Week 3 Flashcards
Trematodes (Flukes), Platyhelminths (flatworms)
What are Digenea?
Parasitic Trematodes (Flukes)- Playhelminths (flatworms)
Parasites of vertebrates (internal); two/ indirect host life cycle
Cestodes (Tapeworms), Platyhelminths (flatworms)
What are features of Platyhelminthes?
* Flattened, and mm- m!
* bilaterally symmetrical
* Tegument (role in diffusion, like a semi ectoderm skin layer)
* Triploblastic (3 layers- ectoderm, mesoderm, endoderm– one of the first with these 3 layers), acoelomate (solid mesoderm)
* Hermaphroditic (male/female reproductive organs in the same organism)
* Flame cells (protoephridium)- early forms of kidney tubules
* Cephalisation- first signs of brains- aggregation of nerve cells
* Blind ended (trematodes) or no gut (cestodes)– i.e. tapeworms have no gut… blinded means there is no anus but they have a gut
* Cephalisation
Digenea
(Platyhelminthes)
* >6000 species
* Indirect life cycle- IH host
- generations of sexual (definitive host) and asexual (larval- intermediate host) generations in alternate hosts
* 2+ hosts
Digenea, Platyhelminthes
Digenea, Platyhelminthes
Digenea, Platyhelminthes
Digenea features (adult worms)
* Non-segmented
* Suckers (oral, ventral or posterior)
* Spines (tegument)
* Digestive tract; usually no anus
* Mostly hermaphrodies (monoecious); some dioecious (two different sexes)– except schistosomes
What are the 4 layers of a flatworm?
* Protective layer
* ectoderm disappears during penetration of definitive host
* microvilli on the surface- role in protection, nutrient absorption, and metabolism (increased surface area, golgi apparatus, and ER)
4 layers:
- Tegument
- Muscle Layer
- Sub-tegument
- Parenchyma– if no body cavity, you will know it is a flatworm
Digestive system of a flatworm (platyhelminth)
Reproductive System of a platyhelminth (flat worm)
* Testes, ovaries, vitallaria glands (yolk), ootype (egg is shaped)
What is the life cycle of a Digenea?
* Definitive host: humans- adults live in bile duct spews out eggs–> eggs come out in faeces–> embryonated (miracidium is in there) hatch–> release miracidium–> eaten by snail OR penetrates snail–> asexual cycle occurs producing thousands of offspring from one egg–>(next stage that comes out is the cercariae- motile form) asexual forms exit the snail and penetrate second IH OR metacercariae form go into a cystic form ingested by the definitive host
(some differences occur like no metacercariae in schistocytes)
Distinguishing feature of all trematode eggs
* Spine assists with motility- helps them get through blood vessels into the bladder and out through the faeces
What is a miracidium?
** looking for snail!! So many sensory nerve endings!!
* Aquatic- ciliated epithelium
* Highly sensory- must find a snail
-light, temp, salinity, chemotaxis (secretions snail), negative geotaxis
* Retractable apical papilla
- sensory nerve endings
- apical galnds- enzymes for penetration
- muscular contractions
- = penetration snail ( ALL OF THIS HELPS WITH PENETRATION)
Ciliated ectoderm lost during penetration (of snail, for example)- become diphoblastic
Cercariae
Metacercariae
Metacercariae are encysted within the second IH (snail–> ant–> cat eats the ant)
Life cycle of Fasciola spp.
PPP? How long does the life cycle take?
* adult in bile duct–> sexual production of eggs excreted into faeces–> eggs are unembryonated when passed (not infective, just blastocyst sgages there– need the proper environment to start embryonating and to produce miricidium) (wet and at least 10 C for embryonation to start)–> 2-3 weeks for miracidium to be formed and hatch, egg is attracted to water–> miracidium has cilia and swims and looks for snail host and actively penetrates–> undergoes asexual multiplication 1000-4000 cercariae per miracidium–> latch onto vegetation and form resistant free living metacercaria–> definitive host eats plants and metacercaria–> metacercaria hatch and penetrate GI tract and migrate through into the peritoneal cavity–> parenchyma of the liver as juveniles and mature in 4-6 weeks into adults
PPP= 3 months (but in total 6 month life cycle outside the host as well)
Morphology of F. hepatica
How do you identify Lymnaea snails?
- Clockwise spiral
- No cover to the hole in the shell
- Triangular ears
L. lessoni is not an IH in Australia
Pathogenesis of Flukes (cattle vs. sheep)
* Acute Phase (usually seen in sheep)
* Chronic Phase (usually seen in cattle, because they have some immunity to Fasciola so unlikely to see massive infections all at once)
(Sometimes seen in organs other than the liver)
* Clostridium novyi adds to the problem (Black disease)- Sudden death in sheep
* If the animal lives through acute phase– mature to adults and live in the bile ducts– cause inflammation and subsequent fibrosis of bile ducts. The parasites themselves get calcified. Animals and humans produce gal stones. Cirrhosis of the liver ensues (no albumin production which = hypoalbuminamia, wasting, etc.)
Acute Fascioliasis
Subacute fascioliasis
Chronic Fascioliasis
Aberrant migration to lungs of fascioliasis
What three things do you need for Fasciola to flourish? What months would you see it in a temperate climate (winter rainfall area)? What about summer rainfall climate? Tropics??
- Rainfall > 50 mm, temp > 10 C
- Parasite
- Freshwater, shallwo, stagnant, pond, trickle streams, irrigation channels
** Not in WA or NT
* Eggs start to embryonate in spring–> 2-3 weeks develop and hatch (egg came from previously infected cattle)–> goes into snail approx 3 months before metacircariae encysted on vegetation–> early summer sheep and cattle infected expect to see acute disease 5-6 weeks later when juveniles have caused destruction in the liver (JANUARY!! Early to mid summer, consider acute fascioliasis if in a temperate region… CHRONIC would be a few months later–> MARCH/ APRIL– takes time for liver to get cirrhosed)
** Reversed in a summer rainfall area
** The whole YEAR! Control needs to be regular
