JPC SYSTEMIC PATHOLOGY
Signalment (JPC 1851279): 10‑day‑old budgerigar (Melopsittacus undulatus)
HISTORY: This bird was from a flock with increased mortality in birds under 15 days of age.
HISTOPATHOLOGIC DESCRIPTION (Slide A): Feathered skin: Multifocally within the epidermis and feather follicle epithelium, individual and clusters of cells are swollen and contain abundant, microvacuolated, pale eosinophilic cytoplasm (vacuolar degeneration). Nuclei of these cells are enlarged and often contain variably shaped, up to 20 um diameter, indistinct, pale amphophilic or clear to glassy intranuclear viral inclusion bodies that marginate the chromatin. Diffusely there is moderate orthokeratotic hyperkeratosis.
MORPHOLOGIC DIAGNOSIS: Feathered skin, epidermal and follicular epithelium: Vacuolar degeneration, multifocal, moderate, with orthokeratotic hyperkeratosis, and amphophilic intranuclear viral inclusion bodies, budgerigar, avian.
ETIOLOGIC DIAGNOSIS: Polyomaviral dermatitis
HISTOPATHOLOGIC DESCRIPTION (Slide B): Kidney: Multifocally the interstitium is infiltrated by moderate numbers of mononuclear inflammatory cells and hemorrhage. Multifocally, scattered tubular epithelial cells are degenerate (characterized by swollen cells with vacuolated cytoplasm), or necrotic (characterized by shrunken cells with hypereosinophilic cytoplasm and pyknotic or karyorrhectic nuclei). Tubules occasionally contain sloughed cellular and karyorrhectic debris. Multifocally, tubular epithelial cells and glomerular cells are enlarged and contain round to oval, up to 20 um diameter, indistinct, pale eosinophilic to amphophilic to clear, glassy intranuclear viral inclusion bodies that marginate the chromatin.
MORPHOLOGIC DIAGNOSIS: Kidney: Nephritis, interstitial, mononuclear, multifocal, chronic, with tubular degeneration and necrosis, and tubular and glomerular intranuclear viral inclusion bodies, budgerigar, avian.
ETIOLOGIC DIAGNOSIS: Polyomaviral nephritis
ETIOLOGY: Avian polyomavirus (APV)
CONDITION: Budgerigar fledgling disease (BFD)
- Budgerigar fledgling disease virus (BFDV-1) is a non-enveloped, double stranded DNA virus in the family Polyomaviridae
- In general, polyomaviruses cause latent infections that become apparent following a stressful event
- APV is highly infectious and causes high mortality (highest in budgerigars less than 15 days old)
- May also infect non-psittacines such as finches
- Polyomaviruses appear antigenically and morphologically similar but show marked differences in clinical presentation, lesion distribution, and epidemiologic effects among susceptible species
- Transmission may occur by vertical and horizontal routes
- Virus replicates at the portal of entrance > viremia develops > virus distributed throughout the body
- Cell mediated immunity, not antibody, is necessary to clear viremia
- May destroy or inhibit development of normal lymphoid tissue
- Most susceptible psittacines include macaws, conures, eclectus, ring-necked parakeets, lovebirds, and budgerigars
- In some species, polyomaviruses are potentially oncogenic
- Large T-antigen is involved in initiation of viral replication and cellular transformation; cell transformation correlates with binding of large T-antigen to Rb
- Small T-antigen binds cellular transcription factors
- Middle T-antigen becomes associated with src proto-oncogene protein product of the plasma membrane, enhancing its tyrosine kinase activity
TYPICAL CLINICAL FINDINGS:
- Hatchlings may develop abdominal distention, subcutaneous hemorrhage, head and neck tremors, ataxia, reduced formation of down and contour feathers
- Hatchlings that survive infection often have dystrophic feathers (French moult)
- Widespread bleeding is often evident terminally
- Disease often occurs in outbreaks
- Commonly, clinical signs (depression, anorexia, weight loss, delayed crop emptying, regurgitation, dehydration, subcutaneous hemorrhages, dyspnea, polyuria) develop at weaning, and death follows in 12 to 48 hours
- Survivors are considered asymptomatic carriers; virus shedding from cloaca may continue for up to 4.5 months
- Feather abnormalities are less common in the larger psittacines
- Occurs in both hand-raised and parent-raised birds
- Disease in adult psittacines is rare and often associated with PBFD
