Human babesiosis is a tick-borne zoonosis caused by protozoa of the genus Babesia
. Although the genus comprises more than 100 species, most cases of human babesiosis in North America are caused by B. microti
usually transmitted by a bite from the deer or black-legged tick, Ixodes scapularis
Current areas where the disease is endemic include the northeastern (notably New York State [specifically Long Island], Connecticut, Rhode Island and Massachusetts [specifically Cape Cod, Nantucket and Martha's Vineyard]) and upper midwestern (notably Wisconsin) United States. As was the case for the infected donor described here, people with babesiosis may remain asymptomatic but parasitemic for months to years after tick transmission of the infection.6
The clinical manifestations of babesiosis range from no symptoms to severe, occasionally fatal disease characterized by fever, intravascular hemolysis and renal failure. Severe disease is more common in asplenic people, elderly patients and those with underlying immunodeficiency, including AIDS.5,7,8
Even with treatment, the case fatality rate in a series of 136 patients in New York State was 5%.5
parasites invade the erythrocytes and remain viable under blood bank conditions, making transfusion-transmitted babesiosis a risk of transfusion with blood components such as platelet concentrates, packed erythrocytes, and frozen, thawed and deglycerolized erythrocytes.9,10,11,12,13,14
At least 21 cases of babesiosis acquired by blood transfusion have been recognized in the United States, which makes babesiosis the most commonly reported transfusion- transmitted tick-borne infection.9,10,11,12,13,14
In a study of transfusion recipients in Connecticut, an area where babesiosis is endemic, Gerber and colleagues13
reported a risk of 0.17% per unit of packed erythrocytes. The risk of acquiring babesiosis from a blood transfusion in Canada is unknown, but we suspect that it is very low.
This is the first reported case of transfusion-transmitted babesiosis in Canada.15
Remarkably, the first recognized case of babesiosis in Canada was reported only 2 years ago, in 1999.1
The present case highlights the rapidity with which newly recognized infectious agents can threaten blood safety.
In Canada, blood banks do not routinely ask donors about travel to Babesia
-endemic areas, tick bites or history of babesiosis. Because most immunocompetent people who acquire babesiosis do not remember receiving a tick bite and most have either minimal or no symptoms, few infected donors would be identified by such questioning. Most cases of babesiosis in the northeastern United States are acquired during peak tick activity (June to September).4
Consequently the risk of transfusion-transmitted babesiosis might be expected to be greatest during the summer.13
However, infected people may remain parasitemic for up to several years and packed erythrocytes are stored for up to 42 days, so even seasonal deferral of potentially high-risk donors could not be expected to prevent this problem.
As in previously reported cases of transfusion-transmitted babesiosis in the United States, the recipient of the infected blood product in this case exhibited moderate to severe manifestations of infection,9
beginning within the typical period of symptom onset (usually 4 to 9 weeks after transfusion9,10,11,12,13,14
). Both the donor and the recipient were treated with a combination of quinine and clindamycin, and both had a satisfactory response. Recent reports have described a number of patients who have not responded optimally to this traditional therapy. These patients generally responded to the combination of azithromycin and atovaquone.16,17
Given the large numbers of Canadians who visit Babesia
-endemic regions of the United States each year, we must anticipate an increase in the number of cases of imported babesiosis and the potential for transfusion-transmitted disease in this country. As the geographic distribution of animal reservoirs and tick vectors increases, the incidence of babesiosis and subsequent transfusion-transmitted infections can also be expected to increase.3,14,18,19
Furthermore, tick-borne and transfusion-transmitted infections with related parasites, including the piroplasms WA1 and MO1, have recently been reported.20,21
Canadian physicians must consider babesiosis in the differential diagnosis of any patient who experiences fever or a hemolytic reaction soon after blood transfusion. Prompt recognition and accurate diagnosis are important, because even though Babesia infections usually respond to therapy, they may be severe or fatal in certain risk groups. Better strategies to prevent transfusion-transmitted babesiosis are required.