Reoviruses Tutorial Materials

Reoviruses Reovirus Rotavirus Structure The virions measure 60-80 nm in diameter and posses two concentric capsid shells, each of which is icosahedral. The double-shelled particle is the complete infectious form of the virus. The reovirus genome consists of double –stranded RNA in 10-12 discrete segments( rotaviruses: 11 segments, orthoreoviruses and orbiviruses: 10 segments, coltiviruses: 12 segments) Classification • The family Reoviridae is divided into 15 genera. • Four of the genera are able to infect humans: Orthoreovirus, Rotavirus, Coltivirus, Orbivirus • There are at least seven species or groups of rotaviruses (A-G) plus one recently proposed group(H), of which three species(A,B,C) infect humans. • Three different serotypes of reovirus are recognized. Reovirus Replication • Viral particles attach to specific receptors on the cell surface • The cell attachment protein for reoviruses is the viral hemagglutinin(σ1 protein) and VP4(in rotavirus) • After attachment and penetration, uncoating of virus particles occur in lysosomes in the cell cytoplasm. • Reovirus cores contain all necessarey enzymes • Viral Polypeptides probably self-assemble to form the inner and outer capsid shells • Rotavirus morphogenesis involves budding of single-shelled particles into the rough endoplasmic reticulum. The pseudoenvelopes are then removed and the outer capsids are added. • Cell lysis results in release of progeny virions. Rotaviruses • Rotaviruses are a major cause of diarrheal illness in human infants and young animals • Infection in adult human and animals are also common • Rotaviruses are the most important cause of infantile gastoenteritis around the world triple-layered rotavirus particle( double shelled) Core: VP1, VP2, VP3 Inner capsid: VP6 Outer capsis: VP4, VP7 VP4 and VP7 carry epitopes important in neutalizing activity Rotaviruses have been classified into seven species (A-G) plus one tentative species (H) based on antigenic epitopes on the internal structural protein VP6 Pathogenesis • Rotaviruses infect cells in the villi of the small intestine • The multiply in the cytoplasm of enterocytes and damage their transport mechanism. • One of the rotavirus proteins,NSP4, is a viral enterotoxin and induces secretion by triggering a calcium dependent signal transducyion pathway • We can see an impaired sodium and glucose absorption Clinical Findings • Rotaviruses cause the major portion of diarrheal illness in infants and children worldwide but not in adults(Group A rotavirus causes severe gastroenteritis in children ( Winter diarrhea in children ) • There is an incubation period of 1-3 days • • Typical symtomps: watery diarrhea, fever, abdominal pain, vomiting, dehydration In infants and children, severe dehydration may be fatal unless treated • Group B rotavirus have been implicated in large outbreaks of severe gastroenteritis in adults in China Laboratory Diagnosis • Enzyme immunoassay • Electron Microscopy • PCR