JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
October2021
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, and increased fibrous connective tissue (fibrosis). Interlobular bile ducts are moderately ectatic and are variably occluded by few, 400 x 700 um 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 um 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). 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, etiology consistent with Athesmia foxi, 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 Capuchin monkeys, squirrel monkeys, tamarins, and Titi monkeys (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

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 but does involve a mollusk as the intermediate host

 

TYPICAL CLINICAL FINDINGS:

• Asymptomatic – most often an incidental finding

 

TYPICAL GROSS 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)

 

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)
• 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 (lack operculated egg and are not hermaphroditic)

 

ADDITIONAL DIAGNOSTIC TESTS:

• Diagnosis depends on the demonstration and identification of the adult in the bile ducts either at necropsy or on histopathological examination of liver sections or by demonstration and identification of the characteristic eggs in the feces

 

DIFFERENTIAL DIAGNOSIS:

• Schistosomiasis (D-P20): Adults inhabit veins; eggs may be found in the liver surrounded by microgranulomas or disseminated throughout body

 

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 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 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; 2012:251-252.

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