Schistosoma Parasites

• Scistosomes are NOT hermaphrodite

(sexes are separate).

• Male is flat and female is cylindrical.

• Eggs are NOT operculated but have a spine.

• Inside the snail: NO redia stage.• Infective stage: Cercaria NOT encysted metacercaria.• Mode of infection: skin penetration NOT by ingestion.

Introduction

FasciolaParagonimus

Heterophyes

S.mansoniS.haematobium

miracidium

sporocyst

redia

Inside snail

operculum

spine

Flat ♂

Cylindrical ♀

Cercaria

Schistosoma causes SchistosomiasisGeographical distribution:

Schistosoma mansoni Distribution

Schistosoma haematobium Distribution

Schistosoma japonicum Distribution

Present in the Far East

Definitive Host Man Habitat

Superior & Inferior mesenteric plexus of

veins

Vesical & pelvic plexus of veins

Where adult S.mansoni live

Where adult S.haematobium live

Blood vesselsThus Schistosomes are

called Blood flukes

Inferior mesenteric plexus of

veinsWhere adult

S.japonicum live

Life Cycle

Infected human

Egg in urine

miracidium

B.truncatusB.alexandrina

Intermediate host

Furcocercous cercaria

Egg in stoolCercaria

penetrate human skin

Fresh water

Definitive host

S.haematobium S.mansoni

Infective stage

Mode of infection

Diagnostic stage

Diagnostic Stage

S.haematobium egg in urine S.mansoni egg in stool

Size:

Shape:

Colour:

Content:

140X60 µ 150X60 µ

Oval, thin shellTerminal spine Lateral spine

Translucent

Miracidium

Mode of Infection Skin penetration by furcocercous cercaria from

contaminated canal water.

Aided by:

- Surface tension of drying droplets of water.

- Proteolytic enzymes secreted by penetration glands.

- Strong lashing movement of the tail pressing the body of the cercaria into the skin.

Development of Schistosoma inside the body of infected human

Cercariae penetrates human skin

Schisto- somula

Venous circulationSystemic circulation

Liver

Portal circulation

Vesical plexus S.haematobium

I III

IV

II

Inf. mesenteric plexus S.mansoni

Direction of venous blood flow

Aorta

Pathogenesis and Clinical Picture

There are 4 progressive stages:

Local dermatitis, irritation.

Papular rash.

I- Stage of invasion

II- Stage of migration

Metabolic products: toxic and allergic manifestations as urticaria, fever, headache, muscle pain. Eosinophilia, leucocytosis.

In the lung: verminous pneumonitis, minute haemorrhage, cough, haemoptysis.

In the liver: enlarged and tender.

By schistosomula

III- Stage of egg deposition and extrusion

The patient may complain of:

Generalized malaise, fever,

rigors, urticaria, abdominal pain

and liver tenderness.

A- Eggs are deposited in the venous plexus

Katayama Syndrome

Blood vessel

Soluble egg antigens are released in blood stream

Occurs mainly in S.japonicum infection

1- ♀ lays large number of eggs2- greater proximity to the liver

immune complex

Deposited in the tissues

Tissue damageThe patient suffers from:Fever, chills, diarrhoea, generalized lymphadenopathy

Eosinophilia

Due to:

Thus also called acute toxoemic schistosomiasis

Circulate in blood

IV- Stage of egg deposition and extrusion:

Terminal haematuria frequency of micturition

burning pain

Dysentery (blood and

mucus in stool)

Vesical & pelvic plexus of veins

Bladder wall

mesenteric plexus of veins

Intestinal wall

This produces tissue damage & haemorrhageIn S.haematobium In S.mansoni & japonicum

B- Eggs escape from the veins to the perivascular tissue

IV- Stage of tissue reaction (chronic stage)

around Schistosoma eggs trapped in various tissues.

Attract inflammatory cells

Deposition of fibrous tissue

Damage of affected organ and its fibrosis

Loss of its function

Egg shellmiracidium

Inflammatory cells

Shell & miracidial antigens

Delayed-type hypersensitivity

e.g.Granuloma formation in bladder

Where?

