JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
October 2021
D-P27 (NP)

Slide A: SIGNALMENT (JPC #2287112): Adult cow

HISTORY:  On routine abattoir examination, meat inspectors found an enlarged, firm liver.

HISTOPATHOLOGIC DESCRIPTION:  Liver: Replacing 20% of hepatic parenchyma and compressing remaining hepatic cords are multiple, irregular, intersecting bands of fibrosis up to 500um thick that bridge portal and centrilobular areas (bridging fibrosis) and are also randomly distributed, contain myriad bile duct profiles (ductular reaction), and are infiltrated by moderate numbers of eosinophils, lymphocytes, macrophages, fewer plasma cells, and small amounts of hemorrhage, fibrin, edema, and basophilic granular material (mineral). Focally an ectatic bile duct contains a section of an intraluminal 250um wide adult trematode with a thin outer tegument overlying a band of somatic musculature, a parenchymatous matrix, and a uterus with numerous, asymmetrical, dark yellow-brown, 100 x 40 um, singly operculated, thick-shelled eggs containing miracidia. Adjacent to bands of fibrosis, there are few individualized hepatocytes that are shrunken with decreased cytoplasm (atrophy).

MORPHOLOGIC DIAGNOSIS:  Liver: Cholangiohepatitis, fibrosing, lymphoplasmacytic, and eosinophilic, chronic, multifocal, moderate, with cholangiectasia, marked ductular reaction, bridging portal and centrolobular fibrosis, and intraductal adult trematodes, breed unspecified, bovine.

ETIOLOGIC DIAGNOSIS:  Hepatic dicrocoeliasis

CAUSE:  Dicrocoelium dendriticum

CONDITION:  Distomiasis

SYNONYMS:  Lancet fluke disease; old world fluke disease

Slide B: SIGNALMENT (JPC #3104055): Adult female intact domestic shorthair cat

HISTORY: None

HISTOPATHOLOGIC DESCRIPTION:  Liver: Expanding portal areas and compressing adjacent sinusoids and hepatic cords are ectactic bile ducts with up to 1mm diameter lumina lined by hyperplastic epithelium that often form small papillary projections (biliary epithelial hyperplasia).  These bile ducts are surrounded by abundant fibrous connective tissue up to 50 um thick that replaces hepatic parenchyma and is infiltrated by eosinophils, lymphocytes, macrophages, fewer plasma cells, and contains small amounts of hemorrhage, fibrin, and edema. Focally a bile duct contains a section of an intraluminal 0.25 mm wide adult trematode with a thin outer tegument overlying a band of somatic musculature, a parenchymatous matrix, and a uterus with numerous, asymmetrical, yellow-brown, 100 x 40 um, singly operculated, thick-shelled eggs containing miracidia. Within the fibrous connective tissue surrounding ectatic bile ducts are increased numbers of bile ductules (ductular reaction). In less affected parenchyma, portal and centrilobular areas are multifocally expanded by fibrous connective tissue that often connects adjacent portal areas (bridging fibrosis), admixed with increased numbers of small bile ducts (ductular reaction) and previously described inflammatory cells, hemorrhage, and mineralization.

MORPHOLOGIC DIAGNOSIS:  Liver: Cholangiohepatitis, lymphoplasmacytic, and eosinophilic, multifocal, moderate, with cholangiectasia, biliary hyperplasia and ductular reaction, bridging portal fibrosis, and intraductal adult trematodes, domestic shorthair, feline.

CONDITION:  Platynosomiasis

CAUSE: Platynosomum fastosum

SYNONYMS: Lizard poisoning

GENERAL DISCUSSION:

• Dicrocoelid flukes inhabit the gallbladder, and bile and pancreatic ducts
• Distributed worldwide; economic losses due primarily to condemnation of cattle livers
• Various species infect cats, sheep, goats, cattle, new world camelids, buffalo, camels, rabbits, horses, and dogs
• Both Platynosomum fastosum and Dicrocoelium dendriticum: Class Trematoda, Order Plagiorchiida, Family Dicroceoliidae
• Platynosomum fastosum: inhabits biliary ducts and gallbladder of cats
  • Possible link to cholangiocarcinoma development
• Dicrocoelium dendriticum: inhabits bile ducts of sheep, cattle, pigs, deer, alpacas, woodchucks, cottontail rabbits; unlikely in cats

PATHOGENESIS:

• A chronic, heavy parasite burden leads to biliary ectasia and chronic cholangitis secondary to obstruction

LIFE CYCLE: 

