Pathogens of the Babesiosis disease are small protozoa of the genus Babesia. The pathogens occur worldwide and are transmitted by ticks of the family Ixodidae to various vertebrates (e.g. mice, dogs, horses, cattle) and humans. In Europe, human infections are dominated by Babesia divergens, in the United States by Babesia microti (on the east coast and in the midwest) and Babesia duncani (on the northwest coast). Babesia microti is transmitted by the same tick species, Ixodes scapularis, which also transmits the borreliosis and ehrlichiosis pathogens. Babesia divergens is transmitted by the Common Woodbuck (Ixodes ricinus).
Since Babesia infect the erythrocytes, they can also be transmitted by blood transfusion and transplantation of organs. For this reason, people suffering from Babesiosis are excluded from blood donation.
Babesiosis is transmitted in many parts of the world, but the highest prevalence is reported in the United States. The first documented human case of babesiosis in the USA was identified in 1968. Other Babesia species such as B. duncani and related organisms are involved in the transmission of Babesia in several western US states.
The vast majority of B. microti infections are asymptomatic and never diagnosed. While the exact duration of B. microti infections in healthy adults is not clearly known, limited studies report that the parasitemic period lasts 2 to 7 months, but parasitemia may last longer than 2 years. Although Babesia transmission is seasonal and coincides with tick activity (traditionally May-September), both tick-borne and transfusion-borne infections are reported year-round. Unfortunately, there is insufficient data on the proportion of Babesia infections that persist as asymptomatic, chronic infections. In a study on Block Island, Rhode Island, one third of Babesia infections were asymptomatic, although the sample size was too small to draw firm conclusions. Transfusion of blood and blood components collected from asymptomatic donors can lead to TTB, which can lead to potentially fatal clinical conditions in recipients of blood transfusions.
For this reason, the FDA has issued a document containing recommendations for blood establishments for donor screening, donor testing, donor transfer and product management to reduce the risk of transfusion-borne babesiosis (TTB). The recommendations contained in this guide apply to the collection of blood and blood components, with the exception of source plasma.
For detailed information, please refer directly to the draft recommendation under "Recommendations for Reducing the Risk of Transfusion-Transmitted Babesiosis".