JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

November 2022

I-V04

 

Signalment (JPC# 2788810):  Cockatoo (Cacatua spp.)

 

HISTORY:  This bird lost its feathers and had malformed feathers.

 

HISTOPATHOLOGIC DESCRIPTION: Feathered skin: There are multifocal areas of necrosis, inflammation, and dysplasia of feathers. The affected outer and inner follicular epithelium is often either replaced by eosinophilic cellular and karyorrhectic debris (lytic necrosis) or is disorganized with individual cells characterized by abundant intracellular edema (hydropic degeneration), occasional karyorrhexis, and frequent intracytoplasmic and fewer intranuclear viral inclusions. Intracytoplasmic viral inclusions are botryoid, deeply basophilic, and 3-6µm diameter. Intranuclear viral inclusions are amphophilic, glassy, ovoid, 3-6µm diameter, and peripheralize the chromatin. The feather pulp is infiltrated by abundant heterophils, lymphocytes, plasma cells, and macrophages, and is expanded by congestion and edema. Occasional macrophages within the pulp contain intracytoplasmic botryoid viral inclusions as previously described. Feather follicle keratin is folded and irregular (dysplasia). There are nodules of dermal inflammation occasionally centered on keratin composed of aggregates of macrophages and fewer plasma cells, heterophils, lymphocytes, and multinucleate giant cells surrounded by mild fibrosis.

 

MORPHOLOGIC DIAGNOSIS: Feathered skin, feather follicle: Epithelial degeneration and necrosis, chronic, moderate, with feather follicle dysplasia, heterophilic and granulomatous pulpitis and mural folliculitis, granulomatous dermatitis, and basophilic botryoid intracytoplasmic and glassy intranuclear viral inclusion bodies, cockatoo (Cacatua spp.), avian.

 

ETIOLOGIC DIAGNOSIS:  Circoviral feather epidermitis

 

CAUSE:  Psittacine beak and feather disease virus (PBFDV), Psittacine circovirus (PsCV)

 

CONDITION:  Psittacine beak and feather disease (PBFD)

 

CONDITION SYNONYMS: French moult (budgerigars), black spot (canaries), runting syndrome (geese)

 

GENERAL DISCUSSION: 

• Circoviridae, 14- to 16-nm, nonenveloped virion
• Predominantly seen in parrots of Africa and Australasian parrots less than three years old; all psittacine species are susceptible; spread due to parrot trade; enzootic in Australian parrots
• Most commonly seen in cockatoos, lovebirds, budgerigars, lories, lorikeets, and eclectus and African grey parrots

 

PATHOGENESIS: 

• Replication occurs in portals of entry: bursa of Fabricius and gastrointestinal tract lymph tissue; secondarily in the liver, thymus, and other tissue
• Viral proliferation occurs also in the germinal basal epithelial cells in feather follicles and the rhamphotheca → feather and beak deformities 
• PBFDV is shed in feces, crop secretions, and feather dust; 21-25 day incubation up to several years
• Thymus and bursal necrosis may result in immunosuppression
• Liver lesions generally only present in young birds with systemic disease, can be seen in older birds with severe feather damage

 

TYPICAL CLINICAL FINDINGS: 

• Discoloration of feathers may be the initial clinical finding; African grey parrots may develop red feathers; other parrots may have yellow feathers that replace green
• Clinical presentations 
  1. Peracute to acute: Nestling cockatoos, lorikeets, and uncommonly in other parrot species; all growing feathers affected simultaneously; generalized signs of disease; death in days to weeks; profound lymphoid depletion 
     • Nestling budgerigars: generalized feather dystrophy; similar to nestling cockatoos, but may not be fatal
  2. Chronic form: 8 months to 3 years old or when birds undergo first molt; insidious onset and progression; dystrophic feathers replace normal ones after molting; feathers have thickened sheathes, hemorrhage in shafts, and pinched off bases; wild and wild caught cockatoos, lovebirds, lorikeets, neophemas, African grey parrots, other Australasian parrots, rarely New World parrots 
• Breed specific presentations
  1. White cockatoo: progressive, generalized feather dystrophy, delayed molt, beak elongation and fracture; powder down feathers may be first affected → clean shiny beak
  2. Lovebirds and eclectus parrots: 
     • Peracute to acute: pneumonia, enteritis, feather deformities, and death
     • Chronic: progressive feather degeneration and occasional beak deformities
     • May only show dull plumage with increased broken or worn feathers; advanced cases may have feather dysplasia or new feathers may not develop → unfeathered areas of bird; some will have no signs of disease
  3. African grey parrots
     • Peracute (most common): acute onset of non-specific clinical signs, severe leukopenia and anemia (infected bone marrow cells → pancytopenia), and hepatic coagulation-necrosis
     • Spleen and bursa have nearly complete lymphodepletion
     • Significant immunosuppression → secondary bacterial infection → sepsis, pneumonia, enteritis, and death
       • Fungal pneumonia and hepatic necrosis are common comorbidities 
     • Progressive beak and feather lesions are uncommon and if seen they are often confined to tail feathers
  4. North American lories and lorikeets: do not show signs of disease; some will show characteristic feather lesions
     • Australian wild rainbow lorikeet fledglings: missing tail feathers; present to wildlife rehabilitators; 1/3 develop normal feathers and 2/3 die or have persistent feather dysplasia
• Acute lesions in the periorbital skin (differentiate from poxvirus lesions)

 

TYPICAL GROSS FINDINGS:

