Emerging viruses are viruses that appear suddenly in the human population. These are viruses to which man has no history of exposure and thus no or limited immunity; they are not new evolutionary creations, but are viruses than man meets due to environmental changes, such as deforestation, entering into new habitats, or viruses that are transmitted from one species of animal to humans. Most of these viruses are terrifying, and cause hemorrhagic fever, a complete destruction of the circulation system; they include Lassa fever, Nipah virus, Ebola, HIV, Severe acute respiratory syndrome (SARS), and, recently, Middle East respiratory syndrome (MERS), which is the latest in a series of “new” respiratory viruses infecting man. It is possible that unknown emerging viruses are the cause of death, often listed as “death due to an unknown cause,” as in the retrospective cases of HIV. Emerging viruses might also include poliovirus and influenza, since their introduction into the human population is (was) often sudden and due to changes in the environment or due to contact with other animal species. For examples, polio was a result of changes in sanitation in the countries of North America and Western Europe, and influenza is constantly jumping from aquatic birds to man and other animal species where genomic reassortment occurs.