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Arenavirus is a virus that belongs in a viral family known as Arenaviridae. The name arenavirus derives from the appearance of the spherical virus particles when cut into thin sections and viewed using the transmission electron microscope . The interior of the particles is grainy or sandy in appearance, due to the presence of ribosomes that have been acquired from the host cell. The Latin designation "arena" means "sandy."

Arenaviruses contain ribonucleic acid (RNA ) as their genetic material. The viral genome consists of two strands of RNA, which are designated the L and S RNA. The ribosomes of the host that are typically present inside the virus particle are used in the manufacture of the components that will be assembled to produce the new virus particles. Little is known about the actual replication of new viral components or about the assembly of these components to produce the new virus particles. It is known that the new virus exits the host by "budding" off from the surface of the host cell. When the budding occurs some of the lipid constituent from the membrane of the host forms the envelope that surrounds the virus.

Those arenaviruses that are of concern to human health are typically transmitted to humans from rats and mice. The only known exception is an arenavirus called the Tacaribe virus, which is resident in Artibeus bats. The association between an arenavirus type and a particular species of rodent is specific. Thus, a certain arenavirus will associate with only one species of mouse or rat. There are 15 arenaviruses that are known to infect animals. A hallmark of arenaviruses is that the infections in these rodent hosts tend not to adversely affect the rodent.

Of the fifteen viruses that are resident in the animals, five of these viruses are capable of being transmitted to humans. When transmitted to humans, these arenaviruses can cause illness. In contrast to the rodent hosts, the human illness can be compromising.

Most arenavirus infections produce relatively mild symptoms that are reminiscent of the flu, or produce no symptoms whatsoever. For example an arenavirus designated lymphocytic choriomeningitis virus, usually produces symptoms that are mild and are often mistaken for gastrointestinal upset. However, some infections with the same virus produce a severe illness that characterized by an inflammation of the sheath that surrounds nerve cells (meningitis ). The reasons for the different outcomes of an infection with the virus is yet to be resolved.

A number of other arenaviruses are also of clinical concern to humans. These viruses include the Lassa virus (the cause of Lassa fever), Junin virus (the cause of Argentine hemorrhagic fever), Machupo virus (the cause of Bolivian hemorrhagic fever), and Guanarito virus (the cause of Venezuelan hemorrhagic fever). Hemorrhagic fevers are characterized by copious bleeding, particularly of internal organs. The death rate in an outbreak of these hemorrhagic fevers can be extremely high.

An arenavirus is transmitted to a human via the urine or feces of the infected rodent. The urine or feces may contaminate food or water, may accidentally contact a cut on the skin, or the virus may be inhaled from dried feces. In addition, some arenaviruses can also be transmitted from one infected person to another person. Examples of such viruses are the Lassa virus and the Machupo virus. Person-to-person transmission can involve direct contact or contact of an infected person with food implements or medical equipment, as examples.

As with other hemorrhagic fevers, treatment consists of stabilizing the patient. A vaccine for the Junin virus, which consists of living but weakened virus, has been developed and has been tested in a small cohort of volunteers. The results of these tests have been encouraging. Another vaccine, to the Lassa virus, consists of a protein component of the viral envelope. Tests of this vaccine in primates have also been encouraging to researchers.

Currently, the human illnesses caused by arenaviruses are best dealt with by the implementation of a rodent control program in those regions that are known to be sites of outbreaks of arenavirus illness. Because the elimination of rodents in the wild is virtually impossible, such a program is best directed at keeping the immediate vicinity of dwellings clean and rodent-free.

See also Hemorrhagic fevers and diseases; Virology, viral classification, types of viruses; Zoonoses