October 2018



Signalment (JPC #2550496): Hare




HISTOPATHOLOGIC DESCRIPTION: Liver: Effacing and replacing approximately 70% of the section of liver and compressing adjacent hepatocytes are multifocal to coalescing granulomas composed of a central area of eosinophilic cellular and karyorrhectic debris (lytic necrosis) admixed with numerous aphasmid nematode eggs which are 40 x 60 µm, have a 10-15 µm thick shell with radial striations and variably visible bipolar opercula. Eggs contain either a eosinophilic 15um diameter morula or small amounts of granular eosinophilic debris. Central areas of necrosis are bounded by numerous degenerate neutrophils, epithelioid macrophages and multinucleated giant cells (foreign body and Langhans type) that are up to 200 µm in diameter and contain up to 40 nuclei; few contain a phagocytized nematode egg. Surrounding these areas are concentric layers of numerous fibroblasts, eosinophils, fewer lymphocytes and plasma cells and fibrous connective tissue (fibrosis) with many entrapped bile ductules. Adjacent hepatocytes are multifocally atrophied, occasionally degenerate (swollen and microvacuolated), or rarely necrotic (shrunken and hypereosinophilic with pyknosis). Multifocally there is an increased number of haphazardly arranged bile ducts (hyperplasia) as well as occasional ectatic ducts. Multifocally there is hemorrhage within the hepatic parenchyma. Portal areas are infiltrated by low numbers of eosinophils, lymphocytes and plasma cells.


MORPHOLOGIC DIAGNOSIS: Liver: Granulomas, eosinophilic, chronic, multifocal to coalescing, moderate with bi-operculate aphasmid nematode eggs, etiology consistent with Capillaria hepatica, hare (Lepus sp.), lagomorph.


Signalment (UFSM-1): 12-year-old intact male mixed breed dog.


HISTORY: This dog had a 20-day history of ascites, pleural effusion, vomiting, depression and anorexia which was refractory to treatment. The dog was humanely euthanized and a necropsy was performed.


HISTOPATHOLOGIC DESCRIPTION: Liver: Effacing and replacing approximately 50% of the hepatic parenchyma in the section, and often bridging portal areas, are multifocal to coalescing areas of mature fibrous connective tissue (bridging fibrosis) which replace normal hepatic cords and contain numerous aphasmid nematode eggs which are 40 x 60 µm, have a 10-15 µm thick shell with radial striations and variably visible bipolar opercula. Eggs contain either a eosinophilic 20um diameter morula, a 30um x 10um elongate basophilic larvae or small amounts of granular debris. Within these areas, there are low numbers of lymphocytes and plasma cells. Remaining, adjacent hepatocytes are occasionally degenerate (swollen and vacuolated) or necrotic (shrunken and hypereosinophilic with pyknosis). Multifocally, vessels and lymphatics in the portal areas are ectatic (edema and congestion). Diffusely, hepatic sinusoids are congested.


MORPHOLOGIC DIAGNOSIS: Liver: Bridging fibrosis, periportal, chronic, multifocal to coalescing, marked, with hepatocyte loss and numerous bi-operculate aphasmid nematode eggs, etiology consistent with Capillaria hepatica, mixed breed dog, canine.


ETIOLOGIC DIAGNOSIS: Hepatic capillariasis


CAUSE: Capillaria hepatica (Calodium hepaticum)



·      Capillaria sp. (family Trichuridae) are aphasmid nematodes that parasitize diverse epithelia of a wide range of hosts

·      Unique morphologic features of aphasmids:

  • Row of esophageal gland cells (stichocytes) that form a stichosome (a series of glands along the esophagus); this structure surrounds the esophagus and is very basophilic
  • Bacillary or hypodermal bands: Pore-like structures on the body surface
  • Lack a pair of sensory papillae (phasmids) on the caudal end that is not identifiable in histologic section
  • Do not have lateral cords like the phasmids
  • Bioperculate (bipolar plugged), barrel-shaped, thick-shelled and unembryonated eggs (many genera)

·      Capillaria hepatica is primarily a disease of wild rodents but has been reported in many mammalian hosts, including the dog, cat, rabbit, vole, chipmunk, groundhog, squirrel, mole, shrew, opossum, weasel, fox, skunk, raccoon and porcupine

·      Only species of nematode that has the adult stage in the liver (not in the bile ducts)

·      Capillaria spp. are common nematodes in poultry, occurring in the crop and esophagus; thickening and inflammation of mucosa



·      Not highly pathogenic

·      Eggs and excreta deposited in the liver provoke granuloma formation and subsequent fibrosis.



·      Larvae ingested, hatch and migrate to liver > adults live in liver parenchyma and produce eggs > eggs develop only upon exposure to oxygen when host is eaten by predator or dies and decomposes > eggs pass in feces of predator > passed eggs embryonate in the external environment



·      Hepatomegaly with multiple to coalescing white or yellow patches and nodules under the capsule and/or througout the parenchyma



·      Multiple hepatic granulomas and fibrosis surrounding bioperculate eggs and/or adult nematodes

·      Features of this nematode:

  • Stichosome
  • Bacillary or hypodermal bands
  • Coelomyarian and polymyarian musculature (may be inapparent)



·      Demonstration of adults and eggs in histologic sections of liver

·      Indirect immunofluorescence



·      Gross: Hepatic coccidiosis (Eimeria stiedae)

·      Eggs: Schistosoma sp. eggs are also found in liver but have a prominent lateral spine and lack opercula



·      Eucoleus (Capillaria) aerophilus: Bronchial capillariasis; lungs of dogs, cats and foxes

·      Pearsonema (Capillaria) plica, C. feliscati: Urinary capillariasis; renal pelvis, ureter or urinary bladder of dogs, cats, foxes and wolves

·      Capillaria contorta, C. annulata: Epithelial mucosa of esophagus and crop of birds

·      Capillaria anati: Cecum of birds

·      Capillaria bursata, C. caudinflata: Small intestine of birds

·      Capillaria xenopodis (Pseudocapillaroides xenopi): Cutaneous capillariasis of South African clawed frogs



1.    Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. West Sussex, UK: John Wiley & Sons, Inc.; 2016:153, 301.

2.    Berentsen AR, Vogt S, Guzman AN, et al. Capillaria hepatica infection in black rats (Rattus rattus) on Diego Garcia, British Indian Ocean Territory. J Vet Diagn Invest. 2015;27(2):241-244.

3.    Brash ML, Charlton, BR, et al. Boulianne M ed. Avian Disease Manual. 7th ed. Jacksonville, FL: American Association of Avian Pathologists; 2013: 158-159.

4.    Breshears MA and Confer AW. The Urinary Sytem. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:680.

5.    Gardiner CH, Poynton SL. Aphasmids. In: Gardiner CH, Poynton SL, eds. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC: Armed Forces Institute of Pathology; 1999:40-43.

6.    Lopez A and Martinson SA. Respiratory, Mediastinum, and Pleurae. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:548.

7.    Uzal FA, Plattner BL, Hostetter JM. Alimentary 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.

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