Shigella Species and Fecal WBC Lab Test
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Questions and Answers

What is the cause of intestinal wall bleeding?

  • Intestinal wall bleeding (correct)
  • Invasive diseases
  • Parasitic infections
  • Viral infections
  • What is the purpose of testing for WBC in stool samples?

  • To identify parasitic infections
  • To diagnose invasive diseases
  • To diagnose viral infections
  • To differentiate between invasive diseases and toxin-mediated illnesses (correct)
  • What types of bacteria are typically included in routine stool cultures?

  • Salmonella, Shigella, and Campylobacter (correct)
  • Salmonella, Shigella, and E. coli
  • Salmonella, E. coli, and Vibrio
  • Shigella, Campylobacter, and Yersinia
  • What is the primary goal of treatment for diarrhea?

    <p>To provide supportive care for hydration</p> Signup and view all the answers

    When are antibiotics effective against diarrhea?

    <p>Against invasive bacterial infections</p> Signup and view all the answers

    What is the primary mechanism of action of antidiarrheal medications?

    <p>Reducing bowel motility</p> Signup and view all the answers

    What is the recommended approach to preventing diarrhea when traveling?

    <p>Boiling, peeling, cooking, or avoiding food</p> Signup and view all the answers

    What is the most important measure to prevent diarrhea?

    <p>Access to safe drinking water</p> Signup and view all the answers

    What percentage of health problems in Ethiopia are attributed to communicable diseases due to unsafe water supply and poor sanitation?

    <p>80%</p> Signup and view all the answers

    What is the recommended approach to dealing with nausea and vomiting while traveling?

    <p>Drinking plenty of fluids and avoiding solid food</p> Signup and view all the answers

    Study Notes

    Types of Diarrhea

    • Acute bloody diarrhea (also called dysentery) and acute watery diarrhea (including cholera) typically last for several hours or days.
    • Persistent diarrhea lasts for several weeks (2-4 weeks).
    • Chronic diarrhea lasts for more than 5 weeks.

    Pathogenesis/Pathophysiology

    • Diarrhea occurs when there are subtle abnormalities in input or output at any level of the GI tract, resulting in excessive osmotic load, increased secretion, or diminished fluid resorption.
    • The causes of diarrhea include inflammatory, osmotic, secretory, motility, and other factors.

    Common Causes of Diarrheal Diseases/Food Poisoning

    • Bacterial causes:
      • Staphylococcus aureus
      • Vibrio cholerae
      • Shigella spp.
      • Escherichia coli
      • Salmonella spp.
      • Campylobacter jejuni
      • Bacillus cereus
      • Clostridium botulinum
      • Yersinia enterocolitica
    • Non-bacterial causes:
      • Viruses (e.g., Rotavirus, Norovirus, Adenovirus, Hepatitis A)
      • Parasites (e.g., Giardia lamblia, Entamoeba histolytica)

    Invasive Diarrhea

    • Caused by bacterial invasion of the bowel mucosal surface
    • Organisms involved: Salmonella spp., Campylobacter spp., Shigella spp., E. coli, Vibrio spp.

    Shigella Species

    • Gram-negative, facultatively anaerobic rods
    • Most communicable of the diarrheal bacteria
    • Requires a low microbial load
    • Symptoms include fever, malaise, fatigue, anorexia, and diarrhea with blood and pus
    • Symptoms appear 12-50 hours after exposure

    Fecal WBC Lab Test

    • Observe blood, WBCs, and pus
    • Culture: Colorless colonies on MAC, blue-green colonies on HE, and red/colorless on XLD

    Escherichia coli

    • Gram-negative, facultative anaerobic rods
    • At least five different pathogenic groups cause gastroenteritis:
      • ETEC: Enterotoxigenic (cause of traveler's diarrhea)
      • EIEC: Enteroinvasive (bacteria dysentery)
      • EPEC: Enteropathogenic (diarrhea outbreaks in infants in hospital setting)
      • EHEC: Enterohemorrhagic (presence of Shiga-like toxin)
      • EAEC: Enteroaggregative (chronic diarrhea in HIV patients, travelers, and children in poor countries)

