JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
September 2018
D-P05

Signalment (JPC #3166610):  Young male turkey (Meleagris gallopavo).

HISTORY:  Found dead.

HISTOPATHOLOGIC DESCRIPTION:  Liver:  Approximately 70% of the section is effaced by a single, large focus of lytic necrosis, characterized by abundant eosinophilic cellular and karyorrhectic debris, hemorrhage, and fibrin admixed with numerous macrophages that are often hemosiderin-laden, lymphocytes, scattered foreign body type multinucleated giant macrophages, and heterophils.  Multifocally within these areas of necrosis there are numerous extracellular and intrahistiocytic, 10-20 um diameter, irregularly round, lightly eosinophilic, protozoal trophozoites (histomonads) that occasionally contain single, central, 3-5 um diameter basophilic nuclei. Trophozoites are often surrounded by a 3-5um clear zone.  Bile ducts are multifocally ectatic and contain luminal debris and low numbers of heterophils and macrophages, and often exhibit piling up of epithelial cells (bile duct hyperplasia).  Hyperplastic bile duct epithelia occasionally contain previously described trophozoites.  Adjacent less affected hepatic parenchyma is characterized by swollen hepatocytes with microvacuolated cytoplasm (degeneration), and there are increased numbers of small bile duct profiles (bile ductular reaction) and increased numbers of macrophages.  There are low numbers of periportal lymphocytes, plasma cells, and macrophages.

Cecum:  Affecting 95% of the section, there is diffuse, transmural, lytic necrosis and granulomatous inflammation characterized by loss of normal, well-defined intestinal layers and replacement by large numbers of macrophages, lymphocytes, fewer plasma cells and heterophils, admixed with eosinophilic and karyorrhectic debris, fibrin, edema and mild hemorrhage.  Transmurally there are numerous previously described protozoal trophozoites, often found within vacuoles or within macrophages.  The overlying mucosa is diffusely effaced to the level of the muscularis mucosa aside from one small focus of remaining crypts, which are are either hyperplastic, characterized by cells piling up to 2-3 layers deep with increased mitoses, or dilated and filled with necrotic cellular debris, fibrin, degenerate protozoal trophozoites, macrophages, and heterophils (crypt abscess).  The inflammatory infiltrate surrounds and separates often necrotic or degenerate myofibers of the tunica muscularis. 

MORPHOLOGIC DIAGNOSIS

  1. Liver: Hepatitis, necrotizing and granulomatous, random, multifocal to coalescing, marked, with numerous intrahistiocytic and extracellular protozoal trophozoites, turkey, avian.
  2. Cecum: Typhlitis, fibrinonecrotic, lymphohistiocytic, and heterophilic, diffuse, transmural, marked, with numerous intrahistiocytic and extracellular protozoal trophozoites.

ETIOLOGIC DIAGNOSIS:  Hepatic histomoniasis

CAUSEHistomonas meleagridis

CONDITION:  Histomoniasis

SYNONYMS:  Blackhead, infectious enterohepatitis, typhlohepatitis

GENERAL DISCUSSION:

LIFE CYCLE:

 

PATHOGENESIS:

TYPICAL CLINICAL FINDINGS:

TYPICAL GROSS FINDINGS:

TYPICAL LIGHT MICROSCOPIC FINDINGS:

ADDITIONAL DIAGNOSTICS TESTS:

DIFFERENTIAL DIAGNOSIS:  

Necrotic cecal cores:

Other histomonads of the cecum:

COMPARATIVE PATHOLOGY:

REFERENCES:

  1. Clarke LL, Beckstead RB, Hayes JR, Rissi DR. Pathologic and molecular characterization of histomoniasis in peafowl (Pavo cristatus).  Vet. Diagn. Invest.  2017;29(2):237-241.
  2. Crespo R, Franca MS, Fenton H, Shivaprasad HL. Galliformes and columbiformes.  In:  Terio KA, McAloose D, St. Leger J.  Pathology of Wildlife and Zoo Animals.  London, England: Elsevier; 2018:759-761.
  3. Fitz-Coy SH. Parasitic diseases.  In: Boulianne M., ed. Avian Disease Manual. 7th Jacksonville, FL: American Association of Avian Pathologists; 2013:158, 161, 168-169, 175, 178.
  4. Smith DA. Palaeognathae: apterygiformes, casuariiformes, rheiformes, struthioniformes; tinamiformes.  In:  Terio KA, McAloose D, St. Leger J.  Pathology of Wildlife and Zoo Animals.  London, England: Elsevier; 2018:645.


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