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Laboratory 6 and 7
Trematodes I and II
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Trematoda
Subclass: Digenea
Order: Echinostomatiformes
Family: Fasciolidae
Fasciola hepatica
Fasciola gigantica
Fascioloides magna
Fasciolopsis buski
Order: Opisthorchiformes
Family: Opisthorchiidae
Clonorchis sinensis
Family: Heterophyidae
Heterophyes heterophyes
Order: Plagiorchiformes
Suborder: Plagiochiata
Family: Dicrocoeliidae
Dicrocoelium dendriticum
Family: Prosthogonimidae
Prosthogonimus macrorchis
Suborder: Troglotremata
Family: Troglotrematidae
Paragonimus westermani
Paragonimus kellicotti
Order: Strigeiformes
Family: Schistosomatidae
Schistosoma haematobium
Schistosoma japonicum
Schistosoma mansoni
PLATYHELMINTHES:
-“helminth” = worm
-platyhelminthes = flatworm
-very old lineage; fossil evidence from Permian sandstone tracks
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General characteristics of “flatworms”
-dorsoventrally flattened
-bilaterally symmetrical
-no body cavity; internal organs embedded in parenchyma (tissue)
-nervous system (associated sensory and motor elements)
-primitive digestive system (ends in blind sac)
-excretory system – flame cells
-noticeably absent: circulatory, respiratory and skeletal systems
-reproduction prolific – entire life cycle geared to produce lots of offspring
3 patterns:
--monecious (hermaphroditic) majority of the platyhelminths
---self fertilize (e.g., F. hepatica)
---cross fertilize between two hermaphroditic individuals (P. westermani)
--dioecious - two sexes (schistosomes)
-ectolecithal –yolk supplied by cells outside the ovum
-most are parasitic
TREMATODES:
blood flukes; intestinal flukes; tissue flukes
Digenetic:
-Minimum of two hosts: definitive and intermediate
--1st intermediate host usually a mollusk (such as a snail)
---May have more than one intermediate host
--Definitive host: a vertebrate (sexual reproduction occurs)
General Features of Digenetic Trematodes:
-oval in shape and dorsoventrally flattened
-2 suckers usually:
oral (at anterior end) surrounding the “mouth”
acetabulum (ventral sucker)
-tegument is active
-actively secretes neutralizing substances to block host responses
-digestive tract – primitive
mouth within oral sucker
pharynx
esophagus
intestinal ceca (end as blind sacs - no stomach, no anus)
-Nutrition obtained (varies from species to species)
--some feed by forming “plug” with oral sucker and pumping tissue into pharynx
--some nutrients can be absorbed through tegument
--Blood, mucus, tissue or gut contents as food (varies with species)
-primitive excretion system (via tegument, glands)
-muscular: longitudinal, cross and diagonal muscle tissues
Reproductive Tract:
hermaphroditic (exception: schistosomes)
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MALE SYSTEM:
testes, vas efferens, vas deferens, cirrus pouch
- 2 testes typically -- sperm leaves testis through vas efferens
FEMALE SYSTEM:
-Ovary is single (and stains dark)
-Vitelline cells produce the yolk
are produced by vitelline glands which are connected by vitelline ducts
vitelline glands are located down both sides of an adult fluke
-Uterus
extends to genital pore
can be long, coiled or folded
-ovary usually located right behind or right before uterus
-uterus usually full of eggs and covers intestine
-should be able to identify testes, ovary, uterus, vitelline glands and intestines
(ceca) in adult flukes (see photo below)
General forms in life cycle:
Ovum Æ miracidium Æ sporocyst Æredia Æ cercaria Æ metacercaria Æ adult
-ovum (egg) is really an embryo (miracidium) enclosed in a
capsule
operculum – opening at one end of egg through which
larva will escape
(blood flukes eggs are not operculated)
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Miracidium:
-ciliated free-swimming larva hatched from ovum
-water, oxygen and temperature are all required for development and hatching of
larva in external environment
