Two-year-old, intact male African green monkey (Cercopithecus aethiops).The animal was wild caught on St. Kitts. It was part of a group of 22 African green monkeys brought to the institution on 12/17/2014. Health records from vendor indicated heavy growth of Klebsiella pneumonia. All were treated with enrofloxacin at the vendor. The first quarantine exam on 12/22/14 was unre-markable. Decreased appetite was noted on 12/30/14, and it continued to decrease with marked weight loss. Physical examination on 1/2/14 revealed a large, firm mass in the right cranial abdomen. Abdominal fluoroscopy and CT scan revealed a loss of serosal detail mid-abdomen, with a mass effect with intestines displaced cranially and caudally.

Gross Description:  

A 4.5 x 3.5 x 2.2 cm firm, tan, irregular mass was present in the mesentery and involved the ileocecocolic junction. Loops of duodenum, jejunum and colon were adhered to the mass and to themselves multifocally. The serosa of the intestinal loops was roughened, with multifocally light red discolorations. On cut section, 80% of the mass was firm, and tan to yellow. Multifocally, there were half a dozen irregular cavitations, which varied in size from 3-8mm in diameter. These were filled with mucoid white to yellow material. On the left medial lobe of the liver, along the diaphragmatic surface, there was a focal, 15x5 mm pale tan, irregular, flat and friable area.

A 4.5 cm x 1 mm tan nematode was present free within the stomach (Physaloptera sp, presumptive).

Embedded within the mucosa of the cecum were half a dozen tan nematodes, 4.5-5cm x0.5mm diameter with anterior filamentous ends (consistent with Trichuris sp).

Histopathologic Description:

Abdominal mass: The muscularis and serosa of the intestinal sections and adjoining mesenteric fat are obliterated and expanded by large areas of liquefaction necrosis, infiltrates of large numbers of degenerate neutrophils, macrophages, foamy macrophages, moderate numbers of lymphocytes and plasma cells admixed with eosinophilic proteinaceous material, fibrin, necrotic debris, and occasional hemorrhage and dissecting fibrosis. Many arteriolar walls in the mesentery are expanded by fibrillar eosinophilic material (fibrinoid necrosis). There are multifocal areas of liquefaction necrosis in the mesenteric lymph node, with infiltrates of large numbers of foamy macrophages and neutrophils (abscess), and proliferation of fibrous connective tissue that extend to the mesentery. Within the cyto-plasm of macrophages and freely within the necrotic debris, there are large numbers of bacterial rods with a clear thick capsule.

The intestinal mucosa is multifocally infiltrated by moderate numbers of lymphocytes and plasma cells, with fewer eosinophils.

Morphologic Diagnosis:  

Abdominal mass: Severe, locally extensive, chronic necrosuppurative and histiocytic mesenteritis, lymphadenitis and entero-colitis with abscess formation and myriad intrahistiocytic and extracellular encap-sulated rod-shaped bacteria.

Lab Results:  

The CBC was within normal limits with the exception of moderate numbers of reactive lymphocytes and moderate numbers of neutrophils with basophilic cytoplasm. The chemistry panel was within normal limits. Urinalysis revealed moderate blood, ketonuria, mild proteinuria, and large numbers of calcium oxalate crystals. Hypermucoviscosity (HMV) variant of Klebsiella pneumonia was isolated from the abscess and rectal and oropharyngeal swabs.


Klebsiella pneumoniae

Contributor Comment:  

Gross and microscopic examination revealed a locally extensive chronic abscess involving the mesenteric lymph nodes, small and large intestines and mesentery with large numbers of intrahistiocytic and free bacterial rods containing a thick capsule. Hypermu-coviscosity (HMV) variant of Klebsiella pneumonia was isolated from the abscess and rectal and oropharyngeal swabs. The invasive HMV phenotype of Klebsiella pneumoniae has been associated with multisystemic abscesses, and especially abdominal abscess in African green monkeys.(10, 11)

Klebsiella pneumoniae is a gram-negative, aerobic, nonmotile bacillus and is a common cause of a wide range of infections in humans and animals. In Old and New World monkeys, infection with K. pneumoniae causes pneumonia, meningitis, peritonitis, cystitis, and septicemia.(8) K. pneumoniae also constitutes normal fecal and oral flora in many nonhuman primates. In the past 2 decades, a new type of invasive K. pneumoniae disease has emerged in humans in Taiwan and other Asian countries, and more recently from non-Asian countries, including the USA.(4) Fatal human infections with invasive strains of K. pneumoniae involve pulmonary emboli or abscess, meningitis, endoph-thalmitis, osteomyelitis, or brain abscess.(4) Recently, a highly invasive K. pneumoniae causing primary liver abscesses in humans has also been reported.(5) These invasive, abscess-forming strains of K. pneumoniae are associated with the so-called hypermuco-viscosity (HMV) phenotype, a bacterial colony trait identified by a positive string test (>5mm string length).(3) These Klebsiella spp. generally develop prominent polysaccharide capsules which increase virulence by protecting the bacteria from phagocytosis and preventing destruction by bactericidal serum factors.

The HMV phenotype is seen in K. pneumoniae expressing either the capsular serotypes K1 or K2. K1 serotypes of K. pneumoniae have 2 potentially important genes, rmpA, a transcriptional activator of colanic acid biosynthesis, and magA, which encodes a 43-kD outer membrane protein. K2 serotypes of K. pneumoniae also have rmpA but do not have magA. Capsular serotypes K1 and K2 are reported to play an important role in the invasive ability of HMV K. pneumoniae. The role of rmpA and magA in the pathogenesis of invasive K. pneumonia, however, seems less certain.(11)

JPC Diagnosis:  

Intestine, lymph node, mesentery: Enterocolitis, lymphadenitis, peritonitis, pyogranulomatous and necro-, tizing, chronic-active, multifocal, marked with myriad intra and extracellular bacilli.

