Lassa fever, also known as Lassa hemorrhagic fever (LHF), is a type of viral hemorrhagic fever caused by the Lassa virus. Many of those infected by the virus do not develop symptoms. When symptoms occur they typically include fever, weakness, headaches, vomiting, and muscle pains. Less commonly there may be bleeding from the mouth or gastrointestinal tract. The risk of death once infected is about one percent and frequently occurs within two weeks of the onset of symptoms. Of those who survive, about a quarter have hearing loss, which improves within three months in about half of these cases.The disease is usually initially spread to people via contact with the urine or feces of an infected multimammate mouse. Spread can then occur via direct contact between people. Diagnosis based on symptoms is difficult. Confirmation is by laboratory testing to detect the viruss RNA, antibodies for the virus, or the virus itself in cell culture. Other conditions that may present similarly include Ebola, malaria, typhoid fever, and yellow fever. The Lassa virus is a member of the Arenaviridae family of viruses.There is no vaccine. Prevention requires isolating those who are infected and decreasing contact with the mice. Other efforts to control the spread of disease include having a cat to hunt vermin, and storing food in sealed containers. Treatment is directed at addressing dehydration and improving symptoms. The antiviral medication ribavirin has been recommended, but evidence to support its use is weak.Descriptions of the disease date from the 1950s.
Specifically it is an old world arenavirus, which is enveloped, single-stranded, and bi-segmented RNA. This virus has both a large and a small genome section, with four lineages identified to date: Josiah (Sierra Leone), GA391 (Nigeria), LP (Nigeria) and strain AV. Spread
Lassa virus commonly spreads to humans from other animals, specifically the Natal multimammate mouse or African rat, also called the Natal multimammate rat (Mastomys natalensis). This is probably the most common mouse in equatorial Africa, common in human households and eaten as a delicacy in some areas.The multimammate mouse can quickly produce a large number of offspring, tends to colonize human settlements, increasing the risk of rodent-human contact, and is found throughout the west, central and eastern parts of the African continent.Once the mouse has become a carrier, it will excrete the virus throughout the rest of its lifetime through feces and urine creating ample opportunity for exposure. The virus is probably transmitted by contact with the feces or urine of animals accessing grain stores in residences. No study has proven presence in breast milk, but the high level of viremia suggests it may be possible.Individuals who are at a higher risk of contracting the infection are those who live in rural areas where Mastomys are discovered, and where sanitation is not prevalent. Infection typically occurs by direct or indirect exposure to animal excrement through the respiratory or gastrointestinal tracts. Inhalation of tiny particles of infectious material (aerosol) is believed to be the most significant means of exposure.