-limited time to find snail host (a few hours)
-penetrates and burrows in via cytolysis (about 30 minutes)
(some species require ingestion of egg for hatching of miracidium which will
penetrate through gut wall of snail)
-loses cilia upon penetration of host
-mucus of snail “trail” a chemical attractant for miracidia
Sporocyst:
-results from metamorphosis of miracidium as it elongates to form a sac-like
structure
-no mouth, no digestive system, absorbs nutrients from host
-a “germinal sac” - embryos will develop asexually within
-sporocyst may produce more generations of sporocysts: daughter sporocysts or
it may give rise to the next stage redia (plural = rediae) or to cercaria (depending
upon species of fluke involved)
Redia:
-different form of a germinal sac
-burst out of sporocyst in some species, leave by birth pore in others
- active in host (crawls around)
-rudimentary digestive system (muscular pharynx and short sac-like gut) and
actively feeds on host tissues
(may also prey on sporocysts of their own or other species within snail host)
-embryos develop within Æ form daughter redia and repeat process OR
Æ form cercaria
-cercaria out via birth pore
(morphology varies depending upon species; see 15.24 in text)
Cercaria:
-infective stage for definitive host
-usually “free-swimming” but can survive only briefly (must find a host quickly)
-usually have a tail to aid in swimming
-tailless forms creep about until eaten
-some stay within sporocyst or redia that produced them until snail host
is eaten)
-have mouth and digestive system but doesn’t feed
-have penetration glands to aid in penetration of definitive host
-considered juvenile fluke
Metacercaria:
-not found in all fluke life cycles e.g., blood flukes do not have metacercaria
- an encysted form
--can be in or on intermediate host
--some encyst on aquatic vegetation or other things in water
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-1st step: lose the tail
-2nd step: form cyst wall (thick if on vegetation, thinner if inside 2nd intermediate
host)
-cysts within intermediate hosts survive longer, can absorb nutrients
from host.
-value of this stage: a means of transmission to definitive host that does not feed
on the intermediate host or is not in environment of mollusk host.
-must be ingested for excystment in gut and development into adult fluke
migration within host to the preferred niche will vary with species of fluke
-sexual reproduction will occur in adult flukes
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Class: Trematoda
Family: Fasciolidae
Fasciola hepatica
“liver fluke”
causes “Liver Rot”
Found world wide: Europe, USA, S America, China, Africa, Central America
Intermediate host: aquatic snail Lymnea sp
Definitive host:
cattle,sheep, humans
-- Infective stage: metacercaria
-- Host niche:
liver and bile duct
Life cycle:
2 hosts: snail intermediate host and vertebrate definitive host
Ova (must be in water to embryonate and hatch and takes 9-15 days)
ÆMiracidium phototrophic and must quickly find and penetrate snail host; asexually
produces
ÆSporocyst asexual development produces rediae
ÆRedia
produce daughter rediae generations which then produce cercaria
ÆCercaria free-swimming form (has unforked tail)
ÆMetacercaria formed when cercaria attach to aquatic vegetation, lose tail and form
cyst wall
-When eaten by definitive host, excyst in small intestine
-penetrate through gut wall into peritoneal cavity and to liver
ÆAdult fluke migrates in liver of definitive host (sheep, cattle, human)
feeds on liver cells, lining of bile duct, blood
produces operculated eggs which pass down bile duct and out with feces
Fasciola hepatica
Life Cycle
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“Fascioliasis” – the migration creates the clinical symptoms and pathology
- obstruction of bile duct
-liver enlarges
- can form large liver abcesses
-eosinophilia (numbers of circulating eosinophils rise)
Transmission to humans:
still goes back to fecal contamination of water source!
