GI06 - Viral Gastroenteritis and Foodborne Illness

What is gastroenteritis?

Inflammation of the stomach and intestines that typically causes diarrhea, vomiting, abdominal pain, and sometimes fever.

Which two viruses are the most common causes of viral gastroenteritis worldwide?

Rotavirus and norovirus.

Which age group is most commonly infected by rotavirus?

Commonly infects young children, especially those between 6 and 24 months of age.

What type of genome does rotavirus have?

11-segment double-stranded RNA genome.

Is rotavirus enveloped or non-enveloped, and why is that important?

Rotavirus is non-enveloped, which makes it resistant to stomach acid, detergents, drying, and environmental stress.

To which viral family does rotavirus belong?

Reoviridae

Why is rotavirus called “rotavirus”?

Named for its wheel-shaped appearance under electron microscopy (“rota” means wheel).

Which two rotavirus capsid proteins are the main targets of neutralizing antibodies?

VP4 and VP7

Which rotavirus protein mediates attachment to host cells?

VP4

Which rotavirus protein antagonizes the host interferon response?

NSP1 antagonizes the host interferon response and helps the virus evade innate immunity.

Which rotavirus protein acts as a viral enterotoxin and contributes directly to diarrhea?

NSP4 → causes secretory diarrhea

What are histo-blood group antigens (HBGAs)?

Carbohydrate molecules, including ABO and Lewis antigens, expressed on red blood cells and mucosal epithelial surfaces.

Where are histo-blood group antigens expressed in the gastrointestinal tract?

HBGAs are expressed on mucosal epithelial cells and intestinal epithelial cells and are also secreted into mucus in about 80% of the population.

How do rotavirus and norovirus use histo-blood group antigens during infection?

Both viruses attach to histo-blood group antigens on intestinal epithelial cells as part of the initial step of infection.

Who are “non-secretors,” and how does this affect rotavirus susceptibility?

Individuals who do not secrete HBGAs into mucus; they are less susceptible to rotavirus and norovirus infection.

Which blood type is associated with increased susceptibility to rotavirus infection?

Individuals with blood type A are more susceptible to rotavirus infection.

Which antibody class is most important for protection against rotavirus infection?

IgA is the most important antibody for protection because it functions at mucosal surfaces.

How is rotavirus transmitted?

Primarily through the fecal-oral route.

How many infectious particles are required to transmit rotavirus?

Approximately 100 colony-forming units per gram

How many viral particles can be present in the stool of an infected person?

The stool of an infected person may contain 10^6 to 10^9 times the infectious dose.

In which regions are rotavirus deaths most prevalent?

Rotavirus deaths are most prevalent in low-income and developing countries with low vaccination rates.

What factors contribute to higher rotavirus mortality in developing countries?

Malnutrition, limited access to clean water, inadequate healthcare facilities, and lack of access to rehydration therapy.

Which cells in the small intestine does rotavirus infect?

Rotavirus infects mature, non-dividing enterocytes located in the middle and tip of the intestinal villi.

What structural damage does rotavirus cause in the intestine?

Necrosis and destruction of villus tips, leading to villous atrophy.

How often are intestinal epithelial cells normally replaced?

Intestinal epithelial cells are normally replaced every 4 to 6 days

(every 2-4 days)

How does villous atrophy cause malabsorptive diarrhea in rotavirus infection?

Shortened villi reduce surface area for nutrient and water absorption, leading to osmotic or malabsorptive diarrhea.

How does the rotavirus NSP4 protein contribute to secretory diarrhea?

NSP4 acts as an enterotoxin that stimulates intestinal fluid secretion.

How does activation of the enteric nervous system contribute to rotavirus secretory diarrhea?

Rotavirus infection triggers serotonin release and activates the enteric nervous system, increasing intestinal secretion.

What is the incubation period for rotavirus infection?

Approximately 2 days.

How long does rotavirus illness usually last?

3 to 8 days.

What type of diarrhea is characteristic of rotavirus infection?

