Lassa virus (LASV) is an Old World arenavirus that causes Lassa hemorrhagic fever, a type of viral hemorrhagic fever (VHF) in human and non-human 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. Recent discoveries on the Lassa Virus within the Mano River Region provide evidence will require the expansion the endemicity zone between the two known Lassa endemic regions, indicating that LASV is more widely distributed throughout the Tropical Wooded Savanna ecozone in West Africa. Currently, there are no approved vaccines against Lassa fever for use in humans.