Section 1: Digenetic trematodes

what are trematodes

flukes: parasitic flatworms in phylum Platyhelminthes
- primarily found in vertebrates

structure of trematodes

dorso-ventrally flattene

posses oral suckers surrounding the mouth

midventral/posterior acetabulum (ventral sucker)

digestive tract of flukes

short muscular esophagus

• surrounded by muscular pharynx

splits into pair of blind intestinal cecae

what are the types of trematodes

digene flukes: tissue (major organs in many species)

Schistosoma: blood (live in blood vessels; feed on blood; do not have pharynx)

what is the “life cycle” of digene flukes

egg in water → miracidium → snail → cercaria → metacercaria (resistant cyst) → eaten

what is the “life cycle” of a schistosoma

egg in water → miracidium → snail → cercaria → skin → blood vessels →

• no metacercaria

reproduction of trematodes

hermaphroditic (minus schistosomes)

• self-fertilize

male reproductive system

• two testes (each has vas efferens, connect to form vas deferens)

• vas deferens leads to genital pore (has internal seminal receptacle for sperm storage; prostate gland; cirrus, copulatory organ)

female reproductive system

• single ovary, oviduct, seminal receptacle (sperm storage), vitelline glands (provide material for egg shell formation), series of grandular structures (aid in egg shell maturation), uterus (may be filled with eggs), matraterm (muscular modification)

fluke body

tegument

• absorb nutrients

• digest/absorb nutrients across gut wall and across outer body

spines

life cycle of digene

indirect (2+ hosts)

eggs of most (except Schistosomes)

• operculate (with a lid)

• laid embryonated or unembryonated

• some hatch in water, some require ingestion by host

egg hatched

• ciliated miracidium merges (penetrate tissue of host, usually snail)

• depending on species: miracidium may develop into sporocyst (give rise to daughter sporocysts, rediae, cercariae) or rediae (give rise to daughter rediae or cercariae)

final product of asexual reproduction: cercariae

sexual immature forms:

• encysts on vegetation as metacarcariae and remain dormant until eaten by appropriate host

• penetrate skin of an animal and remain dormant as metacercariae until fish is eaten by final host

• penetrate skin of final host directly forming no metacercariae (Schistosomes)

once inside final vertebrate host: cercaria casts of tail, migrates to target organs, matures into adult

Fasciola hepatica adult (slide 1)

adults: large worms, dendritic/tandem testes, dendritic ovary, oral/ventral suckers (located anteriorly)

internal: cephalic cone containing oral sucker, branches intestinal cecae (anterior end of worm)

maturing worms: migrate through liver, consuming tissue resulting in liver damage

Fasciola hepatica adult (slide 1)

• structures, host site, morphology

structures: suckers, reproductive organs, body shape (large, oval)

host site: gall bladder/bile ducts of mammals

• maturing worm: migrate through liver

morphology: liver (consuming tissue causing damage)

Fasciola hepatica eggs (slide 2)

• eggs, specimen source

eggs: very large

• no shoulders, operculum

• pass unembryonated in feces

specimen source: adult flukes in biliary ducts

• become embryonated in water

• Life cycle: miracidium hatch, look for intermediate host (snail), miracidia penetrate body (develop: sporocyst, rediae, cercariae), carcarie released

Clonorchis sinensis adult (slide 3)

• structure, adults, host site

structures: small, elongate worms

• dendritic testes (posterior), ventral sucker (anterior), lateral vitelline follicles (posterior to VS, anterior to ovary)

adults: live in bile ducts of humans

• human infection: eating undercooked fish containing metaceracariae

• structures: suckers, reproductive organs, body shape (small elongate)

host site: bile ducts of humans

• eating undercooked fish containing metacercariae

Clonorchis sinensis eggs (slide 4)

• eggs, specimen source

structure: very small; tan/yellow color

• some have shoulders, passed embryonated, operculum, tiny knob opposite operculum, found in feces

specimen source: adult C. sinensis in human

• life cycle: exit in feces embryonated, eggs ingested by snail, miracidia hatch in snail (miracidium → sporocysts → rediae → cercariae), cercariae leave snail and encyst fish

Schistosoma mansoni male (slide 5)

• structures, shape

structures: separate sexes, anterior suckers (ventral/oral), cavity

shape: slender, elongate, blood-vascular worms

Schistosoma mansoni female (slide 6)

• structures, shape

structure: separate sexes, anterior suckers, ovary, vitelline glands

shape: slender, elongate, blood-vascular worms

Schistosoma mansoni eggs (slide 7)

• structure/features, specimen source

structure: found in feces, large/ellipsoidal, passed embryonated, lateral/large spine

specimen source: feces from human

• cercariae penetrate skin of human (become schistosomulae)

• schistosomulae enter circulation (carried to liver where they mature)

• worms pair in liver (feces: intestine)

• eggs pass embryonated

Schistosoma haematobium eggs (slide 8)

• structure/features, specimen source

structure: found in urine, ellipsoidal, passed embryonated, possess sharp/terminal spine

specimen source: urine in humans

• cercariae penetrate skin of human (become schistosomulae)

• schistosomulae enter circulation (carried to liver where they mature)

• worms pair in liver (urine: bladder)

• eggs pass embryonated

Schistosoma mansoni eggs in liver

• infection, eggs, issue with trapped eggs

infection: eggs become trapped in small blood vessels in liver rather than passing into intestine

• eggs within liver tissue

eggs: lateral spine

trapped eggs: inflammatory response

• chronic infection: result in fibrosis around portal vein

• periportal fibrosis: lead to portal hypertension and spleen enlargement

Schistosoma mansoni miracidia (slide 10)

• miracidium structure, function, life cycle

miracidium: ciliated larval stage that hatches from egg after it reaches freshwater

• elongate/oval body covered with ciliated epidermal plates

function: locate/penetrate snail intermediate host

• short living, free-swimming

life cycle: after entering snail, miracidium develop into a sporocyst

Schistosoma mansoni cercariae (slide 11)

• cercariae, structures, life cycle

cercariae: ciliated free-swimming larval stage released from snail (intermediate host)

structures: distinct forked tail, oval body, long tail (divides near posterior end)

life cycle: penetrate human skin directly, lose tail during penetration, develop into schistosomula

• no metacercariae stage in life cycle

Schistosoma mansoni sporocysts in snail digestive gland (slide 12)

• sporocysts, structures

sporocysts: developing within tissues of snail

• sac-life sporocysts embedded in tissue

• individual: numerous developing cercariae, other recognizable larval forms

structure

• lass mouth/digestive tract

• germinal calls undergo asexual reproduction (produce large number of cercariae)

Fasciolopsis buski (demonstration)

• adults, structures, infection

adults: large, fleshy, leaf-shaped worms, live attached to wall of small intestine

structures

• large size, oral/ventral suckers (anterior), lack cephalic cone, intestinal ceca unbranched

infections

• humans/pigs (definitive host): eat raw/undercooked aquatic vegetation bearing metacercariae

• freshwater snail (intermediate host): cercariae released from snail, encyst as metacercariae on aquatic plants