Classification: ICD-9 078.8; ICD-10 A96.2
Agent: Lassa fever virus (LFV), a spherical, enveloped, bi-segmented negative strand RNA virus of the genus Arenavirus in the family Arenaviridae.
Reservoir: The multi-mammate rat (Mastomys natalensis), which lives in houses and surrounding fields. Previous studies that identified M. erythroleucus and M. huberti as reservoirs may have confused the species. M. natalensis is generally absent in coastal West Africa.
Transmission: By inhalation of aerosolized excreta of the rodent host, or contact with food or household items contaminated with rodent excreta. Nosocomial transmission is regular in resource-constrained settings.
Cycle: Rodent–rodent, with humans as accidental dead-end hosts. Infected reservoir hosts are asymptomatic and excrete infectious virus in the urine.
Incubation period: 6–21 days, usually 7–12 days.