91. Family Reoviridae - Genus Rotavirus. Genus Norovirus.

I. General Characteristics

• Rotavirus (Reoviridae):

• Non-enveloped, double-stranded segmented RNA virus.
• Triple-layered icosahedral capsid.
• Replicates in the cytoplasm.
• Genome is 11 segments, allowing genetic reassortment.
• Transmission: Fecal–oral route.
• Major cause of severe diarrhea in infants and young children.
• Norovirus (Caliciviridae):

• Non-enveloped, single-stranded, positive-sense RNA virus.
• Icosahedral capsid, very small (~27–35 nm).
• Highly infectious and environmentally stable.
• Transmission: Fecal–oral, aerosols from vomitus, contaminated food/water.
• Major cause of adult viral gastroenteritis and outbreaks (e.g., cruise ships, schools).

III. Rotavirus

A. Virulence Factors

• NSP4: acts as a viral enterotoxin → stimulates Cl⁻ secretion, inhibits Na⁺ absorption → watery diarrhea.
• VP4 and VP7: outer capsid proteins responsible for attachment and neutralization.
• Segmented genome: allows antigenic shift (reassortment).
• Resistance to gastric acid → survives passage to intestines.

B. Pathogenesis

• Infects and destroys mature enterocytes in small intestinal villi → malabsorption.
• NSP4 induces secretory diarrhea via Ca²⁺-dependent signaling and enteric nervous system activation.
• Leads to dehydration and electrolyte imbalance, especially dangerous in infants.

C. Clinical Features

• Incubation: 1–3 days.
• Symptoms:
• Vomiting and watery diarrhea (5–7 days)
• Low-grade fever
• Dehydration (major risk)
• Affects mainly children <5 years (peak at 6 months – 2 years).

D. Diagnosis

• Enzyme immunoassay (EIA) for rotavirus antigen in stool.
• RT-PCR or latex agglutination (less common in routine use).

E. Treatment and Prevention

• Supportive care: oral rehydration, IV fluids if needed.
• Vaccination:
• Live attenuated oral vaccines:
• Rotarix (monovalent)
• RotaTeq (pentavalent)
• Given in infancy (starting at 6–8 weeks of age).