• Necrosis and shedding of affected feathers; feathers are stunted or clubbed +/- thickened, hyperkeratotic sheaths, pulp hemorrhage, annular constrictions of the calamus, curling, or stress lines on the vanes; apex may be necrotic
• Beak deformities (most common in the cockatoo): Elongation, fractures, delaminations, palatine necrosis
• African grey parrot: red zonal discoloration of the contour feathers indicates a bird that survived earlier Psittacine circovirus infections; liver lesions, splenomegaly, and mycotic pneumonia are common
• Splenic, thymic, and bursa of Fabricius atrophy; bursal hemorrhage 
• Pale, yellowish bone marrow
• Liver: usually only a few scattered discolored foci; young psittacine birds with secondary bacterial infections may have markedly enlarged and mottled livers; liver may be enlarged and pale orange with necrotic foci; 

 

TYPICAL LIGHT MICROSCOPIC FINDINGS: 

• Basophilic, 3-6µm, botryoid intracytoplasmic and rarely intranuclear inclusion bodies within sections of feather follicular epithelium, feather pulp, dermal and epidermal macrophages, and lymphocytes; intracytoplasmic inclusions in macrophages form clumps of globular basophilic to magenta pigment; eosinophilic intranuclear inclusions are characteristic of epithelial cells (uncommon)
• Necrosis of the basal and intermediate cells of the feather follicle epidermis; more extensive lesions involve cleft formation and separation of the epidermis from the pulp
• Mild to severe feather pulp inflammation: heterophils (especially with self trauma), macrophages, lymphocytes, plasma cells and less frequently multinucleated giant cells +/- hemorrhage
• Follicular epidermal hyperplasia, hyperkeratosis, and degeneration of germinal cells; ballooning and degeneration of epidermal collar; feather shaft is constricted (secondary to necrosis of epidermal collar); macrophage infiltrate +/- inclusions; chronic cases may have small granulomas with keratin fragments and giant cells
• Multifocal to confluent lymphoplasmacytic inflammatory infiltrate
• Bursa of Fabricius: extensive lymphocytolysis; proteinaceous fluid and cell debris may accumulate in medullary cysts; follicular associated epithelium is prominent; necrosis/lymphoid depletion of the thymus and bursa
• Liver: multifocal necrosis and congestion; infrequent inclusion bodies in Kupffer cells; peri-portal lymphoplasmacytic inflammatory infiltrate; coagulative necrosis (classic in fledgling African grey parrots); secondary bacterial infection in immunosuppressed birds

 

ULTRASTRUCTURE: 

 

ADDITIONAL DIAGNOSTIC TESTS: 

• Histopathology 
• PCR - viral DNA
• Immunoperoxidase staining 

 

DIFFERENTIAL DIAGNOSIS: 

• Gross:
  • Avian polyomavirus (I-V03) – Identical signs in nestling budgerigars that can only be differentiated histologically or with PCR; feather dystrophy, petechial and ecchymotic hemorrhages, myocardial and intestinal hemorrhage, hepatomegaly, splenomegaly, ascites;
  • Nutritional deficiency
  • Endocrinopathy
  • Drug reaction
  • Self-induced trauma (feather picking) – will have normal feathers on the head
• Microscopic:
  • Avian polyomavirus (I-V03) – amphophilic (glassy) intranuclear inclusion bodies of the follicular epithelium, myocardium, liver, spleen, GI tract, kidney

 

COMPARATIVE PATHOLOGY: 

Other Avian circoviruses of veterinary importance:

• Pigeon circovirus: 
  • Common in pigeons in the US, Europe, Australia, China, Japan, and South Africa
  • Causes disease primarily in young pigeons (<4 mo) – young pigeon disease syndrome
  • Immunosuppresion due to apoptosis of lymphocytes in the bursa; lymphoid necrosis in bursa; lymphoid depletion in spleen, cecal tonsils, and bone marrow; basophilic botryoid intranuclear and intracytoplasmic inclusions in macrophages and epithelial cells of bursa
• Chicken infectious anemia virus (gyrovirus, formerly classified as circovirus): 
  1. Young chickens (0-4 weeks), thymic and bone marrow atrophy, panmyelophthisis; eosinophilic intranuclear inclusions in thymus and bone marrow; hemorrhage – proventriculus mucosa, subcutis, muscle

• Circovirus-like infections: Gulls; bursal lesions, bursal and splenic lymphoid depletion 
•  

REFERENCES: 

1. Crespo R, Franca MS, et. Al. Galliformes and Columbiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press; 2018: 752, 754, 764.
2. Fenton H, McManamon R, Howerth EW. Anseriformes, Ciconiiformes, Charadriiformes, and Gruiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press; 2018: 709.
3. Sellers H, Ojkic D.  Viral diseases.  In: Boulianne M, et al., eds. Avian Disease Manual. 8^th ed. Jacksonville, FL: The American Association of Avian Pathologists; 2019:40-41.
4. Reavill DR, Dorrestein G. Psittacines, Coliiformes, Musophagiformes, Cuculiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press; 2018: 785-7, 795.e6-14.
5. Schmidt RE, Reavill DR, Phalen DN. Integument. Pathology of Pet and Aviary Birds. Ames, IA: John Wiley and Sons, Inc.; 2015:248-250.
6. Schmidt RE, Reavill DR, Phalen DN. Liver. Pathology of Pet and Aviary Birds. Ames, IA: John Wiley and Sons, Inc.; 2015:102-104. 
7. Schmidt RE, Reavill DR, Phalen DN. Lymphatic and Hematopoietic System. Pathology of Pet and Aviary Birds. Ames, IA: John Wiley and Sons, Inc.; 2015:178-179. 

 

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