Introduction to helminthology
Lecture outcomes
• Describe the characteristics of trematodes of veterinary The Trematodes importance in relation to epidemiology, disease and control. BVM&S Parasitology • Describe, the lifecycle of the Trematodes featured in this lecture in relation to epidemiology, disease and control Tudor W Jones • Compare and contrast characteristics of the lifecycle of Fasciola and Dicrocoelium
The Trematodes 2
Two Groups Digenean Trematodes
• Monogean • One or more suckers – Direct life cycles • Blind gut – no anus – Ectoparasites of fish • Monoecious reproductive system • Digenean • One or more intermediate hosts – Indirect life cycles • Free living stages – Endoparasites of vertebrates
The Trematodes 3 The Trematodes 4
Digenean Life Cycle Flukes of Veterinary Importance
Adult • Liver flukes – Fasciola hepatica Metacercaria Eggs – Dicrocoelium dendriticum • Stomach flukes Miracidium – Paramphistomium sp Cercaria • Lung flukes Cercaria Redia – Paragonimus Sporocyst Cercaria Redia • Blood flukes Redia – Schistosoma sp
The Trematodes 5 The Trematodes 6
T.W.Jones, CTVM 1 Introduction to helminthology
Fasciola hepatica Effects of Fasciola infection • Most common form of liver fluke • Acute • Adults in bile duct – Large numbers of immature forms migrating through the liver tissue • Immature forms in liver parenchyma • Subacute • One intermediate host – amphibious snails - – Smaller numbers of immature forms migrating Lymnaea sp (truncatula) through liver and entering bile duct • Zoonotic • Chronic – Effect of adults on bile ducts
The Trematodes 7 The Trematodes 8
F.hepatica life cycle Epidemiology
Adult fluke • Suitable snail habitats –Wet mud Eggs • Temperature Metacercaria – Snails 10°C Miracidium – Hatching of fluke eggs
Cercaria • Moisture – Rainfall>transpiration Redia Sporocyst
The Trematodes 9 The Trematodes 10
Epidemiology
• Suitable snail habitats –Wet mud • Temperature – Snails 10°C – Hatching of fluke eggs • Moisture – Rainfall>transpiration
The Trematodes 11 The Trematodes 12
T.W.Jones, CTVM 2 Introduction to helminthology
Summer infection of snails Winter infection of snails Eggs from infected animals Eggs from infected Forecasting animals • “Ground surface wetness” Snails infected in – Critical factor for summer infection of snails Overwintered Autumn eggs – Based on monthly rainfall, evapotranspiration
Delayed development and number of wet days May-October Snails infected Spring-Summer Metacercaria on •“Wet day” pasture May-June – Number of wet days/month June-September (>1.0mm rainfall) Metacercaria on Overwintered pasture Aug-Oct metacercaria – Seasonally “normal” temperatures
The Trematodes 13 The Trematodes 14
Control Dicrocoelium dendriticum
• Drug treatment to: • The “small” or lancet liver fluke – Reduce pasture contamination by fluke eggs • Immature and adult forms in the bile ducts (April-august) • No tissue migration – Remove fluke populations (immature vs adults) • Two intermediate hosts • Reduce snail populations • Limited distribution in UK – Improved drainage – Molluscicides • Limited pathogenicity
The Trematodes 15 The Trematodes 16
Fasciola vs. Dicrocoelium Dicrocoelium - life cycle Final host Feature Fasciola Dicrocoelium ingests ant Eggs pass out while grazing in faeces 1st int. host Amphib. snail Land snail Miracidium remains inside egg 2nd int host Not present Ant Miracidium Free-living In egg Metacercaria Cercaria in Sporocyst Snail Snail (2 gens) develops in ant slime ball brain – alters Redia Snail Not present behaviour Cercaria Snail/pasture Slime ball/ant Snail ingests egg Metacercaria Pasture Ant brain Ant ingests slime ball The Trematodes 17 The Trematodes 18
T.W.Jones, CTVM 3 Introduction to helminthology
Other flukes you need to be Summary aware of • Schistosomes • Indirect life cycles – Blood flukes - separate male & females • Mollusc always involved • Paramphistomes • Multi-stage life cycle – Stomach flukes of ruminants, pigs & horses • Impact on host dependent on availability of • Hepatic & pancreatic flukes of dog infective forms – Opisthorchis sp & Metorchis sp • Control - target parasite and/or intermediate • Weird & whacky host
The Trematodes 19 The Trematodes 20
Immature form of F.hepatica
Oral sucker
Spines
Ventral sucker
The Trematodes 21 The Trematodes 22
Fasciola vs Dicrocoelium eggs Dicrocoelium adult (not to same scale) One fork of gut Oral sucker Uterus containing Miracidium remains inside egg eggs until eaten by snail
One of two vitellaria Ventral One of two sucker Ovary testes Miracidium hatches from egg via operculum soon after leaving the host
The Trematodes 23 The Trematodes 24
T.W.Jones, CTVM 4 Introduction to helminthology
Schistosome adults “Flukey” areas
Male
Female
Drainage ditch Poorly drained pasture
The Trematodes 25 The Trematodes 26
Leucochloridium – stacking the odds Chronic fluke infection
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.
The Trematodes 27 The Trematodes 28
Chronic fluke – clinical signs Fasciola eggs
Operculum
Golden- yellow colour
The Trematodes 29 The Trematodes 30
T.W.Jones, CTVM 5 Introduction to helminthology
Miracidium stage Redia stage
• Develops in snail from •Ciliated sporocyst stage •Swims to snail • Gives rise to cercaria •Infects snail though foot stage •Develops into sporocyst stage
The Trematodes 31 The Trematodes 32
Cercaria stage
•Burrows out of snail •Swims to vegetation •Changes to metacercaria by •Loss of tail •Develops thick outer layer •Infects definitive host
The Trematodes 33
T.W.Jones, CTVM 6