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.