TYPICAL GROSS FINDINGS:
- Excellent overall condition; full crops and gastrointestinal tracts, indicating acute death
- Often pallor and hemorrhages in multiple organs
- Hepatomegaly with multifocal necrosis (white pinpoint foci)
- Cardiomegaly and hydropericardium
- Congested and swollen kidneys
- Feather growth and formation abnormalities
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Karyomegaly with hydropic degenerative changes
- Intranuclear inclusion bodies that are large, glassy, clear to opaque to mildly basophilic and marginate chromatin
- Inclusions may be present in the spleen, liver, lung, kidney, heart, brain, skin, feather follicle, intestine, trachea, crop, bursa of Fabricius, and proventriculus
- Skin: Ballooning degeneration, karyomegaly in epithelium, follicular and epidermal hyperplasia, inclusions (epithelial cells)
- Kidney: Membranous glomerulopathy; inclusions (mesangial, endothelial and tubular epithelial cells); vacuolar degeneration
- Spleen: Lymphoid depletion, histiocytosis with inclusions, necrosis
- Liver: Necrosis, histiocytosis, inclusions (hepatocytes, Kupffer cells), hemorrhage, vacuolar degeneration
- Heart: Myocardial degeneration and necrosis, hemorrhage, inclusions (interstitial macrophages, myocytes)
- GI tract: Hemorrhage, necrosis, inclusions
- Brain: Inclusions most prominent in cerebellar neuronal and glial cells
- Larger psittacines frequently have massive hepatocellular necrosis with karyomegalic inclusions
- Virions are intranuclear, icosahedral, and 40 to 50 nm in diameter
- Arranged in paracrystalline arrays
ADDITIONAL DIAGNOSTIC TESTS:
- PCR – swab of cut surface of spleen, liver, and kidney best sample to submit
- Cloacal swab
- Immunohistochemistry with viral specific antibodies
- Causes of acute death in young birds include: Herpesvirus (Pacheco’s disease), chlamydiosis (Chlamydophila psittaci), salmonellosis or other bacterial septicemias
- Differential diagnoses for older birds with feather lesions: Psittacine beak and feather disease (PBFD, avian circovirus) and French moult with symmetrical loss of flight and tail feathers
- Herpesviruses and PBFD may produce amphophilic to basophilic intranuclear inclusions
- Avian adenoviruses may produce karyomegaly and intranuclear inclusions
- Herpes virus (Pacheco’s disease), chlamydiosis (Chlamydophila psittaci), salmonellosis or other bacterial septicemias also cause hepatic necrosis and splenomegaly similar to polyomavirus
- Polyomaviruses are of little or no significance in domestic species<l/i>
- Recent report of polyomavirus-associated nephritis in 2 horses
- Simian virus 40 (SV40): Polyomavirus of rhesus and cynomolgus monkeys; causes nephritis, pneumonia, and neurologic lesions in immunocompromised monkeys (e.g. infected with simian immunodeficiency virus)
- Murine polyomavirus: Multifocal necrosis and inflammation in nude mice followed by tumor formation in multiple tissues; multisystemic wasting disease with paralysis and demyelination also reported in nude mice
- K-Virus (murine pneumotropic virus or Kilham polyomavirus): Carried as a latent infection in mice; not primarily pneumotropic; when orally inoculated into neonatal mice, initially replicates in intestinal endothelium > disseminates hematogenously to other organs > replicates in vascular endothelium > 6-15 days post-inoculation > pulmonary vascular edema and hemorrhage > dyspnea > death
- Hamster polyomavirus: Causes transmissible lymphoma in young hamsters and keratinizing skin tumors of hair follicles (trichoepitheliomas); lymphomas do not have detectable infectious virus while trichoepitheliomas do have viral replication in keratinizing epithelium
- Rabbit kidney vacuolating virus: Intranuclear inclusions in renal tubular epithelium; no known pathogenic effect
- Lesions suggestive of polyomavirus have been seen in nonpsittacine birds
- Finches: Acute mortality; fledglings, young adults, and mature birds; poor feather development and long, tubular misshapen beaks
- Goose hemorrhagic polyomavirus: Causative agent of hemorrhagic nephritis enteritis of geese; fatal disease of European geese
- Recently a novel polyomavirus called raccoon polyomavirus was identified and may be associated with olfactory tumors in raccoons
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