U.S. Blood Supply Vulnerable to Parasitic Infection Spread by Ticks

Babesia, a tickborne parasite of red blood cells, is being transmitted through blood transfusions, according to results of a collaborative study, led by the Centers for Disease Control and Prevention, of data from the past three decades. Transfusion-associated cases of babesiosis have been increasingly recognized since 1979, the year the first known case occurred. The article about the study and an accompanying editorial appear today online in the Annals of Internal Medicine.

In the report, CDC and collaborators describe 159 transfusion-related babesiosis cases that occurred during 19792009, most (77 percent) from 2000 to 2009. No Babesia test approved by the Food and Drug Administration is available for screening prospective blood donors, who can feel fine despite being infected.

Babesiosis is a potentially fatal but treatable complication of transfusion. Severe consequences, such as multi-organ failure and death, are most often seen in persons without a spleen, the elderly, and those with a weak immune system. The study authors say prevention strategies, including development of a screening test, are needed. Some manufacturers are working with investigators at blood establishments to develop FDA-approved tests for Babesia for donor-screening purposes.

"We want clinicians to become more aware of babesiosis, including the small possibility of transmission via blood transfusion," says Barbara Herwaldt, MD, MPH, CDC medical epidemiologist, and lead author of the article. "If a patient develops unexplained fever or hemolytic anemia after a transfusion, babesiosis should be considered as a possible cause, regardless of the season or U.S. region."

Because babesiosis is spread most commonly by ticks, the risk of this disease is another reason for people to prevent tick bites. People who unknowingly become infected through the bite of a tiny tick (about the size of a poppy seed) can transmit the parasite via blood transfusion. Therefore, prevention of tickborne infection can help safeguard the blood supply.

Most U.S. tickborne Babesia cases have occurred in seven states in the Northeast and the upper Midwest (in parts of Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, and Wisconsin), particularly during the warm months of the year. However, transfusion-associated Babesia cases have been identified in 19 states and have occurred year-round.

Herwaldt points out that even severe Babesia cases, not just cases that are asymptomatic or mild, are easily missed unless the diagnosis is considered. Even then, babesiosis often is mistakenly diagnosed as malaria, which also infects red blood cells.

In January 2011, babesiosis became a nationally notifiable disease, which means state health departments are encouraged to share information about cases of babesiosis with CDC. More accurate information about tickborne and transfusion-transmitted cases of babesiosis will help CDC and its partners, including the Food and Drug Administration, in their continued efforts to make the blood supply even safer.