Lassa fever

Lassa fever is an acute viral hemorrhagic fever first described in 1969 in the Nigerian town of Lassa in the Yedseram River valley. Clinical cases of the disease had been known for over a decade earlier but not connected with this viral pathogen.
The infection is endemic in West African countries, causing many deaths. Outbreaks of the disease have been observed in the following countries: more...

• Nigeria
• Liberia
• Sierra Leone
• Guinea
• Central African Republic

but it is believed that human infections also exist in:

• Democratic Republic of the Congo
• Mali
• Senegal

It is also the most common hemorrhagic fever that is exported beyond its endemic area to countries like the United States, United Kingdom, The Netherlands, Japan and Israel.

The virus and epidemiology

The virus belongs to Arenaviridae family; it is an enveloped, single-stranded, bisegmented RNA virus. It has been determined that the virus is zoonotic (transmitted from animals), and that it spreads to man from rodents, specifically multimammate rats (Mastomys natalensis). This is probably the most common rodent in equatorial Africa, ubiquitous in human households and eaten as a delicacy by up to 90% of people in some areas. In these rats infection is in a persistent asymptomatic state. The virus is shed in their excreta (urine and feces), which can be aerosolized.

In fatal cases Lassa fever is characterized by impaired or delayed cellular immunity leading to fulminant viraemia.

The dissemination of the infection can be assessed by prevalence of antibodies to the virus in populations of:

• Sierra Leone 8–52%
• Guinea 4–55%
• Nigeria approx. 21%

Like other hemorrhagic fevers, Lassa fever can be transmitted directly from one human to another. It can be contracted by an airborne route or with direct contact with infected human blood, urine, or semen. Transmission through breast milk has also been observed.

Lassa fever is less deadly compared to ebola, though they share similar symptoms. Because Lassa is a very fast replicating and debilitating virus, the chances of a worldwide epidemic are small. Patients are far too weak to board a plane and spread it to other parts of the world.

Lassa fever is a virus that has emerged relatively recently. It has managed to appear in a relatively short span of history. Because Lassa fever has a reservoir (rodents), it is difficult to get rid of the virus.

The disease

Infection in humans typically occurs via exposure to animal excrement through the respiratory or gastrointestinal tracts. Inhalation of tiny particles of infective material (aerosol) is believed to be the most significant means of exposure. It is possible to acquire the infection through broken skin or mucous membranes that are directly exposed to infective material. Transmission from person to person has also been established, presenting a disease risk for healthcare workers. Frequency of transmission via sexual contact has not been established.

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