Time to Become Familiar With Babesiosis?

Paul G. Auwaerter, MD


July 01, 2015

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I am Paul Auwaerter with the Division of Infectious Diseases at Johns Hopkins University School of Medicine.

Babesiosis is an infection that few people have encountered unless they happen to live in the coastal areas of New England where the disease has historically been present[1] However, babesiosis may soon have a higher profile, in part because of considerations about whether to screen the US blood supply more carefully for Babesia.

The story begins with the Babesia parasite, which behaves like malaria and infects red blood cells, potentially becoming a source of febrile illness. The parasite is transmitted by the black-legged deer tick—Ixodes scapularis—the same vector that transmits Lyme disease. Babesiosis is much less common than Lyme disease, of which there are more than 30,000 cases annually. However, babesiosis is becoming more prominent: 1762 cases were described in 2013.[1,2] Although babesiosis is a nationally reportable disease, only 27 states have decided to conduct passive surveillance. There are also some emerging foci of infection as this disease spreads geographically, even into Pennsylvania and Maryland.

Less well known is the fact that babesiosis is the single most common transfusion-related infection. There were 63 cases from 2004 to 2008, and more than 200 transfusion-related cases of Babesia have been reported since 2000.[2] In part, this is because many people who are infected by the parasite remain entirely asymptomatic and unaware that they have been bitten by a tick and that they have the parasite in their red blood cells.

Blood banks are not currently conducting uniform surveillance for Babesia, although some states (such as Connecticut and Rhode Island) have screened their blood supplies. The US Food and Drug Administration (FDA) recently convened a panel to explore this interesting question.[3] This is a regional disease, but it might have national significance because people travel and can donate blood in a state where the disease is not endemic. The FDA panel recommended a zero-tolerance policy, with national antibody screening of the blood supply for Babesia microti as well as selected molecular testing in endemic states.

Mixed modeling studies have suggested that screening would be extremely costly—more than $1 million [per quality-adjusted-life-year (QALY)] in endemic states in one study,[4] whereas another study indicated that screening would be cost-effective, at less than $50,000/QALY.[5]

It remains to be seen whether the FDA adopts the panel's recommendation. If so, then infectious disease practitioners, family medicine practitioners, and internists may find their frequent blood donors suddenly flagged for being positive for Babesia antibodies. Such antibodies can persist in a subset of patients for years after they have cleared the infection.[6] It does not mean that they still are infectious, [and the antibodies may be the result of cross-reactivity or false positive reactions]. These questions will come up, and the organism will have a much higher profile, if universal screening is adopted.


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