REOVIRUS

1. REOVIRUS reo: respiratory enteric orphan, early recognition that the viruses caused respiratory and enteric infections incorrect belief they were not associated with disease, hence they we re considered "orphan " viruses

2. First recognized in 1959 ‑ • previously classified as echoviruses • >150 species in the family Reoviridae. • infect invertebrates, vertebrates and plants, • Abs found in all species of mammals tested except whales • genera are serologically unrelated. • unique feature ‑‑ d/s RNA.

3. Family Reoviridae

4. Family: Birnaviridae (Bisegmented dsRNA Virus Group) • Genus: Aquabirnavirus • Type species: Infectious Pancreatic Necrosis Virus • 2 segments of ds RNA • Genus: Avibirnavirus • Type species: Infectious bursal disease virus • Genus: Entomobirnavirus • Type species: Drosophila X virus • Family: Totiviridae (Monopartite dsRNA mycovirus group) • Genus: Totivirus • Type species: Saccharomyces cerevisiae Virus L‑A • 1 segment of ds RNA, 4.6 ‑ 6.7 kbp • Genus: Giardiavirus • Type species: Giardia Lamblia Virus • 1 segment of ds RNA, 7 kbp • Genus: Leishmaniavirus • Type species: Leishmania RNA virus • 1‑1 1 segement of ds RNA, 5.3 kbp

5. Family: Partitiviridae ( dsRNA fungal and plant viruses with divided genomes) • Genus: Partitivirus • Type species: Gaeumannomyces Graminis Virus 019/6‑A • 2 unrelated segments of dsRNA • Genus: Chrysovirus • Type species: Penicillium chrysogenum virus • Genus: Alphacryptovirus • Type species: white clover cryptic virus 1 • Genus: Betacryptovirus • Type species: white clover cryptic virus 2

6. Genus: Rotavirus • Type species: Human Rotavirus • 11 segments of ds RNA • rota: from Latin rota, "wheel " • Mammals

7. Some times called DUO viruses

8. Rotaviruses • Early work • some animal rotavirus strains can grow in cell cultures • Human rotaviruses • do not produce new infectious virus in routine cell cultures • partial replication takes place In several cell types, • e.g. LLC-MK2, • production of intracellular viral antigens.

9. Rotaviruses • Now efficient techniques available cultivation of most animal rotaviruses in cell culture . • virus is pretreated with trypsin • trypsin is incorporated in the maintenance medium. • Simian MA104 cells, primary AGMK or cynomologus MK cells • some human strains can be adapted to grow in cell cultures • prior treatment with small amounts of trypsin • probably facilitates the release of the nucleic acid into the cells

10. Rotaviruses possess group, subgroup and serotype antigens. • AG on the outer surface of the 60nm rough particle • 5 groups are designated A to E. • Based on VP7 • Group A viruses further subdivided into subgroups I and II, • based on VP6. • 9 serotypes, • types 1-4, 8 and 9 have been found in humans. • majority of human and animal and animal strains gp a • minority of human and animal strains belong to the other 4 groups. • human strains belonging to groups B and C • Group B strains are rare outside China.

11. structure • very stable environmentally • Non‑enveloped • nearly spherical icosahedral particles • 70‑85nm diameter, • capsid = double shell of proteins • Outer shell ~80nm diameter; Inner shell ~60nm diameter • all enzymes required for d/s RNA transcription

12. structure • Rotavirus particles = wheel with spokes radiating out from the inner capsid • three shells - • an outer capsid, • VP7 (the glycoprotein or G protein) and VP4 (the protease cleaved or P protein) • major antigens involved in virus neutralization • inner capsid • core • surrounds the 11 segments of double-stranded RNA.: • Orbivirus particles appear smooth.

15. Genome • 10(reo)‑12 (rota)segments d/s RNA • 3 distinct size classes: • L ‑ encodes proteins designated lambda ~3.9kbp • M ‑ encodes proteins designated mu • S ‑ encodes proteins designated sigma ‑ 1kbp • 30% of the RNA in the particles is small s/s oligonucleotides, • synthesized internally by the viral polymerase ‑ • possibly abortive transcripts? • viral RNA species are mostly monocistronic

16. Reoviruses contain exactly one segment of each of the 10-12 segments of dsRNA that constitute the viral genome, encapsidated in a single complex virus particle comprised of 6-8 proteins dsRNA 1 dsRNA 2 dsRNA 3 dsRNA 4 dsRNA 5 dsRNA 6 dsRNA 7 dsRNA 8 dsRNA 9 dsRNA 10

20. attachment • Receptor(s) contain sialic acid • not definitively identified. • Penetration • Particles are internalized & partially uncoated in endolysosomes in the cytoplasm • resistant to protease digestion‑ • if completely uncoated, virus destroyed Core Virion Infectious Subvirion Particles (ISVPs)

