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January 09 2015

Cryptosporidium

Write short notes on Cryptosporidium

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Neuros
Neuros
January 09 2015 #

Infection with cyptosporidium is usually seen in the immunocompromised. 

Source of infection: fecal-oral transmission

Infective form: Cyst

Pathogenesis: the infection begins with ingestion of the oocysts. In the gut, the gastric acids and the proteolytic enzymes cause the excystation of the sporozoites. These sporozoites attach to the apical membranes of the enterocytes (on the luminal wall of the intestines). The sporozoites release molecules which cause the microvilli to fold around it thus making a compartment which seems intracellular but is extracytoplasmic - this is called Parasitophorous vacuole. A feeder organelle forms between the parasite and the host cells. through which it feeds. Now the sporozoites undergo diferentiation into tropozoites which undergo asexual reproduction to form type 1 meronts. These meronts have 6-8 merozoites in them. The merozoites are released with the rupture of meronts, these released parasites then either transform into type 1 meronts or type 2. These type 2 meronts have 4 merozoites in them which undergo sexual reproduction and become a male or female gamonts. When the male and female gamonts use, they form zygotes which develop into oocysts. These oocysts cause auto-infection and also become source of infection through feces. 

Source: Clinical Microbiology Reviews

It is believed that the parasite causes alterations in the intestinal epithelial cell function when it attaches to it, this causes the diarrhea in the host. 

CLINICAL FEATURES:

  • Diarrhea: transient watery diarrhea in healthy individuals and severe in immunocompromised
  • GI symtoms" vomiting, abdominal discomfort
  • Low grade fever
  • Biliary disease: RUQ pain, mostly seen in immunocompromised individuals

DIAGNOSIS:

  • Acid Fast stain: of stool samples to detect cysts
  • Polymerase chain reaction
  • Serology: using ELISA to detect IgM and IgG antibodies

TREATMENT: no effective medical treatement seen, the best initial approach is oral rehydration for diarrhea. For immunocompromised individuals steps should be taken to treat the underlying cause of immunosuppression. 

References:

  1. Upinder Singh, William Petri Jr. Principles and Practice of Clinical Parasitology: Cryptosporidiosis (pg 149-54)
  2. Tao Le, Vikas Bhushan, Jeffrey Hofmann. First Aid for the USMLE Step 1 (2012) Parasitology: Protozoa GI infection (pg 175)
  3. USMLE Step 1 Lecture Notes by Kaplan (2004). Section 1 - Medical Parasitology: Protozoan parasites (pg 129)

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