JPC SYSTEMIC PATHOLOGY
Signalment (JPC #2130811): Beagle
HISTORY: This dog was found dead.
HISTOPATHOLOGIC DESCRIPTION: Pleura: Diffusely, the pleura is expanded up to 10mm, often forming papillary projections, by granulation tissue, inflammation and areas of necrosis. Foci of lytic necrosis are characterized by loss of normal architecture with replacement by necrotic cellular debris, degenerate neutrophils, fibrin, and areas of drop-out, often centered on large (up to 1.5mm) mats of 2um, beaded, filamentous bacilli admixed with finely granular basophilic material (sulfur granules). Surrounding necrotic areas and markedly expanding the surrounding pleura there are numerous viable and degenerate neutrophils, epithelioid macrophages, few multinucleated giant macrophages, and aggregates of lymphocytes and plasma cells, admixed with hemorrhage, fibrin, eosinophilic cellular and karyorrhectic debris, and abundant loose (edematous) to hyalinized fibrous connective tissue with plump reactive fibroblasts and numerous small caliber vessels (granulation tissue). Endothelial cells are diffusely hypertrophied (reactive), vessel walls are often expanded by previously described inflammatory cells, and there are scattered fibrin thrombi. Villous projections are multifocally lined by hypertrophied mesothelial cells that occasionally pile up to 3 cells deep (mesothelial hyperplasia).
MORPHOLOGIC DIAGNOSIS: Pleura: Pleuritis, proliferative, pyogranulomatous, and necrotizing, diffuse, severe, with granulation tissue, sulfur granules and large colonies of filamentous bacteria, beagle, canine.
ETIOLOGIC DIAGNOSIS: Actinomycotic pleuritis
CAUSE: Actinomyces sp.
- Mechanisms of defense within the pleura are weaker than those of the lung
- Gram-positive, non-acid fast, branching, filamentous, facultative ( canis, A. catuli, A. coleocanis, A bowdenii, A. denticolens, A. hordeovulneris, A. naeslundii, A. odontolyticus, A. viscosus, A. pyogenes) or obligate (A. bovis, A. israelii, A. meyeri) anaerobes
- Pathogenic infections are most common in young, large breed, male, outdoor dogs (hunting dogs)
- Actinomyces sp. are normal flora of oral mucus membranes, tooth surfaces (dental plaque), and the gastrointestinal tract
- Infection is often focal at the site of inoculation and spreads by direct extension
- Lesions are commonly linked to the oropharyngeal area
- Actinomyces sp are opportunistic pathogens, and require mechanical disruption of normal mucosal barriers (foreign body perforation (grass awn), bite wound, chronic gingivitis-periodontitis, etc)
- Actinomyces sp generally requires other commensal organisms from the oral cavity or GI tract to produce and maintain an anaerobic local environment; pathogenicity is low with pure Actinomyces sp infection
- Actinomyces fimbriae bind to other bacteria and form large mixed bacterial aggregates, which resist neutrophil phagocytosis and degranulation
- Actinomyces induce chemotaxis of neutrophils, activate macrophages, stimulates production/release of cytokines, and cause B-cell hyperplasia
- Enzymes from macrophages, neutrophils, and bacteria destroy surrounding connective tissue and facilitate spread of infection through fascial planes
- Hematogenous spread is rare
TYPICAL CLINICAL FINDINGS:
- Chronic fever, emaciation, lethargy, dyspnea and fistulous tracts
- Subcutaneous soft tissue swelling in the head or neck region, especially mandible, submandibular area, ventral or lateral cervical areas, thorax or abdomen
- Cough and dyspnea with pleuritis
- Abdominal masses and distension with peritonitis
- Rear leg lameness and paralysis are typical in retroperitoneal infections; there may be radiographic evidence of periosteal new bone formation or osteomyelitis of ventral vertebral bodies, especially T13-L3
TYPICAL GROSS FINDINGS:
- Poorly defined masses (abscesses) with red-brown exudate (“tomato soup”) that may contain sulfur granules
- Diffuse red velvety to granular thickening of pleura and peritoneum; visceral pleura and peritoneum are less affected; there is copious cellular exudate in pleural or peritoneal cavity
- Multiple nodular masses may involve heart, mediastinum, lung, diaphragm, and chest wall and extend into the subcutis, producing an ulcerated subcutaneous mass or fistulous tract
- Regional lymphadenopathy
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Large dense colonies of filamentous bacteria surrounded by pyogranulomatous inflammation and fibrosis (sulfur granules)
- Tissue granules consist of a tangled mass of gram-positive, beaded, filamentous, sometimes branched organisms
- Occasionally associated with Splendore-Hoeppli material (most common in cattle with bovis infection)
- Variably dense, moderately vascular connective tissue separates many abscesses from one another and encapsulates the entire lesion
- Colonies may become calcified in chronic cases
- Nocardia: Slender, beaded, filamentous, gram-positive, aerobic and variably acid-fast (Fite-Faraco, modified Kinyoun stain); sulfur granules rare; high mortality
- Staphylococcus aureus: A cause of botryomycosis; gram-positive coccus
- Sparganosis due to larval cestodes of Spirometra can cause pleuritis in dogs: Plerocercoids or spargana with multiple invaginations of tegument, subtegumental muscle, and a paucicellular, loose stroma with osmoregulatory canals; lack coelomic cavity, reproductive and digestive tracts
- Cats: Pyothorax and subcutaneous abscesses secondary to bite wounds are the most common clinical presentations; there is often yellow to sanguineous exudate without a granulomatous mass
- Other causes of pleuritis in cats: FIP, Pasteurella multocida, Strep, Staph
- Cattle: Actinomyces bovis causes lumpy jaw
- Swine: Actinomyces suis causes mastitis in sows; mammary tissue is markedly swollen, and there is granulation tissue
- Horses: A. bovis may be recovered with Brucella abortus and B. suis from the supraspinous bursa of horses with "poll evil" or "fistulous withers"
- Ottter: Actinomyces with closest match to A. bowdenii was isolated in river otter in British Columbia
- Biberstein EL, Hirsh DC. Pathogenic Actinomycetes (Actinomyces and Nocardia). In: Hirsh DC, Zee YC, eds. Veterinary Microbiology. Malden, MA: Blackwell Science, Inc; 1999:250-3.
- Britton AP, Zabek E, Schwantje H. J Zoo Wildl Med. 2011;42(4):751-4.
- Caswell JL, Williams KJ. Respiratory system. In: Maxie ME, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier; 2016:521-522.
- Lopez A, Martinson SA. Respiratory system, mediastinum, and pleurae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2016:557-8.
- Sykes JE. Actinomycosis and nocardiosis. In: Greene CE, ed. Infectious Diseases of the Dog and Cat. 4th ed. St. Louis, MO: Elsevier Saunders; 2012:484-90.