Babesia: impact of cold storage on the survival and the viability of parasites in blood bags.

Babesiosis is a tick-borne zoonotic disease endemic in the north-east and Midwest US[1]. There are multiple species of Babesia that invade and infect the red blood cells of various animal species, however, only a few of them have been shown to be zoonotic. Primarily among these are B. microti, a rodent parasite that is responsible for most of the infection in the US; B. divergens, a cattle parasite seen primarily in Europe [2], although B. divergens like variants have been found in the US [3]; and B. duncani, a few cases of which have been identified in California [4,5]. Besides their natural route of transmission through tick bites, the spread of Babesia is becoming increasingly common and problematic through blood transfusions. In fact, babesiosis has become the most frequent transfusion-transmitted infection with approximately 162 cases reported since 1980 and 12 associated fatalities in the period 2005–2008 [6–9]. These figures probably undercount the actual number of transfusion-associated cases [6]. This is because the disease is clinically silent in most healthy adults who are the bulk of blood donors. In the absence of a licensed test, current safeguards against babesia remain a questionnaire relating to past history of the infection and have not proven to be effective in protecting against the parasite [10]. In order that the parasite be successfully transmitted by transfusion, it has to survive at 4°C, under the same conditions used for storing donor blood [11]. A recent paper on P. falciparum, the malaria parasite showed that the parasite remains detectable in blood smears upto 28 days, although after 14 days it is no longer viable [12]. As this question has not been reliably investigated for babesia, we performed a similar study, using B. divergens, which is currently the only babesial pathogen capable of causing disease in man that can be cultured in human RBCs in vitro. B. divergens, however, has been shown to be a transfusion threat only in Europe and not in the US.