Arenavirus

Arenavirus: One of a family of viruses called Arenaviridae whose members are generally associated with diseases transmitted by rodents to humans. Each arenavirus is usually 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.”

The genome of arenaviruses is composed of RNA only, and while their replication strategy is not completely understood, it is known that new viral particles, called virions, are created by budding from the surface of their hosts’ cells.

The first arenavirus, lymphocytic choriomeningitis virus (LCMV), was isolated in 1933. By the 1960s, several similar viruses had been discovered and they were classified into the new family Arenaviridae. Since Tacaribe virus was found in 1956, new arenaviruses have been discovered on the average of every one to three years.

A number of arenaviruses cause hemorrhagic disease. Junin virus, isolated in 1958, was the first of these to be recognized. This virus causes Argentine hemorrhagic fever in a limited agricultural area of the pampas in Argentina. Several years later, in 1963, in the remote savannas of the Beni province of Bolivia, Machupo virus was isolated. The next member of the virus family to be associated with an outbreak of human illness was Lassa virus in Africa in 1969. Most recently, Guanarito and Sabia viruses were added to this family.

Lymphocytic choriomeningitis virus (LCMV) was found to be a cause of aseptic (nonbacterial) meningitis. Lassa virus causes Lassa fever. Junin virus causes Argentine hemorrhagic fever; Machupo virus causes Bolivian hemorrhagic fever; Guanarito virus causes Venezuelan hemorrhagic fever; and Sabia virus causes Brazilian hemorrhagic fever.

These viruses are zoonotic: in nature, they are found in animals. Each virus is associated with one species or a few closely related species of rodents, which constitute the virus’ natural reservoir. Tacaribe viruses are generally associated with the New World rats and mice. The LCMV/Lassa viruses are associated with the Old World rats and mice. Taken together, these types of rodents are located across the greater proportion of the earth’s land mass, including Europe, Asia, Africa, and the Americas. One notable exception is the Tacaribe virus, found in Trinidad, which was isolated from a bat.

Human infections with arenaviruses are incidental to the natural cycle of the viruses. They occur when an individual comes into contact with the excretions or materials contaminated with the excretions of an infected rodent. This may be by ingestion of contaminated food, or by direct contact of abraded or broken skin with rodent excrement. Infection can also occur by inhalation of tiny particles soiled with rodent urine or saliva (aerosol transmission).

The types of incidental contact depend on the habits of both humans and rodents. For example, where the infected rodent species prefers a field habitat, human infection is associated with agricultural work. In areas where the rodent species’ habitat includes human homes or other buildings, infection occurs in domestic settings.

Some arenaviruses, such as Lassa and Machupo viruses, are associated with secondary person-to-person and nosocomial (health-care setting) transmission. Person-to-person transmission is associated with direct contact with the blood or other excretions of infected individuals. Airborne transmission has also been reported. Contact with objects contaminated with these materials, such as medical equipment, is also associated with transmission. In these situations, use of protective clothing and disinfection procedures (together called barrier nursing) help prevent further spread of illness.