Question
Viral diarrhea
Answer
Viral diarrhoea is caused by a group of viruses that infect and damage the small intestinal epithelium, producing acute, generally self-limiting watery diarrhoea, and collectively constituting the most common cause of acute gastroenteritis worldwide.
Major causative viruses:
- Rotavirus (double-stranded RNA, family Reoviridae) — the leading cause of severe, dehydrating diarrhoea in infants and young children worldwide, particularly significant in developing countries as a major cause of childhood mortality before widespread vaccination; a safe and effective rotavirus vaccine is now part of many national immunization programmes.
- Norovirus (a calicivirus) — a leading cause of acute gastroenteritis outbreaks in people of all ages, notorious for outbreaks in closed/semi-closed settings (cruise ships, hospitals, nursing homes, schools) given its very low infectious dose and high environmental stability/resistance to routine disinfection.
- Adenovirus (enteric serotypes 40/41) — an important cause of diarrhoea in young children, generally milder and more prolonged than rotavirus.
- Astrovirus — causes mild-to-moderate diarrhoea, particularly in young children and the elderly/immunocompromised.
Pathogenesis: these viruses infect and damage mature enterocytes at the tips of small intestinal villi, causing villous atrophy/blunting, which reduces the intestinal absorptive surface area and disaccharidase enzyme activity — producing an osmotic component to the diarrhoea (undigested/unabsorbed carbohydrate drawing water into the lumen), alongside some direct secretory effects (e.g., rotavirus NSP4 protein acts as a viral enterotoxin, stimulating secretion).
Laboratory diagnosis: ELISA (antigen detection) is the most widely used rapid method, particularly for rotavirus and adenovirus; electron microscopy of stool (historically important, direct visualization of characteristic viral particles, now largely superseded); RT-PCR — increasingly used, offering high sensitivity and the ability to detect multiple viral (and other) pathogens simultaneously via multiplex panels.
Management: primarily supportive — oral or intravenous rehydration therapy is the cornerstone of treatment, since no specific antiviral therapy is routinely available for most causes of viral gastroenteritis; most cases are self-limiting within days.