Ch. 16 - Schistosomes Flashcards
What are the characteristics of schistosomes?
- blood parasites –> feed on RBC
- dioecious
- cercariae penetrate skin of definitive host
- no metacercaria
- nonoperculate –> embryonated egg that hatches immediately after contacting water
How does the female enter the male schistosome?
gynecophoral canal
What 3 species infect humans?
1) S. mansoni
2) S. japonicum
3) S. haematobium
What are the differences in the types of schistosomiasis?
S. mansoni + S. japonicum:
- hepatic/intestinal
S. haematobium:
- urinary
What are the morphological differences between the 3 species that infect humans?
S. mansoni:
- 3-13 testes (male)
- grossly tuberculated tegument (male)
- long reunited ceca (male)
- short uterus (female)
- anterior ovary (female)
- vitelline glands (female)
S. japonicum:
- 6-8 testes (male)
- smooth tegument (male)
- short reunited ceca (male)
- long uterus (female)
- middle ovary (female)
S. haematobium:
- 4-5 testes (male)
- finely tuberculated tegument (male)
- intermediate reunited ceca (male)
- long uterus (female)
- posterior ovary (female)
Where is S. mansoni located in the world?
south america, caribbean, middle east, and africa
Where is S. japonicum located in the world?
china
Where is S. haematobium located in the world?
africa + middle east + india
What is the diagnostic stage?
eggs
what is the infective stage?
cercariae
What is the life cycle of schistosomas?
1) eggs shed in stools or urine
2) eggs hatch releasing miracidia
3) miracidia penetrate snail tissue
4) sporocysts in snail
5) cercariae released by snail into water + free swimming
6) penetrate human skin
7) cercariae lose tails during penetration + become schistosomulae
8) circulation
9) migrate to portal blood in liver + mature into adults
Will cooking food prevent infection of schistosomas?
no
What is the 2nd intermediate host of schistosomas?
none –> does not have one
What is the location in the definitive host that S. mansoni stays?
inferior mesenteric veins –> drain to liver via hepatic portal vein
What is the first intermediate host of S. mansoni?
Biomphalaria sp. (snails) –> aquatic
How many eggs per day are released from the oviposition?
200 eggs/day/female
what do granulomas do?
transport eggs to lumen in S. mansoni
Miracidium penetrates Biomphalaria spp. snails, and does what?
gives rise to 2 sporocyst generations:
- mother (1) sporocyst
- daughter (2) sporocyst
Which sporocyst produces cercariae by 30 days?
daughter sporocysts
What type of environment are cercaria attracted to?
warmth + skin lipids
Describe the “prepatent period”.
Adults migrate to mesenteric veins, produce eggs by 5-8 weeks post-infection
Where are the adult S. japonicum located in the human body?
superior mesenterics
What is the intermediate host of S. japonicum?
Oncomelania hupensis –> amphibious
What is the egg production in S. japonicum?
2000 eggs/day
Which schistosoma species has smaller eggs with small lateral spine?
S. japonicum
Which schistosoma species has many reservior hosts (a zoonosis)?
S. japonicum
What is the acute phase of pathogenesis in S. mansoni and S. japonicum?
- Katayama fever
- PI
- fever, rash, enlarged liver + spleen
What is the chronic phase of pathogenesis in S. mansoni and S. japonicum?
- due to eggs
- eggs washed into liver in portal circulation
- soluble egg antigen –> granuloma –> fibrosis
- hypersensitivity disease
Describe Schistosomiasis due to S. mansoni and S. japonicum.
1) blockage of blood flow through liver
(8% of cases)
- hemorrhage
2) eggs enter systemic circulation
- blockage of lung capillaries
- CNS lesions
3) gastrointestinal hemorrhage + fibrosis
Where are the adult S. haematobium located in the human body?
venous plexus surrounding urinary bladder
What is unique about the egg morphology in the S. haematobium?
conspicuous terminal spine
What is the intermediate host of S. haematobium?
Bulinus truncatus –> aquatic
What is the pathogenesis of S. haematobium?
- granulomas around eggs in wall of bladder + ureters
- damage to epithelium
What does Schistosomiasis due to S. haematobium look like?
1) hematuria –> very dangerous
2) fibrosis, calcification of bladder wall + ureters
3) increased pressure on ureters + kidneys –> hydronephrosis
4) squamous cell carcinoma of the bladder
5) increased HIV transmission due to lesions in genital tract –> infertility high among women
What does the spine of S. mansoni egg look like?
prominent lateral spine
What does the spine of S. japonicum egg look like?
inconspicuous lateral spine
What does the spine of S. haematobium egg look like?
terminal spine
What is the prevalence of schistosomiasis worldwide?
240 million
what is the morbidity of schistosomiasis around the world?
100-200 million w/symptoms + 20 million w/severe disease
what is the mortality of schistosomiasis around the world?
200,000/year in sub-sahara africa alone
Despite an effective drug, why is schistosomiasis still a problem?
1) increased population
2) increased irrigation
3) increased dams
What 2 factors contribute to transmission of schistosomiasis?
1) contamination of snail habitats w/waste
2) human water contact
How can schistosomiasis be controlled?
1) snail control –> molluscicides
2) chemotherapy –> praziquantel
3) education
What is the immune response?
IgE/complement-mediated eosinophil killing
What is the immunopathology?
immune response to eggs in liver, intestine, and bladder causes disease (hypersensitivity)
Describe schistosome dermatitis.
- due to avian schistosomes
- cercariae penetrate + die in skin –> inflammation –> accidental parasite
- more severe response w/repeated exposures
What does praziquantel do?
interferes w/ worm metabolism
what does oxamniquine do?
works to paralyze worms
what does metrifonate do?
interferes w/worm metabolism
The black pigment in muscle is a response to _________ stage of schistosome.
metacercariae
The 2nd intermediate host for many non-Schistosome flukes is:
fish
What form is the Schistosome when it leaves the snail host?
cercaria
What Schistosome species lives in Asia?
Schistosoma japonicum
What Schistosome species lives in Brazil?
Schistosoma mansoni
What Schistosome species lives in Egypt?
Schistosoma haematobium
