JPC SYSTEMIC PATHOLOGY

URINARY SYSTEM

November 2023

U-F02

 

Signalment (JPC #1923797): German shepherd dog military working dog (MWD)

 

HISTORY: This MWD presented with anorexia, weight loss, and a painful abdomen.

 

HISTOPATHOLOGIC DESCRIPTION (Slide A): Kidney: Affecting approximately 40% of this section, are multifocal poorly forming granulomas often centered on arcuate vessels within the corticomedullary junction. The affected vessel walls are markedly thickened and contain the following changes: the endothelium is discontinuous and lost; the tunica media is effaced and replaced by abundant eosinophilic cellular and karyorrhectic debris admixed with fibrin, edema, and few transmigrating inflammatory cells (necrotizing vasculitis); the tunica adventitia is thickened by edema, fibrin and fibrosis with moderate numbers of infiltrating lymphocytes, plasma cells, macrophages including epithelioid macrophages and few multinucleated giant cells (Langhans and foreign body type), and neutrophils that extend into the surrounding renal parenchyma. The lumina of several affected vessels contain fibrin thrombi admixed with few previously described inflammatory cells and necrotic debris. Within vessel lumina, vessel walls, multinucleate giant cell macrophages, and the perivascular connective tissue are moderate numbers of poorly discernible fungal hyphae with 4 – 6 µm wide parallel walls, septations, and 15 µm terminal bulbous structures. Diffusely within the cortex and medulla, there is abundant interstitial hemorrhage. Multifocally, effacing up to 50% of the medullary architecture in the section is the previously described inflammation admixed with similar fungal hyphae. Multifocally, tubules exhibit one or more of the following changes: epithelium undergoing degeneration, characterized by pale and vacuolated cytoplasm and swollen nuclei; or necrosis, characterized by hypereosinophilic cytoplasm and shrunken, pyknotic nuclei; tubule lumina are filled with an eosinophilic granular homogenous debris (hyaline cast) with small amounts of hemosiderin, and/or deeply basophilic material (mineral), or lumina contain sloughed necrotic epithelial cells admixed with necrotic debris (granular cast). Glomeruli occasionally exhibit periglomerular fibrosis, hypertrophied parietal epithelium and synechia. The renal capsule is multifocally mineralized.

 

Gridley's stain (Slide B): Diffusely, within foci of necrotizing vasculitis, there are abundant positive staining, septate fungal hyphae with acute angle, dichotomous branching, parallel walls of relatively uniform width (3 – 6 µm), and up to 15 µm bulbous dilations of the walls.

 

MORPHOLOGIC DIAGNOSIS: Kidney, corticomedullary junction: Vasculitis, necrotizing and granulomatous, multifocal, severe, with numerous fungal hyphae, marked interstitial hemorrhage, pyogranulomatous nephritis, and tubular degeneration and necrosis, German shepherd dog, canine.

 

ETIOLOGIC DIAGNOSIS: Renal aspergillosis

 

CAUSE: Aspergillus terreus 

 

CONDITION: Systemic Aspergillosis

 

GENERAL DISCUSSION:

• Aspergillus is a ubiquitous saprophytic fungus that is an opportunist rather than a primary pathogen; common in air, soil and animal feed
• Debilitated, immunocompromised animals are at increased risk
• In contrast to mammals, birds, especially those from colder climates, are particularly susceptible to invasive aspergillosis
• A. fumigatus, A. flavus, A. niger, A. nidulans and A. terreus most commonly infect mammals and birds
• Two forms - Nasal/respiratory (most common; P-F06) and systemic (disseminated); locations of systemic involvement vary among species, but common locations include organs with terminal capillary loops or slowed blood flow (e.g. kidney)

 

PATHOGENESIS:

• Inhalation or ingestion of conidia > +/- localized infection of lung or GI > vascular invasion (angioinvasion; mycelial emboli) > hematogenous dissemination 
• In dogs, aspergillosis is usually limited to the nasal cavity, sinuses and/or lower respiratory system; in other domestic species, it usually begins in the respiratory tract and disseminates to other sites via leukocyte trafficking or via angioinvasion 
• Beta-glucan, melanin, and other molecules block reactive oxygen species and phagolysosomal acidification in macrophages and neutrophils
• Aspergillus and Penicillium produce nephrotoxic mycotoxins (i.e. ochratoxin, citrinin, fumonisin, oxalate, etc) that may contaminate feed; ochratoxin A is most significant and may cause disease in pigs but toxicity unlikely in ruminants 

 

TYPICAL CLINICAL FINDINGS:

