Emerging pathogens and possible threats to blood services

New pathogens emerge regularly. These new agents include both bacterial and viral pathogens. Many viral agents have a viremic phase during the course of infection and are transmitted by blood transfusion. New infectious agents provide a major challenge for blood services. The extend and mode of transmission through blood is initially unclear. Serological tests and molecular tools are used to detect infectious donors. A residual risk remains due to the diagnostic window period and sensitivity limits of the tests systems. Some detection systems proved to be extremely helpful, e.g. for HIV, HCV or WNV, but sometimes provide in certain periods of the infection false‐negative results due to sensitivity problems or to escape mutants (e.g. Hepatitis B). WNV provides an excellent example, how rapid and efficient blood donation services coped with this new threat for blood safety. Not all emerging infectious agents transmissible by blood represent a threat for the health. A number of putative pathogens turned out later not to be associated with pathogenesis. Prion diseases represent a particular challenge for detection in blood donors. Since the ‘normal’ cellular form the host protein is widely distributed, the usual nucleic acid amplification systems or serological tests are not feasible. Extremely sensitive tests (picogram range) are required for detection of the pathological protein in the asymptomatic period. Variants of existing viruses e.g. newly emerging Influenza A subtypes with the potential for pandemic spread represent an enormous threat for public health and for the safety of blood. Blood services should take precautions for an influenza pandemic. The mosquito borne Chikungunya virus turned out to be transmitted by blood transfusion and caused many infections in the islands of the Indian Ocean and in India. Newly emerging infectious agents require attention and rapid actions in order to guarantee a safe and reliable blood supply.