Summary
- Arenaviruses: Zoonotic viruses transmitted via rodents mainly, but for some also via secondary person-to-person transmission and nosocomial infection
- Clinically atypical febrile, haemorrhagic, neurological or pulmonary syndrome.
- Ribavirin is used in Lassa fever
General
The name of arenaviruses refers to their granular appearance under an electron microscope (L. arena = sand). This structure is created by the inclusion of electron dense host cell ribosomes in the viral envelope. They are RNA viruses, of which the genome consists of a short and a long RNA fragment. Some viruses from this group are pathogenic for humans. Our knowledge concerning these viruses is clearly incomplete. Most arenaviruses have a rodent reservoir. The rodent hosts are chronically infected with the virus, without causing them an obvious illness. Human infection occurs when a person comes into contact with excretions or other materials contaminated with excretions of the infected rodent via ingestion, via direct contact through broken skin/mucosa or via aerosol transmission. Taracibe virus was isolated from fruit-eating bats.
Known pathogenic arenaviruses:
- Lymphocytic choriomeningitis virus
- Lassa virus (with substrains Josiah, Nigeria, LP, AV)
- Junin virus
- Machupo virus
- Lujo virus
Non-pathogenic arenaviruses and viruses with unknown pathogenicity:
- Old World: Mopeia, Mobala, Ippy, Acar
- New World : Tacaribe, Tamiami, Parana, Amapari, Flexal, Pichende, Latino, Oliveros
Incubation time
Nosocomial transmission and transmission via infected body fluids are known for Lassa fever, Ebola and Marburg virus as well as other non-arboviral haemorrhagic fevers. The Bunya-, Filo- and Flaviviruses are cytolytic. They destroy cells particularly endothelial cells. The incubation time is usually less than one week.
Arenaviruses are not cytolytic. They act indirectly by forming antigen-antibody complexes and activating complement. The incubation time tends to be longer than in the other groups.
New Arenaviruses
It is very likely that new viruses will be discovered in the future. An example is Lujo virus, a new member of the family Arenaviridae. This haemorrhagic fever virus was discovered in 2008, when it was responsible for an outbreak in South Africa (the index patient came from Zambia, 5 cases in total). Human disease is characterized by nosocomial transmission and a very high case fatality rate of 80 percent.
Lymphocytic choriomeningitis virus
The first arenavirus to be isolated was lymphocytic choriomeningitis virus (LCM). It was discovered in 1933 during an epidemic of St Louis encephalitis in the USA. The virus can infect mice. Neonatally infected mice become chronic carriers and excrete the virus for a long time in their urine. The course of the infection is determined by age, immunological resistance, the virus strain and the genetic makeup of the rodent. Both Mus musculus and Mus domesticus (the common house mouse) can be infected. Other rodents, such as hamsters, which are sometimes kept as pets, can also become infected and can be responsible for transmission. Lymphocytic choriomeningitis virus can also be transmitted via organ transplantation.
In humans it is mainly known for causing an “aseptic” meningitis, with or without fever about 10 days before the meningeal signs appear, though infection is more often without symptoms or a mild febrile illness. LCMV infection in immune compromised patients tends to be severe. Sometimes there is severe damage to the central nervous system. Transient hydrocephalus has been described. Chorioretinitis and congenital hydrocephalus may occur in foetal infection. The cerebrospinal fluid exhibits lymphocytic pleocytosis, an elevated protein content and in 25% of patients there is also reduced sugar. Rarely transverse myelitis, ascending myelitis or bulbar paralysis occur. Some cases of residual deafness have been described after LCM infection. At present, a significant fraction of cases of neonatal mental retardation and blindness remain unexplained. Congenital LCMV infection is an understudied potential cause of a portion of these cases.
There is no specific treatment. There is no vaccine. In general, mortality is less than 1%.
