GI infections

What type of virus is Rotavirus?

dsRNA virus, non-enveloped

Which age group is most commonly affected by Rotavirus infection?

Infants and young children (6 months to 2 years)

What is the primary clinical manifestation of Rotavirus infection?

Severe watery diarrhea leading to dehydration in infants and young children

How is Rotavirus transmitted?

Fecal-oral route

What part of the intestine does Rotavirus primarily infect?

Enterocytes at the tips of the villi in the small intestine, causing malabsorption

Which vaccine is used to prevent Rotavirus infection?

Live attenuated oral Rotavirus vaccine (e.g., RotaTeq, Rotarix)

What type of diarrhea is caused by Rotavirus?

Secretory diarrhea due to enterocyte damage and NSP4 enterotoxin

What diagnostic test is commonly used for Rotavirus?

ELISA or PCR detecting viral antigen in stool

What is the mainstay treatment for Rotavirus diarrhea?

Supportive care with oral rehydration therapy

What type of organism is Escherichia coli?

Gram-negative facultative anaerobic rod, part of the normal intestinal flora

Which strain of E. coli is associated with traveler's diarrhea?

Enterotoxigenic E. coli (ETEC)

What toxins are produced by ETEC?

Heat-labile (LT) and heat-stable (ST) enterotoxins

Which E. coli pathotype causes bloody diarrhea and hemolytic uremic syndrome (HUS)?

Enterohemorrhagic E. coli (EHEC), especially serotype O157:H7

What toxin is responsible for the pathogenesis of EHEC?

Shiga-like toxin (verotoxin), which inhibits the 60S ribosome

Why should antibiotics be avoided in EHEC infection?

They increase the risk of HUS by triggering more Shiga-like toxin release

Which E. coli strain causes persistent diarrhea in children and HIV patients, often with mucus?

Enteroaggregative E. coli (EAEC)

Which E. coli strain invades intestinal epithelial cells and causes a dysentery-like illness?

Enteroinvasive E. coli (EIEC)

Which E. coli strain is associated with infantile watery diarrhea in developing countries?

Enteropathogenic E. coli (EPEC)

How does EPEC cause diarrhea?

It disrupts microvilli and forms attaching-and-effacing lesions, leading to malabsorption

What is the main treatment for most diarrheagenic E. coli infections?

Supportive care with fluids and electrolytes; antibiotics are generally avoided unless severe or extraintestinal

What is a serious renal complication of EHEC infection, especially in children?

Hemolytic uremic syndrome (HUS): hemolytic anemia, thrombocytopenia, and acute renal failure

What type of organism is Salmonella?

Gram-negative, facultative intracellular, motile rod in the Enterobacteriaceae family

How is Salmonella transmitted?

Fecal-oral route; commonly through contaminated poultry, eggs, dairy, or reptiles

Which Salmonella serotype causes typhoid fever?

Salmonella enterica serovar Typhi (S. Typhi)

What are the symptoms of typhoid fever?

Gradual onset fever, abdominal pain, rose spots on abdomen, hepatosplenomegaly, and constipation or diarrhea

Which organ can harbor S. Typhi in chronic carriers?

Gallbladder (especially in those with gallstones)

What distinguishes Salmonella from Shigella in terms of motility and H2S production?

Salmonella is motile and produces H₂S (black colonies on Hektoen agar); Shigella is non-motile and H₂S negative

What is the clinical presentation of non-typhoidal Salmonella (e.g., S. enteritidis, S. typhimurium)?

Acute self-limited gastroenteritis with watery or bloody diarrhea, fever, and abdominal cramps

Is antibiotic treatment recommended for non-typhoidal Salmonella gastroenteritis?

No, it's usually self-limited; antibiotics may prolong carrier state unless severe or invasive disease is present

What is the pathogenesis of Salmonella in the GI tract?

Invades M cells in Peyer's patches, survives in macrophages, and induces inflammatory diarrhea

What vaccines are available for S. Typhi?

Live oral (Ty21a) and injectable Vi capsular polysaccharide vaccines.

What type of diarrhea is caused by Salmonella infection?

Inflammatory (often bloody with PMNs in stool)

What type of organism is Vibrio cholerae?

Gram-negative, comma-shaped, oxidase-positive rod with a single polar flagellum

What is the main clinical feature of Vibrio cholerae infection?

Profuse watery "rice water" diarrhea leading to severe dehydration

How is Vibrio cholerae transmitted?

Fecal-oral route, often through contaminated water or food

What toxin is produced by Vibrio cholerae?

Cholera toxin—an AB5 exotoxin that activates adenylate cyclase via Gs → ↑cAMP → Cl⁻ secretion → water loss

Does Vibrio cholerae invade the intestinal mucosa?

No, it does not invade; it adheres to the epithelium and acts via toxin-mediated secretion

What is the mainstay of treatment for cholera?

Aggressive fluid and electrolyte replacement with oral rehydration therapy

What type of diarrhea is caused by Vibrio cholerae?

Secretory diarrhea (non-inflammatory, watery, no leukocytes or blood)

What medium is used to culture Vibrio cholerae?

Thiosulfate-citrate-bile salts-sucrose (TCBS) agar—produces yellow colonies

Is there a vaccine available for Vibrio cholerae?

Yes, oral killed whole-cell and live attenuated vaccines are available for travelers to endemic areas

Which patients are at higher risk for severe disease from Vibrio cholerae?

Those with blood group O, malnutrition, or reduced stomach acid (e.g., chronic PPI use)

What type of organism is Shigella?