-drink water containing metacercaria
-eat aquatic vegetation such as watercress with metacercaria attached
(big problem in orient – raise aquatic vegetables for human consumption)
-fascioliasis in humans is rare in USA, even though parasite is common
Liver: damage and scarring (fibrosis) from migration of adults in liver and bile duct
in slaughter animals (sheep and cattle), infected livers are always condemned
Morphology: -leaf-shaped, large with cone-shaped projection on anterior end
“anterior cone and shoulders” -help ID this fluke
-extensive vitellaria –fills most of posterior space
-tegument covered with scale-like spines
Slides: ova, miracidium, rediae, cercaria, adult
look for anterior cone and shoulders
(oral sucker at end of cone)
Testes large and branched, in tandem behind ovary (hard to see)
Branched intestine up by head (can see it)
Fascioloides magna ( no slides) liver fluke
Cycle and history similar to F. hepatica Liver is definitive host niche.
Definitive hosts: herbivores – sheep (sheep die), cattle (dead end hosts – eggs
never leave liver), deer
Morphology similar to F. hepatica except no anterior cone or shoulders. and is larger
North America and Europe
Fasciola gigantica (no slides) liver fluke
very similar to F. hepatica in biology (no human hosts!!)
larger – like its name implies
different snail vector from F. hepatica
Asia, Africa, Hawaii
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Fasciolopsis buski
intestinal fluke
-common parasite of humans and pigs in Orient
-largest fluke to infect humans
-intestinal fluke –lives in small intestine
-produces thousands (25,000) of eggs per day
-Snail intermediate host
-Metacercaria on underwater vegetation (water chestnuts, bamboo)
(boiling vegetation for a few sec will kill metacercaria)
-Biology similar to F. hepatica
Clinical signs:
-adult flukes feed on intestinal epithelial cells
-can cause ulceration, hemorrhage and abcesses of small intestine
Slides: ova and adult
Large adult (20-75mm long– 20mm wide)
branched ovary anterior to testes
Intestinal ceca not branched
acetabulum large and close to oral sucker
Large, branched testes are tandem in posterior half of fluke
extensive vitellaria
Order: Opisthorchiformes (cercaria with 2 eyespots, rediae without spines
cercaria encyst in a 2nd intermediate host)
Family: Opisthorchiidae
Clonorchis sinensis
“Chinese liver fluke”
Far East: endemic in China, Japan, Viet Nam, Korea
(approximately 25% of Chinese immigrants to USA today harbor this parasite)
Reservoir hosts: dogs and cats
-1st intermediate host: aquatic snail
-2nd intermediate host: fresh water fish (esp cultivated grass carp)
-Definitive host: man, dog, cat
-Infective stage for definitive host: metacercaria in 2nd intermediate host
Niche: lumen of bile duct (adults feed on bile duct epithelium)
Adults self-fertilize and eggs pass out with feces.
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Ovum must be eaten by snail host. Miracidium hatches and penetrates into gut wall and
transforms into sporocyst. Sporocyst gives rise to rediae. Rediae produce cercaria with eye
spots. Released cercaria hang upside down in water, slowly sink to bottom and then swim
back up. If it contacts a suitable host – fish, it infects the fish and encysts as a metacercaria.
For the cycle to continue, a definitive host must eat the 2nd intermediate host raw or
incompletely cooked. The metacercaria excysts and migrates to liver where it crawls up the
bile duct. Adults pass eggs into bile duct which opens into the intestine. Eggs out with feces.
Light infection: asymptomatic –no disease
Moderate to heavy infection – clinical disease
- chronic infections have been associated with the development of cholangiocarcinoma
(bile duct cancer)
Dx: eggs in stool (are very small, see size comparison chart in handout)
Control: Leave the sushi alone! Don’t eat raw, pickled, salted, frozen, dried or
otherwise uncooked fish or crab.
