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Schistosoma haematobium
Common Name: Vesical blood fluke, Bilharzia worm
Geographical distribution: Sub-Saharan Africa and Middle east countries
200 million people infected worldwide. The number of people infected is not decreasing.
Habitat: Adult worm is found in vesical (bladder) venous plexus of Humans
Larval stages can be found in fresh water snails
Morphology:
Adult male and female worms are found together (in copula) lying in the venous plexus capillaries of the urinary bladder in humans.
Male worm: thicker, stouter than female
Size: 1-1.5 cms X1mm with Finely tuberulated outer layer and carries Testes: 4-5 in groups
2 suckers are present: Oral Sucker and ventral sucker
Male holds the female worm in the gynaecophoric canal and produces sperms from the gynaecophore to fertilize the female worm.
Female worm: thinner and smoother, lies in the gynaecophoric canal of the male
Size: 2 cms X 0.25 mm.
2 suckers are present: Oral Sucker and ventral sucker
Ovary is present behind middle of body and Uterus carries nearly 20-30 eggs
Periodically leaves the male to lay eggs in the venous capillaries.
Eggs: Large, non-operculated
Size: 150 x 50 μm
Shape Oval
Spine: Terminal spine present
Larvae:
Miracidium: ciliated, free swimming larvae hatch from embryonated eggs
Sporocysts: stage in snails
Cercaria: larvae released from snails and infect humans by penetrating through the skin (sub-cutaneously)
(Redia and metacercaria stage are absent in Schistosomes)
Life Cycle
Definitive host: Man
Intermediate host: fresh water Snails
e.g. Bulinus truncatus, Biomphalaria sp., Ferrissia tenuis
Life Cycle
The embryonated eggs are passed in urine of the definitive hosts (man) and reach water.
Ciliated larvae called as Miracidium larvae emerge out of the eggs.
Miracidium larvae then reach the intermediate hosts fresh water snails (eg Biomphalaria sp.) and penetrate its body to reach the liver of snail
Here they multiply asexually during the next 4-8 weeks to be transformed through many developmental stages. First it forms tubular sporocyst and this again multiplies into another generation of sporocysts.
Finally fork taied (bifid) cercaria emege from the snail which swim in water and are infective to humans.
Skin of humans (walking, wading, bathing or swimming in infected water) is penetrated by the cercaria after it attaches to the skin with its ventral sucker.
On entry into sub-cutaneous tissues the cercaria leave their tails (now called as schistosomulae) and gain access to the peripheral venules.
From venules they reach the systemic circulation and are distributed by blood to the whole body. Majority of schistosomulae reach the portal circulation in about 5 days and grow into adult worms (reach sexual maturity) in the next 3-4 weeks.
After becoming sexually mature these adult worms move out of liver circulation and reach the vesical (bladder) venous plexus of veins in 1-3 months.
Females are fertilized here by the males in its gynaecophoric canal and lay eggs in the veinules.
Eggs are released in urine and the cycle is repeated. Eggs carry a terminal spine and cause injury to the bladder epithelium causing bleeding resulting in haematuria (blood in urine).
Pathogenesis
Initially: reversible granulomatous inflammatory reaction to eggs of schistosomes in the bladder wall epithelium
Later: Irreversible Fibrosis & calcification
Following chronic infections Cancer of bladder may develop.
Clinical Features of Bilharziasis:
Cercarial penetration can cause dermatitis with papular, pruritic rash (schistosomal dermatitis or swimmer’s itch) at the site of larval entry (local reaction). Mostly are asymptomatic
Toxic metabolites from growing schistosomes: Fever, Urticaria, Eosinophilia. Leukocyosis, hepatomegaly, spleenomegaly (4-5 weeks later)
Eggs in bladder: can cause dysuria (difficulty in passing urine), painless terminal hematuria, increased frequency of urination.
Bladder involvement
Bladder involvement can result in hematuria, hypertension, obstructive uropathy, secondary urinary tract infections, and ultimately, renal failure and even cancer.
Genital disease is present in about 1/3rd of infected women vulvar and perineal disease, including ulcerative, fistulous, or wart-like lesions. Vulvar schistosomiasis may also facilitate the transmission of HIV
Lab diagnosis
􀁺Blood: Eosinophilia, anaemia, Hypoalbuminemia, high urea/ creatinin
􀁺Urine Examination: Centrifuged deposit shows eggs with terminal spine, RBCs.
􀁺Biopsy of Vesical mucosa: Granulomatous lesions around eggs.
􀁺Radiological diagnosis:
X ray: to picture calcified eggs, strictures or dilatations of kidney, ureters & bladder
USG/ CTscan
􀁺Immunological tests: ELISA, IHA
Eosinophilic cationic protein (ECP) or Circulating cathodic Ag (CCA): prognosis
Treatment
􀁺Praziquantel: single doze for adults
􀁺Artemether: for migrating larvae
􀁺Metrifonate
􀁺Oxamniquine: combination with Praziquantel
Prevention & Control
Eradication of human disease
Sanitary disposal of human waste
Destruction of snails using molluscicides
Avoiding swimming /bathing, wading or washing in infected waters
Summary
􀁺Definitive host: Man
􀁺Intermediate host: Fresh water snail
􀁺Stage of infection for man: cercaria
􀁺Mode of infection: Subcutaneous
􀁺Stage of infection for snail: Miracidium
􀁺Diagnostic stage: Eggs in Urine

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