Negin Torabi

Ph.D. in Medical Parasitology

Zanjan University of Medical Sciences
 Trematoda
(Schistosoma spp.)

Schistosomes (Blood flukes)

• Schistosomes are dioecious, (sexes are separate) trematodes, which lead to Schistosomiasis (bilharziasis).
• Estimates show that at least 251.4 million people required preventive treatment in 2021.
• Schistosomiasis transmission has been reported from 78 countries (Africa, Asia, and Latin America).

disease species Geographical distribution

Intestinal shistosomiasis Schistosoma mansoni Africa, the Middle East, the Caribbean, Brazil,
Venezuela and Suriname
S. japonicum China, Indonesia, the Philippines

S. mekongi Several districts of Cambodia and the

Lao People’s Democratic Republic
S. guineensis/ S. intercalatum Rain forest areas of central Africa
Urogenital shistosomiasis Schistosoma haematobium Africa, the Middle East, Corsica (France)
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 Schistosoma spp.

• Morphology
• The sexes are separate
• The male worm is boat- shaped, with a central canal
(gynaecophoric canal) in which the female lives
• The cuticle of the male is smooth in S.japanicum but has
tuberculations in other species
• There are two small suckers and a varying number of
testes in the different species
• The female is longer than the male but much thinner
and circular in cross-section
• The two suckers of the female are very small and weak
• All schistosomes live in venous plexuses in the body of
the definitive host, the location varying with the species
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Schistosoma spp.
Morphology

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 Schistosoma spp.
Morphology
• Morphology of the eggs
• Schistosoma eggs are eliminated with feces or urine, depending on species
• Unlike other tremadoes, the eggs are not operculated
• Oval in shape with prominent lateral spine (S.mansoni), conspicuous terminal spine (S.
haematobium), and more rounded with smaller spine and less conspicuous (S.
japonicum)
• They contain a fully formed miracidium when passed to environment

• Morphology
• The larval stages inside the snail are first and second generation sporocysts
• Large number of cercariae with forked tail escape from the snail 5
 Schistosoma spp.
life cycle
• Eggs shed from infected human (in feces or in
urine)
• Eggs hatch and release miracidia
• Miracidia swim and penetrate snail tissue
• The stages in the snail include two generations
of sporocysts
• Free- swimming cercariae released from the
snail into water and penetrate the skin of
human host

S. japonicum------- Oncomelania
S. Mansoni ------- Biomphalaria
S. haematobium------ Bulinus 6
 Schistosoma spp.
Pathogenicity and clinical features
• Symptoms of schistosomiasis are not caused by the worms themselves but by the body’s reaction to the eggs
• Many infections are asymptomatic

Invasive stage:
• A cercarial dermatitis (swimmer’s itch) may appear 24 h after first infection (rarely met in
indigenous people)
• More common after penetration by non- human species of Schistosomes
• Transient itching and petechial lesions

Acute phase (egg deposition and extrusion) and Chronic phase (tissue proliferation and repair)
Depend in the species of the schistosome

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 Schistosoma haematobium
Acute phase
• There are usually no symptoms until 5- 10 weeks after infection (mild allergic manifestations) specially in visitors not
in indigenous populations

Chronic phase
• Maximum egg production begins 10–12 weeks after infection
• The majority of eggs pass through the bladder but an unknown proportion are trapped in the bladder wall
and ureters and eventually die and calcify
• The earliest bladder lesion is the pseudotubercle
• In long-standing infections nests of calcified ova (sandy patches) are surrounded by fibrous tissue in the
submucosa
• Haematuria (50%), dysuria and increased frequency of micturition are typical clinical signs and may persist
intermittently for years.
• hyperplasia of the epithelium Cystitis reduced bladder capacity + urethritis hydroureter,
hydronephrosis and uraemia
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 Schistosoma haematobium
Chronic phase
• Fibrosis of the ureteral wall usually leads to dilatation
• Cancer of the bladder is particularly common in Egypt and Mozambique and is clearly predisposed to by
urinary schistosomiasis (Squamous carcinoma is more common than transitional carcinoma)
• Pulmonary arteritis progressing to irreversible and lethal cor pulmonale because of capillary damage by
eggs sometimes occurs when eggs are swept back into the lungs
• The presence of adult worms in the lungs following drug treatment is also a possible cause of pulmonary
damage
• In women, eggs may cause lesions in the ovaries, Fallopian tubes and uterus or in the lower parts of the
genital tract, including the cervix, vagina and vulva, and about 6–27% of such cases result in sterility.

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Schistosoma haematobium

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 Schistosoma japonicum & Schistosoma mansoni
Acute phase
• Allergic manifestations, such as fever, headache, edema, cough, dysenteric symptoms, pruritus and urticaria, occur 3–8
weeks after infection with S. japonicum (Katayama syndrome)
• Tenderness in the liver region, mild abdominal pain, lymphadenopathy and splenomegaly, with an accompanying
eosinophilia

Chronic phase
• In the majority of individuals, infection is light and symptoms are entirely absent
• The symptomatology is mainly intestinal
• Patients develop colicky abdominal pain and bloody diarrhea, which may go on intermittently for many years
• The eggs deposited in the gut wall cause inflamatory reactions leading to microabscesses, granulomas, hyperplasia, and
eventual fibrosis
• In S. mansoni egg granulomas are found in the distal part of the colon and rectum.
• In S.japonicum Intestinal disease manifests as colicky abdominal pain, bloody diarrhea and anemia.
• Ectopic lesions include hepatosplenomegaly and periportal fibrosis (clay pipe stem fibrosis), portal hypertension, as
some of the eggs are carried through portal circulation into liver.
• Portal hypertension may cause gastrointestinal hemorrhage 11
Schistosoma japonicum & Schistosoma mansoni

Chronic phase
• In S.japonicum Cerebral and pulmonary involvement may occur in some cases

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 Diagnosis

• Parasitological examination: Urine microscopy & stool microscopy

• Histopathology: Biopsy of bladder or rectal mucosa
• Serological diagnosis
• Imaging
• Blood examination (eosinophilia)

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 Treatment

• Praziquantel is the drug of choice (40 mg/kg for 1 day)

• Metriphonate is the alternative drug of choice in schistosomiasis due to S. haematobium.
(7.5 mg/kg. weekly for 3 weeks)
• S. japonicum infection is more resistant to treatment than other schistosomiasis. A
prolonged course of intravenous tartar emetic gives good results. Praziquantel is the drug of
choice

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 Prophylaxis
• Eradication of the intermediate molluscan hosts.
• Prevention of environmental pollution with urine and feces
• Effective treatment of infected persons (mass chemotherapy)
• Avoid swimming, bathing, and washing in infected water

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