Phylum PLATYHELMINTHES Flashcards
General classification
• Members are soft bodied and have no body cavity (acoelomate)
• Internal organs are embedded in a spongy parenchymatous tissue
- The parenchyma is the functional parts of an organ in the body. This is in contrast to the stroma, which refers to the structural tissue of organs, namely, the connective tissues.
• Three classes of parasitic flatworms:
- Monogenea
- Trematoda
- Cestoda
- All three have no circulatory or respiratory system
- Diffuse O2 and CO2 across a tegument
- All are herphroditic
• Attachment organs such as suckers, hooks and spines are present in most species
• Monogenea & Trematoda (Flukes)
- Incomplete gut
• Cestoda (Tapeworm)
- Absent gut
• Trematoda & Cestoda
- Complex indirect lifecycle which involves two host species
Class MONOGENEA Location Characterisitcs Hazards Treatment
• Primarily ectoparasitic (outside) on the skin or gills of fish
• Some can be internal – fish, turtles and frogs
• Mammals – hippopotamus eye Oculotrema hippopotami
• Characterised:
- High host
- Site specific
- Well developed adhesive organs (to gills or external surface of fish)
- Simple direct life cycle (one larval stage a oncomiracidium - free-swimming, ciliated larval form of a fluke)
• Hazard:
- Not to wild populations
- When in aquaculture environment it can be hazardous, more so for economic importance when crowded together.
• Treatment:
- Immersion in fresh water
- Immersion in diluted formaldehyde
Class TREMATODA
Location
Characteristics
Subclasses
• All are endoparasidic (inside) or ectoparasitic • Characterised - Unsegmented flatworms - Functional alimentary tracts - Well developed attachment organs • Three subclasses (only one for VET278) - Digenea
Class TREMATODA
Subclass DIGENEA
Lifecycle
Reproduction
• Endoparasites of vertebrates • Lifecycle: - Alternation of sexual and asexual - One or more intermediate hosts - First host is always a mollusc • Reproduction: - Majority (except schistosomes) are monoecious – have both male & female reproductive systems - Internal fertilization (cross or self) - Single ovary - Usually two testes
Class TREMATODA Subclass DIGENEA Fasciola hepatica (liver fluke)
Identification Diagnosis Life Cycle Treatment & Control Importance
• Identification
- Leaf like structure
- Lives in bile duct or intestine of mammals
- Gut and reproductive systems are branched
- Suckers are close together
• Diagnosis
- Presence of eggs in faeces
- Large eggs (130-150 x 65-90 μm)
- Unembryonated
- Yellow-brown colour
- Eggs have a terminal operculum
- Eggs are distinguishable from paramphistome eggs by colour
- Paramphistomum is a genus of parasitic flat worms belonging to the digenetic trematodes.
• Life cycle
- Two host life cycle
- Snail intermediate hosts that are in Australia and New Zealand:
• Lymnaea tomentosa (freshwater snail)
• L. viridis (frog)
• L. columella (American ribbed fluke snail)
• Galba truncatula (freshwater snail)
- Other species of Lumnaea act as a intermediate host elsewhere
- Not all species of Lumnaea are susceptible to F. hepatica, including several in Australia
- Definitive hosts are: cattle, sheep, horses, kangaroos and humans
• Treatment and control
- Several anthelminthics (A group of antiparasitic drugs that expel parasitic worms and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host.)
- Some cases of resistance to commonly used anthelminthics
- Once lifecycle is established, eradication is hard to control due to infected wildlife
- Control of intermediate snail host is not feasible unless on a narrow scale due to environmental concerns.
