Adult male African green monkey (Chlorocebus aethiops). All monkeys described in this report were maintained in a facility at the US Army Medical Research Institute of Infectious Diseases accredited by the American Association for Accreditation of Laboratory Animal Care. All research was conducted under approved animal protocols in adherence with the Guide for the Care and Use of Laboratory Animals (Committee on Care and Use of Laboratory Animals of the Institute of Laboratory Animal Resources, National Research Council, National Institutes of Health Publication No. 8623, revised 1996). The African green monkey (AGM) was received at our facility on 13 June, 2003 and in good condition. ITS telemetry surgery was performed on 1 March 2006 and the AGM recovered without incident. The next month, on 18 April 2006, prior to being placed into biocontainment, a routine physical examination was performed. An 8- to 10-cm-diameter mass was found on the right dorsal flank. No other abnormal findings were observed at the time. Within 24 hours of initial discovery, the fluid-filled mass ruptured and was draining a thick, mucoid discharge. The abscess was cultured, surgically debrided and lavaged, a Penrose drain was placed, and antibiotic treatment was initiated. An abdominal mass was palpated 24 hours following surgery and was described as a 3 cm by 1 cm irregularly shaped, firm mass in the cranial abdomen. The mass enlarged over several days, and exploratory laparotomy revealed mesenteric abscesses centered at the ileocecocolic junction and also involving the duodenum, ileum, cecum, colon, the right ureter, and the body wall inferior to the right kidney. Surgical removal was not possible, and the animal was euthanatized.

Gross Description:  

The most significant findings at necropsy were chronic pyogranulomatous peritonitis and polyserositis; chronic pyogranulomatous panniculitis of the right flank (surgical abscess site); and a defect in the abdominal wall subjacent to the panniculitis. There were multiple fibrous adhesions present in the cranial abdomen. Buried within these adhesions were multiple chronic abscesses that sometimes contained a viscous fluid. Serosal and mesenteric adhesions enveloped and intertwined loops of small and large bowel, adhered to the right ureter and kidney, and extended into the retroperitoneal space with fingerlike projections. The abdominal wall inferior to the subcutaneous lesion of the right flank was disrupted, or breached, and an abdominal fibrous band of tissue was present extending to the cecum.

Histopathologic Description:

Diffusely, the serosa of the small intestine (ileum at ileocecocolic junction) and mesentery are greatly expanded by broad bands of fibrous tissue that strongly adhere mesentery and serosa into a mass. There are mesenteric lymph nodes surrounded and entrapped by fibrous tissue. Interspersed sporadically within the fibrous tissue are abscesses composed primarily of macrophages that contain abundant cytoplasm, fewer lymphocytes and plasma cells, rare neutrophils, cellular debris, and sometimes hemorrhage (Fig. 1-1).

Select mesenteric lymph nodes are multifocally expanded and disrupted by large numbers of macrophages that contain abundant cytoplasm, cellular and karyorrhectic debris, edema, and hemorrhage (Fig. 1-2). 

The mucosa of the small intestine is multifocally eroded. Occasionally cellular debris may be found in the lumen and in the submucosa. Lymphocytes and plasma cells mildly expand the submucosa. There are moderate numbers of bacilli multifocally within the lumen, on the surface of erosive areas, and invading the mucosa and submucosa.

Morphologic Diagnosis:  

1. Mesentery and ileum: Peritonitis and serositis, histiocytic, chronic, multifocal, marked, with fibrosis, necrosis, and rare hemorrhage, African green monkey (Chlorocebus aethiops)

2. Lymph node, mesenteric: Lymphadenitis, histiocytic, subacute, multifocal, moderate, with necrosis and hemorrhage

3. Small Intestine: Enteritis, erosive, multifocal, mild to moderate, with bacilli

Lab Results:  

