Mammalian orthoreovirus 2 (MRV‑2) is one of three serotypes of mammalian orthoreoviruses, non‑enveloped double‑stranded RNA viruses in the genus Orthoreovirus (family Reoviridae).
Genome, life cycle and host range
Like other orthoreoviruses, MRV‑2 has a segmented genome comprising ten double‑stranded RNA segments designated L1–L3, M1–M3 and S1–S4. The S1 segment encodes the cell‑attachment protein σ1, and variation in this segment defines serotype and host cell tropism. Prototype MRV‑2 strains include type 2J, isolated from a child with diarrhoea, and type 2C from a cow, highlighting its ability to infect multiple mammalian species. The virus particle consists of an inner core and outer capsid; after endocytosis it undergoes proteolytic uncoating to form infectious subviral particles that transcribe capped mRNAs. Replication and assembly occur in cytoplasmic inclusion bodies, and newly formed virions are released by cell lysis. MRV‑2 is environmentally stable due to its double‑layered capsid, allowing persistence in water and on surfaces. Transmission occurs via faecal–oral and respiratory routes. In humans and other mammals the virus replicates in the gastrointestinal and respiratory mucosa and can disseminate to lymphoid tissues. In immunocompetent hosts infection is often asymptomatic or associated with mild gastroenteritis or upper respiratory symptoms; however, certain strains have been linked to encephalitis or pneumonia. There are no licensed vaccines or specific antiviral therapies.
Occurrences and research relevance
MRV‑2 has been isolated from a variety of hosts including cattle, pigs, bats, dogs and humans, underscoring its broad host range and potential for interspecies transmission. Sporadic human cases of MRV‑2‑associated pneumonia were reported in China in 2014, and an MRV‑2 strain was detected in children with acute necrotising encephalopathy, illustrating its capacity to invade the central nervous system. Surveillance studies show that antibodies to MRV‑2 are common in adult sera, indicating frequent exposure without notable illness. In domestic animals the virus has been recovered from calves with diarrhoea and from pigs with respiratory disease, though causality is often difficult to establish because of co‑infections. On the scientific front, MRV‑2 has been used in reassortment experiments to map determinants of tissue tropism and immune evasion, and its stability makes it a useful model for studying segmented RNA virus genetics. MRV‑2 circulates widely among mammals but rarely causes severe disease in humans. Understanding its biology helps to elucidate general principles of orthoreovirus replication and reassortment and provides context for interpreting sporadic disease outbreaks. Related Terms: Mammalian Orthoreovirus 1, Mammalian Orthoreovirus 3, Avian orthoreovirus, Rotavirus, Bovine rotavirus