JPC SYSTEMIC PATHOLOGY
Signalment (JPC #2288032): 5-year-old Rhesus monkey
HISTORY: This single-housed, SRV and SIV negative Rhesus monkey was depressed for 3 days after anesthesia. On the 4th day, the animal was found down in his cage, dehydrated, and in shock. All lung lobes appeared firm and consolidated, and there were multiple purulent and hemorrhagic foci on the pleural surfaces.
HISTOPATHOLOGIC DESCRIPTION: Lung: Diffusely, alveolar lumina are filled with macrophages containing 1 x 3 um bacilli that are surrounded by a thin clear capsule, admixed with degenerate neutrophils, fibrin, and eosinophilic cellular and karyorrhectic debris (necrosis). Alveolar septa are often discontinuous and replaced with fibrin and cellular debris (septal necrosis). Bronchiolar walls and epithelium are frequently necrotic with lumina containing degenerate neutrophils, fibrin, macrophages, and eosinophilic cellular and karyorrhectic debris (necrosis). Multifocally, vessels walls are necrotic and infiltrated by neutrophils, macrophages, and fibrin (fibrinonecrotizing vasculitis); there is marked perivascular hemorrhage and edema; and there are frequent fibrin thrombi that often occlude the lumens. Multifocally, the pleura is moderately expanded by similar inflammatory cells, hemorrhage, fibrin, and edema.
MORPHOLOGIC DIAGNOSIS: Lung: Bronchopneumonia, fibrinosuppurative, necrotizing, acute, diffuse, severe, with vasculitis, fibrinous pleuritis, and numerous intrahistiocytic encapsulated bacilli, Rhesus monkey (Macaca mulata), nonhuman primate.
ETIOLOGIC DIAGNOSIS: Pneumonic klebsiellosis
CAUSE: Klebsiella pneumoniae
- A gram-negative, non-motile, facultative anaerobic, heavily encapsulated, non- spore forming, non-flagellated, 0.3-1.0 x 0.6-6.0um bacillus of the Enterobacteriaceae family that occurs singly, in pairs, and in short chains
- Important cause of severe pneumonia, meningitis, peritonitis, cystitis, and septicemia, and abortion in humans and nonhuman primates
- Significant cause of morbidity and mortality in owl monkey and chimpanzee colonies, especially in the young, and in other non-human primates associated with shipping, quarantine, and overcrowding
- Occurs as a minor commensal organism in the intestinal tract of humans and animals; also occurs in soil and water as free-living forms
- Normal intestinal flora interfere with colonization by Klebsiella; any disruption of normal microflora can result in colonization or overgrowth; antibiotic therapy is an important pre-disposing factor
- Emerging highly virulent hypermucoviscosity (HMV) phenotype can cause localized or disseminated infections in healthy hosts; predominantly associated with African green monkeys
- Plasmid-mediated antibiotic resistance has become common, and most strains are resistant to several antibiotics (multiple drug resistance)
- Most strains are unlikely to produce disease unless animal is immunodeficient or stressed (opportunistic pathogen)
- Various mechanisms of innate immunity are required to resist infection as the adaptive immune system cannot provide a sufficiently rapid, efficient response to a high number of invading pathogens
- Many strains possess fimbriae (pili) that act as adhesins, permitting colonization of mucosal surfaces and inhibiting phagocytosis and intracellular killing
- The thick polysaccharide capsule (K antigen) creates a barrier that prevents opsonization and phagocytosis
- The HMV phenotype virulence due to capsular serotypes (K1 and K2) that carry genes MagA (mucoviscosity-associated gene/K1 specific capsular polymerase gene) and rmpA (regulator of mucoid phenotype) which make the bacteria more invasive and highly resistant to phagocytosis
- The outer membrane contains lipopolysaccharide (LPS) of which the lipid A portion is endotoxic and the O (somatic) antigen is serotype specific; the somatic (O antigen) shields the bacteria from complement-mediated killing
TYPICAL CLINICAL FINDINGS:
- Signs are not specific and vary in severity
- Early signs include coughing and sneezing accompanied by facial edema and a serous to mucopurulent nasal discharge
- Severely affected animals are febrile, depressed, anorectic, and markedly dyspneic
- With septicemia, the course is rapid, and animals may die suddenly
- High case fatality (90%) in untreated patients
TYPICAL GROSS FINDINGS:
- Bronchopneumonia with a tendency for abscess formation, consolidation, and pleuritis
- Fibrinopurulent exudates on pleura, meninges, & peritoneum
- Liver may be enlarged, firm, and mottled tan or purple
- HMV phenotype has been identified in African green monkeys in which abscesses were found in the liver, lungs, cerebellum and skin
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- The organism has a characteristic evenly-spaced distribution and a thick clear capsule visible on H&E and Gram stained sections
- Variably severe, focal to diffuse, suppurative bronchopneumonia
- Necrosis and abscessation are possible
- Exudate fills alveoli and plugs smaller bronchioles
- Multifocal atelectasis, congestion, alveolar hemorrhage, and edema
- Suppurative meningitis in some septicemic animals
- Capsule has a fibrous appearance on EM with slender thread-like capsular fibrils at regular intervals
ADDITIONAL DIAGNOSTIC TESTS:
- Bacterial culture/isolation of the organism on standard bacterial media is the mainstay of diagnosis; the organism can be isolated from the lungs, blood, or other organs
- Bacterial colonies appear mucoid and have a positive string test (an inoculation loop is pulled through the bacterial colony forming a long mucoid string of more than 5 mm)
- Mixed infections are common
- The most common bacterial isolate from non-human primates with pneumonia is Klebsiella pneumoniae; others include Escherichia coli, Streptococcus pneumoniae, Bordetella bronchiseptica, Pasteurella multocida, and Hemophilus influenzae (differentiate by culture)
- Cattle and swine: Mastitis; can progress to fatal endotoxic shock (cows)
- Horses: Metritis, infertility, and abortion; neonatal septicemia in foals with failure of passive transfer
- Neonatal swine: Rare cause of villous atrophy and diarrhea
- Bitches: Urinary tract infection
- Owl monkeys: Air sacculitis
- Guinea pigs: Septicemia and/or acute necrotizing bronchopneumonia
- Mice: oxytoca and K pneumonia: Suppurative female reproductive tract infections, opportunistic infections
- Rats: Abscesses in lymph nodes and kidneys and suppurative rhinitis
- Rabbits: Severe hemorrhagic enterotyphlitis
- California sea lions: HMV phenotype identified; Severe purulent bronchopneumonia and fibrinonecrotic pleuritis with pyothorax
- Multiple species: Opportunistic pathogen of wounds, especially when skin or mucosae are breached by disease, trauma, burns, surgical instrumentation, venous catheterization, tracheal intubation, etc
- Bueno MG, Iovine RO, et al. Pneumonia and bacteremia in a golden-headed lion tamarin (Leontopithecus chrysomelas) caused by Klebsiella pneumoniae pneumoniae during a translocation program of free-ranging animals in Brazil. J Vet Diagn Invest. 2015; 27(3):387-391.
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