OSPE Gastrointestinal

• Macroscopic examination includes recording consistency, liquidity, color, smell, presence of blood, mucus, and pus
• Microscopic examination methods for intestinal parasites in stool specimens:

  • Direct wet film (using normal saline 0.85%, Lugol’s solution 1%, Eosin solution 2%)
  • Concentration techniques
  • Permanent stained slides
• Intestinal Protozoa stages:

  • Trophozoite stage usually found in liquid or soft stools
  • Cysts stage usually found in fully formed specimens
• Entamoeba histolytica diseases:

  • Amebiasis
  • Amebic dysentery
  • Amebic hepatitis/Liver abscess
• Laboratory diagnosis of Entamoeba histolytica:

  • Finding trophozoites in diarrhea stools or mature cysts in formed stools
• Giardia lamblia life cycle:

  • Trophozoite stage: symmetrical in shape, resembling a 'badminton racket' with oval nuclei and 4 pairs of flagella
  • Cyst stage: thick-walled with 4 small nuclei
• Balantidium coli disease:

  • Balantidiasis/Dysentery
• Cryptosporidium sp. disease:

  • Cryptosporidiosis
• Humans are infected with Cryptosporidium when they ingest cryptosporidium oocysts
• The most common species of Cryptosporidium in humans are C. parvum and C. hominis
• Paromomycin is a nonabsorbable aminoglycoside used in antiparasitic therapy for Cryptosporidium
• The recommended dosage for Paromomycin is 500 mg q.i.d. for 14 to 28 days
• Nitazoxanide is a synthetic antiparasitic with antiprotozoal activity through PFOR inhibition
• Azithromycin (Zithromax) has shown clinical activity against cryptosporidial enteritis and can be used if Paromomycin fails
• Diagnosis of cryptosporidiosis is done through stool specimens or duodenal aspirate/biopsy with modified acid-fast stain
• Blastocystis hominis causes blastocystosis and is an emerging pathogen with a life cycle involving vacuolar, granular, amoebic, and cystic stages
• Clonorchis sinensis is an intestinal fluke with a characteristic egg stage resembling a glowing light bulb
• Fasciolopsis buski is an intestinal fluke with adult worms that have specific characteristics like non-branching ceca and multiple branched testes
• Ascaris lumbricoides causes Ascariasis, and infection occurs by ingesting worm eggs found in contaminated food or water
• Enterobius vermicularis eggs are not usually found in feces, and the best method for diagnosis is through an anal swab or cellulose adhesive tape
• Examination of intestinal parasites in stool specimens can be done through direct wet film, concentration techniques (sedimentation and flotation), and permanent stained slides
• Fecal cultures can be used for Strongyloides and hookworm larvae detection using the Harada-Mori modification
• Normal flora of the gastrointestinal tract:

  • Birth: sterile, then normal flora develops
  • Breast-fed child: lactic acid streptococci, more lactobacillus
  • Bottle-fed child: less lactobacillus, mixed flora
• Helicobacter pylori:

  • Characteristic: Gram-negative curve rod, Motile due to a polar tuft of flagella, Microaerophile, obligately respiratory metabolism
  • Disease: Gastric and duodenal ulcers, Ulcers associated with development of gastric cancer (3%), Carcinogenic bacteria
  • Diagnostic laboratory test:
  • Specimen: Gastric biopsy, Blood antibodies assay, Stool follow-up treatment
  • Special test: Rapid test to detect urease activity
• Clostridium botulinum:

  • Characteristic: Gram-positive rods, Spora (+), Obligate anaerob
  • Toxin: Neurotoxin (heat-labile, rapidly destroyed at 100ºC)
  • Disease: Botulism (several clinical forms)
  • Laboratory diagnosis: Toxin detection in feces, serum, or food
• Clostridium perfringens:

  • Enterotoxin: Small, heat-labile protein
  • Symptoms: Nausea, abdominal cramp, and diarrhea occurs 8-18 hours after eating contaminated food
• Staphylococcal food poisoning:

