia microti can rarely be transmitted from mother to baby.
3. An infant may appear healthy at birth and develop symptoms days or weeks later.
4. Congenital babesiosis can cause severe anemia, thrombocytopenia, and neutropenia.
5. A positive PCR result may precede the appearance of symptoms or visible parasites on a blood smear.
6. Some infants may require hospitalization and blood transfusion.

Questions Raised by These Cases

• How should pregnant women with Lyme disease in Babesia-endemic areas be evaluated for coinfection?
• Would the maternal infections have been recognized without the erythema migrans rashes?
• How should an asymptomatic newborn with a positive Babesia PCR test be monitored or treated?
• Could earlier recognition of Babesia in the second infant have prevented severe anemia and hospitalization?
• What are the safest and most effective treatment options for Babesia during pregnancy?

Clinical Takeaway

Congenital babesiosis is uncommon, but it should be considered when an infant from a Babesia-endemic area develops unexplained fever, pallor, jaundice, anemia, thrombocytopenia, or an enlarged spleen.

A newborn may initially appear healthy, and symptoms may not develop until several weeks after birth. Prompt clinical evaluation is particularly important when the mother had Lyme disease, a tick bite, an unexplained febrile illness, or possible Babesia exposure during pregnancy.

These two cases also demonstrate why clinicians should consider possible tick-borne coinfections when evaluating Lyme disease during pregnancy. Additional research is needed to determine the optimal screening, monitoring, and treatment strategies for pregnant women and exposed infants.

Frequently Asked Questions

Can Babesia be transmitted during pregnancy?

Yes. Although uncommon, Babesia microti can be transmitted from a pregnant mother to her baby. This is called congenital babesiosis or vertical transmission.

Can a baby appear healthy at birth despite congenital babesiosis?

Yes. Both infants in this report appeared healthy at birth but subsequently developed clinical illness. Symptoms may be delayed for days or weeks.

What are the symptoms of congenital babesiosis?

Reported findings include fever, sleepiness, irritability, pallor, jaundice, rapid heart rate, anemia, low platelet counts, low neutrophil counts, and enlargement of the spleen.

How is congenital babesiosis diagnosed?

Diagnosis may involve a blood smear, PCR testing, antibody testing, blood counts, and assessment of the infant’s symptoms and maternal exposure history.

Can congenital babesiosis be treated?

Yes. The two infants in this report recovered following antimicrobial treatment. One infant also required a red blood cell transfusion because of severe anemia.

This article is for educational purposes and is not a substitute for individualized medical evaluation or treatment.

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Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention