JPC SYSTEMIC PATHOLOGY

NERVOUS SYSTEM

January 2023

N-F03 (NP)

 

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 phagocytized, ill-defined, negatively staining, thin-walled fungal hyphae. The adjacent neuropil has increased clear space (edema, rarefaction) and vacuolation (spongiosis) with increased numbers of glial cells (gliosis). Multifocally, Virchow-Robin space is often expanded by moderate numbers of lymphocytes and macrophages, and the vascular endothelium is often mildly hypertrophied (reactive). 

 

Slide B: GMS: Multifocal granulomas contain rare fragments of slender, 2 µm wide, thin-walled, septate, fungal hyphae that display irregular, non-dichotomous branching and have nonparallel walls.

 

MORPHOLOGIC DIAGNOSIS: Cerebrum: Encephalitis, granulomatous, multifocal to coalescing, moderate, with rare dematiaceous fungal hyphae, chicken, breed not specified, avian.

 

ETIOLOGIC DIAGNOSIS: Cerebral ochroconosis

 

CAUSE: Ochroconis gallopavum (formarly Dactylaria gallopava)

 

CONDITION: Dactylariosis; epizootic encephalitis; mycotic encephalitis

 

GENERAL DISCUSSION: 

• Weakly dematiaceous, neurotrophic, thermophilic fungus that can cause epizootic encephalitis in young chickens and turkey poults and quail
• Occurrence has been associated with contaminated litter and egg incubators; common sources include saw dust, soil, and decaying plant material 
• Two forms of phaeohyphomycosis are generally described:

• Subcutaneous infection following trauma
• Systemic or disseminated infection via inhalation

• Cell mediated immunity is important in preventing infection; immunosuppression is an uncommon finding in affected animals

 

PATHOGENESIS:

 

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 
• Pulmonary granulomas, often adjacent to airways

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Necrotizing to granulomatous meningoencephalitis with many heterophils, macrophages, and multinucleated giant cells
• Septate, irregularly branched, 1 - 2 µm diameter, yellow to red 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

 

DIFFERENTIAL DIAGNOSIS:

• Other fungal encephalitidies:  Aspergillus spp., Mucor spp.: Granulomatous to necrotizing meningoencephalitis 
• O. gallopavum is pigmented, often with increased malacia, hemorrhage, and giant cells
• Nutritional encephalomalacia (vitamin E deficiency; N-M22):   Cerebellar necrosis, hemorrhage and edema due to capillary thrombosis
• Enterococcal encephalitis caused by Enterococcus hirae (N-B10)

 

COMPARATIVE PATHOLOGY:

 

REFERENCES:

1. Abdul-Aziz T, et al. Avian Histopathology. 4^th ed. Jacksonville, FL: American Association of Avian Pathologists; 2016: 198, 478, 515, 516, 523.
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; 2018:765.
3. Dykstra MJ, et al. Fungal diseases. In: Swayne DE, et al. eds. Diseases of Poultry. 13th ed. Ames, IA: Wiley-Blackwell; 2013: 1091-1092.
4. Noga EJ. Fish Disease: Diagnosis and Treatment. 2^nd ed. Ames, IA: Wiley-Blackwell; 2010: 254, 256.
5. Shivaprasad HL. Fungal diseases. In: Boulianne M., ed. Avian Disease Manual. 7^th ed. Jacksonville, FL: American Association of Avian Pathologists; 2013:145, 246,257.

 

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