The genus Orthoreovirus belongs to the family Reoviridae and contains viruses that infect mammals and birds on several continents. They are spread by respiratory or oral-fecal routes. Bats as reservoior might contribute to virus evolution and genetic diversity, giving orthoreoviruses the potential to become more virulent.
Orthoreoviruses are composed of an inner protein shell (core) and an outer protein shell known as outer capsid. These viruses are very stable to heat, to a wide range of pH, and are very stable in aerosols.
Mammalian Orthoreoviruses (MRVs) are non-enveloped, segmented double-stranded RNA viruses. They are widespread and infect a broad spectrum of mammals.
MRVs have long been considered non-pathogenic, although mild respiratory and enteric diseases have occasionally been reported in young animals and children. Recent evidence show MRVs can cause severe diseases such as hemorrhagic enteritis, acute respiratory infections, and central nerve system infections. Cases of newborn diarrhea and neurological symptoms in children were registered in Europe and North America. There is consequently increasing concern about the widespread nature and disease causing ability of these viruses.
The transmission of reoviruses from one host to another is not limited to close contacts but extends to indirect transmission. Since the virions are very stable and have been detected in sewage and river water, infection through contaminated food, water, or other factors in the environment is highly possible. Viral persistence outside the host is one of the advantageous features that enables them to spread efficiently.2
Mammalian orthoreoviruses have been found only rarely in dogs with respiratory disease and dogs with enteritis.
In horses, orthoreoviruses cause upper and lower respiratory illness: cough, laryngitis, rhinitis, and conjunctivitis. In cattle, sheep and swine, orthoreoviruses cause hepatitis, meningitis, and tissue necrosis.
Avian orthoreoviruses do not infect mammalian species but may cause lethal diseases in birds with symptoms ranging from arthritis and feather abnormalities to hepatitis, stunted growth, and weight loss. In turkeys, orthoreoviruses cause infectious enteritis and infect egg yolk sac.3