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Protozoa• Pathogenic protozoa: Protozoa that exist in human body and cause harm to infected
human (E.histolytica, G.lamblia, B.coli)
• Commensal protozoa: Protozoa that exist human body but does not cause harm to
infected human ( e.g. E.coli, E.dispar, E.hartmanni)
• Opportunistic protozoa: weak protozoa that cause minimal effect to infected healthy
man but has severe effect on infected immunocompromized man ( e.g. Cryptosporidium parvum)
• Potentially pathogenic free-living protozoa: free-living in nature away from man but some of them may
cause disease if they enter the human body by certain route.
Unicellular organisms
DR. RAAFAT MOHAMED
Cryptosporidium parvum
Cyclospora cayetanensis
Isospora belli
Causes cryptosporidiosis
Causes cyclosporiasis
Causes isosporiasis
Geog. Distribution: worldwide
Parasite takes the shape of oocyst containing sporozoites
Man is infected by ingestion of the sporulated oocyst
4-6µ 8-10µ 30X12µ
DR. RAAFAT MOHAMED
Habitat of Sporozoa Small intestine
villiAffect epithelial cells
Cryptosporidium
Cyclospora
Isospora
Infected human complains of
watery diarrhoea
Sporozoite
DR. RAAFAT MOHAMED
Development of Cryptosporidium in human body
Meront with merozoites
♂
♀
Zygote
Thick-walled oocystsExternal autoinfection
Thin-walled oocystsInternal autoinfection
Sporozoite attack brush border of epithelial cells
Merogony (asexual reproduction)
Gametogony (sexual reproduction)
gametocyte
DR. RAAFAT MOHAMED
Mode of Infection with Cryptosporidium parvum
Ingestion of thick-walled oocysts:
In contaminated food or drink (called heteroinfection).
By faeco-oral route (hand to mouth) in already infected patient ( called external autoinfection).
Thin-walled oocysts in intestinal lumen of already infected patient causes internal autoinfection.
Thick-walled
Thin-walled
DR. RAAFAT MOHAMED
DR. RAAFAT MOHAMED
Life cycle of Cryptosporidium in human body
The sporozoites are released from the oocyst
Merogony and gametogony occur within the brush border of the infected cells
Meronts released merozoites which invade adjacent cells and repeat the cycle
Gametogony: micro and macrogametes are formed by some merozoite
Zygote is formed by fusion of gametes
Thin wall oocyst is formed(endogenous autoinfection)Thick walled oocysts are excreted in stool
DR. RAAFAT MOHAMED
CryptosporidiumCryptosporidium
20%
80%
DR. RAAFAT MOHAMED
Development of Cyclospora in human body
merozoites
♂
♀
Zygote
Sporozoite attack brush border of epithelial cells
gametocyte
Unsporulated oocystPass in stool of the patient
Sporulated oocyst Infective stage
Autoinfection DOES NOT occur
DR. RAAFAT MOHAMED
DR. RAAFAT MOHAMED
Development of Isospora in human body
merozoites
♂
♀
Zygote
Sporozoite enters epithelial cells
gametocyte
Unsporulated oocyst
Pass in stool of
the patient
Sporulated oocyst Infective stage
Autoinfection MAY OCCUR
DR. RAAFAT MOHAMED
Mode of Infection of
Ingestion of sporulated oocysts in contaminated food or drink.
Cyclospora cayetanensis Isospora belli
Autoinfection DOES NOT occur
Unsporulated oocyst
Pass out in patient’s stool
Sporulation occurs on the
ground
Autoinfection MAY occur
Patient passes both unsporulated and
sporulated oocysts in stoolDR. RAAFAT MOHAMED
Pathogenesis of Intestinal SporozoaIntestinal villi show:
Inflammatory changes
Atrophy
Crypt hyperplasia
In immunosuppressed patients
Dissemination of the parasite to:
Oesophagus, gall bladder, respiratory tract, urinary bladder
DR. RAAFAT MOHAMED
CryptosporidiumClosely associated to the apicalplasma membrane inPARASITOPHOROUS VACUOLE
enterocyte
DR. RAAFAT MOHAMED
Clinical Picture of Intestinal Sporozoa
In immunocompetent subject Mild self-limited diarrhoea for 2 weeks
In childrenAbdominal discomfort, diarrhoea, anorexia, fever,
nausea, weight loss
In immunocompromized patient Severe life-threatening diarrhoea, dehydration,
malabsorption
DR. RAAFAT MOHAMED
Diagnosis of Cryptosporidium
Clinical picture: diarrhoea Stool analysis is done by:
1- Direct smear method.
2- Concentration method using Shaether’s sugar floatation technique.
Oocysts are seen by:
- Staining stool smear with modified Ziehl Neelsen stain.
- Immunofluorescence assay.
Intestinal biopsy: to detect meronts and gamonts Meronts
Gamonts
DR. RAAFAT MOHAMED
Unstained oocyst
Stained oocyst by MZN stain
Stool examination to detect unstained and stained oocysts
Diagnosis of Cyclospora & Isospora
Cyclospora Unsporulated
IsosporaSporulated Isospora
Cyclospora
Unsporulated Isospora
Sporulated Isospora
DR. RAAFAT MOHAMED
DR. RAAFAT MOHAMED
Cyclospora cayetanensis Oocysts in faeces
Cryptosporidium
8-10m
3-5 m
DR. RAAFAT MOHAMED
Isospora belliin intestine
Oocysts in faeces
DR. RAAFAT MOHAMED
Treatment Immunocompetent: self-limited
Immunocompromized:
Paromomycin (Cryptosporidium)
Trimethoprim + Sulphamethoxazole (Cyclo /Isospora)
Fluid and electrolyte replacement
Cryptosporidiosis is a zoonotic disease Oocysts are highly resistant to chemicals
Faeco-oral infection occurs (external autoinfection) Proper washing of green vegetables
Pure water supply
Epidemiology and Control
DR. RAAFAT MOHAMED
State True Or False
• Cryptosporidium parvum produces severe watery diarrhoea in the immunocompetent patient.
• Cryptosporidium parvum can be detected in stool only after staining stool smear by MZN stain.
• Autoinfection may occur in isosporiasis.
• Both unsporulated and sporulated Cyclospora oocysts are infective to man.
• Cryptosporidiosis is a pure human disease.
• Cryptosporidium sporozoites invade the brush border of epithelial cells lining the rectum.
False
True
True
False
False
False
DR. RAAFAT MOHAMED
Case
An AIDS patient developed severe watery diarrhoea with no mucus or blood. Stool examination showed no eggs of helminths. Diagnosis was confirmed by microscopic examination of stained stool smear by special stain.
a- What is (are) the revealed causative parasite (s)? C.parvum, C.cyaetenensis, I.belli, Microsporidia.
b- Name the type of stain used to reveal the causative parasite (s)?
Modified Ziehl-Neelsen stain.
c- If the parasite could be transmitted by autoinfection, what would be your diagnosis?
C.parvum infection and may be I.belli infection.DR. RAAFAT MOHAMED
MicrosporidiaMicrosporidia
Polar FilamentInjects Sporoplasm
DR. RAAFAT MOHAMED