Introduction
Schistosoma haematobium is a parasitic
trematode responsible for urinary schistosomiasis, a significant public health
problem in endemic regions, primarily in Africa and the Middle East. This
parasite inhabits the venous plexus of the urinary bladder and is transmitted
through freshwater snails of the genus Bulinus.
Morphology
Schistosoma haematobium
is a dioecious trematode with distinct male and female forms. The male is
shorter and thicker (10–15 mm in length) with a gynecophoric canal to hold the
female. The female is longer and slender (20 mm in length), residing within the
male’s gynecophoric canal. Eggs are oval with a characteristic terminal spine,
measuring about 112–170 µm in length.
Life
Cycle
The life cycle of Schistosoma haematobium
involves two hosts: a freshwater snail (Bulinus species) as the
intermediate host and humans as the definitive host. The detailed life cycle is
as follows:
1. Eggs
Excretion and Hatching:
The adult worms reside in the
venous plexus of the urinary bladder, where the female lays eggs. These eggs travel
through the bladder walls and are excreted in urine.Upon contact with
freshwater, the eggs hatch into free-swimming miracidia within a few hours.
2. Infection
of Snail Host:
The miracidia actively search
for and penetrate the soft tissues of the intermediate host, freshwater snails
of the genus Bulinus. Inside the snail, they undergo asexual
reproduction, developing into primary sporocysts and subsequently into
secondary sporocysts. The sporocysts further mature and produce free-swimming
cercariae, which are released into the water.
3. Cercarial
Penetration of Human Skin:
The cercariae are highly motile
and actively seek human hosts when they come in contact with infested water. Using
enzymes, the cercariae penetrate the skin, shedding their tails to become
schistosomula.
4. Migration
and Maturation in Humans:
The schistosomula enter the
bloodstream and migrate through the venous system to the lungs and liver. After
maturing in the liver for about 4-6 weeks, they migrate to the venous plexus of
the urinary bladder, where they mature into adult male and female worms.
5. Egg
Production and Pathogenesis:
The paired adult worms produce
eggs, some of which are excreted through urine, while others remain trapped in
tissues, causing inflammation and fibrosis. The cycle continues when the
excreted eggs reach freshwater and hatch into miracidia.
Prevalence
and Epidemiology
1. Found
predominantly in Africa, the Middle East, and parts of the Indian Ocean
islands.
2. Transmission
is highest in regions with stagnant freshwater bodies, poor sanitation, and
human water contact.
3. Children
and agricultural workers are at higher risk.
Pathogenicity
1. The
disease primarily affects the urinary bladder, causing hematuria (bloody urine).
2. Chronic
infection leads to fibrosis, calcification, and bladder dysfunction.
3. Long-term
complications include squamous cell carcinoma of the bladder and kidney damage.
4. Egg
deposition in tissues induces granuloma formation and inflammation.
Diagnosis
1. Microscopic
Examination: Detection of eggs with a terminal spine in urine samples.
2. Serological
Tests: ELISA and PCR for antigen/antibody detection.
3. Imaging
Techniques: Ultrasound to assess bladder and kidney damage.
4. Urinalysis:
Hematuria and proteinuria indicate infection.
Prophylaxis
1. Avoiding
contact with contaminated water.
2. Proper
disposal of human waste to prevent snail contamination.
3. Snail
control measures (molluscicides, environmental management).
4. Health
education and awareness campaigns.
Treatment
1. Praziquantel
(40 mg/kg body weight, single dose) is the drug of choice.
2. Repeated
treatment may be required in highly endemic areas.
3. Supportive
therapy for complications like bladder cancer and kidney failure.
References
1. Gryseels,
B., Polman, K., Clerinx, J., & Kestens, L. (2006). Human schistosomiasis. The
Lancet, 368(9541), 1106-1118.
2. Colley,
D. G., Bustinduy, A. L., Secor, W. E., & King, C. H. (2014). Human
schistosomiasis. The Lancet, 383(9936), 2253-2264.
3. WHO
(2023). Schistosomiasis. World Health Organization Website. https://www.who.int
4. Centers
for Disease Control and Prevention (CDC). (2023). Schistosomiasis. CDC
Parasitic Diseases Website. https://www.cdc.gov
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