C. sinensis slides: ova and adults
Adults have lancet appearance
Weakly developed suckers
Branched testes, in tandem near posterior end
Tegument lacks spines
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Family: Heterophyidae
Heterophyes heterophyes
-tiny flukes (1.0 mm long, 0.4 mm wide)
-intestinal flukes
-all species in this group considered potential human pathogens (12 known for sure
including those listed above)
-common in Africa, Asia, Middle and Far East
Life cycle:
eggs out in feces Æ must be eaten by snail Æ miracidium penetrates thru snail gut
(contains miracidium)
Æ sporocyst Æ rediae Æ cercaria Æ
with eye spots
contacts fish and penetrates skin Æ
(fresh and brackish water fish
especially mullet)
Æ encyst as metacercaria in fish muscle Æ metacercaria ingested when raw or
undercooked fish eaten
Æ metacercaria excyst in Small intestine
Æ burrow between villi of S.I. Æ eggs out with feces
Clinical Disease: occurs with heavy infections
gastric distress
malaise
fatigue
diarrhea
Fatal cases on record:
- went to heart and damaged valves and heart muscle causing heart failure.
--Both adults and eggs have been involved in cardiac pathology
- eggs in brain and spinal cord Æ neurological problems Æ fatal cases
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Order: Plagiorchiformes
Family: Dicrocoeliidae
(body usually pointed on both ends in adults, simple ceca)
(all in this family parasitize terrestrial vertebrates using land snails as
intermediate hosts - NO aquatic component to the life cycle)
Dicrocoelium dendriticum “the Lancet fluke”
liver fluke common in sheep, cattle, goats, pigs Rare in man!
North America, Europe, Asia, Australia
1st intermediate host: land snail (Cionella lubrica)
2nd intermediate host: common brown ant (Formica fusca)
Definitive Host Niche: bile ducts of host
Life cycle:
egg in feces Æ eaten by snail -Æhatches Æmiracidium transforms to sporocyst Æ daughter
sporocyst Æcercaria Æ accumulate in snail “lung” Æ irritate snail tissues,
and snail surrounds accumulation of cercaria with slime ball Æ slime ball expelled by snail into
environment (slime ball protects cercaria from drying out Æ slime ball eaten by brown ant.
Cercaria become metacercaria in the tissues of the ant, but one or two cercaria migrate to the
superior nerve ganglion (brain) of the ant. The parasite in this location creates behavioral
changes in the ant. Infected ants climb up on blades of grass at night instead of returning to
ant hill. Their mandibles fasten on to the blade of grass and remain locked onto the plant
overnight. Æ This behavior enhances the possibility of ingestion of the ant (and thus the
parasite) by the definitive host.
In definitive host, metacercaria excyst, migrate to liver and climb up bile duct. There is not
trauma to gut wall or liver by migrating juveniles. Damage: general biliary dysfunction by
adults in bile duct.
Dx: eggs in stool
Slides: adult only
Look for: unbranched (lobate) testes anterior to ovary
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Order: Plagiorchiformes
Family: Prosthogonimidae
Prosthogonimus macrorchis
“oviduct fluke of birds”
1st Intermediate host: snail
2nd intermediate host: dragon fly nymph
Definitive host: bird
Embryonated egg does not hatch until eaten by snail. Sporocysts
produce cercariae which enter anus of dragon fly nymph and encyst in muscle. When nymph
metamorphoses into adult dragon fly, metacercaria remain in muscle. When dragon fly is
eaten by bird, metacercaria excyst in small intestine and migrate down to cloaca where they
enter the bursa of Fabricius or the oviduct. Infection in male bird ends when bursa atrophies.
In female, effects are detrimental to the reproductive success of bird host species. Damage to
the oviduct in female birds can result in decreased or complete prevention of egg laying.
Slides of adults only
-huge testes
-vitellaria concentrated
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Order: Plagiorchiformes
Suborder: Troglotremata
Family: Troglotrematidae
Paragonimus spp. lungs, nasal passages, cranial cavities
Paragonimus westermani
“human lung fluke”
- Most prevalent species: Japan, China, Korea, Viet Nam, Thailand Cambodia, Asia,
Africa, Central and South America
- Very diverse, numerous reservoir hosts
Paragonimus kellicotti
- Found in North America
- Numerous mammalian definitive hosts, including man
Host Niche: lungs (flukes encapsulated in pairs – flukes induce host formation of
fibrotic capsule)
1st Intermediate host: aquatic snail
2nd intermediate host: crustacean such as crayfish or crab
snail host lives in fast-moving streams – this decreases chances of a miracidium encountering
snail host but this is offset by the number of eggs produced by adults.
