Depicted here in this 2007 photograph. was Centers for Disease Control microbiologist. and Special Pathogens Branch (SPB) staff member. Zachary Braden as he was in the process of counting viral plaques within fixed monolayers of cells. which had been set atop a light box. While inside the organizationˇs Biosafety Level 4 (BSL-4) laboratory. this activity was taking place so that Mr. Braden would be able to titrate a viral stock. Zachary was outfitted in an orange air-tight. self-contained. positively-pressurized suit. which kept him free of possible contamination. The Special Pathogens Branch's (SPB) charter is the study of highly infectious viruses. many of them causing hemorrhagic manifestations in humans. Our daily work involves the investigation of viruses such as Ebola hemorrhagic fever. Marburg hemorrhagic fever. Lassa fever. Rift valley fever virus. Crimean-Congo hemorrhagic fever virus. arenaviruses and hantaviruses. and other recently identified and emerging viral diseases. Almost all of these viruses are classified as Biosafety Level 4 (BSL-4) pathogens and as such must be handled in special facilities designed to contain them safely. SPB operates one of the world's few BSL-4 laboratories. In addition. SPB provides technical and research/diagnostic materials to many international laboratories and collaborators. SBP staff members are trained to respond to global disease outbreaks and to provide assistance for disease detection and control measures.