Rotavirus

Virology

• Core: VP1, VP2, VP3 + the 11-segment dsRNA genome (~18 kilobases)
• Intermediate layer: VP6 - the most abundant and antigenic protein; determines group/species classification
• Outer layer: VP7 (G protein, glycoprotein) and VP4 (P protein, protease-sensitive)

• Nine species (A through I) based on antigenic epitopes and genetic relatedness
• Species A - responsible for most human disease
• Species B - sporadic outbreaks of adult diarrhea in China; some pediatric cases in India
• Species C - mainly veterinary; rare human cases
• Species D-G - animals only (avian primarily)

Epidemiology

• Leading cause of severe diarrhea and diarrhea-related deaths in children worldwide, particularly those aged 6-24 months
• Incidence is similar in both developed and developing countries - clean water and public hygiene alone do not prevent rotavirus
• Children <6 months are partially protected by maternal antibodies (transplacental + breast milk); protection beyond age 2 reflects immunity after first infection
• Prior to vaccination, rotavirus caused ~528,000 deaths/year globally; by 2013, this fell to ~215,000; currently ~130,000 deaths/year, with >85% in Africa and Asia
• Seasonal pattern: winter-spring peak in temperate zones (December-June); endemic year-round within 10 degrees of the equator
• After US vaccine introduction (2006), the annual winter season became a biennial pattern; norovirus became the leading cause of childhood gastroenteritis seeking medical care
• Reinfections are common but typically milder
• Secondary spread to adults occurs in ~20% of household contacts; elderly and immunocompromised are at risk for severe/prolonged illness

Transmission

• Primarily fecal-oral route or contact with contaminated surfaces
• Highly infectious - minimal infective inoculum is estimated at 1-10 viral particles
• Virus is environmentally stable

Pathophysiology

1. NSP4 enterotoxin - encoded by gene segment 10; activates calcium signaling, stimulates intestinal secretion (secretory diarrhea), and activates the enteric nervous system
2. Loss of brush border enzymes - rotavirus selectively destroys mature absorptive enterocytes at villus tips; villus surface is repopulated by immature secretory cells, reducing disaccharidase levels and causing malabsorption of carbohydrates, fats, and protein (osmotic diarrhea)
3. ENS activation - stimulates intestinal motility through NSP4 and purinergic signaling (infected cells release extracellular ADP, activating P2Y1 receptors, inducing calcium waves, serotonin release, and diarrhea)

Clinical Features

• Incubation period: 1-3 days (<48 hours in most references)
• Classic presentation: sudden-onset vomiting followed by watery, non-bloody diarrhea, with fever (~1/3 of children)
• Duration: 5-7 days on average (range 3-8 days)
• Fever, nausea, loss of appetite, dehydration (dry mucous membranes, reduced urine output)
• Rotavirus diarrhea tends to be more severe than norovirus-related gastroenteritis
• CNS complications: seizures (including afebrile seizures - a known, benign association), encephalopathy, encephalitis
• Viral shedding persists for 10 days in most; up to 57 days possible; ~1/3 shed asymptomatically for weeks post-infection
• Adults: milder disease; immunocompromised and elderly may have severe, prolonged illness

Diagnosis

• Most cases are diagnosed clinically
• ELISA (antigen detection): sensitive, specific, practical - preferred for clinical diagnosis
• RT-PCR / quantitative RT-PCR: highest sensitivity but ~30% of healthy infants <1 year may be PCR-positive, making it hard to attribute illness; quantitative PCR with a threshold is preferred when used
• Oral swabs have lower sensitivity than stool specimens
• Stool specimen is the sample of choice

Management

• Supportive care - rotavirus is self-limited in healthy individuals
• Oral rehydration therapy (ORS) is the cornerstone of management; WHO-recommended ORS solution is standard
• IV fluids for severe dehydration or inability to tolerate oral intake
• No specific antiviral therapy
• Zinc supplementation in developing country settings reduces severity and duration

Prevention: Vaccines

• 70-80% against any rotavirus disease in developed/middle-income countries
• 90-100% against severe gastroenteritis in developed/middle-income countries
• ~50% efficacy against severe disease in the poorest developing countries (still cost-effective)
• Neither natural infection nor vaccine provides complete, lifelong protection from reinfection

• Goldman-Cecil Medicine, Chapter 350 (Viral Gastroenteritis)
• Rosen's Emergency Medicine, Chapter 80
• Robbins & Kumar Basic Pathology
• Sleisenger & Fordtran's Gastrointestinal and Liver Disease, Chapter 110