JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1945809): Adult male Magellanic penguin
HISTORY: This penguin was found dead in its pen.
HISTOPATHOLOGIC DESCRIPTION: Slide F06a: Lung: Affecting nearly 100% of the lung are multifocal, randomly distributed, 0.5-1.0 mm granulomas that are characterized by a central core of lytic necrosis admixed with viable and degenerate heterophils, bounded by lymphocytes, macrophages, rare multi-nucleated macrophages (foreign body type), fibroblasts and sparse collagen. Throughout the granulomas are multiple fungal hyphae characterized by thin parallel walls which are 5-8 microns in diameter, acute angle dichotomous branching and distinct infrequent septations. Diffusely, the airway capillaries are infiltrated by increased numbers of macrophages, hemorrhage, fibrin and edema. The airway capillary septa are frequently discontinuous and replaced by eosinophilic cellular debris (septal necrosis), heterophils, lymphocytes and histiocytes. There is segmental to diffuse necrosis and loss of the walls and epithelium of the secondary mesobronchi and parabronchi by the granulomas and lumina are filled with an exudate of heterophils, rare multinucleated macrophages, fungal hyphae, hemorrhage, fibrin and edema. The tunica media and endothelium of blood vessels are infiltrated by the aforementioned inflammatory cells, necrotic debris (vasculitis), hemorrhage, fibrin and edema, which also expand the pleura up to 100 um in thickness (pleuritis).
MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, granulomatous and heterophilic, necrotizing, multifocal to coalescing, severe, with vasculitis and fungal hyphae, etiology consistent with Aspergillus sp., Magellanic penguin, avian.
Signalment (P-F06B; JPC #1785683): Pregnant 7-year old Morgan horse
HISTORY: This horse was euthanized due to extreme dyspnea.
HISTOPATHOLOGIC DESCRIPTION: Slide F06b: Lung: Affecting 70% of the lung are multifocal to coalescing, randomly distributed, up to 5 mm infarcts that are characterized by necrotic blood vessels and alveolar capillaries which contain high numbers of fungal hyphae and moderate numbers of neutrophils which infiltrate the endothelium and tunica media (vasculitis) admixed with lytic cellular debris, fibrin, hemorrhage, edema, variable numbers of degenerate and viable neturophils, macrophages, lymphocytes and plasma cells. Fungal hyphae extend into the adjacent alveoli and are characterized by thin parallel walls which are 5-8 microns in diameter, acute angle dichotomous branching and distinct infrequent septations and often admixed with numerous degenerate neutrophils, macrophages and lymphocytes. Within the affected areas of the lung, bronchi and bronchioles are infiltrated by fewer aforementioned inflammatory cells. The less affected alveolar septa are expanded by congestion and few alveolar macrophages and lymphocytes.
MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, necrotizing and embolic, subacute, multifocal to coalescing, severe, with infarction, vasculitis and fungal hyphae, etiology consistent with Aspergillus sp., Morgan, equine.
ETIOLOGIC DIAGNOSIS: Pulmonary aspergillosis
CAUSE: Aspergillus sp.
SYNONYMS: Brooder pneumonia; mycotic pneumonia; pneumomycosis
- Aspergillus species are saprophytic molds common in air, soil and animal feed; they are mucosal commensals that are normally not invasive but can cause serious infections in debilitated, neutropenic animals and those on prolonged antibiotic therapy
- fumigatus, A. flavus, A. niger, A. nidulans and A. terreus most commonly infect mammals and birds
- In contrast to mammals, birds, especially those from colder climates, are particularly susceptible to invasive aspergillosis
- Pneumonia (+/- dissemination), superficial infections of the skin and cornea occur in most mammalian species (typically sporadic)
- Primary routes of infection are through inhalation of spores or entry through the gastrointestinal tract
- Hematogenous spread is common because Aspergillus invades blood vessels and forms mycelial emboli
- Pulmonary aspergillosis in horses represents hematogenous spread of fungal hyphae resulting from colitis, as a consequence of both neutropenia and disruption of the mucosal barrier
- Toxins and virulence factors:
- Inhibition of ciliary movement by gliotoxin, fumagillin and helvolic acid
- Oxalic acid especially in nidulans reacts with blood and tissue calcium to precipitate calcium oxalate, heparin-like factors, proteases, elastase, endotoxins, and mycotoxins (aflatoxin)
- Aflatoxin, a hepatotoxin, is typically produced in feed or crops by flavus and A. parasiticus
- fumigatus produces molecules that block the killing mechanisms in neutrophils and macrophages including β-glucan, melanin and others that block reactive oxygen species and phagolysomal acidification
- Host defense: Cell mediated immunity (CMI) is the main mechanism of defense against infection, but certain types of antibody responses can also protect
- Th1-type CMI à IFN-γ à promotion of phagocyte activation à clearance of an infection
- Th2-type CMI à production of IL-3 and IL-4 à promotion of antibody production à usually results in susceptibility to infection or allergic response
- Neutrophils are the primary effector cells in preventing infection
- fumigatus evades the host immune response by germination into hyphae with subsequent loss of TLR-4 recognition, whereas the TLR-2 mediated IL-10 pathway remains intact, thus shifting towards a permissive Th2-type response
