Gastrointestinal Viruses

Viral gastroenteritis is caused by several distinct virus groups with overlapping clinical presentations. Norovirus, enteric adenovirus, rotavirus, astrovirus, and sapovirus can be compared directly by structure, transmission, age pattern, and clinical disease.

Genome. Double-stranded RNA, segmented, eleven segments, a genuinely distinctive genome structure among gastrointestinal viruses, since most other medically important RNA viruses carry a single-stranded genome. Double-stranded RNA viruses form their own distinct Baltimore classification group. Envelope. Absent.

Transmission. Faecal-oral, highly efficient given a low infectious dose and environmental stability consistent with its nonenveloped structure.

Age distribution. The leading global cause of severe dehydrating gastroenteritis in infants and young children, typically under five years, historically responsible for a substantial proportion of global childhood diarrhoeal mortality before widespread vaccine introduction. Infection in older children and adults is common but generally milder, reflecting at least partial immunity acquired from earlier childhood exposure.

Pathogenesis. Infects and destroys mature enterocytes at the tips of small intestinal villi, impairing normal absorptive function, particularly disaccharidase enzyme activity, contributing to a transient secondary lactose intolerance in some affected children, and producing a net secretory, osmotic diarrhoeal state. The viral nonstructural protein NSP4 additionally functions as a direct enterotoxin, contributing to the secretory component of the diarrhoea via a mechanism distinct from simple villous destruction alone.

Major clinical pattern. Acute-onset vomiting followed by watery, often voluminous diarrhoea, with a substantial risk of clinically significant dehydration in young children specifically, historically the dominant reason for paediatric hospitalisation and, in resource-limited settings without ready access to oral or intravenous rehydration, a leading cause of death from this cause.

Diagnosis. Antigen detection, enzyme immunoassay, historically the standard rapid test, or PCR from stool.

Prevention. Live-attenuated oral rotavirus vaccines, now part of the routine infant immunisation schedule in most countries, have produced a dramatic global reduction in severe rotavirus disease and associated hospitalisation and mortality.

Nonenveloped, positive-sense ssRNA calicivirus, with an extremely low infectious dose and marked environmental and detergent resistance. It is the leading cause of acute gastroenteritis outbreaks across all age groups, in contrast to rotavirus's specific concentration in young children, classically in closed settings such as cruise ships, hospitals, and care homes. It requires soap-and-water hand hygiene given alcohol hand sanitiser's limited effectiveness against this nonenveloped virus.

Specific enteric-tropic adenovirus serotypes, distinct from the respiratory and ocular-tropic serotypes, nonenveloped double-stranded DNA, causing gastroenteritis predominantly in young children, generally with a longer symptom duration than rotavirus or norovirus but otherwise producing a broadly similar acute watery diarrhoeal illness.

Genome. Positive-sense ssRNA. Envelope. Absent.

Transmission. Faecal-oral.

Age distribution. Predominantly young children, and, similar to several other nonenveloped enteric viruses, also a recognised cause of outbreaks in elderly and immunocompromised populations in institutional settings.

Pathogenesis. Infects mature enterocytes, broadly analogous in general mechanism to rotavirus, though generally producing a milder overall clinical picture.

Major clinical pattern. Watery diarrhoea, generally milder than rotavirus, often with limited or no vomiting, distinguishing its typical clinical severity profile from the more classically vomiting-predominant early course of rotavirus and norovirus infection.

Diagnosis. PCR, increasingly standard, with antigen detection available in some settings.

Genome. Positive-sense ssRNA. Envelope. Absent. A calicivirus, taxonomically related to norovirus, same family, but a genuinely distinct genus with its own separate epidemiological pattern.

Transmission. Faecal-oral.

Age distribution. Predominantly young children, though, like norovirus, capable of causing outbreaks across all age groups in appropriate settings.

Pathogenesis. Broadly analogous to norovirus, given the shared family membership and general viral structure.

Major clinical pattern. Acute gastroenteritis with vomiting and diarrhoea, clinically similar to but generally somewhat milder than typical norovirus infection.

Diagnosis. PCR, increasingly included in standard multiplexed gastrointestinal PCR panels alongside the other organisms in this group.

All of these gastrointestinal viruses are nonenveloped, meaning environmental stability, faecal-oral transmission efficiency, and consequent resistance to alcohol-based hand sanitiser is a shared property across this entire syndrome group.