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

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Isospora belliin intestine

Oocysts in faeces

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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