P13 Trematodes 2009-10 - The University of Edinburgh
Transcript of P13 Trematodes 2009-10 - The University of Edinburgh
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The Trematodes
BVM&S ParasitologyTudor W Jones
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The Trematodes 2
Lecture outcomes
• Describe the characteristics of trematodes of veterinary importance in relation to epidemiology, disease and control.
• Describe, the lifecycle of the Trematodes featured in this lecture in relation to epidemiology, disease and control
• Compare and contrast characteristics of the lifecycle of Fasciola and Dicrocoelium
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The Trematodes 3
Two Groups
• Monogean– Direct life cycles– Ectoparasites of fish
• Digenean– Indirect life cycles– Endoparasites of vertebrates
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Digenean Trematodes
• One or more suckers• Blind gut – no anus• Monoecious reproductive system• One or more intermediate hosts• Free living stages
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Digenean Life CycleAdult
Eggs
Miracidium
Sporocyst
Metacercaria
RediaRedia
RediaCercaria
CercariaCercaria
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Flukes of Veterinary Importance
• Liver flukes– Fasciola hepatica– Dicrocoelium dendriticum
• Stomach flukes– Paramphistomium sp
• Lung flukes– Paragonimus
• Blood flukes– Schistosoma sp
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The Trematodes 7
Fasciola hepatica
• Most common form of liver fluke • Adults in bile duct• Immature forms in liver parenchyma• One intermediate host – amphibious snails -
Lymnaea sp (truncatula)• Zoonotic
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The Trematodes 8
Effects of Fasciolainfection
• Acute– Large numbers of immature forms migrating
through the liver tissue• Subacute
– Smaller numbers of immature forms migrating through liver and entering bile duct
• Chronic– Effect of adults on bile ducts
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The Trematodes 9
F.hepatica life cycleAdult fluke
Eggs
Miracidium
SporocystRedia
Cercaria
Metacercaria
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The Trematodes 10
Epidemiology
• Suitable snail habitats– Wet mud
• Temperature – Snails – Hatching of fluke eggs
• Moisture– Rainfall>transpiration
10°C
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The Trematodes 11
Epidemiology
• Suitable snail habitats– Wet mud
• Temperature – Snails – Hatching of fluke eggs
• Moisture– Rainfall>transpiration
10°C
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The Trematodes 12
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The Trematodes 13
Summer infection of snails Winter infection of snails
Overwinteredeggs
Eggs from infected animals
Snails infected Spring-Summer
Metacercaria on pasture Aug-Oct
Eggs from infected animals
Snails infected in Autumn
Metacercaria on pasture May-June
Overwinteredmetacercaria
Delayed development
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The Trematodes 14
Forecasting
• “Ground surface wetness”– Critical factor for summer infection of snails– Based on monthly rainfall, evapotranspiration
and number of wet days May-October• “Wet day”
– Number of wet days/month June-September (>1.0mm rainfall)
– Seasonally “normal” temperatures
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Control
• Drug treatment to:– Reduce pasture contamination by fluke eggs
(April-august)– Remove fluke populations (immature vs adults)
• Reduce snail populations– Improved drainage– Molluscicides
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Dicrocoelium dendriticum
• The “small” or lancet liver fluke• Immature and adult forms in the bile ducts• No tissue migration• Two intermediate hosts• Limited distribution in UK• Limited pathogenicity
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The Trematodes 17
Dicrocoelium - life cycleEggs pass out
in faeces
Miracidium remains inside egg
Snail ingests egg
Cercaria in slime ball
Ant ingests slime ball
Metacercaria develops in ant brain – alters
behaviour
Final host ingests ant
while grazing
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The Trematodes 18
Fasciola vs. Dicrocoelium
Ant brainPastureMetacercaria
Slime ball/antSnail/pastureCercaria
Not presentSnailRedia
Snail (2 gens)SnailSporocyst
In eggFree-livingMiracidium
AntNot present2nd int host
Land snailAmphib. snail1st int. host
DicrocoeliumFasciolaFeature
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The Trematodes 19
Other flukes you need to be aware of
• Schistosomes– Blood flukes - separate male & females
• Paramphistomes– Stomach flukes of ruminants, pigs & horses
• Hepatic & pancreatic flukes of dog– Opisthorchis sp & Metorchis sp
• Weird & whacky
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The Trematodes 20
Summary
• Indirect life cycles• Mollusc always involved• Multi-stage life cycle• Impact on host dependent on availability of
infective forms• Control - target parasite and/or intermediate
host
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The Trematodes 21
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The Trematodes 22
Immature form of F.hepatica
Oral sucker
Ventral sucker
Spines
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The Trematodes 23
Dicrocoelium adultOral sucker
Ventral suckerOne of two
testesOvary
One fork of gut
Uterus containing eggs
One of two vitellaria
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Fasciola vs Dicrocoelium eggs(not to same scale)
Miracidium remains inside egg until eaten by snail
Miracidium hatches from egg via operculum soon after
leaving the host
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The Trematodes 25
Schistosome adults
Male
Female
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“Flukey” areas
Poorly drained pasture
Drainage ditch
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The Trematodes 27
Leucochloridium – stacking the odds
The antennae of infected snails become swollen and can’t be retracted.
Birds, the definitive host, can easily pick off the antennae and become infected.
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Chronic fluke infection
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The Trematodes 29
Chronic fluke – clinical signs
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Fasciola eggs
Operculum
Golden-yellow colour
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Miracidium stage
•Ciliated•Swims to snail•Infects snail though foot•Develops into sporocyst stage
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Redia stage
• Develops in snail from sporocyst stage
• Gives rise to cercaria stage
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Cercaria stage
•Burrows out of snail•Swims to vegetation•Changes to metacercaria by
•Loss of tail•Develops thick outer layer
•Infects definitive host