JPC SYSTEMIC PATHOLOGY

DIGESTIVE SYSTEM

October 2024

D-P19 (NP)

 

Signalment (JPC #11991476): Squirrel monkey 

 

HISTORY: Incidental finding

 

HISTOPATHOLOGIC DESCRIPTION: Liver: Multifocally, portal areas are expanded by moderate numbers of lymphocytes, plasma cells, fewer eosinophils, dilated lymphatics, and increased fibrous connective tissue (fibrosis). Bile ducts are moderately ectatic and variably occluded by few, 400 x 700 µm diameter, adult trematodes characterized by a thin tegument, narrow band of smooth muscle, and spongy parenchyma that contains poorly defined paired ceca, vitellarian glands, a testis, and uterine ducts containing numerous yellow, anisotropic, thick shelled, oval, operculate eggs that are approximately 20 X 30 µm and often contain deeply eosinophilic, basophilic, or black, multinucleate structures (miracidia). The bile duct epithelium is multifocally piled up to 2-3 layers thick (biliary epithelial hyperplasia), and there are increased numbers of small duct profiles (biliary ductular reaction). Bile ducts are surrounded by few eosinophils, fibrocytes, and fibrin. Multifocally, central veins are mildly dilated and contain eosinophilic fluid, with mild proliferation of circumferential collagen (centrilobular fibrosis). Diffusely, hepatocytes are mildly swollen with a lacy to clear cytoplasm (vacuolar change, glycogen type).

 

MORPHOLOGIC DIAGNOSIS: Liver: Cholangiohepatitis, portal, lymphoplasmacytic and eosinophilic, chronic, multifocal, mild, with biliary hyperplasia, biliary ductular reaction, portal edema, and few intraductal adult trematodes, Squirrel monkey (Saimiri sciureus), nonhuman primate

ETIOLOGIC DIAGNOSIS: Biliary athesmiasis or biliary dicrocoeliasis

 

CAUSE: Athesmia foxi

 

SYNONYMS: Athesmia heterolecithoides 

GENERAL DISCUSSION: 

• Athesmia foxi commonly parasitizes the bile ducts of susceptible nonhuman primates more commonly the Capuchin monkeys, squirrel monkeys, tamarins, and Titi monkeys obtained from South America (New World monkeys)
• Phylum Platyhelmintha, Class Trematoda, Family Dicrocoeliidae
• Dicrocoeliidae flukes infect biliary/pancreatic ducts of amphibians, birds, and mammals
• Flukes may cause biliary obstruction, cholangiectasis, and mild biliary stasis
• This parasite has not been reported in humans
• Transmission in laboratory cannot occur due to its obligatory need of intermediate host. No special control measures required.

 

PATHOGENESIS: 

• Mechanical blockage of bile ducts > cholangiectasis, biliary obstruction, and biliary stasis 
• There is no hepatic parenchymal damage from migration

 

LIFE CYCLE:

• The complete life cycle is not known for Athesmia sp. but does involve a mollusk as the intermediate host
• Belongs to the Dicrocoeliidae family, and might have similar to patterns to Dicrocoelium dendriticum (D-P27A) and Platynosumum fastosum (D-P27B)
• Infection occurs by eating intermediate or paratenic hosts à Cercariae are released into the upper digestive tract à enter the biliary tree à complete their life cycle

 

TYPICAL CLINICAL FINDINGS:

 

TYPICAL GROSS FINDINGS: 

• Presence of small trematodes in the interlobular bile ducts
• Flukes are very small (7-9 mm long and 0.7mm wide) and often missed during post-mortem examination (may be mistaken for inspissated bile)
• May see moderate to marked distension of affected bile ducts

 

TYPICAL LIGHT MICROSCOPIC FINDINGS: 

• Presence of small trematodes in the interlobular bile ducts
• Flukes are very small (7-9 mm long) and often missed during post-mortem examination (may be mistaken for inspissated bile)
• Eggs are ovoid with thick shells that are operculated and golden brown in color
• Moderate to marked distention of affected bile ducts with little damage or host inflammatory response
• Heavy infection can result in hyperplasia of the biliary epithelium and fibroplasia around eggs and the ducts
• Extremely severe infections can result in pronounced thickening of the bile ducts with resultant pressure and trauma to adjacent hepatic parenchyma, leading to fatty degeneration of affected hepatocytes
• Chronic portal hepatitis and trematodes within bile ducts
• Trematode characteristics:
  • Tegument, outer longitudinal muscle layer, inner circular muscle layer
  • No body cavity
  • Spongy parenchyma
  • Oral sucker; may be ventral
  • Paired ceca; may contain “blood pigment” - black pigment associated with breakdown of blood cells
  • Vitellaria; peripherally located and contain eosinophilic globules (yolk forming glands)
  • Hermaphroditic with operculated, thick shelled yellow-brown eggs (except schistosomes which lack operculated egg and are not hermaphroditic)

 

ADDITIONAL DIAGNOSTIC TESTS: 

 

DIFFERENTIAL DIAGNOSIS:

 

COMPARATIVE PATHOLOGY: 

· Other common Dicrocoeliidae flukes:

• Dicrocoelium dendriticum (D-P27A): All domestic species, except the cat; Europe/Asia; most important in sheep and cattle; bile ducts and gallbladder
• Dicrocoelium hospes: Cattle in countries south of Sahara; compatible to D. dendriticum
• Eurytrema pancreaticum: Ruminants, swine; Asia, Madagascar, South America; prefers pancreatic ducts, but also bile ducts
• Eurytrema procyonis: Raccoon pancreatic fluke reports of pancreatitis in cats
• Platynosomum fastosum (D-P27B): Cats; North America and Amazon basin in South America; bile ducts and gallbladder

· Fasciolidae flukes

• Fasciola hepatica: Bile ducts of sheep/cattle
• Fascioloides magna (D-P23): Hepatic parenchyma of ruminants
• Fasciola gigantica: Similar to F. hepatica; found in Africa/Asia/Hawaii

REFERENCES: 

1. 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. Philadelphia, PA: Elsevier Ltd; 2016:320-324.
2. Strait K, Else JG, Eberhard ML. Parasitic Diseases of Nonhuman Primates. In: Abee CR, Mansfield K, Tardif S, Morris T, eds. Nonhuman Primates in Biomedical Research: Diseases, San Diego, CA: Academic Press, Inc; 2012: 247, 251-252.
3. Van Wettere AJ, Brown DL. Hepatobiliary System and Exocrine. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:544. 

 

 

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