Shigella : Clinical Findings, Pathogenesis, Lab Diagnosis and Treatment

Shigella : Clinical Findings, Pathogenesis, Lab Diagnosis and Treatment


 Introduction:

SOURCE:

  • MAN: CASE OR CARRIER

MODE OF SPREAD:

  • CONTAMINATED FINGERS, FOOD, FLIES, FOMITES
  • PERSON TO PERSON TRANSMISSION
  • Gut pathology is due to toxin

INFECTIVE DOSE:

  • 10-100 VIABLE BACILLI
  • HIGHEST CONCENTRATION IN STOOL DURING EARLY/ACUTE INFECTION:
  • 103 TO 109 VIABLE BACILLI PER GRAM OF STOOL
PATHOGENESIS

Invasiveness (main):

  • Bacteria invade basolateral surface of colon epithelium
  • Intracellular replication
  • Cell to cell spread with the help of microbial protein
    •  ICS A (ATP-ase)
    •  Host protein cadherin L – CAM.
  • Responsible for late dysentery.
  • Nontoxic mutants can cause dysentery but non-inttasive can’t produce dysentery.

Toxins:

  • Endotoxin 
    • LPS
    • Cause irritation of bowel.

Shigella Dysenteriae-

  • Produces heat labile exotoxin (Shigabacillus exotoxin)

Affect gut and CNS:

  • Show  neurotoxicity on blood vessel of CNS
  • Can lead to miningsmus and coma.
  • Cytotoxicity = Verotoxin I or Shiga like toxin
  • Toxin has two peptide subunit.Toxins produce early, non bloody voluminous diarrhea.
    • A unit (N-glycosidase) of cytotoxin hydrolyzes adenine from specific sites of 60s RNA
    • Inhibits protein synthesis.
    • Contributes to fatal nature.

CLINICAL SYMPTOMS:

  • Shigella  Associated with hemolytic uremic Syndrome
  • Ranges from asymptomatic infection to severe bacillary dysentery
  • Two-stage disease: watery diarrhea changing to dysentery with frequent small stools with blood and mucus, tenesmus, cramps, fever

Early stage:

  • Watery diarrhoea attributed to the enterotoxic activity of Shiga toxin
  • Fever attributed to neurotoxic activity of toxin  
  • Majority of lesion are in distal colon.

COMPLICATIONS

  • Toxic dilatation
  • Colonic perforation
  • Thrombotic thrombocytopenic purpura
  • Reactive arthritis
  • Reiter’s syndrome.
  • HUS
    • Schistocytes are suggestive of hemolytic-uremic syndrome (HUS)

DIAGNOSIS

  • Sampling: fresh stool, mucus flakes and rectal swabs
  • Selenite F broth(0.4%) is used as enrichment and transport media (for 9-12hours)
  • Total blood count reveals anemia and thrombocytopenia, and schistocytes
  • Increase blood urea nitrogen(BUN)
  • Invasive test for shigella is Rabbit ileal loop

TREATMENT:

  • Oral rehydration therapy (No antibiotics) for mild to moderate dehydration.
  • Ciprofloxacin, Fluoroquinol,  Azithromycin, Pivmecillinam, Ceftriaxone
  • Preventing infected individuals from handling food
  • DOC for multiresistant Nalidixic acid.

Exam Important

 Introduction:

  • PERSON TO PERSON TRANSMISSION
  • Gut pathology is due to toxin

INFECTIVE DOSE:

  •  10-100 VIABLE BACILLI

Toxins:

  • Endotoxin 
    • LPS
    • Cause irritation of bowel.

Shigella Dysenteriae-

  • Produces heat labile exotoxin (Shiga bacillus exotoxin)

Affect gut and CNS:

  • Show  neurotoxicity on blood vessel of CNS
  • Cytotoxicity = Verotoxin I or Shiga like toxin
  • Toxins produce early, non bloody voluminous diarrhea.

CLINICAL SYMPTOMS:

  • Shigella  Associated with hemolytic uremic Syndrome
  • Ranges from asymptomatic infection to severe bacillary dysentery
  • Two-stage disease: watery diarrhea changing to dysentery with frequent small stools with blood and mucus, tenesmus, cramps, fever

Early stage:

  • Watery diarrhoea attributed to the enterotoxic activity of Shiga toxin
  • Fever attributed to neurotoxic activity of toxin  
  • Majority of lesion are in distal colon.

COMPLICATIONS

  • HUS
    • Schistocytes are suggestive of hemolytic-uremic syndrome (HUS)

DIAGNOSIS

  • Sampling: fresh stool, mucus flakes and rectal swabs
  • Selenite F broth(0.4%) is used as enrichment and transport media (for 9-12hours)
  • Total blood count reveals anemia and thrombocytopenia, and schistocytes
  • Increase blood urea nitrogen(BUN)
  • Invasive test for shigella is Rabbit ileal loop

TREATMENT:

  • Oral rehydration therapy (No antibiotics) for mild to moderate dehydration.
  • Ciprofloxacin, Fluoroquinol,  Azithromycin, Pivmecillinam, Ceftriaxone
  • DOC for multiresistant Nalidixic acid.

 

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