- In canine sino-nasal aspergillosis (SNA), expression of TLRs 1-4, 6-10 and NOD2 is increased compared to control tissues; TLRs 1, 4, 6-10 and NOD2 are increased compared to idiopathic lymphoplasmacytic rhinitis (LPR)
- Primary routes of infection are through inhalation of spores or entry through the gastrointestinal tract
TYPICAL CLINICAL FINDINGS:
- Serosanguineous to mucopurulent nasal discharge
- Lethargy and dyspnea
- Neurologic signs in CNS infection
- Epistaxis (horses with guttural pouch mycosis)
- Corneal ulceration and opacity (mycotic keratitis, especially in chickens and horses)
- Skin lesions
TYPICAL GROSS FINDINGS:
- Lungs or other affected organs: Solitary or disseminated gray to yellow, discrete, irregular nodules often surrounded by a rim of hyperemia and hemorrhage
- Caseous plaques in air sacs are common in mycotic air sacculitis
- Compact mycelial mass (“aspergilloma” or “fungal ball”) may form in respiratory tract cavities
- Cotton-like superficial plaques produced by conidiophores (bread-mold appearance) may be present on air-exposed sites (especially in birds)
- Guttural pouch mycosis: Usually unilateral; mucosal surfaces first covered by raised plaque of fibrinonecrotic exudate that over time may be confluent and grow into a large confluent mass; may result in invasion of vital structures including the internal carotid artery leading to recurrent epistaxis or mycotic embolic causing cerebral infarcts; glossopharyngeal nerve leading to dysphagia; cranial cervical ganglion and sympathetic fibers leading to Horner’s syndrome; or laryngeal nerves leading to laryngeal hemiplagia
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Hyphae are 3-6 um in width, regularly septate, parallel walled, with dichotomous, progressive, acute angle branching
- In chronic lesions, the hyphae may form short globose and distorted hyphae up to 12 um wide
- Vascular invasion of fungal hyphae results in vasculitis, thrombosis and infarction
- Generally the inflammatory reaction is mixed purulent and necrotizing, but may form classic granulomas
- Granulomatous lesions and abscesses may occur in many organs
- Conidiophores (fruiting bodies) form only on surfaces with high-oxygen tension such as the lung or sinus cavities and are characterized by a central flask-shaped, hemispherical or globose vesicle with one or two rows of peg-like sterigmata which form unbranched chains of conidia on the distal end
- Local depositions of birefringent calcium oxalate crystals may be present
- Organisms may be surrounded by intensely eosinophilic, radiating clubs (Splendore-Hoeppli material) that are composed of antigen-antibody complexes
- Guttural pouch mycosis: Necrotic inflammation of the mucosa and submucosa with widespread vasculitis and fungal hyphae
ADDITIONAL DIAGNOSTIC TESTS:
- Culture is required for species identification
- Special stains: Gomori-Methenamine Silver (GMS), Periodic Acid-Schiff (PAS) or Gridley
- PCR: On fresh or paraffin embedded tissue
- Immunoassays: Immunohistochemistry, ELISA, AGID
- Zygomycetes: Broader hyphae (up to 15 um), infrequently septate, non-parallel walls which are often collapsed and twisted, orthogonal right angle branching, well stained by H&E
- Fusarium: Septate but with characteristic right angle, irregularly branching (+/- acute angle branching) and constrictions at branch points
- Pseudoallescheria boydii (scedosporium): More narrow hyphae, usually branch haphazardly rather than progressively and at less acute angles
- Mortierella in bovine abortions
- Beauvaria bassiana in reptiles
- Candida form pseudohyphae and budding yeast cells in addition to hyphae
- Ochroconis gallopavum (formerly Dactylaria gallopava) for lesions in lung and/or brain of chicks and poults; a dematiaceous fungi (hyphal pigment is characteristic)
- Mycoplasma gallisepticum: For avian pulmonary granulomas
- Other bacteria that typically cause granulomatous lesions: Actinomyces , Mycobacteria sp., Nocardia sp.
- For Splendore-Hoeppli material: Staphylococcus aureus, Actinomyces, Nocardia sp., Sporothrix sp., Zygomycetes, Coccidioides sp., Blastomyces sp., Candida sp.
- For guttural pouch infection: Streptococcus equi (more suppurative inflammation)
- Mycotic arthritis
- Forestomachs, especially the omasum, are mostly affected, from which the infection spreads to other organs resulting in mycotic placentitis, mastitis and abortion
- Dermatitis in aborted calves
- Nasal sinus infection (more common in young, dolichocephalic dogs)
- terreus and A. deflectus are the most commonly reported isolates of systemic aspergillosis, and typically involves young to middle-aged female German shepherd dogs
- 33% of normal and diseased canine ears contain saprophytic fungi and Aspergillus was the second most common (behind Penicillium sp.) genus of saprophytic fungus cultured; Aspergillus sp. can cause otomycosis in ear canals compromised by pre-existing allergic or bacterial otitis and previous antibiotic therapy
- Rare, more likely to be disseminated with pulmonary or intestinal lesions as primary sites
- Often associated with panleukopenia
- Nasal and cutaneous nodules
- Marine mammals:
- Pulmonary form with miliary spread to abdominal organs
- Associated with morbillivirus infection
- Sporadic pulmonary, systemic, dermal and ocular aspergillosis
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