GENERAL INTRODUCTION: REOVIRIDAE

REOVIRIDAE

The family Reoviridae is comprised of genetically diverse viruses that include the agents of several clinically and economically important diseases. Members of the family infect mammals and birds, as well as fish, molluscs, reptiles, amphibians, crustaceans, insects, plants and fungi. The viruses that belong to this family share a number of characteristics that were, at the time of discovery at least, quite unique in the biological world. The most important of these is the possession of a double-stranded RNA (dsRNA) genome. When Gomatos and his colleagues discovered in 1962 that the RNA in reovirus is double-stranded, it created quite a stir among virologists and a wider biological audience. At that time, viruses were the only living organisms known to have an RNA genome and in every case until then the RNA was single-stranded.  All viruses with genomes of 9, 10, 11 or 12 distinct segments of dsRNA are now classified within the family Reoviridae, whereasthose with 2 segments of dsRNA are included in the families Birnaviridae or Picobirnaviridae.

The name reovirus, an acronym for “respiratory enteric orphan virus”, was coined in 1959 to distinguish a group of human virus isolates originally lumped together with others in a group called echoviruses (“enteric cytopathic human orphan viruses”), most of which are now classified as enteroviruses (genus Enterovirus in the family Picornaviridae, order Picornavirales)1. Distinguishing features of the reovirus group were their larger size and distinctive cytopathology in cell cultures. As indicated by the term ‘orphan’, these viruses were not associated with any particular disease.  Despite the large genomic differences the family Reoviridae is currently organized into two subfamilies and 15 officially recognized genera 1 (Table 1) including Rotavirus and Orbivirus. The two subfamilies, called Spinareovirinae and Sedoreovirinae, are distinguished by the presence or absence of so-called “turrets” or spikes (from Latin spina=spike) in the capsid structures of their member viruses. Rotaviruses (genus Rotavirus) are important pathogens of humans and animals, typically neonates. The genus Orbivirus is by far the most important as far as animal health is concerned; diseases such as bluetongue, African horse sickness and equine encephalosis are caused by members of this group.2 The Orbivirus genus is large and includes many viruses without known veterinary or medical significance. The relationship between the viruses in this group is complex. At present 22 species (Table 2) are recognized.1 Each species is further subdivided into serotypes (Table 2), based largely on plaque neutralization assays and cross-protection studies. However, with the advent of whole genome sequencing, genetically-based typing is increasingly used.

Table 1 Taxonomic organization of the family Reoviridae1

SUBFAMILY

GENUS

TYPE SPECIES

HOST ANGE

SEDOREOVIRINAE

Cardoreovirus

Eriocheir sinensis reovirus

Crabs

Mimireovirus

Micromonas pusilla reovirus

Marine protists

Orbivirus

Bluetongue virus

Animals, insects

Phytoreovirus

Wound tumor virus

Plants

Rotavirus

Rotavirus A

Animals*

Seadornavirus

Banna virus

Animals, insects

SPINAREOVIRINAE

Aquareovirus

Aquareovirus A

Fish, shellfish

Coltivirus

Colorado tick fever virus

Animals, insects*

Cypovirus

Cypovirus 1

Insects

Dinovernavirus

Aedes pseudoscutellaris reovirus

Insects

Fijivirus

Fiji disease virus

Plants

Idnoreovirus

Idnoreovirus 1

Insects

Mycoreovirus

Mycoreovirus 1

Fungi

Orthoreovirus

Mammalian orthoreovirus

Animals*

Oryzavirus

Rice ragged stunt virus

Plants

* group includes viruses that infect humans

Table 2 Species in genus Orbivirus and number of serotypes of important viruses pathogenic to livestock

VIRUS SPECIES

SEROTYPES

African horse sickness virus

9

Bluetongue virus

currently 27, possibly more

Changuinola virus

Chenuda virus

Chobar Gorge virus

Corriparta virus

Epizootic haemorrhagic disease virus

7

Equine encephalosis virus

7

Eubenangee virus

Great Island virus

Ieri virus

Lebombo virus

Orungo virus

Peruvian horse sickness virus

Palyam virus

St Croix River virus

Umatilla virus

Wad Medani virus

Wallal virus

Warrego virus

Wongor virus

Yunnan orbivirus

References

  1. INTERNATIONAL COMMITTEE FOR TAXONOMY OF VIRUSES. https://talk.ictvonline.org/taxonomy
  2. PALMARINI, M., 2017. Reoviridae. In: MACLACHLAN, N.J. & DUBOVI, E.J., (eds). Fenner’s Veterinary Virology, 5th Edition, Amsterdam: Academic Press.