Podcast
Questions and Answers
What is the primary mechanism by which Schistosoma species cause tissue damage in schistosomiasis?
What is the primary mechanism by which Schistosoma species cause tissue damage in schistosomiasis?
- Secretion of toxins by cercariae during skin penetration.
- Mechanical obstruction of blood vessels by migrating schistosomula.
- Direct enzymatic degradation of host tissues by adult worms.
- Inflammatory responses triggered by the presence of eggs in tissues. (correct)
Why is diagnosis of Schistosoma japonicum infections by fecal examination more challenging compared to other Schistosoma species?
Why is diagnosis of Schistosoma japonicum infections by fecal examination more challenging compared to other Schistosoma species?
- Schistosoma japonicum eggs are not excreted in feces but are exclusively found in urine.
- Schistosoma japonicum eggs are significantly smaller and harder to detect under a microscope.
- Schistosoma japonicum eggs are produced in lower numbers and deposited irregularly. (correct)
- Schistosoma japonicum adults primarily reside in the liver, reducing egg deposition in feces.
How does the dioecious nature of schistosomes contribute to their pathogenicity and life cycle?
How does the dioecious nature of schistosomes contribute to their pathogenicity and life cycle?
- Dioecy enables schistosomes to switch between sexual and asexual reproduction based on host availability.
- The need for male and female worms to copulate prolongs the parasite's lifespan within the host.
- Separate sexes ensure genetic diversity, enhancing adaptation to different hosts.
- Copulation stimulates the female worm to produce a higher number of eggs, exacerbating tissue damage. (correct)
In the Schistosoma life cycle, what evolutionary advantage does the migration of schistosomula through the lungs and liver provide to the parasite?
In the Schistosoma life cycle, what evolutionary advantage does the migration of schistosomula through the lungs and liver provide to the parasite?
What specific adaptation enables cercariae to effectively penetrate the skin of a human host?
What specific adaptation enables cercariae to effectively penetrate the skin of a human host?
How does the environmental stability of Schistosoma eggs influence the transmission dynamics of schistosomiasis?
How does the environmental stability of Schistosoma eggs influence the transmission dynamics of schistosomiasis?
Why might mass drug administration (MDA) programs targeting schistosomiasis with praziquantel face challenges in achieving complete disease elimination?
Why might mass drug administration (MDA) programs targeting schistosomiasis with praziquantel face challenges in achieving complete disease elimination?
What is the significance of understanding the specific venous plexuses inhabited by different Schistosoma species for diagnosing and managing schistosomiasis?
What is the significance of understanding the specific venous plexuses inhabited by different Schistosoma species for diagnosing and managing schistosomiasis?
How does schistosomiasis increase the risk of bladder cancer specifically in cases of Schistosoma haematobium infections?
How does schistosomiasis increase the risk of bladder cancer specifically in cases of Schistosoma haematobium infections?
What challenge does the ability of Schistosoma species to move between different venous sites within the host pose for treatment and control strategies?
What challenge does the ability of Schistosoma species to move between different venous sites within the host pose for treatment and control strategies?
Flashcards
Schistosoma: Definitive Host
Schistosoma: Definitive Host
Humans
Schistosoma: Intermediate Host
Schistosoma: Intermediate Host
Snails
Schistosoma Transmission
Schistosoma Transmission
Penetration of the skin by cercaria larvae in water
Schistosomiasis Effects
Schistosomiasis Effects
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Schistosomiasis Diagnosis
Schistosomiasis Diagnosis
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Schistosomiasis Treatment
Schistosomiasis Treatment
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Schistosoma mansoni
Schistosoma mansoni
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Schistosoma haematobium
Schistosoma haematobium
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Schistosoma japonicum
Schistosoma japonicum
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Schistosoma Eggs
Schistosoma Eggs
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Study Notes
- Schistosoma is a trematode parasite with separate sexes (dioecious)
Hosts
- Definitive hosts are humans
- Intermediate hosts are snails
Species
- Schistosoma mansoni is prevalent in Africa and Latin America; frequently resides in the superior mesenteric veins near the small intestine & damages the colon
- Schistosoma haematobium is prevalent in Africa and the Middle East; inhabits the vesical and pelvic plexuses of the bladder and can also be found in the rectal venules, affects the bladder and predisposes to carcinoma
- Schistosoma japonicum is prevalent in Asia; often found in the inferior mesenteric veins near the large intestine & damages the small intestine
Stages
- Adult worms
- Eggs
- Larvae (cercaria larvae are the infective stage)
Transmission
- Occurs through penetration of the skin by cercaria larvae present in the water
Schistosomiasis
- The disease caused by Schistosoma
- The presence of eggs in tissues causes inflammation, granulomas, fibrosis, and obstruction, especially in the liver and skin.
Diagnosis
- Diagnosis involves observing eggs in the feces and urine, except for Schistosoma japonicum
- The preterminal spine is a characteristic feature of Schistosoma eggs; Schistosoma mansoni eggs are more common
Treatment
- Praziquantel is used to treat schistosomiasis
Life Cycle
- Eggs are eliminated with feces or urine
- Under appropriate conditions, eggs hatch and release miracidia that swim and penetrate specific snail intermediate hosts
- Parasites mature in the snail, going through two generations of sporocysts and producing cercariae
- Cercariae are released from the snail, swim, and penetrate the skin of the human host, where they mature into schistosomula
- Schistosomula migrate via the venous circulation to the lungs, then to the heart, and finally develop in the liver
- Mature male and female adults exit the liver via the portal vein system, copulate, and reside in the venous plexuses, a location which varies by species.
- Female worms deposit eggs in the small venules of the portal and pelvic systems
- Eggs migrate progressively toward the lumen of the intestine, bladder, or uterus, where they are eliminated in feces or urine, respectively
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