Rotavirus causes profuse, watery, non-bloody diarrhea.

What is the most dangerous complication of rotavirus infection in children?

Severe dehydration, which can lead to shock.

Why are children between 6 and 24 months at highest risk for severe rotavirus infection?

Maternal IgG transferred during pregnancy declines, and IgA from breast milk decreases after breastfeeding stops, leaving the child immunologically vulnerable.

What is the “double burden” of rotavirus and undernutrition?

Undernutrition combined with malabsorptive diarrhea worsens nutritional deficiency and impairs immune response.

What is the “triple burden” in certain regions?

Undernutrition, rotavirus infection, and HIV infection together increase morbidity and mortality.

What is the primary treatment for rotavirus infection?

The primary treatment is fluid and electrolyte replacement.

Why should antidiarrheal medications such as loperamide not be given to young children with rotavirus?

They can cause sedation, bowel obstruction, and delay pathogen elimination.

What type of vaccines are used to prevent rotavirus infection?

Live-attenuated oral vaccines.

How effective are rotavirus vaccines in the United States?

They provide 85–98% protection against severe illness and reduce hospitalizations by about 96%.

How effective are rotavirus vaccines in high-mortality countries?

They provide approximately 50% protection against laboratory-confirmed illness.

What are the two main rotavirus vaccines?

Rotariz (2 and 4 months) and RotaTeq (2, 4, and 6 months)

What type of virus is norovirus?

Non-enveloped, single-stranded RNA virus in the Caliciviridae family.

Is norovirus related to influenza virus?

No, norovirus is not related to influenza virus and is not prevented by the flu vaccine

What is the incubation period of norovirus infection?

12 to 48 hours.

How long does norovirus illness typically last?

Illness usually lasts 1 to 3 days but may last up to 6 days in vulnerable populations.

What type of diarrhea does norovirus cause?

Non-bloody diarrhea, often accompanied by vomiting.

What is the leading cause of foodborne illness in the United States?

Norovirus

What are the four major routes of norovirus transmission?

Fecal-oral transmission, infected food handlers, contaminated surfaces (fomites), and aerosolized droplets from vomit.

What is the approximate infectious dose of norovirus?

10 viral particles

(Very highly transmissable)

How long can individuals shed norovirus after recovery?

Individuals can shed norovirus for an average of 28 days after recovery.

What percentage of norovirus infections are asymptomatic?

30% of infections are asymptomatic but still contagious.

Why are alcohol-based hand sanitizers ineffective against norovirus?

Norovirus is non-enveloped and resistant to ethanol-based disinfectants.

What is the most effective method to prevent norovirus transmission?

Handwashing with soap and water for at least 20 seconds.

What disinfectant is recommended for environmental decontamination of norovirus?

Bleach solutions containing 1000–5000 ppm chlorine are recommended.

Why is it difficult to develop a norovirus vaccine?

Norovirus mutates rapidly, multiple strains circulate, immunity is short-lived, and it is difficult to culture in laboratory systems.

Is there a commercially available norovirus vaccine?

No, there is currently no commercially available vaccine.

What type of bacterium is Campylobacter jejuni?

Corkscrew-shaped, microaerophilic, Gram-negative rod.

Which Campylobacter species causes most human disease?

Campylobacter jejuni

What is the primary reservoir of Campylobacter jejuni?

Chickens

Where does Campylobacter colonize in chickens?

Campylobacter colonizes the intestines, liver, and other organs of chickens without causing disease.

Which foods are most commonly associated with Campylobacter infection?

Undercooked poultry is the most common source, but infection can also come from raw milk, seafood, untreated water, produce, and pet store puppies.

What percentage of raw chicken in the United States is contaminated with Campylobacter?

More than half of raw chicken in the United States is contaminated.

What is the infectious dose of Campylobacter?

Fewer than 500 bacteria can cause infection.

Why is Campylobacter infection easily transmitted during food preparation?

One drop of raw chicken juice may contain enough bacteria to cause infection.

What is the incubation period of Campylobacter infection?

