Adult, female crocodile (Crocodylus niloticus).This crocodile was kept in a local zoo for over 2 years and was listless and anorexic for 5 weeks.

Gross Description:  

All lung lobes contained multiple, 0.5-1.0 cm diameter, irregularly-shaped, well-defined, firm, homogenous white to yellow nodules. Several firm, large nodules, 2.0-2.5 cm in diameter, white to yellowish in color, surrounded by dark red foci, were found in some part of the lungs. Visceral surfaces in the lung and pleural surfaces appeared dull and rough with a yellowish fibrous appearance. The liver and spleen were enlarged and cut surfaces revealed several gray to pale nodules.

Histopathologic Description:

Microscopic examination of the lung consists of a hemorrhagic, necrotizing bronchopneumonia with massive aerial mycelial growth within the airways. These affected airways are filled with numerous degenerated heterophils admixed with macrophages, necrotic debris, and bacillary colonies. The fungal organisms contain 3-5 μm chains of conidia, 4-7 μm dichotomous-branching, septate fungal hyphae. Airways are markedly dilated and the mucosal epithelium is extensively ulcerative with hemorrhage, many heterophils and macrophages are invading into the adjacent lung parenchyma. In these pneumonic areas, inflammation is associated with the appearance of numerous birefringent crystals with radiating spokes; the morphology of these crystals is suggestive of calcium oxalate. Histochemistry reveals many PAS-positive fungal hyphae scattered throughout the necrotic foci of lungs, liver, and spleen, primarily along the margins of the necrotic lesion.

Morphologic Diagnosis:  

Lung: Bronchopneumonia, necrogranulomatous and hemorrhagic, severe, subacute to chronic, multiple, with intralesional fungal hyphae, oxalate crystals, necrotic vasculitis, and pleuritis, crocodile (Crocodylus niloticus), reptile.

Lab Results:  

Escherichia coli and Aeromonas sp. were isolated from the lungs and liver.


Aspergillus sp.

Contributor Comment:  

Clinically, oxalate is produced by a variety of fungi, including saprophytic (e.g. Aspergillus niger and A. flavus) and phytopathogenic species, and other sources including methoxyflurane, ethylene glycol, large doses of ascorbic acid (vitamin C), primary hyperoxaluria (humans, cats, and tibetan spaniels), pyridoxine (vitamin B6) deficiency, and plants (e.g. Halogeton glomeratus, Sarcobatus vermiculatus, Rheum rhaponticum, Oxalis cernua, Rumex sp., Russian vine, etc.). Several pathways have been described for oxalic acid production, but the mechanism of oxalate crystal production is not known. In Aspergillus niger, the organism apparently possesses oxaloacetate acetylhydrolase (OAH), one of the enzymes of the tricarboxylic acid cycle, and degrades oxaloacetate to oxalate by this route (i.e. oxaloacetate + H2O → oxalate + acetate). In humans, similar morphological findings have been reported, with often localized deposition of calcium oxalate crystals around a pulmonary A. niger fungal ball.(1-3,5,6)

Aspergillus, a ubiquitous environmental organism, is an opportunistic pathogen in mammals and birds. Aspergillus fumigatus is the most commonly reported cause of aspergillosis in animals, whereas A. flavus, A. terreus, A. nidulans, and A. niger are incriminated less frequently. In animals, localized deposition of massive numbers of calcium oxalate crystals in tissues has been reported in association with Aspergillus infections.(5,7-9) This is the first report of pulmonary oxalosis in a crocodile.

JPC Diagnosis:  

Lung: Pneumonia, necrohemorrhagic, multifocal to coalescing, severe, with pleuritis, myriad fungal hyphae, and abundant anisotropic crystalline material (oxalate crystals).

Conference Comment:  

The GMS method highlights the fungal conidia and is helpful in demonstrating the other hyphal characteristics described by the contributor; while these features, in combination with oxalate crystal formation, are certainly suggestive of aspergillosis, the results of confirmatory testing (e.g. fungal culture) would be particularly valuable for solidifying the specific etiologic diagnosis. Furthermore, while the morphology of the prismatic crystalline material is consistent with oxalate crystals, histochemical stains (e.g. Yasues sliver nitraterubeanic acid), though not performed, may be employed to definitively identify oxalate crystals.(5)

In domestic species, oxalate crystals are more commonly encountered in the renal tubules due to ethylene glycol toxicosis in cats and dogs, or intoxication with one of the oxalate-containing plants listed above in sheep and cattle. Interestingly, the rumen microflora have some capacity to degrade oxalate to bicarbonate and carbonates, conferring sheep and cattle with a degree, albeit limited, of resistance to oxalosis; yet, remarkably, horses are far more resistant to oxalate-induced nephrosis. Because oxalate chelates calcium, hypocalcemia is a characteristic finding in both ethylene glycol toxicosis and oxalate toxicosis.(4)


1. Blackmon JA: Aspergillus niger. Am J Clin Pathol 76:506, 1981
2. Kauffman CA, Wilson KH, Schwartz DB: Necrotizing pulmonary aspergillosis with oxalosis. Mykosen 27:535-538, 1984
3. Kurrein F, Green GH, Rowles SL: Localized deposition of calcium oxalate around a pulmonary Aspergillus niger fungus ball. Am J Clin Pathol 64:556-563, 1975
4. Maxie MG, Newman SJ: Urinary system. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed., vol. 2, pp. 470-472. Elsevier Saunders, Philadelphia, PA, 2007
5. Muntz FH: Oxalate-producing pulmonary aspergillosis in an alpaca. Vet Pathol 36:631-632, 1999
6. Severo LC, Londero AT, Geyer GR, Picon PD: Oxalosis associated with an Aspergillus niger fungus ball: report of a case. Mycopathologia 73:29-31, 1981
7. Tham VL, Purcell DA: Fungal nephritis in a grey-headed albatross. J Wildl Dis 10:306-309, 1974
8. Wobeser G, Saunders JR: Pulmonary oxalosis in association with Aspergillus niger infection in a great horned owl (Bubo virginianus). Avian Dis 19:388-392, 1975
9. Wyand DS, Langheinrich K, Helmboldt CF: Aspergillosis and renal oxalosis in a white-tailed deer. J Wildl Dis 7:52-56, 1971

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2-1. Lung

2-2. Lung

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