Viral GIT Infections

📌 Gastroenteritis Overview

Gastroenteritis is inflammation of the stomach and intestines caused predominantly by viruses.

Common Viral Causes:

• Rotaviruses – Affects young children

• Caliciviruses – Includes Norovirus

• Astroviruses

• Adenoviruses

Seasonal Trends:

• Norovirus is most common in winter

• Often referred to as Winter Vomiting Disease

🌀 Rotavirus

Structure & Characteristics:

• Spherical, non-enveloped virus

• Has glycoprotein spikes on the capsid aiding in attachment

• Transmitted via the faecal-oral route

• Extremely contagious – up to 100 trillion virions/g of stool

Clinical Impact:

• Major cause of infantile gastroenteritis

• Self-limiting with proper fluid and electrolyte support

• Vaccination available in the UK

  • Proven to reduce hospitalisations significantly (e.g. Ireland: 840 → 309 cases/year)

🧬 Viral Entry & Replication:

• Targets mature enterocytes at tips/middle of villi in the small intestine

• Enters cell via endocytosis into endosomes

• Released into cytoplasm

• Lipid droplets form viroplasms for viral replication

🔄 Rotavirus Replication Cycle:

• Requires elevated intracellular Ca²⁺

• Produces NSP4 (an enterotoxin)

  • Binds epithelial cells → increases Ca²⁺

  • Activates Cl⁻ channels → osmotic diarrhoea

  • Stimulates 5-HT (serotonin) → increases gut motility

🦠 Norovirus (a Calicivirus)

General Info:

• First identified in 1968 (Norwalk, Ohio)

• Belongs to Caliciviridae

• Includes 7 genogroups, subdivided into genotypes

• Major cause of outbreaks in England and Wales

🐚 Transmission Sources:

Shellfish:

• Linked to outbreaks due to sewage contamination

• 76% of UK oysters (2011) tested positive for Norovirus

Fresh Produce:

• Leafy greens and berries can carry virus

• Contamination via irrigation water, equipment, handlers

🧬 Infection & Symptoms:

• Low infective dose

• Incubation: 15–48 hours

• Duration: 1–2 days

• Symptoms:

  • Nausea, projectile vomiting, watery diarrhoea

  • Occasionally: fever, headache, aches, cramps

🌍 Spread & Prevention:

• Virus-laden vomit contaminates environment

• Transmitted via surfaces, hands, objects

• Preventative Steps:

  • Avoid food handling while ill

  • Use disinfectants

  • Avoid sharing personal items

  • Stay away from school, A&E, etc.

🧬 Hepatitis E Virus (HEV)

• Once thought to be a calicivirus, now in its own family

• Transmitted via the faecal-oral route

• Infects the liver (Enteric hepatitis)

• Fatalities more likely in pregnant women

  • Possibly due to immune and hormonal changes

  • May replicate in placenta

✨ Astroviruses

• Causes diarrhoea, typically no vomiting

• Common in young children (90% seroprevalence by age 5)

• Symptoms last 1–4 days

• May work by disrupting gap junctions between gut cells

🧬 Enteroviruses

• Includes:

  • Poliovirus

  • Echovirus

  • Coxsackievirus

• Transmission: Waterborne, faecal-oral

• Seasonal: More common in summer & autumn

🦠 Poliovirus:

• Affects CNS but transmitted enterically

• 3 serotypes, 4 disease outcomes:

  1. Asymptomatic – 90%

  2. Minor polio – fever, malaise, sore throat

  3. Non-paralytic – CNS involvement, back pain

  4. Paralytic polio – spinal cord & brain invasion → paralysis

🦠 Echoviruses:

• Echovirus 30 (E30): major pathogen

• Transmitted faecal-orally

• Causes viral meningitis, colds

• Significant outbreaks (2016–2018)

🦠 Coxsackieviruses:

Coxsackie A:

• Causes lesions, fever, hand-foot-and-mouth disease

• Self-limiting

Coxsackie B:

• Transmitted orally

• Affects heart (myocarditis) and pancreas

  • Can lead to diabetes by destroying islets of Langerhans

🧬 Hepatitis A Virus (HAV)

• Spread via faecal-oral route

• Not cytolytic

• Resilient – survives on surfaces, chlorine-resistant

• Incubation: ~1 month

• Symptoms:

  • Fatigue, nausea, anorexia, fever

  • Jaundice – caused by immune attack on infected liver cells

  • Children often asymptomatic

🦠 Emerging Virus: Aichi Virus

• Family: Kobuvirus, named for its bumpy structure

• Hosts: Humans, pigs, cats, dogs

Replication:

• Enters via endocytosis

• Uncoating poorly understood

• Uses host ribosome for protein synthesis

• Proteins drive production of viral RNA and particles

Symptoms:

• Targets intestinal villi, causing diarrhoea

• Immature cells can't absorb properly → nutrient and water loss

• Riskier for immunocompromised individuals

✅ Key Takeaways

• Rotavirus and Norovirus are leading causes of viral gastroenteritis; both spread faecal-orally and cause diarrhoea.

• Vaccination has significantly reduced Rotavirus-related hospitalisations.

• Norovirus spreads rapidly via vomit and contaminated surfaces—hygiene is critical.

• Hepatitis A and E affect the liver but have different severities and population risks.

• Astroviruses, Enteroviruses, and Emerging viruses like Aichi contribute to varying GI illnesses, often seasonal or age-specific.

• Enteroviruses can also have systemic effects—e.g., polio, myocarditis, or meningitis.

• Understanding transmission and replication mechanisms is crucial to prevention and control.