JPC SYSTEMIC PATHOLOGY
RESPIRATORY SYSTEM
August 2023
P-B05
Signalment (JPC #1947706): Adult female Long-Evans rat
HISTORY: This rat had recently whelped.The dam and pups appeared healthy until five days after whelping, at which time the dam became lethargic, ataxic, dyspneic, and would not nurse her pups.
HISTOPATHOLOGIC DESCRIPTION: Lung: Affecting 50% of the section, there are multifocal to coalescing randomly distributed areas of necrosis composed of abundant karyorrhectic and eosinophilic cellular debris centered on large (up to 200 µm diameter) colonies of 2 µm diameter bacilli and admixed with numerous viable and degenerate neutrophils, fewer macrophages, and small amounts of hemorrhage. Necrotic foci are surrounded by many macrophages and fewer reactive fibroblasts. In less affected areas, the perivascular interstitium and alveolar septa are infiltrated and expanded by variable numbers of macrophages, neutrophils, and lymphocytes. Alveoli are often filled with proteinaceous fluid (edema), as well as few neutrophils and macrophages. The pleura is mildly expanded by edema and occasional macrophages and neutrophils and is frequently lined by reactive mesothelium.
MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, embolic, necrosuppurative, multifocal to coalescing, marked, with numerous large colonies of bacilli, Long-Evans rat, rodent.
ETIOLOGIC DIAGNOSIS: Corynebacterial pneumonia
CAUSE: Corynebacterium kutscheri
CONDITION: Corynebacteriosis
SYNONYMS: Pseudotuberculosis
GENERAL DISCUSSION:
- C. kutscheri is a gram-positive, aerobic, diphtheroid bacillus that infrequently causes fatal epizootics in rodent colonies (rats, mice, and guinea pigs)
- Natural infection is usually subclinical with low morbidity and mortality
PATHOGENESIS:
- C. kutscheri gains entry through oral or enteric mucosa and spreads to regional lymph nodes, with septicemia and bacterial emboli to lungs, kidney, liver, and joints
- Rats can carry the organism for several weeks in the oropharynx and adjacent lymph nodes
- Disease and mortality are typically associated with concomitant disease states such as immunosuppression or nutritional deficiency, but not with viral pathogens
TYPICAL CLINICAL FINDINGS:
- All age groups may be infected
- Infection is usually subclinical, except in immunosuppressed, environmentally/experimentally stressed, or nutritionally deficient rodents
- Clinical infection: Weight loss, respiratory distress, ruffled haircoat, dark red encrustations around eyes/nares, mucopurulent nasal discharge; death usually occurs within 1-7 days without treatment
TYPICAL GROSS FINDINGS:
- Lung: Variably sized, multifocal to coalescing, raised, pale, suppurative foci with a characteristic peripheral hyperemic zone; may coalesce to involve entire lung lobe(s); fibrinous exudate may be present on pleura and/or pericardium
- Kidney, liver, heart, skin, joints: Abscesses
- Joints: Rarely, arthritic lesions of pedal extremities and subcuticular abscesses
- Lymph nodes: Lymphoid hyperplasia of regional nodes
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Lung:
- Disseminated hematogenous pattern of foci of coagulative to caseating necrosis with leukocytic infiltration (predominantly neutrophils in early lesions, and mononuclear cells in later stages); not associated with airways
- Intralesional large amorphous bacterial colonies (pathognomonic); groups of bacteria may remain attached to each other in a palisade or picket fence arrangement, resembling "Chinese letters"
- Concomitant interstitial pneumonia, hypercellularity of alveolar septa, perivascular cuffs, pulmonary edema
- Kidney, liver, other organs: Foci of suppurative inflammation with peripheral mononuclear cell infiltration and fibrosis
ADDITIONAL DIAGNOSTIC TESTS:
- Gram stain, Warthin-Starry, or Giemsa stains
- Culture
- PCR
- Serology
DIFFERENTIAL DIAGNOSIS:
- Pseudomonas aeruginosa: Gram negative; necrosis with abscessation in the lung
- Mycoplasma pulmonis (P-B01, murine respiratory mycoplasmosis, MRM): Gram-negative; multifocal abscesses with bronchiectatic airways and lymphoid hyperplasia
- Streptococcus pneumoniae (P-B07): Gram-positive diplococcus; fibrinopurulent exudate on multiple serosal surfaces
- Filobacterium rodentium (P-B16, formerly CAR bacillus): Gram-negative filamentous bacillus; chronic suppurative bronchitis/bronchiolitis with lymphoid hyperplasia
COMPARATIVE PATHOLOGY:
C. kutscheri infection in other species:
- Mice:
- Immunocompromised (IL-10 knockout) mice: Occasional disease; necrotizing glomerulitis, renal and hepatic abscesses, suppurative arthritis, and less commonly pulmonary abscesses
- Aged B6 mice: Keratoconjunctivitis with ulcerative keratitis has been reported
- Syrian hamster: Experimental C. kutscheri infection can result in localized abscesses without systemic infection; hamsters may be a reservoir hosts
- Guinea pig: Corynebacteria appear to be normal flora, rarely associated with disease
REFERENCES:
- Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016: 69, 140-141, 185, 225.
- Jeong E, Young-Suk W, Hyoung-Chin K, Myung-Hawn C, Yang-Kyu C. Role of IL-10 deficiency in pneumonia induced by Corynebacterium kutscheri in mice. J Microbiol Biotechnol. 2009;19(4):424-430.
- Herbert RA, Janardhan KS, Pandiri AR, et al. Lung, Pleura, and Mediastinum. In: Suttie, AW, ed. Boorman’s Pathology of the Rat. 2nd ed. San Diego, CA: Elsevier Academic Press, 2018:444-445.
