Schistosomiasis

Ahmed Adel Fouad Abdelhakeem

Introduction

Schistosomiasis, also known as bilharziasis or snail fever, is a primarily tropical parasitic disease caused by the larvae of one or more of five types of flatworms or blood flukes known as schistosomes.

The name bilharziasis comes from Theodor Bilharz, a German pathologist, who identified the worms in 1851.

The main forms of human schistosomiasis

Schistosoma haematobium

Schistosoma mansoni

Schistosoma intercalatum

Schistosoma japonicum/Schistosoma mekongi

GEOGRAPHICAL DISTRIBUTION

S. haematobium Africa: most of the countries of North

Africa; widespread in Central and West Africa; in eastern Africa present from Somalia to the Cape and on the islands offshore, including Madagascar and Mauritius.

Middle East: present in most countries. There might also be small foci in India

around Bombay and in Madras State. A total of about 90 million people are

infected worldwide.

S. mansoni:

Africa: North Africa (Morocco, Tunisia, Egypt, southern Sudan); East Africa (from Ethiopia down to South Africa and Madagascar); most countries of Central and West Africa.

Middle East (Lebanon, Oman, Saudi Arabia, Somalia, Yemen).

Americas: in South America and some of the Caribbean islands.

S. intercalatum:

There are limited foci in :

Central Africa including Cameroon, Congo, Congo Democratic Republic (Zaire), Equatorial Guinea, Gabon, and possibly in Central African Republic, Chad, Mali and Nigeria.

S. japonicum:

China, Indonesia.

Philippines.

Thailand.

MORPHOLOGY

S. haematobium :

The male measures 10–20 mm _ 0.9 mm and the cuticle has fine tuberculations. There are 4–5 testes.

The female has a long uterus, with the ovary in the posterior third of the body.

There are 10–100 eggs in the uterus at one time.

S. mansoni:

The adults are smaller than those of the other species.

The male measures 6–13 mm _ 0.75–1.0 mm and the cuticle has coarse tuberculations.

There are 4–13 (usually 6–9) testes.

The ovary of the female is situated anteriorly.

There is usually only 1 egg in the uterus at one time.

S. japonicum:

The male measures 12–20 mm _ 0.5–0.55 mm and has no cuticular tuberculations.

There are 6–7 testes.

The female has the ovary at about the middle of the body. There are 5–200 eggs in the uterus at one time.

S. intercalatum:

The male measures 11–14 mm _ 0.3–0.4 mm. There are 2–7 testes.

The female has 5–60 eggs in the uterus

at one time.

Life cycle

Ciliated miracidium. Note anterior penetration glands.

Dark field. Actual size 80 m.

Swimming cercaria

Adults of Schistosoma sp. in lung tissue, stained with H&E

Higher magnification of one of the worms, showing the tuberculate exterior of the adult worm

Clinical Presentation of schistosomiasis

Urinary

S. hematobiu

m

Clinical Presentation of schistosomiasis

Intestinal

S. mansoni

S. japonicumS.

intercalatum

S. mekongi

S. haematobium

Invasive stage

A cercarial dermatitis (‘swimmer’s itch’) may appear 24 h after first infection but seldom lasts more than 48 h.

Acute phase .

There are usually no symptoms until 5–10 weeks after infection, when there may be mild allergic manifestations in visitors but these are rare in indigenous populations.

Chronic phase . Maximum egg production begins 10–12

weeks after infection.

Haematuria (found in about 50% of cases), dysuria and increased frequency of micturition are typical clinical signs and may persist intermittently for years.

hydroureter, hydronephrosis and uraemia.

Schistosoma near urethra

Inner surface of the bladder showing nests of calcified ova (‘sandy patches’) (arrowed) of S.

hematobium.

Intravenous pyelogram of a woman infected with S. haematobium showing bilateral hydronephrosis

with deformity of both ureters.

Section of bladder. Eggs of S. haematobium (many are calcified or ‘black’ eggs) can be seen

with epithelial squamous cell metaplasia (arrowed).

S. japonicum.

S. mekongi.

S. mansoni.

S. intercalatum

Invasive phase:

As for S. haematobium.

Acute phase:

Allergic manifestations

Katayama syndrome

serum sickness

Chronic phase portal hypertension with splenomegaly oesophagial varices hypersplenism ascitis pulmonary hypertension CNS lesions: spine - transverse myelitis cerebral – seizures (S. japonicum) intestinal polyposis: both sessile and

pedunculated chronic salmonellosis intestinal granulomatosis: contractures of colon, intusseception

Egg granuloma of S. mansoni in liver with surrounding epitheloid cells and some leucocytic

infiltration

Granuloma in the liver due to Schistosoma mansoni.

The S mansoni egg is at the center of the granuloma.

Two boys with advanced schistosomiasis mansoni. Note collateral venous circulation in nearest

patient.

DIAGNOSIS

Parasitological

The presence of eggs in the faeces or urine is still the most widely used method of diagnosis.

Schistosoma mansoni

Schistosoma mansoni eggs are large (114 to 180 µm long by 45-70 µm wide) and have a characteristic shape, with a prominent lateral spine near the posterior end.  The anterior end is tapered and slightly curved.  When the eggs are excreted in stool, they contain a mature miracidium.

Schistosoma mansoni

Schistosoma hematobium

The eggs of Schistosoma haematobium are large (110-170 µm long by 40-70 µm wide) and bear a conspicuous terminal spine.  Eggs contain a mature miracidium when shed in urine.

Schistosoma hematobium

Schistosoma japonicum

The eggs of Schistosoma japonicum are large and more rounded than other species, measuring 70-100 µm long by 55-64 µm wide.  The spine on S. japonicum eggs is smaller and less conspicuous than other species.  Eggs are shed in stool.

Schistosoma japonicum

Schistosoma intercalatum

Schistosoma intercalatum is related to S. haematobium, but restricted to east-central Africa.  The eggs are similar to S. haematobium in general shape and in possessing a terminal spine, but are usually longer (140-240 µm), often have an equatorial (central) bulge and are shed in stool, not urine.

Schistosoma intercalatum

Other Methods For Diagnosis Sedimentation

Ceroscopy

Rectal biopsy

Clinical Diagnosis

Schistosoma hematobium

hematuria (terminal) urinary frequency pyuria pyelonephritis obstructive uropathy cancer of bladder (squamous cell) distant metastases (spinal column) (pulmonary hypertension)

intestinal schistosomiasis

History of freshwater exposure portal hypertension with splenomegaly oesophagial varices hypersplenism ascitis pulmonary hypertension CNS lesions: spine - transverse myelitis cerebral – seizures (S. japonicum)

Immunological Diagnosis

ELISA & immunoblotting techniques are the most convenient.

A dipstick ELISA for urine samples, using an SEA can effectively diagnose schistosomiasis and correlates well with quantitative egg counts.

Circulating cathodic antigen (CCA)

TREATMENT

Chemotherapy

Chemotherapy

Praziquantel Metrifonate

Atropine sulphate

Oxamniquine

PREVENTION AND CONTROL

Intrinsic Factors (deal with man)

Extrinsic factors (snail control): Mechanical control Biological control Chemical control (molluscicides)

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