GI infections

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67 Terms

1
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What type of virus is Rotavirus?

dsRNA virus, non-enveloped

2
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Which age group is most commonly affected by Rotavirus infection?

Infants and young children (6 months to 2 years)

3
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What is the primary clinical manifestation of Rotavirus infection?

Severe watery diarrhea leading to dehydration in infants and young children

4
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How is Rotavirus transmitted?

Fecal-oral route

5
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What part of the intestine does Rotavirus primarily infect?

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

6
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Which vaccine is used to prevent Rotavirus infection?

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

7
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What type of diarrhea is caused by Rotavirus?

Secretory diarrhea due to enterocyte damage and NSP4 enterotoxin

8
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What diagnostic test is commonly used for Rotavirus?

ELISA or PCR detecting viral antigen in stool

9
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What is the mainstay treatment for Rotavirus diarrhea?

Supportive care with oral rehydration therapy

10
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What type of organism is Escherichia coli?

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

11
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Which strain of E. coli is associated with traveler's diarrhea?

Enterotoxigenic E. coli (ETEC)

12
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What toxins are produced by ETEC?

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

13
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Which E. coli pathotype causes bloody diarrhea and hemolytic uremic syndrome (HUS)?

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

14
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What toxin is responsible for the pathogenesis of EHEC?

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

15
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Why should antibiotics be avoided in EHEC infection?

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

16
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Which E. coli strain causes persistent diarrhea in children and HIV patients, often with mucus?

Enteroaggregative E. coli (EAEC)

17
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Which E. coli strain invades intestinal epithelial cells and causes a dysentery-like illness?

Enteroinvasive E. coli (EIEC)

18
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Which E. coli strain is associated with infantile watery diarrhea in developing countries?

Enteropathogenic E. coli (EPEC)

19
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How does EPEC cause diarrhea?

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

20
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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

21
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What is a serious renal complication of EHEC infection, especially in children?

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

22
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What type of organism is Salmonella?

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

23
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How is Salmonella transmitted?

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

24
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Which Salmonella serotype causes typhoid fever?

Salmonella enterica serovar Typhi (S. Typhi)

25
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What are the symptoms of typhoid fever?

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

26
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Which organ can harbor S. Typhi in chronic carriers?

Gallbladder (especially in those with gallstones)

27
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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

28
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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

29
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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

30
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What is the pathogenesis of Salmonella in the GI tract?

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

31
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What vaccines are available for S. Typhi?

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

32
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What type of diarrhea is caused by Salmonella infection?

Inflammatory (often bloody with PMNs in stool)

33
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What type of organism is Vibrio cholerae?

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

34
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What is the main clinical feature of Vibrio cholerae infection?

Profuse watery "rice water" diarrhea leading to severe dehydration

35
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How is Vibrio cholerae transmitted?

Fecal-oral route, often through contaminated water or food

36
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What toxin is produced by Vibrio cholerae?

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

37
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Does Vibrio cholerae invade the intestinal mucosa?

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

38
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What is the mainstay of treatment for cholera?

Aggressive fluid and electrolyte replacement with oral rehydration therapy

39
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What type of diarrhea is caused by Vibrio cholerae?

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

40
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What medium is used to culture Vibrio cholerae?

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

41
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Is there a vaccine available for Vibrio cholerae?

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

42
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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)

43
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What type of organism is Shigella?

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

44
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How is Shigella transmitted?

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

45
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What is the characteristic clinical presentation of Shigella infection?

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

46
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Which species of Shigella is most severe and produces Shiga toxin?

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

47
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How does Shigella invade the GI tract?

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

48
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What is the mechanism of Shiga toxin?

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

49
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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

50
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What type of diarrhea is caused by Shigella?

Inflammatory diarrhea (with leukocytes and blood)

51
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Is antibiotic treatment indicated for Shigella?

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

52
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Which population is most at risk for seizures in Shigella infection?

Children — febrile seizures are common in pediatric shigellosis.

53
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What type of organism is Entamoeba histolytica?

A protozoan parasite that causes amoebiasis

54
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How is Entamoeba histolytica transmitted?

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

55
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What are the two major clinical manifestations of E. histolytica infection?

Amoebic dysentery (bloody diarrhea with mucus) and liver abscess

56
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What is the classic presentation of an E. histolytica liver abscess?

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

57
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Which part of the intestine is typically affected by E. histolytica?

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

58
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How is Entamoeba histolytica diagnosed?

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

59
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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

60
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What is the treatment for symptomatic E. histolytica infection?

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

61
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Is E. histolytica associated with travel?

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

62
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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

63
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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.)

64
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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.

65
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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

66
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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.

67
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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