JPC SYSTEMIC PATHOLOGY
Signalment (JPC 1491335): 2-week-old broiler chick
HISTORY: This is one of fifteen 2-week-old broiler chicks with a history that the birds were "getting down on their sides." These chicks were from a flock of 65,000 and 205 chicks with similar signs had died. Gross lesions were seen in the brain and consisted of yellowish necrotic areas involving either the right or left cerebral hemisphere and occasionally the corresponding optic lobes. No other lesions were found.
HISTOPATHOLOGIC DESCRIPTION (Slide A): Cerebrum: Within the gray matter, there are multifocal to coalescing areas of granulomatous inflammation that have a dense core of brightly eosinophilic homogenous material admixed with basophilic karyorrhectic debris (necrosis) surrounded by a rim of epithelioid macrophages, fewer heterophils and scattered multinucleated giant cells (foreign body and Langhans type). Rarely, multinucleate giant cells contain ill-defined, negatively staining phagocytized, thin walled fungal hyphae. The adjacent neuropil has increased clear space (spongiosis) with increased numbers of glial cells (gliosis). Multifocally, Virchow-Robin space is expanded by moderate numbers of lymphocytes and macrophages and the vascular endothelium is mildly hypertrophied (reactive).
Slide B: GMS: Multifocal granulomas contain rare fragments of slender, 2 µm wide, thin-walled, septate, hyphae with irregular, non-dichotomous branching and nonparallel walls.
MORPHOLOGIC DIAGNOSIS: Cerebrum: Encephalitis, granulomatous, multifocal to coalescing, moderate, with rare dematiaceous fungal hyphae, chicken, breed not specified, avian.
ETIOLOGIC DIAGNOSIS: Cerebral ochroconiasis
CONDITION: Dactylariosis; epizootic encephalitis; mycotic encephalitis
· Weakly dematiaceous, thermophilic fungus that can cause epizootic encephalitis in young chickens and turkeys
· Occurrence has been associated with contaminated litter and egg incubators
· Two forms of phaeohyphomycosis are generally described
o Subcutaneous infection following trauma
o Systemic or disseminated infection via inhalation
· Cell mediated immunity is important in preventing infection; immunosuppression is an uncommon finding in affected animals
· Respiratory infection followed by the hematogenous spread of the neurotropic fungus to the central nervous system
TYPICAL CLINICAL FINDINGS:
· Torticollis, paresis, incoordination, muscle tremors
· Respiratory and ocular infections may cause dyspnea and blindness
TYPICAL GROSS FINDINGS:
· Well delineated meningeal or encephalitic necrosis with hemorrhage, primarily in the cerebellum and caudal cerebral cortex
· Tan nodules adjacent to airways within the lungs
TYPICAL LIGHT MICROSCOPIC FINDINGS:
· Necrotizing to granulomatous meningoencephalitis with many heterophils, macrophages and multinucleated giant cells
· Septate, irregularly branched, 1.4 - 2.4 µm in diameter, yellow to pale brown pigmented (dematiaceous) hyphae
· Fungal elements are frequently located within multinucleated giant cells
· Congestion, hemorrhage and thrombosis
· Pulmonary: Multifocal granulomas containing pigmented hyphae
ADDITIONAL DIAGNOSTIC TESTS:
· Fontana Masson for melanin pigment in fungal cell walls
· Culture required for a definitive diagnosis
o O. gallopavum is pigmented often with more malacia, hemorrhage and giant cells
· Nutritional encephalomalacia (vitamin E deficiency): Cerebellar necrosis, hemorrhage and edema due to capillary thrombosis
· Enterococcal encephalitis caused by Enterococcus hirae
· Cerebral and pulmonary ochroconiasis (Ochroconis gallopavum) has been reported sporadically in birds, fish, dogs and cats
· In domestic animals, central nervous system phaeohyphomycosis infections are most commonly caused by Cladosporium spp
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