• Importance
- Rarely found in WA
- Common parasite of ruminants in east coastal area of Australia
- Causes acute disease in lambs when juvenile flukes invade the liver
- Adult flukes invade the bile duct and responsible for:
• Thickened bile ducts
• Anaemia
• Progressive weakness
- Animals imported into WA must be drenched and checked for eggs in faeces
Class TREMATODA
Subclass DIGENEA
The paramphistones
Family Paramphistomidae
Identification Diagnosis Life Cycle Treatment & Control Importance
• Consists of
- Paramphistomum
- Calicophoron
- Orthocoelium
• Identification
- Large conical (cone shape) flukes
- Posterior sucker
- Parasitic in the rumen and reticulum in sheep & cattle
• Diagnosis
- Eggs found in faeces
- Similar shape and size as Fasciola
- Distinguished by their pale grey egg colour
• Life Cycle
- Two host life cycle
- Snail intermediate host are:
• Flat coiled planobrids (found in fresh water)
• Treatment and control
- A limited number of anthelminthics are effective against juvenile and adult paramphistomes
- Strategies are:
• Keep young ruminants away from areas that are known to harbour intermediate hosts
• Importance
- When in adult rumen and reticulum they seldom cause any serious problems
- Though can be responsible for production loss
- Immature flukes in the small intestine in young cattle and sheep can cause:
• Severe diarrhoea (scours)
• Anaemia
Class TREMATODA
Subclass DIGENEA
Dicrocoelium dendriticum
Family dicrocoeliidae
Identification Diagnosis Life Cycle Treatment & Control Importance
• Identification
- Medium size
- Translucent flukes
- Found in bile ducts of ruminants
• Life Cycle
- Does not require aquatic hosts
- First intermediate host is a terrestrial snail with 2 sporocyst (a parasitic fluke in the initial stage of infection in a snail host, developed from a miracidium; in parasitic sporozoans an encysted zygote in an invertebrate host.) generations
- Cercariae are excreted in mucus where an ant is the second intermediate host
- Metacercariae develop in the ant and cause behaviour changes
- This causes a rumen to ingest and become the definitive host
• Treatment and control
- Several anthelminthics
• Importance
- Not present in Australia
- Significant in adult sheep
- Progressive cirrhosis of the liver may develop
Class TREMATODA
Subclass DIGENEA
Paragonimus westermani (oriental lung fluke)
Family Troglotrematidae
Identification Diagnosis Life Cycle Treatment & Control Importance
• Identification
- Medium sized
- Flukes covered in tiny spines
- Found in lungs (human and carnivorous animals in Asia)
• Diagnosis
- Eggs found in sputum or faeces
- Eggs are 100μm long
- Distinct operculum (gill cover)
- Unembryonated when passed
• Life cycle
- Sporocysts & redial generations occur in freshwater snails in fast flowing streams
- Several species of freshwater crabs & crayfish are intermediate hosts
- Metacercariae develop in the muscle tissue and gill vessels of hosts
• Treatment and control
- Several effective anthelminthics
- Simple prevention for humans
- Most infections come from eating:
• Raw or pickled crabs or crayfish
• Importance
- Not all developing worms end up in the lungs
- Pathology depends on site of establishment
- Adults become encapsulated in:
• Cysts
• Lungs
- Can be responsible for:
• Chronic pneumonia
• Other sites such as: brain, liver and abdomen
Class TREMATODA
Subclass DIGENEA
Clonorchis sinensis (Chinese liver fluke)
Family Opithorchiidae
Identification Diagnosis Life Cycle Treatment & Control Importance
Clonorchis sinensis (Chinese liver fluke)
Family Opithorchiidae
• Identification
- Slender
- Flat
- Transparent
- Can be up to 20mm long
• Diagnosis
- Found in bile ducts of humans, dogs and cats in S. China, Vietnam, Japan and Korea
- Eggs are small, (30 x 16 μm)
- Unembryonated
- Thick shell
- Distinct operculum
• Life Cycle
- Sporocyst and redial generations are found in freshwater snails
- Metacericae develop in the skin or muscle of freshwater fish
- Definitive host becomes infected when eating raw or undercooked fish
• Treatment and control
- Anthelminthics
- Humans: ensuring all freshwater fish is cooked before eating
• Importance
- Repeated exposure can cause cirrhosis in the liver
- Cirrhosis: Chronic liver damage from a variety of causes leading to scarring and liver failure.
Class TREMATODA
Subclass DIGENEA
Schistosoma mansoni (blood fluke)
Family Schistomatidae
Identification Diagnosis Life Cycle Treatment & Control Importance Pathology
Schistosoma mansoni (blood fluke)
Family Schistomatidae
• Identification
- Adults occur in mesenteric blood vessels
- Long and thin
- Male and female are joined
• Diagnosis
- The female is found in the gynecophoric canal of the male
- Eggs are large (60 μm)
- Distinctive lateral spine
• Life cycle
- Eggs are deposited Unembryonated
- Pass through the intestinal wall, they contain a miracidium ready to hatch
- Aquatic snail is the intermediate host
- Two sporocyst generations followed by a cercarial production
- Definitive host is a human or other mammal
- Takes place when cercaria penetrates skin
• Treatment and control
- Several anthelmintic drugs
- Prevent faeces reaching the aquatic snail habitat
- Educate people to avoid contaminated water
• Importance
- Schistosomiasis is the second most prevalent tropical disease after malaria
- Over 200 million people thought to be infected
- 20 million endure severe consequences
- Can be found in cattle, sheep, pigs, horses and dogs
- Pathology is caused by eggs as they move through the intestinal wall or become trapped in liver
Other species of Schistosoma
S. japonicum
Host: Man and most domestic animals Site: Mesenteric veins
Distribution: Indonesia China, Indo-China and Japan
Other species of Schistosoma
S. haematobium
Host: Man
Site: Vessels of urinary bladder
Distribution: Africa and Indo-pacific
Other species of Schistosoma
S. mansoni
Host: Man (and other animals experimentally)
Site: Mesenteric veins
Distribution: Africa and S. America
Other species of Schistosoma
S. Bovis
Host: Cattle, sheep and goats
Site: Mesenteric veins
Distribution: Africa, S. Europe and Asia
Other species of Schistosoma
S. mattheei
Host: Ruminants, primates (Inc. man), rodents
Site: Mesenteric veins
Distribution: S. Africa and Malawi
