Echinostomatidae
Species ofEchinostoma
oftenaccidentally
infecthumans.
Final host, mammals, birdswith aquatic habits: adults inintestine
First Intermediate, Lymnaeidaesnails: sporocyst, redia;ceracariae released
Second Intermediate host,e.g., snails, tadpoles, clams,etc.: metacercariae.
Fasciolidae–Giant Liver flukes
Fasciola hepatica
Adults in bile ductsof ruminants
Sporocyst, rediae,ceracriae inLymnaeid snails.Metacercariae inaquaticvegetation.
Sources of human infection: watercress, lettuce, etcfrom areas where there are infected livestock.
Pathogenesis
• Metacercariae penetrate gut to peritoneum.Penetrate Glisson’s capsule (outer coveringof liver) and make their way through liverparenchyma to bile duct:
• Cause cirrhosis (proline Excretion elicitscollagen deposition); edema, thickening ofbile ducts, jaundice, even death
Other Fasciolidae
• Fasciolopsis buski: human intestine.Worms cause lesions where they feed;chronic diarrhea, obstruction, verminoustoxicity.
• Fascioloides magna: liver fluke in deer, elk.
• Fasciola gigantica: ruminants of Africa, SEAsia
ParamphistomatidaeDigenea in rumen of ruminants. Harmless as adults (unless invery large numbers); migrating larvae cause disease.
Paramphistomatidae: Rumen flukes: metacercariae hatch insmall intestion, migrate forward through reticulum to rumen.
Megalodiscus temperatus
• Colon of frogs.
Gastrodiscoides hominis
• Humans and swine: lower smallintestine, upper colon.
• SE Asia.
• Involves Helicorbus snails, butlife cycle not completely known.
• Causes diarrhea
Plagiorchiformes
• Diverse forms parasitizing all classes ofvertebrates. Cercaria with stylet.Metacercariae in various invertebrates.
• Often occur in highly terrestrial hosts
Dicrocoelidae
• Dicrocoelium dendriticum: in bile ducts ofruminants (sheep, deer, cattle) in Europe(introduced to some parts of Eastern NorthAmerica).
• Uses snails and ants as intermediate hosts.
Life cycle of D.dendriticum
Pathogenesis:infections mayinvolves 10,000+worms. Biliaryobstruction; liverdegeneration,jaundice.
Haematoloechusmedioplexus
• Parasites in lungs of frogs andtoads
• Sporocysts in Planorbula snailsrelease cercariae which encystas metacercariae on dragonflynaiads (rectal gills)
• Frogs access the parasiteswhen feeding onmetamorphosed dragonflies
Prosthogonimus spp.
• Oviduct of birds.• Sporocysts in snails
release ceracriae whichencysts asmetacercariae in rectalgills of Odonates.
• Birds acquire infectionsfrom feeding oninfectedmetamorphosedodonates.
• Can interfere with eggproduction
Paragonimus spp.• Lung flukes in Carnivores;
may accidentally occur inman
• Sporocysts in Thieridaesnails release short tailedcercariae
• Metacercariae in freshwatercrabs, crayfish
• Final host infected when iteats infected crustacea
Paragonimus in the final host
• Metacercariae penetrate intestine, migrateanterior to penetrate diaphragm and wait formates in the lung pleura. Pairs enter lungparynchyma and encyst.
• In humans metacercariae may wander intissues and cause problems.
Nanophyetus salmincola
• Parasites in intestinalcrypts of fish eatingmammals and birds.
• Sporocysts inOxytrema snails releaseshort tailed cercariae.
• Metacercariae inmuscle of fish.
Opisthorchiformes
• Adults in bile system of all classes ofvertebrates.
• Clonorchis sinensis, Opisthorchis spp.Metorchis spp. in humans
Heterophyes heterophyes
• Heterophyes spp commonly infect manaccidantally.
• H. heterophyes: North Africa, Middle East,Far East.
• Adults between villi. Can cause breakdownof mucosa, release eggs into blood asembolisms.
Top Related