  • Cause by heat-stable enterotoxin of S. aureus
  • Symptoms: Fever, nausea, vomiting, diarrhea
  • Diagnosis: Based on symptoms
• Bacillus cereus gastroenteritis:

  • Considered harmless but causes food-borne illness
  • Symptoms: Nausea and vomiting 2–5 hours after ingestion, diarrhea 6 – 16 hours after ingestion
• Gastroenteritis:

  • Cholera:
  • Causative agent: Vibrio cholerae
  • Symptoms: Massive diarrhea, shock, collapse, death
  • Diagnosis: Based on symptoms, culturing of V. cholerae from feces
• Salmonella:

  • Characteristics: gram-negative bacilli, facultative anaerobic, motile, non-spore forming, non-lactose fermenter, urease negative
  • Strains can cause localized gastroenteritis or systemic infection
  • Different strains include S. enterica, S. bongori, S. typhimurium, and S. typhi
  • Diagnosis involves distinguishing lactose-fermenting strains
  • S. typhi is an encapsulated pathogen carrying "K" antigen
  • Etiology agent for Shigellosis is Shigella, including S. sonnei, S. dysenteriae, S. flexneri, S. boydii
• Shigellosis:

  • Severe dysentery caused by S. dysenteriae and mild dysentery by S. sonnei
  • Severe dysentery is caused by Shiga toxin released by S. dysenteriae
  • Diagnosis involves finding bacteria from rectal swabs
  • Therapy includes antibiotics and rehydration
• Escherichia coli:

  • Characteristics: gram-negative rods, motile, facultative anaerobic, glucose-fermenting, catalase-positive
  • Pathogenic E. coli strains can cause diarrhea, dysentery, hemolytic uremic syndrome, urinary tract infections, and meningitis
  • Different pathogenic strains include EPEC, EHEC, EAEC, and EIEC
  • Diagnosis involves culturing on specific agar mediums
  • Prevention involves efficient refrigeration and proper cooking techniques
• Campylobacter Gastroenteritis:

  • Caused by C. jejuni, symptoms include fever, cramping, abdominal pain, and diarrhea
  • Diagnosis involves culturing in specific conditions
  • Unusual complication includes Guillain-Barre syndrome
• Clostridium difficile Associated Diarrhea:

  • Caused by C. difficile, symptoms range from mild diarrhea to life-threatening colitis
  • Diagnosis involves history of antibiotic use and immunoassays
  • Risk factors include recent antibiotic use, elderly age, and immunocompromised status
  • Prevention includes preventing spread of contamination in the kitchen and proper food handling
• Hepatitis A:

  • Antigen: Hepatitis A virus (HAV)
  • Corresponding Antibody: Anti-HAV
  • Comments: RNA virus; present in stool and serum early in course of hepatitis A
• Hepatitis C:

  • Antigen: Hepatitis C antigen
  • Corresponding Antibody: Anti-HCV
  • Comments: RNA virus; previously known as posttransfusion NANB hepatitis
• Hepatitis B:

  • Antigen: Hepatitis B surface antigen (HBsAg)
  • Corresponding Antibody: Anti-HBs
  • Comments: DNA virus; found in serum in > 90% of patients with acute hepatitis B; anti-HBs appears after infection and confers immunity
  • Antigen: Hepatitis B core antigen (HBcAg)
  • Corresponding Antibody: Anti-HBc
  • Comments: Anti-HBc detected in serum during and after acute infection
  • Antigen: Hepatitis B envelope antigen (HBeAg)
  • Corresponding Antibody: Anti-HBe
  • Comments: HBeAg correlates with infectivity; suggestive of active viral replication
• Hepatitis D:

  • Antigen: Hepatitis D antigen
  • Corresponding Antibody: Anti-HDV
  • Comments: Defective RNA virus; requires presence of HBsAg
• Hepatitis E:

  • Antigen: Hepatitis E antigen
  • Corresponding Antibody: Anti-HEV
  • Comments: RNA virus present in stool; cause enteric NANB hepatitis
• Injection, heterosexual and homosexual sex: HCV

  • Fecal/oral: HAV, HBV, HDV, HEV