Arenavirus

Arenaviruses are single-stranded RNA viruses. The hallmark of arenaviruses is their tendency to cause persistent silent infections in their natural hosts (rodents) and severe, often fatal, disseminated disease in humans. Fifteen arenaviruses are known to infect animals and five of them cause disease in humans: Junin virus (Argentine hemorrhagic fever), Machupo virus (Bolivian hemorrhagic fever), Guanarito virus (Venezuelan hemorrhagic fever), Lassa virus (Lassa fever), and lymphocytic choriomeningitis virus.The first four viruses cause severe hemorrhagic fever with a mortality of about 15 percent among hospitalized patients in endemic areas. Lymphocytic choriomeningitis (LCM) virus, is much more widely distributed and causes milder neurological infections.

Each virus is associated with a particular rodent host species that is chronically infected. Some rodents transmit arenaviruses to their offspring during pregnancy. Human infection with arenaviruses occurs when individuals come into contact with excretions, or materials contaminated with excretions, from an infected rodent. Infection can also occur by inhalation of aerosols containing rodent urine or saliva. Some arenaviruses, such as Lassa and Machupo, have caused person-to-person and hospital acquired infections. Person-to-person transmission is associated with direct contact with blood or other body fluids from infected individuals. Contaminated medical equipment has caused nosocomial infections. 

The clinical presentation of Junin virus, Machupo virus, Guanarito virus, and Lassa virus is similar. The incubation period is 10 to 14 days. Disease onset usually begins with a 2 to 4 day period of general malaise and fever. Junin, Machupo, and Guanarito infections usually progress to thrombocytopenia, leukopenia, hemorrhage, neurologic deficits. Hepatitis occurs more often in Lassa fever than in the three Latin American hemorrhagic fevers. Extreme elevation of AST is associated with a poor prognosis.

About 70 percent of human infections with LCM virus are asymptomatic or so mild that they are indistinguishable from common respiratory or gastrointestinal illnesses. The more severe LCM infections cause headache, photophobia, listlessness, apathy, memory defects, and confusion. LCM infections can be temporarily debilitating, but are rarely fatal.

RT-PCR tests have been validated for Lassa fever virus but not all arenaviruses. Some assays

detect a wide range of arenaviruses, while others are specific for one or more viruses. Arenaviral antigens can be detected with antigen-capture ELISAs, though this test is sometimes negative in the later stages of the illness. 

Lassa virus-specific IgM can usually be detected by the second week of illness, and many patients are seropositive on presentation. Antibodies usually appear more slowly in patients with hemorrhagic fevers, typically in the third week.

Reference

The Center for Food Security & Public Health, Viral Hemorrhagic Fevers Caused by Arenaviruses including Lassa, Junin, Machupo, Guanarito, Chapare, Sabia and Lujo viruses. February 2023; www.cfsph.iastate.edu.