• SARS
• severe acute respiratory syndrome

History is replete with accounts of novel viral epidemics. Many of these viruses, like the human immunodeficiency virus or influenza virus, have become endemic. Others, like Ebola or Sin Nombre viruses, cause outbreaks when conditions facilitating their transmission from animal to human hosts (still unknown in the case of Ebola) are met. Some epidemics, such as the one caused by Nipah virus in Malaysia and Singapore, have occurred only once, but the potential for recurrence exists because of the presence of animal reservoirs. Even when diseases are apparently eradicated, the possibility of unnatural recurrences because of acts of bioterrorism must be considered. Although smallpox …