Clinical Implications of Viral Infections

Clinical Implications of Viral Infections of the Bowel

• Gastrointestinal Tract (GIT) Viruses cause diarrheal illness or illness elsewhere.
• Enteroviruses are a family of viruses that include Polioviruses, Coxsackie A and B viruses, ECHO viruses, and other Enteroviruses.
• Poliovirus is transmitted via the faecal-oral route.
• Poliovirus infection has three possible clinical presentations: nil or mild illness (90-95%), influenza-like illness (4-8%), and biphasic illness (1-2%).
• Paralytic poliomyelitis is a rare complication of poliovirus infection, occurring in 1 in 1000 cases.
• Poliovirus is eradicated in high-income countries, but still a major source of illness and death in low-income countries.
• Non-polio enteroviruses are transmitted via the faecal-oral route, direct contact, indirect contact, oral-oral route, and peri-natal transmission.
• Non-polio enteroviruses can cause a wide range of symptoms, including: fever, sore throat with rash, meningitis, diarrhea, rubella-form rash, pericarditis, and myocarditis.
• Enterovirus D68 is a non-polio enterovirus that can cause mild upper respiratory tract infections and severe lower respiratory tract infections (LRTI).
• Viral Gastroenteritis is a significant cause of morbidity and mortality worldwide, particularly in overcrowded areas with a low socioeconomic status.
• Rotavirus is the most common cause of acute diarrheal illness in infants and young children.
• Norovirus is a very common cause of gastroenteritis worldwide and "winter vomiting bug".
• Astrovirus causes symptoms similar to norovirus but with a longer incubation period.
• Adenovirus can cause infantile diarrhea, respiratory infections, meningitis, and conjunctivitis.
• Caliciviruses and Astroviruses are associated with outbreaks of acute diarrhea and vomiting in bivalve shellfish.
• Outbreaks of Rotavirus are most common in crèches and children's hospitals.
• Hand hygiene, good environmental cleaning, and disinfection are essential measures to prevent the spread of Norovirus.
• Surveillance, isolation, and cohorting are important measures to control Norovirus outbreaks in healthcare settings.
• Vaccines are available to prevent Rotavirus infection, but they are not effective against Norovirus.

Gastrointestinal (GIT) Viruses and Infections

• Viruses can cause diverse illnesses, including those affecting the gastrointestinal tract.
• The focus is on viral infections that cause diarrhoeal illness, particularly those transmitted via the faecal-oral route.
• Key GIT viruses: Rotavirus, Caliciviruses (including Noroviruses), Astroviruses, and Adenoviruses.
• Enteroviruses, a family of viruses within the Picornavirus, are also discussed. This includes Poliovirus, Coxsackie A and B viruses, ECHO viruses, and other Enteroviruses.

Poliovirus

• Epidemiology: Human-only reservoir, incubation period typically 7 days, transmitted via the faecal-oral route, and highly infectious.
• Clinical Manifestations: Three main presentations:
  • Asymptomatic: Most common, exhibiting mild or no symptoms.
  • Influenza-like Illness: Fever, lack of energy, and pharyngitis.
  • Biphasic Illness: Initial GIT symptoms followed by fever, headache, aseptic meningitis, and occasionally paralytic poliomyelitis.
• Diagnosis: Early in illness, viral culture from throat and faeces; CSF PCR.
• Treatment: Supportive care, including pain relief, physical therapy, mechanical ventilation if necessary, and monitoring for autonomic dysfunction.
• Vaccines: Two types:
  • Oral Poliovirus Vaccine (OPV): Live attenuated virus, administered orally, induces IgA and humoral immunity.
  • Inactivated Poliovirus Vaccine (IPV): Contains inactivated polio serotypes administered via injection, produces antibody immunity, and induces little IgA.

