This 2007 image depicted Centers for Disease Control microbiologist Dr. Thomas Stevens as he was peering out from inside the BSL-4 laboratory autoclave room into the outer corridor. The Special Pathogens Branch works with Biosafety Level 4 (BSL-4) viruses. These viruses are highly pathogenic and require handling in special laboratory facilities designed to contain them. Our mission focuses mainly on viral hemorrhagic fevers (VHFs). such as Ebola hemorrhagic fever. Lassa fever. hantavirus pulmonary syndrome (HPS). and hemorrhagic fever with renal syndrome (HFRS). Our work also includes the study of other emerging viral disease agents that do not cause hemorrhagic fever. but require BSL-4 handling. such as Nipah virus and tick-borne encephalitis virus. All of the viruses we work with are zoonotic (animal-borne). lipid-enveloped RNA viruses. Some of them are rare. whereas others are quite common and cause frequently debilitating or fatal disease in many thousands of people. Some of the virus types are found in relatively small geographic areas. others are distributed over continents. If you were to draw a map showing where these viruses were found collectively. your map would cover most of the inhabited regions of the globe.