JPC Systemic Pathology

Digestive System

October 2024

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 500 µm 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 250 µm 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 µm, singly operculated, thick-shelled eggs containing miracidia. Adjacent to bands of fibrosis, there are few individualized hepatocytes that are shrunken with decreased cytoplasm (atrophy), swollen with vacuolated cytoplasm (degeneration) or shrunken and hypereosinophilic with pyknotic nuclei (necrosis). 

 

MORPHOLOGIC DIAGNOSIS: Liver: Cholangiohepatitis, fibrosing, lymphoplasmacytic, and eosinophilic, chronic, multifocal, moderate, with biliary ductal ectasia, marked ductular reaction, bridging portal and centrilobular 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 ectatic 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 µm 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 µm, 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. There are multifocal scattered hepatocytes that are swollen with vacuolated cytoplasm (degeneration).

 

MORPHOLOGIC DIAGNOSIS: Liver: Cholangiohepatitis, lymphoplasmacytic, and eosinophilic, multifocal, moderate, with biliary duct ectasia, 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:

 

LIFE CYCLE: 

• Indirect; two intermediate hosts required
• Platynosomum fastosum
  • First intermediate host: Sublima octona snail 
  • Second intermediate host: Anolis spp. 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: 

 

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 F. hepatica
• Fascioloides magna: “large liver fluke of North America”; 80 µm × 300 µm 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 E. 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
• Dicrocoelium hospes (mostly sheep and cattle, but can infect other species) is prevalent in tropical regions; resembles D. 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. Agnew D. Camelidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018:200. 
2. Bowman DD. In: Bowman DD, ed. Georgis’ Parasitology for Veterinarians. 10th ed. St. Louis, MO: Saunders Elsevier; 2013:3,133-134.
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. Van Wettere AJ, Brown DL. Hepatobiliary System and Exocrine. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:519-520.

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