    Enterotoxin-Mediated Diarrhea

    • Caused by toxins produced by bacteria
    • Examples: S. aureus, Clostridium botulinum, Bacillus cereus, Vibrio cholerae, Enterotoxigenic E. coli

    Staphylococcus aureus

    • Found on the skin, hair, noses, and throats of people and animals
    • Can multiply quickly at room temperature and produce a toxin that causes food poisoning
    • Sources: Salads, macaroni, bakery products, cream pies, milk, and dairy products

    Clostridium perfringens

    • Part of the normal flora of the vagina and GIT
    • Produces multiple toxins, including alpha toxin that causes lysis of endothelial and blood cells
    • Generates spores in improperly cooked foods
    • Causes loss of fluid in intracellular protein

    Bacillus cereus

    • Gram-positive rods that are spore-forming
    • Also acquired by penetrating injuries and intravenous injections
    • Produces toxins (diarrheal toxin, emetic toxin)
    • Incubation period: 1-6 hours
    • Source: Soil, and in raw, dried, and processed foods
    • Lab diagnosis: Produces hemolytic colonies on blood agar

    Vibrio species

    • Gram-negative rods, highly motile, facultative anaerobes, with one to three flagella at one end
    • Associated with raw or undercooked seafood harvested from contaminated water
    • Infects the small intestine
    • Enterotoxin activates adenylate cyclase, which initiates an outpouring of fluid into the intestine
    • Watery diarrhea (rice water stools) evident

    Lab Diagnosis

    • Utilize TCBS media (Thiosulphate Citrate Bile Salt Agar)
    • Yellow and profuse colonies
    • Inhibits colonic flora
    • Differentiates sucrose fermenters from species of Vibrio that are non-fermenters
    • Stool contains no RBCs or WBCs since it is toxin-mediated and non-inflammatory

    Viral Agents

    • Rotavirus: Primarily affects children < 5 years old, spread by fecal-oral route, peak incidence from December to June
    • Calicivirus: Norovirus, spread by fecal-oral route, outbreaks on cruise ships, cause of stomach flu

    Parasitic Infections

    • Giardia lamblia: By ingestion of contaminated water or person-person spread, only lives in the host, chronic infection results in malabsorption syndrome
    • Entamoeba histolytica: Exists in cyst and trophozoite form, transmitted by feco-oral with food, water, or hand, symptoms include abdominal discomfort, intense pain in the right side, and dysentery

    Diagnosis

    • Stool Sample: Direct saline wet mount microscopy, Trichrome Stain (for trophozoites), Biopsy
    • Histologically, villi appear flattened
    • Fluorescent Antibody Tests

    Risk Factors

    • Number of ingested organisms: Median infectious dose (ID50)
    • Achlorhydria: Inadequate stomach acidity
    • Reduction in normal flora: Use of antibiotics
    • Age, improper food handling, personal hygiene

    Laboratory Dx of Gastrointestinal Pathogens

    • Specimen Collection and Handling: Collect within 4 days of onset of symptoms, process ASAP, do not refrigerate
    • Fecal Leukocytes: Direct microscopic exam to detect presence of WBCs and RBCs
    • Routine stool cultures: Test for Salmonella species, Shigella species, and Campylobacter jejuni

    Treatment of Diarrhea

    • Patients must be watched for dehydration
    • Antibiotics are not effective against viral pathogens, give supportive care for hydration
    • Antibiotics may shorten illness due to invasive bacteria or an enterotoxin-mediated process
    • Antidiarrheal medications: Decrease bowel motility or the acid (Lomotil, Pepto-Bismol), primarily used with enterotoxin-mediated diarrhea or viral gastroenteritis

    Prevention

    • Key measures to prevent diarrhea include:
      • Access to safe drinking water
      • Use of improved sanitation
      • Hand washing with soap
      • Exclusive breastfeeding for the first 6 months of life
      • Good personal and food hygiene
      • Health education about how infections spread
      • Rotavirus vaccination

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    2-Diarrheal Diseases-2024.pptx

    Description

    This quiz covers the characteristics of Shigella species, a type of diarrheal bacteria, and how to diagnose it through a fecal WBC lab test. Learn about the symptoms and laboratory tests used to identify Shigella.

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