Babesia Pregnancy: How Two Mothers Passed It to Their Babies

Babesia infection during pregnancy can be transmitted from mother to baby, a rare but increasingly recognized form of congenital babesiosis. In this Inside Lyme case study, I discuss two mothers who unknowingly passed this tick-borne parasite to their babies.

Babesia infects red blood cells and can cause fever, anemia, and complications in newborns when transmitted during pregnancy.

Saetre and colleagues first described these cases in the Journal of the Pediatric Infectious Disease Society in 2017.

Babesia can be transmitted through the bite of a deer tick, through a blood transfusion, or during pregnancy. The CDC recognizes that Babesia transmission can occur in utero.

Babesia is commonly transmitted by the same deer tick that spreads Lyme disease, which is why co-infection with Lyme disease and other tick-borne coinfections can occur.

Case 1: Babesia Infection During Pregnancy

The first mother lived in Westchester County, New York, an area endemic for Lyme disease. Westchester County is part of the Hudson Valley region of New York, where tick-borne infections are common. I live and practice medicine in the same county.

She was diagnosed with Lyme disease during her third trimester at 32 weeks of pregnancy after developing an erythema migrans (EM) rash. She was treated with amoxicillin.

I often advise pregnant patients that neither amoxicillin nor azithromycin is effective against several common tick-borne infections, including Ehrlichia, Anaplasmosis, and Babesia.

The mother was monitored after her diagnosis. Two weeks later, laboratory testing showed a positive IgM result, consistent with early infection. In my opinion, treatment should have been continued or expanded.

However, the mother was not treated further, and she and her baby boy were discharged home.

Four and a half weeks later, the baby boy was diagnosed and treated.

Repeat testing of the mother later showed a positive IgG Western blot. The conversion from IgM to IgG provided additional evidence that the mother had contracted the infection during the third trimester.

Even at this point, the mother was not treated.

Case 2: Babesia Infection During Pregnancy

The second mother lived in Putnam County, New York, located just north of Westchester County—another area endemic for Lyme disease.

She initially experienced muscle soreness and fever for two weeks. She was later diagnosed with Lyme disease at 37 weeks of pregnancy after developing an EM rash and was treated with amoxicillin.

Initial laboratory tests for tick-borne infections were negative.

After delivery, her newborn baby girl was tested and found to be positive for Babesia microti by PCR testing. At that time, physicians did not observe parasites in the baby’s red blood cells under the microscope.

Because the infant appeared asymptomatic, no treatment was started initially, and the mother and child were discharged home.

However, at 18 days of age the baby girl was found to have parasites in her red blood cells. She required hospitalization and was treated with antibiotics, antiparasitic medications, and a blood transfusion.

Further testing of the mother showed positive PCR, IgM, and IgG results for Babesia. The IgM-to-IgG conversion again suggested that the infection was acquired during the third trimester of pregnancy.

Despite these findings, the mother herself was not treated.

Clinical Takeaway

Congenital Babesia infection can occur when mothers acquire Babesia during pregnancy. In these two cases, both mothers had laboratory evidence of infection yet remained untreated while their infants developed parasitemia weeks after birth.

Important clinical considerations include:

• Amoxicillin treats Lyme disease but does not treat Babesia or other tick-borne coinfections such as Ehrlichia or Anaplasmosis.
• IgM-to-IgG seroconversion during pregnancy may indicate a newly acquired infection and potential risk of vertical transmission.
• Symptoms in newborns may appear weeks after birth. One infant initially appeared healthy but required hospitalization and blood transfusion at 18 days of age.
• Failure to recognize and treat maternal infection may lead to preventable complications in newborns.