Life Cycle:
Eggs coughed up and out with bloody sputum. Some may be swallowed and pass
out with feces into water.
Miracidium penetrates aquatic snail and transforms into sporocyst.
Sporocyst gives rise to rediae.
Rediae produce microcercous cercaria – have a knob-like tail.
released cercaria don’t swim, instead creep along bottom
Cercariae attach to crayfish or crabs and encyst as metacercaria in viscera and muscles.
Definitive host eats raw crayfish or crab and metacercaria excyst in small intestine.
Juvenile flukes penetrate through gut wall and migrate through peritoneal cavity,
penetrate through diaphragm and into lungs and bronchioles.
Cross fertilization between pairs is the rule in Paragonimus sp.
Paragonimus kellicotti is here in Louisiana and its second intermediate host is the good, old
crawfish that you and I find so delicious at crawfish boils.
Lesson here: don’t eat raw or undercooked crustaceans and don’t let your dog or cat
do it either. Marination in wine, vinegar or brine will not kill metacercariae.
Pathology: lung lesions “pseudotubercles” (called pseudotubercles because they
resemble the lesions caused by Mycobacterium tuberculosis and the symptoms of
paragonamiasis also resemble TB symptoms- especially the deep, blood-tinged
cough, pleural pain and dyspnea [difficult breathing].)
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Slides: ova, metacercaria, adults
“coffee-bean fluke” small, dark reddish brown color
Thick testes oblique to each other
Finger-like lobed ovary, ovary and uterus easy to see
(orientation of reproductive organs, hallmark for id of parasite)
Eggs:
ovoid (pointed end and flat end)
operculated (operculum set in a rim; this is the flat end!)
Dx: eggs in sputum
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Family: Schistosomatidae
-snail is intermediate host
-no second intermediate host
-Definitive host: birds, turtles, fishes, humans
-mature in blood vascular system of definitive host
-dioecious (separate sexes)
Schistosoma species: 3 of medical significance
NO snail hosts for human Schistosoma sp indigenous to USA.
1. Schistosoma haematobium (urinary) eggs in urine (terminal spine)
- found in most of Africa and parts of Middle East
-niche: veins of urinary bladder plexus
2. Schistosoma mansoni (intestinal)
eggs in feces (lateral spine)
-found in Africa (Egypt and Sudan), parts of middle East, parts of South America,
Caribbean (thought brought to New World by slave trade)
-niche: veins draining large intestine (inferior mesenteric veins)
3. Schistosoma japonicum (intestinal)
eggs in feces (rudimentary spine)
-found in Japan, China, Malaysia, Philippines, Indonesia
-niche: veins draining small intesting (superior mesenteric veins)
Males and females: live in permanent pairs in copula
-both feed on blood
-male shorter and stouter worm with well developed suckers
-female longer and slender with small suckers; remains in gynecorporal canal of male
(female that is not in this canal cannot survive. It is thought that the muscular
pumping action of the muscles forming the canal in the male help pump
blood into the intestine of female allowing her to obtain nutrients)
Eggs cause most pathology
• must traverse wall of vein and the intervening tissue to reach the intestine.
• must traverse through intestinal wall to lumen to go out with feces
(S. haematobium –traverse through bladder wall to lumen to go out with urine)
• Thought that spines on eggs aided travel through tissues but spineless eggs do
same
Approximately 2/3 of the eggs released do not make it to the lumen of intestine or
bladder.
