Trematodes 2

• Adult Echinostoma

  • Measures 2.5 to 6.5 x 1.1 mm
  • Elongated, rounded tapering ends, posterior more attenuate
  • Has a horseshoe-shaped collar, bearing one or two rows of straight spines, which surrounds the dorsal and lateral sides of the oral sucker
  • Testes deeply bilobed and in tandem
  • Intestinal ceca are simple and unbranched
• Echinostoma ilocanum


  Also known as Garrison's Fluke
• Echinostoma ilocanum

  • Habitat: Small Intestine
  • Reservoir Hosts: Dogs, cats, rats, pigs
  • 1st Intermediate Host: Gyraulus convexiusculus, Hippeutis umbilicalis
  • 2nd Intermediate Host: Pila luzonica (kuhol), Vivipara angularis (susong pampang)
  • Final Hosts: Humans, Aquatic Birds
• Echinostoma ilocanum transmission

  Ingestion of Metacercariae encysted in snails
• Echinostoma ilocanum diagnostic stage

  Unembryonated Eggs
• Echinostoma ilocanum eggs

  • Straw colored, ovoid
• Artyfechinostomum malayanum


  Another species of Echinostoma
• Artyfechinostomum malayanum

  • 1st Intermediate Host: Unknown (similar to Echinostoma)
  • 2nd Intermediate Host: Lymnea cumingiana (birabid), Ampullarius canaliculatus
• Artyfechinostomum malayanum eggs


  • Larger, golden brown, operculated
• Trematodes

  • Equipped with an oral sucker
  • Equipped with a ventral sucker called an acetabulum
  • Some have a third sucker called a genital sucker or gonotyl (observed only among the heterophyids)
  • They are all hermaphroditic
• Intermediate hosts


  Trematodes require two intermediate hosts in their life cycle
• Infective stage

  The encysted larva, the metacercaria, that develops in the second intermediate host (except for schistosomes where the infective stage is the cercaria)
• First intermediate host

  • Snail
• Second intermediate host

  • Fish
  • Crustacean
  • Another snail
  • Fresh water plants
• Adult schistosomes

  Found in the mesenteric veins, hence called blood flukes
• Adult Paragonimus worms

  Found in the lung parenchyma
• Flukes inhabiting the liver and bile passages

  • Fasciola
  • Clonorchis
  • Opisthorchis
• Flukes inhabiting the intestines

  • Fasciolopsis
  • Echinostoma
  • Heterophyids
• Mature eggs


  Contain an embryo called the miracidium
• Eggs passed out by an infected host

  • Mature (Schistosoma, Clonorchis, Opistorchis, Heterophyids)
  • Immature (Paragonimus, Fasciola, Fasciolopsis, Echinostoma)
• Miracidium


  The first larval stage that emerges from the egg in fresh water
• Trematode eggs

  • Smooth, hard shell, transparent
  • Yellow-brown or brown
  • Conventional egg shape
  • Have an operculum or lid - escape hatch
  • Schistosomes eggs are non-operculate and irregularly ruptured
• Trematode eggs cannot successfully be concentrated by the zinc-sulfate technique, as both operculate and the nonoperculate forms rupture and fail to float
• Formalin-ether concentrates or the sediment of the zinc-sulfate concentrate may be examined for the eggs, which are still recognizable even when ruptured
• Stages of Development

  • Egg
  • Miracidium
  • Sporocyst
  • Rediae
  • Cercariae
  • Metacercariae
  • Adult
• HETEROPHYID WORMS

  • Collective group of worms

  Major Species:

  • Heterophyes heterophyes (Von Siebold’s) – Fish; Smallest fluke (not found in Philippines)
  • Metagonimus yokogawai (Yokofawa’s) – Salmonoid and Cyprinoid Fish; Most common intestinal fluke in SEA or Far East
  • Haplorchis yokogawai
  • Haplorchis taichui

  Both the intermediate host can be found in different habitats,  not only on fresh waters but also in brackish water, and salt water and of course in different climates
• Morphology (Von Siebold’s)

  • Intestinal Fluke
  • Large and Strong ventral sucker
  • Genital sucker (gonotyle), with spines, is adjacent to ventral sucker
  • Absence of genital sucker in Metagonimus yokogawai
  • Two (2) oval testes situated posterior part of the body.
• HETEROPHYID WORMS Pathogenesis

  • Main symptoms are diarrhea and colicky abdominal pain (comes and goes in waves)
  • Migration of the eggs to the heart resulting in potentially fatal myocardial and valvular damage (reported in the Phippines)
  • Migration to other organs (brain)
• HETEROPHYID WORMS Diagnosis

  • Microscopic identification of eggs in stool
  • DFS, modified Kato thick method (higher sensitivity), FECT
  • The eggs of the different heterophyid species are difficult to distinguish.
  • Similar to Clonorchis and Opisthorchis eggs.
  • Opisthorchid-like eggs where the liver fluke is endemic
  • Polymerase chain reaction (PCR) may be useful as a sensitive diagnostic tool, particularly for low-intensity heterophyid infections
• HETEROPHYID WORMS Treatment

  • Three doses of praziquantel may be given at 25 mg/kg per dose over 1 day.
• HETEROPHYID WORMS Eggs

  • Light brown, ovoid, operculated, fully developed miracidium when laid
• HETEROPHYID WORMS Epidemiology

  • Endemic in Egypt, Middle East, Far East, Philippines
• HETEROPHYID WORMS

  Common Name: Minute intestinal flukes

  Habitat: Small Intestine

  Reservoir Host: Dogs, cats, birds

  1st Intermediate Host: Brackish water or Marine Species snails

  • Melania Juncea – H. taichui
  • Pironella – H. Heterophyes
  • Semisulcospira – M. Yokogawai
  • Procerovum calderoni – Thiaria riquetti

  2nd Intermediate Host: Brackish and Saltwater fish: Tilapia

  • Mugil cephalus – or mullet for H. Heterophyes

  Final Host: Humans, Birds, various fish-eating mammals

  Mode of Transmission: Ingestion of Metacercariae encysted in fish

  Infective Stage: Metacercaria

  Diagnostic Stage: Embryonated Eggs
• CLONORCHIS SINENSIS

  The liver flukes, C. sinensis, Opisthorchis felineus, and Opisthorchis viverrini, have similar life cycles
• Clonorchis sinensis

  • Spindloid flukes (with shoulders)
  • Flat, transparent, elongated, rounded posteriorly
  • Attenuated anteriorly
  • Spatulate in appearance
  • Deeply branched testes arranged in tandem
  • Lobed ovaries
  • Intestinal ceca are simple and unbranched
  • Largest oral sucker among other flukes
• Pathogenesis

  Most pathologic manifestations result from inflammation and intermittent obstruction of the biliary ducts
• Acute phase

  1. Abdominal pain

  2. Nausea

  3. Diarrhea

  4. Eosinophilia
• Long-standing infections

  1. Cholangitis

  2. Cholelithiasis

  3. Pancreatitis

  4. Cholangiocarcinoma
• Diagnosis

  • Microscopic demonstration of eggs in the stool or in duodenal aspirate
  • The adult fluke can also be removed at surgery
  • Serologic reactions (ELISA)
  • Cholangiography
  • Polymerase Chain Reaction (PCR) – DNA probing
  • FECT, Kato-Katz
  • Stoll's Dilution
  • Radiological features: Arrowhead sign
• Clonorchis sinensis is endemic in Korea, China Taiwan, Vietnam