21. Replication: • transcription • Early transcription • d/s RNA genome • viral polymerase • inside this sub‑viral particle. • various genome segments are transcribed/translated at different frequencies

22. Replication: • RNA is transcribed conservatively ‑ • only (‑)sense strands are used, • resulting in synthesis of (+)sense mRNAs, • capped inside the core ‑ • not polyadenylated • without de novo protein synthesis. • Secondary transcription • later • in particles produced inside the infected cells and results in uncapped non-polyadenylated transcripts. • mRNAs leave core & are translated in the cytoplasm. • 5 enzymatic activities are present in reovirus particles to carry out this process • not necessarily all separate peptides

25. mRNAs are likely transcribed at the transcription complexes at each of 12 vertices of the icosahedral particles

26. Capped, methylated mRNAs are transcribed by reovirus core particles

27. RNA replication • genome is replicated in the cytoplasm in a conservative fashion • excess of (+)sense strands are produced • serve as late mRNA • template for (‑)sense strand synthesis • each (‑) strand leads to many (+) strands ‑ • not one‑for‑one as semi‑conservative replication

28. assembly • mechanism responsible for segregation of the various genome segments into developing particles is not known. • Particles assemble in the cytoplasm 6‑7h after infection ‑ inclusion bodies. • RELEASE • Rotaviruses bud from the E.R. into internal spaces • released when the the cell lyses.

29. Proteolysis during entry through lysosome activates RNA synthesis Capped ss(+) RNA [mRNAs] synthesized [10 dsRNA genome segments] RdRP: m1 packaged in virion Reovirus: dsRNA Virus Strategy Subviral particles in cytoplasm are sites of RNA synthesis ‘core’ Extruded into cytoplasm through channels in 5-fold axes Remain in cytoplasm: translated Packaged into new subviral particles: templates for –RNA synthesis to produce new dsRNAs

32. Pathogenesis: • majority of human Orthoreovirus infections • gastrointestinal & upper respiratory tracts • Usually asymptomatic, • occasionally producing mild febrile illness, • Rotaviruses: • Diarrhoea: from the Greek dia (through) and rhein (to flow). • trigger the intestinal nervous system to secrete more water

33. Pathogenesis: • majority of human Orthoreovirus infections • gastrointestinal & upper respiratory tracts • Usually asymptomatic, • occasionally producing mild febrile illness, • Infections cause endemic/epidemic gastroenteritis and infantile diarrhoea • a major cause of death in the 3rd World: • around half a million deaths in infants in developing countries per year • US, up to 500 deaths per • second to U.R.T. infections in infants <24 months ‑ • rare in adults

34. Pathogenesis: • messy but self‑limited infections, infants • may kill without ‑ oral rehydration therapy (O.R.T.) • major cause of mortality in calves, piglets, etc ‑ highly infectious. • Rotavirus outbreaks appear at regular outbreaks in the winter in temperate climate. • prevalence of different serotypes varies dramatically year to year • Point mutations - RNA polymerase has a high error rate. • 10-4 for each site. • errors accumulate very quickly.

35. Pathogenesis: • Reassortments - natural reassortments occur, rather like influenza A. • Introduction of animal rotavirus into the human population, • the group B rotaviruses, responsible for causing disease in China • found in household animals.

36. vaccine • GOAL • prevent severe rotavirus gastroenteritis during the first 2 years of life • reinfections with rotaviruses are common • homotypic immunity is effective against diarrhoeal illness. • MULTIPLE SEROTYPES • 4 epidemiologically important human rotaviruses (serotypes 1, 2, 3 and 4) • effective coverage requires a quadravalent vaccine. • most evaluated approach • live animal virus • results of the trials of these vaccines ranges from very encouraging to disappointing • A rotavirus vaccine (Rotashield, Wyeth) was licensed in the USA

37. Orbiviruses: • >130 serotypes of orbivirus • infect birds & mammals, including humans, • causing a variety of haemorrhagic fevers, encephalitis

38. Orbiviruses: • African Horse Sickness ‑ • fever followed by death within hours in >90% affected animals. • Transmitted by midges, ticks. • Vaccine available. • Colorado Tick Fever ‑ • Tick transmitted disease endemic in USA. • Acute febrile illness, • usually without lasting consequences.

39. Orbiviruses • Blue Tongue ‑ • Disease of sheep, also infects cattle, producing mild disease; • severe economic pest ‑ • causes fetal loss • Transmitted by midges. • No vaccine yet. • Non-infectious subunit vaccines • Virus-like particle (VLP) vaccines • successfully produced • protect sheep from disease against a homologous challenge • Core-like particle (CLP) vaccines • not serotype specific • Show promise as a generic vaccine