Lassa virus (LASV) is an arenavirus that causes Lassa hemorrhagic fever, a type of viral hemorrhagic fever (VHF), in humans and other primates. Lassa virus is an emerging virus and a select agent, requiring Biosafety Level 4-equivalent containment. It is endemic in West African countries, especially Sierra Leone, the Republic of Guinea, Nigeria, and Liberia, where the annual incidence of infection is between 300,000 and 500,000 cases, resulting in 5,000 deaths per year.