Viral Gastroenteritis: Rotavirus, Adenovirus, Calicivirus, Astrovirus Flashcards
Define gastroenteritis.
Gastroenteritis refers to the vomiting or diarrhea due to infections of the stomach, small and large intestine. It may be caused by parasites, bacteria and viruses.
List the main viruses that cause viral gastroenteritis.
rotavirus, adenovirus, calicivirus, astrovirus
Viruses are responsible for up to ____% of infective diarrhoeas.
75
List some viruses found in the gut which aren’t necessarily associated with gastroenteritis.
poliovirus, coxsackie A and B viruses, enteroviruses (68-71), hepatitis A virus, hepatitis E virus, adenovirus (1-39), reovirus
Rotavirus is a leading cause of severe gastroenteritis in ____________ worldwide.
infants and young children.
(a) Rotavirus family: ____________
(b) There are several species of Rotavirus. Which of them is the most clinically significant?
(a) Reoviridae
(b) Rotavirus A is the most clinically significant, being responsible for over 90% of rotavirus infections in humans.
Discuss the structure and genome of rotaviruses.
🚽 Rotaviruses are non-enveloped and possess a triple-layered protein capsid. The three layers are as follows:
(i) Inner core: contains viral RNA and the proteins VP1, VP2 and VP3
(ii) Middle layer: Formed by the protein VP6, which is highly antigenic and used for serotyping.
(iii) Outer layer: Composed of the proteins VP4 and VP7, which are involved in host cell attachment and entry.
🚽 The virus particles exhibit icosahedral symmetry.
🚽 The rotavirus genome consists of 11 segments of double-stranded RNA (dsRNA), which encode six structural proteins (VP1-VP4, VP6, VP7) and six non-structural proteins (NSP1-NSP6).
Discuss the transmission and pathogenesis of rotaviruses.
🚽 Rotaviruses are transmitted via the fecal-oral route hence they enter the body through the mouth, typically through contaminated food, water or surfaces.
🚽 The virus targets the epithelial cells lining the small intestine, particularly the villous epithelium.
🚽 Once inside the epithelial cells, rotaviruses replicate rapidly, causing cell damage and death.
🚽 The infection leads to the destruction of mature enterocytes (intestinal cells), resulting in villous atrophy (shortening of the villi) and a loss of microvilli. This damage impairs the intestine’s ability to absorb nutrients and water.
🚽 The virus produces a nonstructural protein known as NSP4, that acts as a viral enterotoxin. It disrupts calcium homeostasis by increasing intracellular calcium levels, which is crucial for virus replication and morphogenesis.
🚽 NSP4 induces diarrhea by causing Ca²⁺-dependent transepithelial secretion, leading to fluid loss into the intestinal lumen.
[Diagram 1] [Diagram 2] [Diagram 3]
Further notes:
Ca²⁺-dependent transepithelial secretion:
Mechanism: NSP4 induces diarrhea by causing calcium-dependent secretion of chloride ions and water into the intestinal lumen.
The elevated intracellular calcium levels activate chloride channels in the intestinal epithelial cells. This activation leads to the secretion of chloride ions into the intestinal lumen, followed by water, resulting in diarrhea.
Enteric nervous system: NSP4 also interacts with the enteric nervous system, stimulating the release of neurotransmitters that increase intestinal motility and secretion, further contributing to diarrhea.
Discuss the clinical presentation of rotavirus.
Early symptoms: fever, vomiting
Main symptoms: watery diarrhea, abdominal pain, loss of appetite, dehydration [dry mouth and throat, decreased urination, crying with few or no tears, sunken fontanelle, decreased skin turgor]
By what age have approximately 90% of children developed serum antibodies to one or more types of rotavirus?
By age 3 years
What is the role of secretory IgA (sIgA) in rotavirus infections?
sIgA is an antibody that plays a crucial role in mucosal immunity. It is found in mucous secretions and can neutralize rotavirus in the gut, preventing it from attaching to and infecting intestinal cells.
What are three techniques used in the detection of rotavirus in stool samples?
(a) ELISA test
(b) Latex agglutination
(c) PCR
Discuss treatment of rotavirus infection.
Treatment of rotavirus infection is supportive, aimed at correction of loss of water and electrolytes; failure to which, acidosis, shock and death are consequential.
Briefly discuss prevention and control of rotavirus infections.
🚽 Vaccination
🚽 Proper sanitation and hygiene practices
🚽 Isolation and supportive care of infected individuals
🚽 Proper waste water management and ensuring safety of water supplies
Adenovirus
(a) Family
(b) Basic structure
(c) Genome type
(d) Serotypes responsible for gastroenteritis
(a) Family: Adenoviridae
(b) Basic structure: naked, icosahedral symmetry
(c) Genome type: double-stranded DNA
(d) Serotypes responsible for gastroenteritis: 40, 41
