REOVIRIDAE: Respiratory-Enteric-Orphan viruses.

• STRUCTURE: Non-enveloped, double-stranded segmented (-) RNA, in 10-12 segments. Contains concentric inner and outer capsids.
• VP4: Viral glycoprotein neutralization antigen.
• VP7: Viral glycoprotein neutralization antigen, derived from host-cell ER.
• RNA-dependent RNA-Polymerase can make messenger RNA's out of the double-stranded viral genome.
• Rigid capsule makes fecal-oral transmission possible.
• REPLICATION: The inner capsid always remains intact.
• The outer capsid is removed upon entry into the cell.
• Inside the capsid, the RNA-dependent RNA-polymerase makes subgenomic (+) mRNA's. These mRNA's are transported into host-cell cytoplasm and translated into proteins.
• Inside the capsid, the (-) RNA's are used as templates to make new ds-RNA genomes, which are then released outside the capsid.
• The new genomes are assembled along with the viral proteins to make new infectious particles.
• EPIDEMIOLOGY: Fecal-oral transmission.
• Infection occurs in 6 months to 2 years old. Neonates, older children, and adults are usually asymptomatic. Breast-milk IgA probably provides protection for neonates.
• Prevalent in winter, but throughout year in tropical climates. Unexplained west-to-east trend in seen in its incidence: Nov ------> Feb as you go from West ------> East in United States.
• REOVIRUS: (ORTHOREOVIRUS)
• STRUCTURE: 3 serotypes.
• MANIFESTATIONS: Commonly infects, but asymptomatic, hence they are orphan viruses.
• ROTAVIRUS: Group-A Rotavirus has 4 serotypes, based on the VP7 antigen.
• MANIFESTATIONS: Gastroenteritis, which can be life threatening. It is the major cause worldwide, in infants and young children.
• MECH is believed to be decreased absorption at brush border, but not sure.
• IMMUNITY: Serotype-specific, and incomplete.
• DIAGNOSIS: ELISA of stool samples
• TREATMENT: IV-fluid replacement. Oral rehydration therapy.
• VACCINE: In clinical trials are re-assortment-viruses containing genomes that encode VP4 or VP7. These are human viruses that infect the cell and reassort with the segmented genome of the rotavirus, rendering it non-pathogenic.
• ORBIVIRUS: All are arboviruses. Most are asymptomatic. 10 segments.
• COLORADO TICK FEVER VIRUS:
• MANIFESTATIONS: Standard common viremia symptoms: fever, myalgia, rash, vomiting. May see maculopapular rash.
• STRUCTURE: Has 12 segments, not 10.

Category: Microbiology Notes