Non-Polio Enteroviruses

• Epidemiology: Human-only infection, incubation period and clinical presentation vary with virus type, can be detected for several weeks in faeces.
• Transmission: Faecal-oral route (e.g., direct contact, contaminated water), oral-oral route (less common), and Peri-natal transmission.
• Pathogenesis: Replicate in the upper respiratory and GI tracts, multiplying in the intestinal tract, and spreading to lymphoid tissue. Viraemia is common, leading to damage to target organs.
• Clinical Presentation: More common in children, with most cases being asymptomatic. Can cause a wide range of symptoms, including mild flu-like illness, pharyngitis, respiratory infections, headache, conjunctivitis, rash, meningitis, and paralysis.
• Diagnosis: Enterovirus PCR from stool or clinical specimens.
• Treatment: Supportive treatment, including rehydration and analgesia. Antivirals are not indicated.

Coxsackie Viruses

• Epidemiology: Numerous antigenic types, divided into two groups (A & B), transmitted via the faecal-oral route, inhalation, and direct contact.
• Clinical Manifestations:
  • Coxsackie A: Fever, common cold, rash, herpangina (vesicular lesions around the soft palate and uvula).
  • Coxsackie B: Fever, rash, meningitis, epidemic myalgia (Bornholm’s disease), respiratory infections, myocarditis, and pericarditis.

ECHO (Enteric Cytopathogenic Human Orphan) Viruses

• Epidemiology: At least 33 antigenic types, spread via the faecal-oral route or oropharyngeal secretions.
• Clinical Manifestations: Usually asymptomatic, but can cause fever, sore throat with rash, meningitis, diarrhoea, rubella-form rash, pericarditis, and myocarditis.

Enterovirus D68

• Epidemiology: Non-polio enterovirus, cases peak in summer and autumn, affecting children predominantly, often associated with underlying respiratory illness.
• Transmission: Via inhalation of infected particles and manual transfer of infected material.
• Clinical Manifestations: Mild upper respiratory tract infection to severe LRTI, and acute flaccid paralysis.
• Diagnosis: PCR from throat swabs, nasopharyngeal swabs, BAL, or CSF.
• Treatment: Supportive care, antivirals are not indicated.

Viral Gastroenteritis

• Epidemiology: Significant cause of morbidity and mortality worldwide, especially in crowded, lower socioeconomic regions, transmitted via the faecal-oral route and sometimes by droplets.
• Key Viruses: Rotavirus, Caliciviruses (including Noroviruses), Astroviruses, and Adenoviruses.

Rotavirus

• Epidemiology: Group A is the most common serogroup, a major cause of acute diarrhoeal illness in infants and young children, often causing outbreaks in childcare settings.
• Pathogenesis: Multiplies in the small intestine, damaging cells, shortening villi, and causing malabsorption, resulting in hyperosmotic diarrhoea.
• Clinical Presentation: Diarrhoea lasting about 5 days (ranging from mild to severe watery diarrhoea with dehydration), vomiting, and rarely CNS complications.
• Diagnosis: Stool antigen detection or PCR.
• Management: Rehydration, post-gastroenteritis lactose intolerance is common, and a vaccine is available for infants.

Caliciviruses

• Epidemiology: Small RNA viruses, most well-known is Norovirus (common cause of gastroenteritis worldwide).
• Pathogenesis: Replication occurs in the small intestine, asymptomatic excretion is common.
• Clinical Presentation: Short incubation period (12-72 hours), nausea, abdominal cramps, malaise, myalgia, headache, acute vomiting, and less frequently diarrhoea. Spontaneous resolution within 24-48 hours, but rehydration is important.
• Diagnosis: Based on clinical presentation and faeces PCR.

Astroviruses

• Epidemiology: Star-shaped appearance, similar symptoms to Noroviruses but with a slightly longer incubation period.
• Clinical Presentation: Watery diarrhoea and vomiting, more prominent in Calicivirus infections.
• Outbreaks: Can occur in bivalve shellfish (oysters, clams, mussels).

Adenovirus

• Epidemiology: Double-stranded DNA virus, over 40 serotypes, transmitted via the faecal-oral route, respiratory route, or direct inoculation.
• Clinical Presentation: Commonly asymptomatic, but some serotypes cause infantile diarrhoea, respiratory infections, meningitis, and conjunctivitis.