• Indirect; two intermediate hosts required
• Platynosomum fastosum
  • First intermediate host: Sublima octona snail
  • Second intermediate host: Anolis lizards, marine toads, geckos, various arthropods
  • Cat becomes infected by ingesting second intermediate hosts à cercariae enter the upper digestive tract à cercariae migrate up the biliary tree à adults form à eggs shed into feces in 8-13 weeks
• Dicrocoelium dendriticum
  • First intermediate host: eggs embryonated when laid and hatch when swallowed by snail à cercariae expelled as “slime balls” from the snail’s lung during damp weather
  • Second intermediate host: ant Forma fusca eats the “slime ball”
  • Grazing animals ingest infected ants
  • Metacercaria excyst in the small intestine and migrate up the bile duct into its fine ramifications and into the gallbladder
  • Total life cycle takes 6 months
  • The prepatent period for the definitive host is 7-9 days

TYPICAL CLINICAL FINDINGS:

• Usually none; often subclinical
• Severe infections (non-specific): anorexia, vomiting, lethargy, jaundice, death
• Anemia, emaciation, decreased lactation, and lowered wool production (in sheep)

TYPICAL GROSS FINDINGS: 

• Small, narrow flukes, 0.5-1.0cm long and 1mm wide, easily mistaken for small masses of inspissated bile pigment, lancet-shaped, pied (blotchy because of brown uterus and white vitellaria visible through semitransparent tegument)
• Bile ducts: intraluminal flukes with bile duct wall thickening
• Early lesions: superficial erosions or visible scarring with sclerotic areas
• Chronic: extensive biliary fibrosis; liver margins are shrunken and sclerotic
• Severely affected livers enlarged, friable, +/- bile stained with thickened, distended gallbladders, dilated common bile or cystic ducts, and dilated intrahepatic ducts.

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Trematodes are characterized by an outer tegument +/- spines; a digestive tract consisting of paired blind ceca; spongy parenchyma (acoelomate); vitellaria (yolk forming glands); and one or two prominent suckers; trematodes are monoecious (hermaphroditic- contain both male and female reproductive organs)
• Variable chronic cholangitis, fibrosing cholangiohepatitis, cholecystitis
• Bile ducts: dilation, epithelial hyperplasia, bridging portal fibrosis, mucous gland hyperplasia within large ducts
• Flukes and their eggs within or adjacent to bile ducts with mucous exudate and cellular debris

ADDITIONAL DIAGNOSTIC TESTS:

• Oval, brown, operculate eggs 36-48um in diameter containing a miracidium; demonstrable in the feces using high density flotation solution (ZnSO₄)

DIFFERENTIAL DIAGNOSIS:  

For Gross Lesions:

• Fasciola hepatica (common liver fluke of sheep and cattle): within bile ducts and gall bladder
  • Young flukes are found in the bile ducts but can become encysted within the liver
  • Mature flukes in large bile ducts results in cholangitis
• Fasciola gigantica: within bile ducts and gall bladder; 2-3x larger than hepatica
• Fascioloides magna: “large liver fluke of North America”; 80um × 300um fluke found within liver parenchyma, often with associated black pigment deposits with migration in liver; less severe disease in tolerant wild ruminants than in domestic ruminants such as sheep
• Eurytrema pancreaticum and coelomatium: Mostly in pancreas, but can be in bile ducts in heavy burdens

COMPARATIVE PATHOLOGY:

Parasites of the biliary and/or pancreatic ducts:

• Dicrocoelium sp. infections in new world camelids: hepatic fibrosis, biliary hyperplasia, and associated with pulmonary arterial lesions
• Dicrocoelium hospes (mostly sheep and cattle, but can infect other species) is prevalent in tropical regions; resembles dendriticum infection
• Dicrocoelium supperei is found in Austrian mouflons and roe deer
• Flukes (trematodes) of Opisthorchis family: Opisthorchis tenuicolis, Opisthorchis viverrini, Clonorchis sinensis, Metorchis albidis, Metorchis conjunctus
• Flukes (trematodes) of Dicroceliidae family: Eurytrema pancreaticum, Concinnum (Eurytrema) procyonis, Dirocoelium dendriticum
• Nematodes (ascarids) and cestodes can aberrantly migrate into pancreatic duct
• Platynosomum concinnum: liver fluke of cats

REFERENCES:

1. Bowman DD. In: Bowman DD, ed. Georgis’ Parasitology for Veterinarians. 10th ed. St. Louis, MO: Saunders Elsevier; 2013:3,133-134.
2. Brown DL, Van Wettere AJV, Cullen JM. Hepatobiliary system and exocrine pancreas. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:446-447.
3. Cullen JM, Stalker MJ.  Liver and biliary system.  In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier Ltd; 2016:320-324.
4. Hamir AN, Smith BB. Severe biliary hyperplasia associated with liver fluke infection in an adult alpaca. Vet Pathol. 2002;39(5):592–594.
5. Hilbe M, Robert N, Pospischil A, Gerspach C. Pulmonary arterial lesions in new world camelids in association with Dicrocoelium dendriticum and Fasciola hepatica Vet Pathol. 2015;52(6):1202-1209.
6. Pinto HA, Mati VLT, deMelo AL. New insights into the life cycle of Platynosomum (Trematoda: Dicrocoeliidae). Parasitol Res. 2014;113:2701–2707.

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