Lassa fever is a viral hemorrhagic fever caused by Lassa virus (Lassa mammarenavirus), a negative-sense singlestranded RNA virus of the Arenaviridae family. [1][2] In most cases Lassa virus infection is asymptomatic (presenting no symptom). [1] When symptomatic it is characterized by mild acute febrile disease to a chronic fatal disease with severe toxaemia, capillary leak, hemorrhagic situations, shock and multiple organ failure. [3] Early diagnosis of Lassa fever is very important because of the transmissibility of infection, the need for potent isolation of infected persons and for containing potentially infectious specimens during laboratory testing. [4][5] Lassa fever was first elucidated in the 1950s, but the virus was not recognized until 1969 when it infected two missionary nurses in Lassa Village, Borno State, Northeastern Nigeria. [1] Natal multimammate rat or common African rat of Mastomys genus are the reservoir of Lassa virus. [1] When the rodents become infected with Lassa virus, they infect humans through their urine and faeces, but remain unharmed. [6] Because of its similarities with other febrile diseases such as malaria, typhoid, Ebola hemorrhagic fever, early detection is difficult. Thus when persons have persistent fever not responding to normal conventional therapies, they should be screened for other possible causes (especially in endemic regions). When the presence of Lassa fever is established in a community, immediate isolation of infected individuals, screening, standard infection prevention and control practices and meticulous contact tracing can halt outbreaks. [1] Treatment involves supportive measures and early use of the antiviral drug ribavirin.
Note: This article has been updated since its initial publication on 15 Jun 2019 (summary of changes). The previous version is archived at this link as a record.
Pathophysiology
Main article: Lassa virusLassa virus is a single-stranded, negative-sense RNA virus (Figure 1). [4] The transmission of Lassa virus to humans can occur through direct contact and aerosols generated from the urine or feces of an infected rodent. [6] Natal multimammate rats shed the virus in urine and droppings, direct contact with these excreta, through touching soiled objects, eating contaminated food, or exposure to open cuts or sores, can lead to infection. [6][7] There have been reports of sexual transmission of Lassa fever but it is rare. [8] High serum virus titres, combined with disseminated replication in tissues and absence of neutralizing antibodies (immuno-compromisation), lead to the development of Lassa fever. [4] However, an intact and active immune response is protective against developing symptoms by mounting the early innate immune response in order to prevent further infection and virus growth, which in turn attenuates humoral and cell-mediated immunity. [6][9][10] Due