Gram-negative, non-motile, facultative intracellular rod; member of Enterobacteriaceae

How is Shigella transmitted?

Fecal-oral route via contaminated hands, food, or water; highly infectious (low ID₅₀)

What is the characteristic clinical presentation of Shigella infection?

High fever, abdominal cramps, and bloody diarrhea with mucus (dysentery)

Which species of Shigella is most severe and produces Shiga toxin?

Shigella dysenteriae—produces Shiga toxin that inhibits the 60S ribosomal subunit

How does Shigella invade the GI tract?

Invades M cells in Peyer's patches → escapes phagosome → spreads cell-to-cell using actin polymerization

What is the mechanism of Shiga toxin?

Inhibits protein synthesis by inactivating the 60S ribosome → cell death and mucosal ulceration

How is Shigella distinguished from Salmonella in the lab?

Shigella is non-motile, does not produce H₂S, and causes more frequent blood/pus in stool

What type of diarrhea is caused by Shigella?

Inflammatory diarrhea (with leukocytes and blood)

Is antibiotic treatment indicated for Shigella?

Yes, to shorten disease duration and reduce transmission (e.g., ciprofloxacin, azithromycin)

Which population is most at risk for seizures in Shigella infection?

Children — febrile seizures are common in pediatric shigellosis.

What type of organism is Entamoeba histolytica?

A protozoan parasite that causes amoebiasis

How is Entamoeba histolytica transmitted?

Fecal-oral route via ingestion of cysts in contaminated food or water.

What are the two major clinical manifestations of E. histolytica infection?

Amoebic dysentery (bloody diarrhea with mucus) and liver abscess

What is the classic presentation of an E. histolytica liver abscess?

Right upper quadrant pain, fever, and a "anchovy paste" consistency of abscess fluid

Which part of the intestine is typically affected by E. histolytica?

The cecum and ascending colon—may show flask-shaped ulcers on histology

How is Entamoeba histolytica diagnosed?

Stool O&P (ova and parasites), antigen detection, or serology; trophozoites with ingested RBCs are diagnostic

How can E. histolytica be differentiated from nonpathogenic amoebas like E. dispar?

Molecular testing or antigen detection; E. histolytica ingests RBCs, E. dispar does not

What is the treatment for symptomatic E. histolytica infection?

Metronidazole (for tissue trophozoites) + luminal agent (e.g., paromomycin) to eliminate cysts

Is E. histolytica associated with travel?

Yes, commonly seen in travelers to endemic areas (e.g., Mexico, India, Southeast Asia)

A 9-month-old infant is brought to the clinic in winter with 2 days of profuse watery diarrhea, vomiting, and fever. He is listless, has dry mucous membranes, and sunken eyes. No blood is seen in the stool.

Key Points:

Most common cause of severe diarrhea in infants and young children.

Double-stranded, segmented RNA virus (Reoviridae).

Peaks in winter; vaccine preventable.

Dehydration is the main complication.

Diagnose clinically or with ELISA for viral antigen in stool.

Rotavirus

A 25-year-old traveler returns from Mexico with 3 days of watery diarrhea, no blood or fever. Another case is a 6-year-old with bloody diarrhea and later signs of anemia and kidney failure.

Key Points:

ETEC → Traveler's diarrhea: watery, toxin-mediated.

EHEC (O157:H7) → Bloody diarrhea + risk of HUS; Shiga-like toxin.

Do not give antibiotics in EHEC → ↑HUS risk.

EPEC → Pediatric diarrhea.

EIEC → Dysentery-like illness.

Diagnosis: Stool culture, PCR, toxin assays.

Escherichia coli (ETEC, EHEC, EPEC, etc.)

A 6-year-old develops fever, abdominal cramps, and diarrhea after eating undercooked chicken. Another case is a man with fever, bradycardia, and rose spots after travel to India.

Key Points:

Non-typhoidal: Foodborne gastroenteritis (poultry, eggs).

Typhoidal (S. Typhi): Typhoid fever (rose spots, bradycardia, constipation).

Motile, H2S-positive.

Invades M cells → intracellular survival in macrophages.

Diagnose via stool and blood cultures.

Salmonella spp.

A 30-year-old aid worker in Bangladesh presents with massive, painless watery diarrhea that looks like rice water. He is hypotensive with signs of volume depletion.

Key Points:

Comma-shaped, oxidase-positive, motile.

Cholera toxin → ↑cAMP → secretory diarrhea.

No invasion or leukocytes in stool.

Rapid dehydration = major risk.

Culture on TCBS agar; treat with fluids.

Vibrio cholerae

A 5-year-old child in daycare has sudden onset of high fever, abdominal cramps, and bloody, mucoid diarrhea. Febrile seizures occurred at home.

Key Points:

Low infectious dose (person-to-person spread).

Non-motile, H2S-negative.

Invades M cells → intracellular spread.

Shiga toxin: inhibits 60S ribosome.

Diagnose via stool culture; antibiotics shorten illness.

Shigella spp.

A 34-year-old man recently returned from India presents with RUQ pain, fever, and diarrhea. Imaging reveals a solitary liver abscess. Stool shows trophozoites with ingested RBCs.

Key Points:

Bloody diarrhea + liver abscess (anchovy paste).

Flask-shaped ulcers in colon.

Transmitted via cysts in contaminated water.

Diagnose: Stool O&P, antigen testing, serology.

Treat with metronidazole + luminal agent (paromomycin).

Entamoeba histolytica