JPC SYSTEMIC PATHOLOGY
SIGNALMENT (JPC Accession #1142242): Cow
HISTOPATHOLOGIC DESCRIPTION: F02-A: Rumen: Extending transmurally from the mucosa into the tunica muscularis and serosa is a focally extensive wedge-shaped area of coagulative necrosis characterized by retention of tissue and cellular architecture, loss of differential staining. Within the affected and adjacent areas, the vessel walls to include tunica media and adventitia are expanded by lymphocytes, plasma cells, macrophages, and fewer neutrophils, as well as fibrin, edema, karyorrhectic and cellular debris (necrotizing vasculitis). Vascular lumina are occluded by fibrin admixed with cellular and karyorrhectic debris (fibrinthrombi) and multiple fungal hyphae, which extend through the tunica media into the surrounding perivascular space. Fungal hyphae are 5-15 um wide, pauci-septate, with non-parallel walls, non-dichotomous, irregular or right angle branching, and bulbous dilatations. The infarcted area is bound transmurally by a 5 mm thick band composed of degenerate and viable neutrophils, macrophages, lymphocytes, plasma cells, and eosinophilic cellular and karyorrhectic debris (lytic necrosis) that multifocally extend into and replace tunica muscularis and expand into overlying serosa. The epithelium adjacent to the infarct is thickened up to 3 times normal with prominent anastomosing rete ridges (epithelial hyperplasia), intracellular and intercellular edema, multifocal erosions and ulceration, and intraepithelial aggregates of degenerate and viable neutrophils (microabscesses). The lamina propria, submucosa, and serosa are markedly expanded by increased clear space and ectatic lymphatics (edema), inflammatory cells, and fibrin.
F-02B Gomori methenamine silver (GMS): Rumen: Multifocally throughout the tissue, there are GMS-positive fungal hyphae.
MORPHOLOGIC DIAGNOSIS: Rumen: Rumenitis, necrotizing, acute, focally extensive and transmural, severe, with infarction, necrotizing vasculitis, fibrin thrombi, and numerous non-septate GMS-positive fungal hyphae, breed not specified, bovine.
ETIOLOGIC DIAGNOSIS: Ruminal zygomycosis
CAUSE: Zygomycetes spp.
CONDITION: Mycotic rumenitis
- Implicated fungal organisms: Mucor, Rhizopus, Absidia, (zygomycetes) with lesser frequency by Aspergillus and Mortierella spps
- Ubiquitous saprophytic molds associated within water, soil, decaying matter, and substrates high in carbohydrates
- Cause opportunistic disease in ruminants resulting in disseminated disease in immunocompromised or debilitated animals
- Lesions result from submucosal venular thrombosis caused by fungal invasion
- Secondary to mucosal damage caused by sepsis, ruminal acidosis (grain overload), prolonged antibiotic therapy, reflux of acidic abomasal contents, mucosal disease (bovine pestivirus, flavivirus), immunosuppression, recent parturition and ingestion of young grass
- Occasional metastases to liver, and cause necrotizing thrombophlebitis
- Organism is angioinvasive
- Commonly affects the rumen, reticulum and omasum
- Fungi are common contaminants of feed and are normal GI inhabitants
- High carbohydrate diet > reduction in rumen pH > increase in ruminal volatile fatty acids > changes in ruminal microflora (increased Streptococcus bovis followed by lactobacilli) > decreased rumen motility, movement of fluid into the rumen, and dehydration > ulceration of mucosa > invasion of submucosa and vessels by fungi > thrombosis, infarction, necrosis
- May also occur in the absence of ruminal acidosis, secondary to sepsis and reflux of fluid from abomasum
- Secondary to broad spectrum antibiotic administration
- Secondary to ruminal damage from bovine viral diarrhea
TYPICAL CLINICAL FINDINGS:
- Anorexia, depression, rumen atony, foul-smelling feces
- Increased heart and respiratory rates because of acidosis
- Dehydration from movement of fluid from the circulation into the rumen due to change in osmotic pressure
TYPICAL GROSS FINDINGS:
- Mycotic rumenitis is much more severe and extensive than necrobacillary rumenitis
- Well-circumscribed necrotic areas surrounded by zone of hyperemia that extends to the serosa in the rumen, reticulum, and omasum
- Hemorrhagic and fibrinous peritonitis that mats the omentum to the rumen
- Extensive, well-demarcated infarcts; red to black, thickened, firm and leathery
- +/- fibrinohemorrhagic peritonitis
- Liver: Small irregular tan areas of infarction bordered by a hyperemic margin
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Lesions are hemorrhagic & angiocentric: necrotizing vasculitis, submucosal venular thrombosis, infarctions, and hemorrhagic necrosis
- Diffuse pyogranulomatous inflammation (+/- transmural) with coagulative necrosis and multinucleated giant cells
- Chronic cases: Granulomatous inflammation in the deep mucosa
- Fibrinous exudate; varying leukocytic inflammation
- Pauciseptate, thin-walled 3-25 um wide hyphae with non-parallel walls, non-dichotomous, irregular, often right angle, branching and focal bulbous dilatations
- Hyphae in necrotic/infarcted areas and within blood vessels (angiotrophic)
- Liver: Necrotizing thrombophlebitis of portal radicles with disseminated infections
- Histomorphology, silver stains, PAS
- Fungal culture: Required for identification to genus and species
- Immunohistochemistry, immunofluorescence, enzyme immunocomplex
- Fusobacterium necrophorum (colibacillosis): Usually superficial; affects papillated areas of ventral sac and occasionally ruminal pillars; less hemorrhagic
- Aspergillus fumigatus (Class Hyphomycetes):
- Hyphae are 3-6 microns wide, septate, with parallel walls and acute angle, dichotomous branching which stain poorly with hematoxylin and eosin
- Reproduce asexually via conidia and sexually via an ascus (sac-like structure containing eight ascospores)
- More common in abomasums
- Candida albicans (Class Blastomycetes, Family Cryptococcaceae):
- Masses of branching, septate hyphae, with pseudohyphae, and round to oval budding yeasts (blastospores)
- 3-5 microns in diameter
- Typically an infection of squamous epithelium in young animals (“thrush”)
- Occasional opportunistic invader in aged animals
- Imperfect fungus: Life cycle not completely defined; sexual stages unknown
- Dogs: Ulcerative and granulomatous stomatitis, gastritis, and enteritis, lymphadenopathy with calcification, encephalitis, pneumonia, cutaneous nodules
- Horses: Lips and pharynx, nostrils, nasal mucosa
- Bison: Sever, diffuse fibrinous peritonitis; large area of infarction and hemorrhages on the omasum, abomasum, and reticulum
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