JPC SYSTEMIC PATHOLOGY
Signalment (JPC# 1597220): Young alligator.
HISTORY: This alligator died unexpectedly. At necropsy, a necrotic skin lesion was
present in the flank area in the region where the skin of the leg meets the abdominal
HISTOPATHOLOGIC DESCRIPTION: Scaled skin: There is a focally extensive area
of epithelial ulceration with replacement by abundant eosinophilic cellular and
karyorrhectic debris (necrosis), large numbers of macrophages, fewer heterophils and
lymphocytes, and small basophilic colonies of 2 x 4 um bacilli. Macrophages often
contain intracytoplasmic, brown, granular pigment (melanomacrophages) and there are
increased numbers within the deep dermis (pigmentary incontinence). The inflammatory
infiltrate extends into the deep dermis where there is increased amounts of fibrous
connective tissue. The underlying skeletal myocytes are slightly shrunken and
hypereosinophilic (atrophy), and there is expansion of the perimysium and endomysium
by increased clear space (edema) and fibrosis. The adjacent epidermis is moderately
hyperplastic, and keratinocytes are occasionally shrunken and hypereosinophilic with
pyknotic nuclei (necrotic), or are swollen and rounded with clear cytoplasm (intracellular
edema). There is mild ortho- and parakeratotic hyperkeratosis.
Scaled skin, periodic acid-Schiff (PAS): Within the epidermis and extending into the
deep dermis, there are numerous PAS-positive, 3-5um diameter fungal hyphae with
frequent septation; parallel walls; acute angle, dichotomous branching; and terminal
Lung: Essentially normal tissue.
MORPHOLOGIC DIAGNOSIS: Scaled skin: Dermatitis, necrotizing, subacute, focally
extensive, moderate, with ulceration, superficial bacilli, and many fungal hyphae,
etiology consistent with Aspergillus spp., alligator, reptile.
ETIOLOGIC DIAGNOSIS: Cutaneous aspergillosis
CAUSE: Aspergillus spp.
• Ubiquitous, saprophytic, spore-forming fungus
• Opportunistic infection is associated with immunosuppression, excessive exposure
to fungus, vitamin A deficiency in reptiles, or prolonged antibiotic or corticosteroid
• Reported in crocodilians under poor husbandry conditions or with poor adaptability
to the stresses of captivity, poor diet, or overcrowding
• Cutaneous infection is generally rare among domestic animals, but a common
manifestation in reptiles
• Primary route of infection in most animals is through inhalation of spores or through
the gastrointestinal tract; in reptiles, also entry into skin through abrasions or other
• Aspergillus spp. contain numerous lipid compounds including aflatoxins, gliotoxins,
ochratoxins, and complement activation inhibitors which play a role in evasion of
• Proteinases play a role in the ability of the organism to invade tissues;
hematogenous dissemination can occur
• Gastrointestinal infections are associated with damage to mucous membranes, viral
erosive diseases, stress, and metabolic disturbances
• Protection is mediated by macrophages that phagocytize spores and by neutrophils
that attach to hyphae
• Resistance or recovery from a systemic fungal infection requires strong T-cell
mediated immunity; humoral immunity is not protective
• A. flavus and A. niger can produce large quantities of oxalates in feed (D-T03)
TYPICAL CLINICAL FINDINGS:
• Variable depending on species and route of infection
• Pulmonary and intestinal lesions; chronic rhinitis; vertebral osteomyelitis;
discospondylitis; uveitis; CNS signs
TYPICAL GROSS FINDINGS:
• Mucosa: multifocal to coalescing, necrohemorrhagic foci; epithelialized plaques
• Skin: multifocal to coalescing, raised, irregular, crusty plaques
• Lung (P-F06): non-invasive pulmonary form is characterized by formation of
aspergilloma, consisting of a tangled mycelial mass, usually located within a
preformed pulmonary cavity; may be mistaken for a neoplasm
TYPICAL LIGHT MICROSCOPIC FINDINGS:
• In tissues, 3 to 8 um wide, regularly septate hyphae with thin parallel walls and
dichotomous, acute angle branching
• Primary lesion in invasive aspergillosis is usually pulmonary, with hematogenous
• Multiple septate branching hyphae can radiate from the center of vessels
• Well-aerated necrotic cavities in lungs, air sacs of birds, pleura, or nasal mucosa
may develop conidiophores (fruiting bodies, these may provide definitive
diagnosis but are rarely seen in tissue sections); extensive deposition of birefringent
calcium oxalate crystals may be present in these areas
• Conidiophore stalks are enlarged at the uppermost point to form a globose,
hemispherical, flask-shaped vesicle; peg-like sterigmata form in a single layer
(uniseriate) or two layers (biseriate) with the second row arising from the first;
unbranched chains of conidia form from the distal ends
• Superficial infections mainly in the epidermis with infrequent invasion of the hair
follicles and/or dermis
• Fibrinohemorrhagic granulomas extending through all layers of gastrointestinal tract
ADDITIONAL DIAGNOSTIC TESTS:
• Isolation by culture
• Immunohistochemical staining using monoclonal and polyclonal antibodies
• ELISA, AGDD
Fungal hyphae in tissue:
• Aspergillus spp., Mucor spp., Rhizopus spp., Candida spp., Fusarium spp., and
Trichophyton spp., have been isolated from cutaneous lesions in crocodilians
• Zygomycetes (Mucor spp., Rhizopus spp.)– hyphae (up to 15 um in diameter)
are infrequently septate, have nonparallel walls, often appear collapsed or
twisted; stain less uniformly
• Candida spp. – produce hyphae, pseudohyphae and budding yeast in
• Pseudallescheria boydii – tissue phase is similar; must culture to differentiate
• Cattle – rumenitis and abomasitis (D-F02); gastroenteritis; mastitis; abortions (R-
F01); bronchopneumonia and hyperkeratotic dermatitis (fetal lesions; aborted fetus
lesions resemble ichthyosis or extensive ringworm)
• Horses – dissemination often results from primary intestinal lesion; guttural pouch
and pulmonary mycosis; keratitis; abortions; endocarditis; persistent diarrhea in foals
• Dairy sheep – mastitis in ewes; respiratory, gastrointestinal, and systemic lesions in
• Dogs – granulomatous rhinitis (A. fumigatus), infection of kidneys (U-F02) and other
viscera (A. terreus commonly involved, especially in German Shepherd Dogs)
• Cats – pulmonary and cutaneous infections
• Birds – known as brooder pneumonia; all stages of life can be affected including
embryonating eggs (A. fumigatus), chicks and poults (typically >50% mortality even
with low level contamination), adults (respiratory, digestive, or CNS; chronic
infections more common in older birds); lesions often present as fuzzy gray, blue,
green, or black material or pale yellow plaques; pulmonary granulomas must be
differentiated from Mycoplasma gallisepticum infections; fungal infections in young
chicks and turkey poults must be differentiated from the fungus Ochroconis
gallopava by culture
• Goat – pyogranulomatous rhinitis and dermatitis
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