The protection of patients from diseases carried in blood transfusions is an ongoing effort. The viruses that cause long-term human infection and death have received much of the attention in the United States and testing has significantly diminished the risk of infection from a transfusion. As the risk of these diseases has decreased, other transfusion-transmitted organisms with a lower incidence in the community or newer diseases with rapidly expanding endemic areas are receiving additional attention. One group of these infections are infections in which the normal route of human infection is a vector.