#27: Babesia Parasite Taints the Blood Supply

Blood transfusions have infected 159 patients with the malaria-like parasite.

By Linda Marsa
Jan 5, 2012 6:00 AMNov 12, 2019 5:34 AM


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A report released earlier this year confirmed something that has increasingly concerned public health authorities over the past decade or so: In the last 30 years, blood transfusions caused at least 159 cases of babesiosis, an emerging infectious disease that is normally transmitted by ticks. And the risk may be increasing because the majority of these incidents—77 percent—occurred between 2000 and 2009. Twenty-eight of the patients died soon after their transfusions, and in many cases, the infection may have contributed.

Babesia, a malaria-like parasite that infects red blood cells, “has become the most frequently reported infectious agent transmitted by blood transfusions in the U.S.,” says Barbara Herwaldt, a medical epidemiologist at the Centers for Disease Control and Prevention who was lead author on the report. And these numbers may represent a small fraction of the actual cases, because babesiosis is often missed or misdiagnosed as malaria or flu.

Once known as Nantucket fever because some of the first cases were reported on the Massachusetts island, Babesia can cause such flulike symptoms as fever, headaches, chills, and drenching sweats. It can be treated with antibiotics. But the tickborne disease can become quite serious or even fatal for patients with weak immune systems—like neonates and infants, the elderly, or people without a spleen—causing anemia, organ failure, and death.

The recent spike in reported cases probably resulted both from an actual rise in incidence of the disease and from doctors’ growing skill in identifying it, Herwaldt says. The parasite’s range may also be expanding.

Currently there is no approved test to screen donors for Babesia. Parasitologist David Leiby, head of the Transmissible Diseases Department at the American Red Cross’s Holland Laboratory, hopes the new study, which for the first time gives a clear picture of the threat’s magnitude, will galvanize the search for a screening tool. But contracting babesiosis remains a small risk when one considers the millions of blood transfusions done every year. “It’s not a hidden epidemic,” Leiby says.

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