Conference Comment:  

Conference participants commented on slide variability with some slides containing a section of large intestine and others having small intestine. This is consistent with the excellent gross images provided by the contributor, consisting of overlapping sections of small and large intestine enmeshed within a focally extensive abscess. A gram stain was viewed during the conference, revealing histiocytes with abundant intracellular gram negative rods and a prominent capsule; however, in many cases similar features were readily visible on H&E. Participants discussed other stains which would facilitate visualization of the bacterial capsule, including mucicarmine. There was agreement the appearance of a gram negative bacillus with a large clear capsule is distinctive for Klebsiella sp.; however, one differential diagnosis mentioned for this lesion was melioidosis. Melioidosis, caused by the gram negative bacterium Burkholderia pseudomallei, afflicts humans and many animal species including non-human primates, resulting in a wide range of disease manifestations. It is uncommon in North America, but has been associated with primates imported from endemic areas. Clinical and pathologic findings are often non-specific, resembling a bacterial septicemia, but abscesses can be seen in multiple tissues.(9)

Two conference participants (co-authors on the Twenhafel et al. manuscript) referenced below, discussed in detail the events surrounding the cases described in that publication. At the time of that report, African green monkeys presenting initially with extensive mid-abdominal abscessation (and less commonly in other body systems), caused by hypermuco-viscosity K. pneumoniae was a novel finding.(10) Since, work has been done to characterize the hypermucoviscosity variant of K. pneumoniae as discussed in the contributors comment. The source of infection remains unclear and requires further epidemiologic studies. However, in at least one report in cohoused infected rhesus and cynomolgus macaques, transmission was thought to be fecal-oral and not from environmental contamination.(1) Like the source, the pathogenesis is still debatable particularly in light of extensive abscess formation in the mid-abdominal cavity in many cases. Participants discussed possible pathways to include septicemia or other methods of bacterial translocation from the intestine lumen. Regardless, the hypermucoid variant of K. pneumoniae is better able to resist innate immune defenses, including oxidative killing, and is more cytotoxic to blood monocytes in African green monkeys, compared to the non-hypermucoid variant, likely playing an important role in the pathogenesis.(2)

Conference participants also discussed infections caused by non-hypermucoviscosity K. pneumoniae in different animal species to include: Neonatal septicemia and pneumonia in foals and, abortion and stillbirth in mares;(6) mastitis in cattle; urinary tract infections in dogs; bronchopneumonia and polyserositis in guinea pigs; enterotyphlitis in rabbits; bacteremia, liver and kidney abscesses, pneumonia and myocarditis in mice; and abscesses in multiple locations in rats.(7)


1. Burke RL, Whitehouse CA, Taylor JK, Selby EB. Epidemiology of Invasive Klebsiella pneumoniae with Hypermu-coviscosity Phenotype in a Research Colony of Nonhuman Primates. Comp. Med. 2009;59(6):589-597. 

2. Cox BL, Schiffer H, Dagget G Jr, et al. Resistance of Klebsiella pneumoniae to the innate immune system of African green monkeys. Vet Microbiol. 2015;176(1-2):134-42. 

3. Fang CT, Chuang YP, Shun CT, et al. A novel virulence gene in Klebsiella pneumoniae strains causing primary liver abscess and septic metastatic complications. J Exp Med. 2004;199: 697705. 

4. Lau YJ, Hu BS, Wu WL, et al. Identification of a major cluster of Klebsiella pneumoniae isolates from patients with liver abscesses in Taiwan. J Clin Microbiol 2000;38(1):412-414. 

5. Lederman ER, Crum NF. Pyogenic liver abscess with a focus on Klebsiella pneumoniae as a primary pathogen: An emerging disease with unique clinical characteristics. Am J Gastroenterol 2005;100(2):322-31. 

6. Maxie MG. Jubb, Kennedy and Palmers Pathology of Domestic Animals. 5th ed. Vol 2. Philadelphia, PA: Saunders, Elsevier; 2007:131,632. 

7. Percy DH, Barthold SW. Pathology of laboratory rodents and rabbits. 3rd ed. Ames, IA: Blackwell; 2007:64, 152, 229, 275. 

8. Pisharath HR, Cooper TK, Brice AK, et al. Septicemia and Peritonitis in a colony of common marmosets (Callithrix jacchus) secondary to Klebsiella pneumoniae infection. American association for laboratory animal science 2005;44(1): 35-37. 

9. Ritter JM, Sanchez S, Jones TL, et al. Neurologic melioidosis in an imported pigtail macaque (Macaca nemestrina). Vet Pathol. 2013;50(6):1139-44. 

10. Twenhafel NA, Whitehouse CA, Stevens EL, et al. Multisystemic abscesses in African green monkeys (Chlorocebus aethiops) with invasive Klebsiella pneumoniae: identification of the hypermucoviscosity phenotype. Vet Pathol 2008;45:226231. 

11. Yeh KM, Kurup A, Siu LK, et al. Capsular serotype K1 or K2, rather than magA and rmpA, is a major virulence determinant for Klebsiella pneumoniae liver abscess in Singapore and Taiwan. J Clin Microbiol. 2007;45:466471.

Click the slide to view.

2-1a. Peritoneal mass

2-1b. Peritoneal mass

2-2 Bacterial culture

2-3. Peritoneal mass

2-4. Mesentery

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