Granuloma develops

Polyps in the colon Barium enema that shows polyps in the colon

Tissue fibrosis, nodules, papillomata & sandy patches

IV- Stage of tissue reaction (chronic stage)

Liver: portal hypertension, hepatosplenomegaly, oesophageal varices, ascites.

Lung: pulmonary hypertension, bilharzial cor-pulmonale.

Eggs swept by blood

Eggs trapped in Bladder wall

Eggs trapped in Intestinal wall

Eggs that fail to fix to venule wall cause Embolic lesions

Eggs swept by blood

Eggs extruded in urine Eggs extruded in stool

Diagnosis

• Direct parasitological methods:Detection of S.haematobium eggs in urine.Test for viability.

Detection of S.mansoni eggs in stool by direct smear method or by concentration method.

Kato thick faecal smear: for egg counting to assess the intensity of infection

Rectal swab

• Blood examination: eosinophilia, leucocytosis, anaemia.

I- Laboratory

Serological Tests:

1- IHAT (Indirect Haemagglutination test)

Detection of anti-Schistosoma antibodies or antigen in patient’s serum

2- ELISA (Enzyme-linked immunosorbent assay)

3- IFAT (Indirect Fluorescent Antibody test)

wash wash

wash wash washAb

detected

wash wash wash Ag detected

Coating with Schisto Ag

Coating with anti-Schisto

monoclonal Ab

Latex particlesSensitized sheep RBCs

+ve

-ve

Schisto Ag Patient serum

Ab detected

Calcified bladder with hydroureter

Intestinal affection

Stenosed ureters and

hydronephrosis

II- Radiological imaging

S.haematobium infection S.mansoni infection

III- Endoscopyالمناظير

Cystoscopy S.haematobium

Colonoscopy, sigmoidoscopy S.mansoni

Done in chronic cases to detect lesions and take biopsies

Treatment

Praziquantel

Prevention and Control

- Mass treatment.

- Health Education.

- Snail control:

Physical methods

Biological methods

Chemical methods

X

Balanites aegyptica

Copper sulphate

Cercarial Dermatitis (Bather’s itch(

A condition that occurs due to penetration of cercariae of non-human species of schistosomes the skin of man.

Cercariae cannot go beyond the germinal layer.

Clinical picture:

Dermatitis, itching, oedema and secondary bacterial infection.

Treatment:

Antipruritics, antihistamincs,

antibiotics.

M.C.Q.

The major cause of morbidity in schistosomiasis is: a- Migration of adult worms against blood stream. b- Migration of adult worms in the liver. c- Embolic lesions. d- Deposition of eggs in tissues.

Kato technique is used to diagnose: a- Paragonimiasis c- Schistosomiasis haematobium

Bather’s itch occurs frequently with: a- S.haematobium b- S.japonicum

b- Schistosomiasis mansonid- Fascioliasis

b- S.mansonid- non human schistosomes

M.C.Q.

Katayama syndrome:

a- occurs most frequently in S.haematobium infection.

b- consists of pulmonary hypertension and right-sided heart failure.

c- occurs most frequently in S.japonicum infection.

d- occurs in chronic schistosomiasis.

Give reasons for

Terminal haematuria is due to active deposition of eggs by adult female S. haematobium in vesical venous plexuses.

Eggs escape to the perivascular tissue and become extruded to the lumen of the urinary bladder.

Powerful contraction of the bladder at the end of micturition (to squeeze the last drops of urine( leads to haemorrhage (terminal haematuria(.

Occurrence of terminal haematuria in S.haematobium infection

Lumen of urinary bladder

Give reasons for

Many eggs that fail to be fixed to walls of venules are swept by blood to reach various organs

as the lungs where they form granulomas and fibrosis with obliteration of flow resulting in pulmonary hypertension and right-sided heart failure.

Occurrence of Bilharzial cor-pulmonale in schistosomiasis

Swept by blood

Lung Heart