Lassa fever causes
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: {Ammu}}
Overview
Lassa fever is caused by the Lassa virus, a member of the Arenaviridae family; it is an enveloped, single-stranded, bisegmented RNA virus. Replication for Lassa virus is very rapid, while also demonstrating temporal control in replication. There are two genome segments. The first step involved is making mRNA copies of the negative-sense genome. This ensures that there are adequate proteins, which are required for replication. The N and L proteins are made from the mRNA produced. The -ve sense genome then makes vcRNA (viral circular RNA) copies of itself which are positive-sense. The vcRNA is a template for producing -ve sense progeny but mRNA is also synthesized from it. The mRNA synthesized from vcRNA translates the G (spike) proteins and Z proteins. Thus, with this temporal control, the spike proteins are produced last, making the infection further undetected by the host immune system.
Virus
- The Arenaviridae are a family of viruses whose members are generally associated with rodent-transmitted diseases in humans. Each virus usually is associated with a particular rodent host species in which it is maintained. Arenavirus infections are relatively common in humans in some areas of the world and can cause severe illnesses.
- The virus particles are spherical and have an average diameter of 110-130 nanometers. All are enveloped in a lipid (fat) membrane. Viewed in cross-section, they show grainy particles that are ribosomes acquired from their host cells. It is this characteristic that gave them their name, derived from the Latin "arena", which means "sandy". Their genome, or genetic material, is composed of RNA only, and while their replication strategy is not completely understood, we know that new viral particles, called virions, are created by budding from the surface of their hosts' cells.
Vector
- The reservoir, or host, of Lassa virus is a rodent known as the "multimammate rat" (Mastomys natalensis). Once infected, this rodent is able to excrete virus in urine for an extended time period, maybe for the rest of its life. Mastomys rodents breed frequently, produce large numbers of offspring, and are numerous in the savannas and forests of west, central, and east Africa. In addition, Mastomys readily colonize human homes and areas where food is stored. All of these factors contribute to the relatively efficient spread of Lassa virus from infected rodents to humans.
- Transmission of Lassa virus to humans occurs most commonly through ingestion or inhalation. Mastomysrodents shed the virus in urine and droppings and direct contact with these materials, through touching soiled objects, eating contaminated food, or exposure to open cuts or sores, can lead to infection.
- Because Mastomys rodents often live in and around homes and scavenge on leftover human food items or poorly stored food, direct contact transmission is common. Mastomys rodents are sometimes consumed as a food source and infection may occur when rodents are caught and prepared. Contact with the virus may also occur when a person inhales tiny particles in the air contaminated with infected rodent excretions. This aerosol or airborne transmission may occur during cleaning activities, such as sweeping.
- Direct contact with infected rodents is not the only way in which people are infected; person-to-person transmission may occur after exposure to virus in the blood, tissue, secretions, or excretions of a Lassa virus-infected individual. Casual contact (including skin-to-skin contact without exchange of body fluids) does not spread Lassa virus. Person-to-person transmission is common in health care settings (called nosocomial transmission) where proper personal protective equipment (PPE) is not available or not used. Lassa virus may be spread in contaminated medical equipment, such as reused needles.