Viral Gastroenteritis - Diebel Flashcards
What are the most common viral pathogens that cause gastroenteritis?
-
Major Causes:
- Rotavirus
- Norovirus (Norwalk Virus)
- Minor Causes:
- Adenovirus
- Astrovirus
What is the route of infection for viruses that cause gastroenteritis?
Fecal to oral
What transmission characteristics of Rotavirus allow it to cause gastroenteritis?
- After ingestion → travels to GI tract
- virus particle is stable within the low pH of the GI system
- Infects the villus cells of proximal small intestine
- Virus replicates within villus cells
- Virus causes cell lysis
- causes impaired absorption of carbohydrates and other nutrients
- leads to vomiting followed by watery diarrhea
How is gastroenteritis caused by Rotavirus diagnosed?
- Stool specimen
- Serology for the virus ⇒ ELISA
- Serotypes are based off of the VP4 and VP7 genes → your body will make antibodies against these → can be tested by ELISA studies
- Latex agglutination assay of stool samples possible.
(Electron microscopy/RT-PCR also possible)
What is the treatment for gastroenteritis caused by Rotavirus?
Supportive!
- Rehydration
Is there a vaccine for Rotavirus?
Yes!
- live oral attenuated vaccine
- Rotarix = single strain of a human-infecting rotavirus
- Rotateq = reasortants
- 10 cow rotavirus genes + 1/5 human rotavirus genes
Rotavirus
RNA/DNA
Genome
Shape
Envelope
Unique characteristics
- RNA virus
- Icosahedral Nucleocapsid
- Nonenveloped
- DS, Segmented Genome (Class III)
- Reoviridae
- Unique characteristics:
- DOUBLE-PACKAGED → double capsid
- Stable in the environment.
- Digestive enzymes actually enhance infectivity.
What is the tropism of Rotavirus (where do they infect, grow, replicate)?
- Rotaviruses infect the mature absorptive villous epithelium of the upper two thirds of the small intestine.
- After replication in the upper small intestine, infectious particles are released into the intestinal lumen
- undergo further replication in the distal areas of the small intestine
- Infection is generally confined to the intestinal mucosa.
When is Rotavirus most contagious?
- Large amounts of virus are released during the diarrheal phase.
- Maximal virus shedding 2 to 5 days after the start of the diarrhea phase → CONTAGIOUS!!!
- Incubation period is about 48 hours.
- Outbreaks most common in day care centers, preschools, and among hospitalized infants.
- Higher incidence of cases in the autumn, winter, and spring.
What age group does Rotavirus primarily affect?
- Disease is most serious in individuals under the age of 2.
- By age 3, almost every individual worldwide (~95%) has been infected and develops lifelong immunity.
- Infection before 6 months of age is uncommon due to passive IgA immunity from the mother’s colostrum.
What are the symptoms of gastroenterities caused by Rotavirus?
- Secretory diarrhea
- caused by the infection and damage to the proximal small bowel.
- Stool does NOT contain leukocytes or RBCs.
- Nausea/vomiting
- abdominal pain
What is the most common cause of foodborne disease outbreaks in the United States?
Norovirus Virus
How are Noroviruses transmitted?
fecal-oral route in contaminated water and food
(group-related or institutional diarrhea common)
Norwalk Virus
DNA/RNA
Shape
Envelope
Genome
- RNA virus
- Icosahedral Nucleocapsid
- ragged outlined capsid
- Nonenveloped
- SS (+) Nonsegmented Genome (Class IV)
- Caliciviridae
- Calicivirus (also includes astroviruses)
What is the tropism of Norovirus?
intestinal epithelium
How does Norovirus cause gastroenteritis?
- Only takes 10 virions to initiate infection.
- The virus infects and damages the small intestine
- cytolytic damage and inflammation
- prevents proper absorption of water and nutrients
- causes a watery diarrhea
- Gastric emptying may be delayed, causing vomiting.
- Shedding of the virus may continue for 2 weeks after symptoms have ceased.
What are the symptoms of gastroenteritis caused by Norovirus?
- 24-hour incubation period, symptoms start after
- Diarrhea
- Nausea/vomiting
- more severe than Rotavirus
- Abdominal cramps
- Fever is typically no higher than 101°F
- Headache
- Anorexia and malaise
- Disease resolves after 48 hours, without serious consequences
Why are Norovirus infections the leading cause of gastroenteritis in the US?
Norovirus can mutate quickly (causing drift).
- Results in new strains every few years.
- Immunity is generally short lived at best and may not be protective.
- The large number of strains and high rate of mutation allows reinfection despite antibodies from a previous exposure.
How is gastroenteritis caused by Norovirus diagnosed?
- Not typically diagnosed!
- When it is done:
- visualization of the virus in stool specimens
- RT-PCR
- Serology of stool and/or vomit specimens
- Electron microscopy
- Enzyme-linked assays
What is the treatment for gastroenteritis caused by Norovirus?
- Usually not required → self-limiting infection
- Supportive if necessary
- rehydration
Adenovirus
DNA/RNA
Shape
Envelope
Genome
- DNA virus
- Icosahedral Nucleocapsid
- Nonenveloped
- DS DNA Linear (Class I)
- Adenoviridae
- Mastadenovirus (Adenovirus)
What serotypes of Adenovirus are enteric and are a major cause of acute infantile gastroenteritis?
Serotypes 40, 41, and 42
How is gastroenteritis caused by Adenovirus diagnosed?
- Direct analysis of the clinical sample without virus isolation is possible.
-
Rarely used except for epidemiological purposes.
- Immunoassays (either fluorescent antibody or ELISA)
- PCR detection of the viral genome within a stool sample
- DNA probe analysis
- Above approaches required for serotypes 40 – 42
What is involved in the treatment, prevention, and control of Adenovirus?
- Careful handwashing
- Chlorination of swimming pools
- No approved treatments.
- Supportive care.
- Self-limiting infection in immunocompetent individuals
- Live oral vaccines for types 4 and 7 (military personal only)