• Kidney: Urinary incontinence, intermittent hematuria and weight loss 
• Possible hypocalcemia due to fungal production of oxalic acid with subsequent calcium sequestration in calcium-oxalate crystals 
• Vertebral pain, lameness, paraparesis, swelling, draining tracts
• Possibly uveitis or endophthalmitis prior to generalized illness

 

TYPICAL GROSS FINDINGS:

• Kidney enlarged with pitted capsule
• Multifocal to coalescing pale to yellow cortical streaks which form cavities containing viscous yellow material surrounded by a distinct bright red band
• Osteomyelitis; granulomas in spleen, lymph nodes, myocardium, pancreas, liver

• Lungs or other affected organs: Solitary or disseminated gray to yellow, discrete, irregular nodules often surrounded by a rim of hyperemia and hemorrhage

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Granulomas or pyogranulomas without prominent peripheral fibrosis
• Vascular invasion of fungal hyphae results in vasculitis, thrombosis, and infarction
• Fungal hyphae are 3-6 µm in width, regularly septate, parallel walled, with dichotomous (branching at the terminal bud), progressive, acute angle branching; in chronic lesions, the hyphae may form short globose and distorted hyphae up to 12-15 µm wide
• Oxalate crystals may be associated with fungal hyphae 
• 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

 

ADDITIONAL DIAGNOSTIC TESTS:

• H&E, PAS, Gridley's and GMS stains 
• Fungal culture

• PCR
• Cytology: Septate, branching hyphae with parallel walls and globose terminal ends

 

DIFFERENTIAL DIAGNOSIS:

• Disseminated fungal infections:

1. Similar morphology: Aspergillus spp., Pseudallescheria boydii, Fusarium spp; culture, PCR, or serologic examination for definitive diagnosis 
2. Zygomycetes: Hyphae up to 15um in width, infrequently septate, non‑parallel walls, often appear collapsed and acutely twisted, orthogonal right angle branching, well stained by H&E
3. Candida spp.: Pseudohyphae (chains of blastoconidia which are distinguished from true hyphae by constriction of points of attachment of the individual yeast), septate hyphae and budding yeasts 
4. Fusarium spp.: Septate, characteristic right angle, irregularly branching (+/- acute angle branching) and constrictions at branch points
5. Pseudallescheria boydii (scedosporium): Hyphae are narrower and usually branch at less acute angles 

 

COMPARATIVE PATHOLOGY:

• Wild avians: Captive penguins and eider ducks particularly susceptible; usually A. fumigatus or A. flavus; fungal plaques in air sacs and granulomas in lungs reported in many avian species +/- nodules in other organs secondary to angioinvasion and dissemination (CNS, coelomic cavity, intestines, liver, kidney, pneumatic bone, adrenal glands, spinal column)
• Poultry: Brooder pneumonia (P-F06)
• Dogs: Mycotic rhinitis / nasal sinus infection; more common in young, dolichocephalic dogs
• Cattle: Mycotic rumenitis with angioinvasion resulting in mycotic placentitis, mastitis and abortion; mycotic dermatitis in fetuses; report of necrotizing tracheobronchitis (Silva da costa, JCP 2020)
• Horses: Guttural pouch mycosis; Aspergillus was isolated in two cases of fungal rhinitis in Florida as a superficial copathogen (More, Vet Pathol 2019); identified in association with Salmonella enteritis infection (Hensel JCP, 2020)
• Pigs: Proximal tubule degeneration, atrophy, interstitial fibrosis and possibly perirenal edema related to ochratoxin A (ochratoxicosis) and citrinin toxins produced by Aspergillus and Penicillium 
• Sheep and goats: Pneumonia and mastitis; rhinitis in goats; gross and microscopic lesions are very similar to conidiobolomycosis and cryptococcosis (Silva do Caroma, JVDI 2020)
• Mice: Systemic mycosis rare in immunocompetent mice, but a rising concern in immunosuppressed strains; A fumigatus most common
• NHP: One outbreak of systemic aspergillosis due to A fumigatus reported in conjunction with tuberculosis in captive Old World primates with disseminated lesions in the lungs, liver, kidneys, and spleen
• Porcupine: Recent report of fatal A. flavus rhinitis with marked gaseous gastric distension; porcupines are obligate nasal breathers, rhinitis thought to cause dyspnea and death (Jalenques, JVDI 2019)
• Flamingo: recent report of pulmonary artery aneurysm secondary to A. fumigatus (Veiga, JCP 2023)
• Marine mammals: Sporadic respiratory infections primarily by A. fumigatus +/- dissemination to other tissues (brain, kidney, eye, etc)
• Sea fan corals: A. sydowii; tissue necrosis, purple discoloration, and amoebocytic nodular inflammation (galls); however, recent study showed that these signs are not specific for aspergillosis or fungal infection (Becker, Vet Pathol 2023)

 

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