An acute viral illness of the arenavirus family. A disease native to West Africa, Lassa Fever is endemic in Guinea, Liberia, Sierra Leone and Nigeria. Lassa Fever was first observed and described in the 1950s, but the Lassa virus itself was not isolated until 1969, when two missionary nurses died in Nigeria. The disease was named for the town in Nigeria where the first cases were observed.

Onset of Lassa Fever is gradual, with an incubation period of 6-21 days, and with the acute (symptomatic) phase of the disease running over a period from one to four weeks and presenting the following symptoms:

In severe cases, the following extreme symptoms may occur:

The mortality rate among hospitalised patients is approximately 15%. In cases where the patient is pregnant, miscarriage occurs in over 80% of cases. However, many cases are not so severe as to require hospitalisation, and the overall mortality rate among infected individuals is only about 1%.

Recovering patients often experience hair loss and loss of coordination. Additionally, roughly one patient in four develops temporary or permanent hearing loss. Some immunising effect is known to occur, but the extent of the immunity granted by a past infection is unknown.

Lassa Fever can be difficult to distinguish from severe malaria, septicaemia, and other viral haemorrhagic fevers (such as Ebola). Once diagnosed, treatment in the initial stages of the disease (within the first six days of symptoms) with Ribavirin (an antiviral drug) may be effective.

Like many emergent diseases Lassa Fever is a zoonosis (a disease usually present in an animal reservoir), dwelling in wild rodents, particularly in the multimammate rat, Mastomys natelensis. Disease transmission to humans is usually through contact with rodent excreta. The virus may also spread through person-to-person contact, via direct contact with blood, pharyngeal (throat) secretions, urine and sexual intercourse. A patient is usually infectious for up to three months following onset of the symptomatic phase.

Lassa Fever may be combatted by rodent control, quarantine, isolation of patients. Anything that comes into contact with the patient should be carefully disinfected as appropriate. Once a subject has been identified as being infected, his or her known contacts should be screened for the virus, and possibly be given Ribavirin prophylactically.

Collated from WHO/CDC sources

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