Trematodes

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Trematodes
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Schistosomatoidea

• Flukes that have no second intermediate host in
  the life cycle mature in blood vascular system
  of definitive host
• Most are dioecious have a male and female
• 3 Schistosoma are clinically significance
• S. haematobium
• S. mansoni
• S. japonicum

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Schistosoma

• Male is shorter and stouter than the female
• Ventral and longitudinal groove called
  gynecophoral canal where the female resides
• Have strong oral suckers around mouth
• No pharynx
• Sexual organs varies between species

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Biology

• Adult worms live in the veins that drain certain
  organs
• S. haematobium veins of urinary bladder plexus
• S. mansoni portal veins draining large
  intestine
• S. japonicum veins of small intestine
• Female in gynecophoral canal of male copulation
  takes place male moves them upstream to venules
  where the female lays the eggs
• Young transverse the venule wall and end up in
  area to be shed from the host, immune system may
  help to move the granuloma to either the gut or
  bladder where egg ends up in urine ot feces
• Eosinophils
• Plasma cells
• Macrophages

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Biology (cont.)

• Eggs hatch in fresh water and miracidium is
  released
• Miracidium must enter a snail host that is
  specific for each strain
• In the snail, shed epithelium, begin to develop
  into a mother sporocyst that release daughter
  sporocyst which may move to another area, mother
  continues to make daughters
• Furcocercous cercaria emerge from daughter
  sporocyst
• Cercaria have a head organ for penetration and a
  small ventral sucker
• Swim to the surface and sink to the bottom until
  tthey find the appropriate host
• Wiggle around on the surface looking for a good
  place to penetrate and then they disappear
  rapidly, loose tail and end up in the vascular
  system, move thru the lungs to liver where they
  will stay for awhile and then move to the veins
  in the target organ

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Life Cycle

• Adult in mesenteric veins of definitive host ?
  eggs in feces ? miracidium ? penetrates
  Biomphalaria snail (1st intermediate host) ?
  mother sporocyst ? produces many daughter
  sporocysts which each produces many cercariae ?
  penetrate skin of definitive host ?
  schistosomulum ? migrates to liver, mates,
  migrates to mesenteric veins ? adult

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Snail Vectors of Schistosomiasis


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Epidemiology

• Human waste in the water and the appropriate
  snail in the water will lead to human infection
• Level of infection based on exposure to
  contaminated water
• May develop immune response that prevents
  superinfection

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Pathology

• Pathogenesis is caused by the eggs and not the
  adult worms
• Lesion causes a delayed hypersensitivity reaction
  which is caused by the leaking of antigens from
  the granuloma formed around the egg
• 3 phases of the disease
• Migratory penetration until matuartion
• Acute Katayama fever egg production and
  loosing antigen, Antigen-antibody complexes with
  increased eosinophilia in the blood
• Chronic dominated by macrophages, lymphocytes,
  fibroblasts and multinucleated giant cells
  makes small fibrous granulomas ot pseudotubercles
• S. japonicum is the most fatal with brain and
  neurological disorders and S. haematobium is the
  least serious

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Diagnosis and Treatment

• Should see eggs in the urine or feces, may need
  to use concentration tests to get enough numbers
  for diagnosis
• Can also use serological tests that recognize the
  antigens and may not be super good due to the
  timing of the parasite
• Treat with trivalent antimonials in the old
  days but too toxic so now have praziquantel that
  works on all the Schistosoma species

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Control

• Education
• Control by chemotherapy
• Vector control
• Vaccination

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Schistosoma mansoni

• Adult worms acquired in Africa, S. America, and
  parts of the Caribbean when cercariae from
  Biomphalaria spp. snails penetrate through the
  skin
• Worms have separate sexes
• The female is wrapped within the gynecophoral
  canal of the male
• Single egg within uterus of female

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S. mansoni Eggs

• Note the fully formed miracidium, which hatches
  immediately in fresh water through a tear in the
  shell
• The large lateral spine, which may be
  inconspicuous if pointing straight up, help
  identify the egg
• Transmitted in Africa, the Caribbean, and Brazil
  by snails in the genus Biomphalaria

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a
b
d
c
e
g
i

j
h
f
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6.17 Life cycle of Schistosoma mansoni. a.
Adult worms in copula. b. Egg in feces. Eggs
hatch immediately upon reaching fresh water,
releasing a miracidium. c. Miracidium, which
must penetrate into a susceptible snail within
several hours. d. Miracidia penetrating head
foot of Biomphalaria glabrata. Each miracidium
transforms into a single mother sporocyst at the
site of penetration. e. Mother sporocyst in
tentacle of B. glabrata several weeks after
penetration of the miracidium. f. Squash of
tentacle infected with mother sporocyst, showing
released daughter sporocysts. g. Higher
magnification of daughter sporocyst, showing
typical elongation and enlargement of anterior
end. These migrate posteriorly to the digestive
gland. h. Digestive gland of infected snail
(green), largely replaced by daughter sporocysts
(yellow). These give rise to cercariae. i.
Cercaria, with characteristic forked tail. These
attach to human skin, drop their tail, penetrate,
and are then called schistosomula. j.
Schistosomulum, which pairs with a worm of the
opposite sex in the liver, develops to adulthood,
and migrates to the mesenteric veins.
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S. mansoni in Liver

• Left - low magnification showing three granulomas
  
• Right - higher magnification of single granuloma
  surrounding an egg, which has a clearly visible
  lateral spine

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Schistosoma haematobium Eggs

• Found mainly in urine, because the adult worms
  inhabit veins surrounding the bladder, but eggs
  also are found in feces
• Identified by the terminal spine and fully formed
  miracidium
• Occurs in Africa and the Middle East
• In addition to hematuria and fibrosis of the
  bladder and ureters, infections are associated
  with bladder cancer

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S. haematobium Eggs

• Wall of the urinary bladder
• Left large numbers of calcified eggs in the
  muscularis
• Right - higher magnification of eggs, terminal
  spines of the eggs are not visible in this section

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Schistosoma japonicum

• Fully formed miracidium
• Minute lateral spine, which is not apparent in
  several photographs
• Occurs in Asia
• Most pathogenic of the human-infecting
  schistosomes due to the high egg production by
  females and the tendency of the small eggs to
  pass through the liver and enter the systemic
  circulation, causing pathology in other organs,
  especially the central nervous system