Investigation of transfusion transmission of a WA1-type babesial parasite to a premature infant in California

Background: A premature infant in California developed respiratory distress associated with infection with a protozoal parasite, Babesia. The infant had received two blood transfusions, one from the father and one from an anonymous donor (Donor A). This study describes the follow-up required to identify the source and species of Babesia that infected the infant. Study design and methods: At the time of the infant's illness, whole blood from the infant, father, and mother was evaluated for Babesia infection. Similar evaluation of whole blood from Donor A was performed 2 months after the suspected donation to the infant. Samples were tested using blood smear examination, serology, PCR, and hamster inoculation. Identity of the recovered Babesia parasites was confirmed by DNA amplification by PCR, genetic sequencing of the 18S gene, and phylogenetic analysis. Results: WA1-type Babesia was recovered from the infant. Neither parent was the source of infection. Serology and hamster inoculation confirmed WA1-type Babesia infection in Donor A. DNA sequences of the 18S gene from the infant and donor isolates were 100% identical. Conclusion: WA1-type Babesia infections may be difficult to detect among blood donors because such infections can be subclinical. This is the second WA1-type Babesia transmission via blood transfusion and the first in an infant. Physicians in the western United States should consider Babesia as a possible cause of nonspecific febrile illness after a blood transfusion.