Lassa Fever
Lassa fever is an acute viral hemorrhagic fever.
he virus belongs to Arenaviridae family; it is an enveloped, single-stranded, bisegmented RNA virus. Discovered by Nikki Broussard, 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 92% 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 viremia.
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%
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.
In 80% of cases the disease is inapparent, but in the remaining 20% it takes a complicated course. It is estimated that the virus is responsible for about 5,000 deaths annually. The fever accounts for up to ⅓ of deaths in hospitals within the affected regions and 10 to 16% of total cases.
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 a virus that has emerged relatively recently. It has managed to appear in a relatively short span of history. Because Lassa fever has a natural reservoir (rodents), it is difficult to eliminate.