-trapped in intestinal or bladder wall
-some swept away and lodge in capillaries of lung or liver
Trapped eggs secrete soluble egg antigens (SEA’s) which trigger an inflammatory and
immune response. Result: chronic, granulomatous fibrosing lesions
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General Life cycle:
egg Æ miracidium Æ mother sporocyst Æ daughter sporocyst Æ cercaria Æ adults in definitive
host
Eggs are not operculated and requires water to hatch.
Miracidium is ciliated and must find snail host within 5-6 hours.
No redia generations
Cercaria emerge from daughter sporocyst and snail host 4-7 wks after initial snail infection.
No second intermediate host. Free-swimming cercariae must penetrate definitive host
within 1- 3 days or die.
Cercaria are infective stage for definitive host:
-finds suitable host, attach and moves about till find suitable penetration site
(usually a hair follicle)
-attracted to skin secretions, especially the amino acid arginine
-send chemical signal to alert other cercariae to presence of suitable host – sort
of a “here it is shout!”
--Now called a “schistosomule” which enters the circulation Æ heart Æ lungs Æ
wriggle across Æ back to heart Æ systemic circulation Æ liver (sexes find
each other and pair up during 2 week stay in liver) Æ adult niche:
mesenteric plexus of large or small intestine or bladder plexus Æ produce
eggs
Prepatent period: from penetration to plexus about 5-8 weeks
Life span of adult schistosomes: 20-30 years!
Schistosomiasis – the disease: 3 phases:
1) Migratory: from penetration to maturity and egg production
-usually no symptoms
-if wrong host, can become presensitized and will present with a cercarial
dermatitis often called “swimmer’s itch” and those bumps are itchy!!
usually a bird schistosome
-end result, cercariae in wrong host will be killed
2) Acute: “Katayama fever”
-usually requires a heavy infection
-occurs predominantly with S. mansoni and S. japonicum
3) Chronic:
-chronic granulomas composed of macrophages, lymphocytes, fibroblasts
-become smaller & fibrous with time “pseudotubercles”
-eggs that are swept back to liver Æ granuloma formation and
eventual fibrosis in liver
-Eggs trapped in gut wall can cause erosion and ulceration of gut wall
(trapped eggs still secreting proteolytic enzymes)
-can show mild, chronic or bloody diarrhea with abdominal pain
S. haematobium – pain on urination and bloody urine [hematuria]
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Small % of individuals infected with S. mansoni or S. japonicum will progress
to very severe schistosomiasis:
fibrosis in liver Æ obstruction of portal circulation Æ enlarged liver, enlarged spleen,
End point: ascites – the accumulation of abdominal fluid in huge amounts
S. japonicum is usually the most severe because this species produces about 5 –
10 times more eggs than S. mansoni (S. japonicum produces between 1500
and 3000 eggs per day) This species also causes brain lesions more than the
other two species.
S. haematobium heavy infections can result in fibrosis and calcification of bladder
wall, decreasing its elasticity and creating increased pressure in upper urinary
tract (kidneys and ureters).
The bladder epithelium develops pseudopolyps around trapped eggs that can transform
into a squamous cell carcinoma.
Transmission: 1) human wastes (feces and urine) contamination of water sources
and
2) appropriate species of aquatic snail as intermediate host
Customs and behavior that facilitate transmission of schistosomiasis:
1) using human wastes (“night soil”) as fertilizer for food crops
2) wading in irrigation water for these crops
3) washing, bathing and using water from contaminated streams
Dx: eggs in excreta
Control of Schistosomiasis:
1. Education – difficult, poor, uneducated, resistance to cultural changes
2. Cure (Rx) -- praziquantel safe, effective
3. Vector control – more difficult (review what happened in Nile Valley when Egypt
built the Aswan Dam)
4. Protective vaccine (none yet)
Schistosoma slides:
S mansoni – all stages: ova (lateral spine), miracidium, cercariae, male and
female adults, granulomas
S. japonicum – ova (rudimentary spine), cercaria, adults, granulomas
S. haematobium – ova (terminal spine) and adults
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