JPC SYSTEMIC PATHOLOGY
Signalment (JPC #2070431): Chicken, breed and age unspecified
HISTORY: This bird had multiple raised proliferative lesions over its body.
HISTOPATHOLOGIC DESCRIPTION: Feathered skin: Multifocally, the epidermal and follicular epithelium is disrupted and thickened up to ten times normal thickness by extensive areas of hyperplasia with long rete ridges and thick bands of an eosinophilic coagulum that attaches to or replaces the epithelium. Multifocally there are large areas of coagulative necrosis within the epidermis that extend into the dermis and are characterized by loss of differential staining, karryorhectic and cellular debris, with retention of tissue architecture with many degenerate heterophils and bacterial colonies. There is marked thickening of the stratum spinosum with markedly swollen keratinocytes (ballooning degeneration) containing a 15-30 um eosinophilic intracytoplasmic viral inclusion body (Bollinger body). Within the areas of necrosis and infiltrating into the dermis and subcutis are numerous viable and degenerate heterophils with macrophages, lymphocytes, and plasma cells admixed with abundant fibrin, hemorrhage, and edema. Similar inflammatory cells infiltrate into and surround portions of the panniculus carnosus where the muscle fibers are multifocally necrotic with brightly eosinophilic shrunken cytoplasm with pyknotic nuclei.
MORPHOLOGIC DIAGNOSIS: Feathered skin and subcutis: Dermatitis, necrotizing and proliferative, subacute, multifocal, marked, with ballooning degeneration, and eosinophilic intracytoplasmic viral inclusion bodies, breed unspecified, chicken.
ETIOLOGICAL DIAGNOSIS: Avipoxviral dermatitis
CAUSE: Avian poxvirus
CONDITION: Fowl pox
- Common, slow spreading viral disease of domestic, pet and wild birds; reported in 232 species
- Genus Avipoxvirus; family Poxviridae
- Largest animal virus (300-400 nm); double stranded brick-shaped DNA virus
- Cytoplasmic DNA synthesis and packaging within infectious virus particle are characteristic of pox virus
- Transmission via inoculation from direct contact with injured skin, through mechanical transfer (including cannibalism and artificial insemination), mosquitoes, blood-sucking arthropods, and inhalation of aerosolized feathers and scabs containing virus
- Two forms (can manifest as one or both):
- Cutaneous form (dry pox): Most common form
- Diphtheritic form (wet pox): Lesions in respiratory, GI, nasal cavity and conjunctiva
- Virus enters host cells by fusion with plasma membrane and endosomal uptake
- Poxviruses encode several proteins that affect host cell: e.g. vaccinia virus growth factor (VGF) uses cell receptors for epidermal growth factor (EGF) to stimulate proliferation of keratinocytes
- Increasing metabolism of keratinocytes surrounding infection causes greater susceptibility of those cells
- Other proteins inhibit complement –mediated cell lysis and inhibit inflammatory response to retard immune clearance and analogues of tumor necrosis factor and superoxide dismutase
TYPICAL CLINICAL FINDINGS:
- Gradual onset that may go undetected until cutaneous lesions are numerous
- Turkey infection is generally more chronic that chickens
- Canaries can have systemic infection with high mortality
- Mild reduction in weight gain
- Decreased egg production
- Lack of flock vigor
- Mortality is low
- Lesions in upper respiratory tract or GI tract may lead to dyspnea or inappetence
- Lesions in nasal cavity or conjunctiva lead to nasal or ocular discharge
- Mortality due to suffocation, starvation, and dehydration
TYPICAL GROSS FINDINGS:
- Papular lesions on unfeathered skin of the head, neck, vent, legs and feet
- Papules, vesicles, pustules, crusts which progress to terminal reddish-brown to black scabs; may appear as horny growths
- Pigmented skin will usually be discolored after infection due to epidermal damage
- Raised, buff to yellow plaques on mucous membranes; predominate in mouth but also in sinuses, nasal cavity, conjunctiva, pharynx, larynx, trachea, esophagus
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Eosinophilic intracytoplasmic inclusion bodies (Bollinger bodies) located within epithelial cells - pathognomonic
- Epithelial hyperplasia with ballooning (hydropic) degeneration
- Elementary bodies (Borrel bodies) measure 250 x 354nm and are located within the inclusion bodies (Bollinger bodies)
- Virus is brick shaped and consists of a electron-dense biconcave core with two lateral bodies within each concavity
ADDITIONAL DIAGNOSTIC TESTS:
- Skin scraping can demonstrate squamous epithelium with ballooning degeneration and Bollinger body
- Virus Isolation
- Trichophyton megninii and T. simii: Dermatophytic fungus
- Knemidokoptes gallinae: Mite in basal shafts of feathers
- Knemidokoptes mutans: Mite that lives within unfeathered skin
- Vitamin A deficiency: Pustules on the mucosa of the mouth, pharynx, esophagus and crop in young birds, inflamed eyelids; squamous metaplasia of the nasal mucosa; keratinization of intestinal enterocytes, decreased goblet cells and blunting of villi (severe deficiency)
- Infectious laryngotracheitis: Alphaherpesvirinae (Gallid herpesvirus 1); mucohemorrhagic or caseous exudates of the trachea; intranuclear inclusion bodies in epithelial cells
- Trichomonas gallinae: Raised, caseous lesions in the mouth, pharynx, esophagus, and crop
- Capillaria annulata or contorta: Thickened, inflamed to sloughed mucosa
- Candida albicans: White-grey pseudomembranous patches on the mouth, pharynx, esophagus and crop; pseudohyphae and budding yeast
- Aspergillosis: Yellow-grey nodules in trachea, lungs and airsacs
- Avipoxvirus recognized in several domestic and wildlife avian species with similar lesions (e.g. turkeypox virus, falconpox virus, psittacinepox virus)
- Some avipoxviruses may have oncogenic properties; Passeriformes and Columbiformes may be predisposed to tumor formation after surviving infection
- Canarypox usually has a desquamative pneumonia
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