1 to 3 days.

What are the early symptoms (prodrome) of Campylobacter infection?

High fever, rigors (shaking chills), dizziness, and body aches.

What are the main symptoms during the diarrheal phase of Campylobacter infection?

Diarrhea (often bloody), abdominal cramps, fever, nausea, and vomiting.

How long does the acute diarrheal phase of Campylobacter infection last?

Usually 2 to 5 days, but it may last up to 10 days.

What sequalae can be associated with campulobacteriosis?

• Guillain-Barre syndrome

• Reactive arthritis (can lead to uveitis)

Do most patients require treatment for campuloacteriosis?

No, most recover without specific treatment

What treatments are available for campylobacteriosis?

Fluid replacement; erythromycin or fluoroquinolones may be used in severe cases.

What type of bacterium is Salmonella?

Salmonella are Gram-negative bacteria belonging to the Enterobacteriaceae family.

Where is Salmonella commonly found?

Salmonella is found in the gastrointestinal tracts of virtually all animals.

What are the main clinical syndromes caused by salmonella?

• Gastroenteritis

• Typhoid fever

Which Salmonella serotype commonly causes gastroenteritis?

Salmonella enteritidis

How is Salmonella gastroenteritis typically transmitted?

Ingestion of contaminated poultry, eggs, dairy, improperly cooked meat, water, or contact with infected animals.

Which household pets are common sources of Salmonella?

Turtles, reptiles, and poultry.

What is the incubation period for Salmonella gastroenteritis?

6 to 48 hours.

How long does Salmonella gastroenteritis typically last?

Two days to one week.

What are common symptoms of Salmonella gastroenteritis?

Nausea, vomiting, diarrhea, fever, abdominal cramps, headache, and muscle aches.

Are antibiotics typically recommended for Salmonella gastroenteritis?

No, antibiotics are usually not given because the illness is self-limited (spontaneous resolution)

Which Salmonella species causes typhoid fever (enteric fever)?

Salmonella typhi

What is the incubation period for typhoid fever?

10 to 14 days.

How long does untreated typhoid fever typically last?

Approximately 3 weeks.

What are the main symptoms of typhoid fever?

Prolonged fever, headache, muscle aches, malaise, anorexia, and gastrointestinal symptoms.

Where do Salmonella typhi bacteria replicate during typhoid fever?

They multiply inside monocytes and macrophages of the host.

What percentage of patients become chronic carriers of Salmonella typhi?

1 to 5 percent

Where is the reservoir for chronic Salmonella typhi carriers?

The gallbladder.

What is the mortality rate of untreated typhoid fever?

10 to 30 percent

(high fatality if untreated with antibiotics)

What causes death in untreated typhoid fever?

Intestinal hemorrhage.

What antibiotics are used to treat typhoid fever?

Fluoroquinolones, third-generation cephalosporins, trimethoprim-sulfamethoxazole, or chloramphenicol.

What condition is defined by recurrent Salmonella bacteremia?

Recurrent Salmonella bacteremia is an AIDS-defining illness.

What type of bacterium is Clostridium perfringens?

Anaerobic, Gram-positive, spore-forming bacillus.

Why are spores important in Clostridium perfringens infections?

Spores form a protective coating that allows survival under harsh conditions.

What causes diarrhea in Clostridium perfringens infection?

C. perfringens produces a heat-labile enterotoxin

What types of food are commonly associated with Clostridium perfringens outbreaks?

Foods cooked in large batches and held at unsafe temperatures.

(Refrigeration prevents toxin production, reheating >165 F destroys enterotoxin)

What is the “danger zone” temperature range for bacterial growth in food?

40–140°F (4–60°C).

What is the incubation period for Clostridium perfringens food poisoning?

8 to 24 hours.

How long do symptoms usually last for Clostridium perfringens infection?

24 to 48 hours.

What are the typical symptoms of Clostridium perfringens food poisoning?

Watery diarrhea and abdominal cramps (no fever, nausea, or vomiting.)