Lassa virus is an Old World arenavirus that causes Lassa fever, an acute viral haemorrhagic illness endemic to West Africa. The virus is an enveloped, single‑stranded bi‑segmented RNA virus with an ambisense coding strategy and belongs to the family Arenaviridae. Its natural reservoir is the multimammate rat (Mastomys natalensis), and human infection occurs through exposure to rodent urine or feces or via person‑to‑person transmission.
Explanation
Arenaviruses are spherical, enveloped viruses approximately 80–120 nm in diameter. Their genome comprises two single‑stranded RNA segments (L and S) that encode the RNA‑dependent RNA polymerase, glycoprotein precursor, nucleoprotein and a zinc‑binding protein. Lassa virus was first isolated in 1969 in Nigeria after a cluster of haemorrhagic fever cases in the town of Lassa. It is classified as an Old World arenavirus and is closely related to the viruses that cause lymphocytic choriomeningitis. Lassa virus is endemic in countries of West Africa including Benin, Ghana, Guinea, Liberia, Mali, Nigeria and Sierra Leone. The multimammate rat carries the virus asymptomatically and sheds it in urine and faeces. Humans become infected through ingestion or inhalation of contaminated material and via direct contact with infected body fluids. Person‑to‑person transmission occurs in healthcare settings if proper infection control is not practiced. The incubation period ranges from 2 to 21 days. Most infections (about 80 %) are mild or asymptomatic, but about one in five infected individuals develops severe multi‑system disease with fever, vomiting, hypotension, bleeding and neurological involvement. Overall case‑fatality is around 1 %, but among patients requiring hospitalization mortality exceeds 15 %, and infections during pregnancy are frequently fatal for both mother and fetus. There is currently no licensed vaccine; treatment relies on early administration of ribavirin and supportive care. Prevention focuses on reducing rodent populations, keeping food and household items away from rodents and implementing infection control measures in health facilities.
Examples and public health aspects
Lassa fever causes periodic outbreaks in West Africa. Large epidemics have occurred in Nigeria and Sierra Leone, often associated with dry‑season increases in rodent populations. Healthcare workers are at particular risk when caring for undiagnosed patients, and transmission through contaminated medical equipment has been documented. The disease disproportionately affects rural communities where rodent exposure is common. Programmes to improve housing, store food properly and educate the public about rodent control are key components of prevention. Serological studies indicate that a significant proportion of the population in endemic areas has been exposed to Lassa virus, highlighting its widespread circulation.
Lassa virus is a rodent‑borne arenavirus that remains a major public health concern in West Africa. Continued surveillance, improved diagnostics, development of effective vaccines and strengthening of infection control practices are essential to reduce the burden of Lassa fever.
Related Terms: Lymphocytic Choriomeningitis Virus, Junin Virus, Machupo Virus, Guanarito Virus, Chapare Virus