Bacteria in the abscess fluid were identified as Klebsiella pneumoniae by routine culture and biochemical methods and were further characterized as K. pneumoniae subsp. pneumoniae serotype K2 by capsular serotyping using a slide agglutination technique.(1) Furthermore, bacterial colonies plated on a blood agar plate exhibited a hypermucoviscosity phenotype, as demonstrated by a positive string test (formation of a 0.5 mm mucoviscous string when a loop is passed through a colony). Genetic analysis of the sequence of a 760-bp amplicon of the bacterial 16S rRNA from the isolate was submitted to a basic local alignment search tool search and found to be 99% identical to several K. pneumoniae entries. Additional analysis for 2 novel genes, magA (mucoviscosity-associated gene A) and rmpA gene (regulator of the mucoid phenotype) suggested as potential hypermucoviscosity-associated genes in human cases, was performed by PCR using previously described primers.(8) The bacterial isolate from this case was positive for the rmpA gene and was negative for the magA gene.(6)


Hypermucoviscous Klebsiella pneumoniae

Contributor Comment:  

Within a year and 5 months, six additional AGM with clinical and pathologic features similar to the AGM described here, were positively diagnosed with K. pneumoniae by bacterial culture and/or immunohistochemistry. Clinical signs in these additional monkeys varied from none to palpable abdominal masses noted during routine clinical examination. One monkey was found dead in its cage with no premonitory clinical signs. All seven affected monkeys were either housed within, or were in contact with monkeys housed within, one animal room in our facility.

Klebsiella pneumoniae is a gram-negative, aerobic, nonmotile bacillus and is a common cause of a wide range of infections in humans and animals.(6) Our differential diagnosis for Gram-negative pathogens in nonhuman primates included, but were not limited to, Yersinia enterocolitica (forms large colonies in tissues, which were not present in our cases), Shigella sp. (S. dysenteriae, S. Flexneri, S. boydii, S. sonnei), Campylobacter sp. (C. jejuni, C. coli), Salmonella sp. (S. typhimurium, S. Dublin, S. enteriditis, S. Stanley). In Old and New World monkeys, infection with K. pneumoniae causes pneumonia, meningitis, peritonitis, cystitis, and septicemia.(9) K. pneumoniae also constitutes normal fecal and oral flora in many nonhuman primates. In the past two 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.(3,4,5,7) Fatal human infections with invasive strains of K. pneumoniae involve pulmonary emboli or abscess, meningitis, endophthalmitis, osteomyelitis, or brain abscess. Recently, a highly invasive K. pneumoniae causing primary liver abscesses in humans has also been reported.(3) These invasive, abscess-forming strains of K. pneumoniae are associated with the so-called hypermucoviscosity (HMV) phenotype, a bacterial colony trait identified by a positive string test.(4,5,6) The HMV phenotype is seen in K. pneumoniae expressing either the capsular serotypes K1 or K2. K1 serotypes of K. pneumoniae have two potentially important genes, rmpA, a transcriptional activator of colanic acid biosynthesis, (10) and magA, which encodes a 43-kD outer membrane protein. Five 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.(3,10) The role of rmpA and magA in the pathogenesis of invasive K. pneumoniae, however, seems less certain. K. pneumoniae expressing the HMV phenotype has not been reported to cause natural disease in nonhuman primates, nor in other animal species. 

The means by which the causative K. pneumonia may have spread or caused disease in individual monkeys in our colony is unknown. The only significant epidemiologic factor we identified was that affected monkeys were maintained in the same room or had contact with a monkey housed in that room. African green monkeys may be quite susceptible to invasive K. pneumoniae infection. Therefore, veterinarians, laboratory workers, and research pathologists should be aware of this pathogen as a cause of abdominal masses and multisystemic abscessation in the AGM. In addition, the AGM may provide another useful animal model to understand the pathogenesis of this emerging human pathogen.

JPC Diagnosis:  

1. Ileocecocolic junction: Serositis and peritonitis, granulomatous, multifocal to coalescing, severe with marked fibrosis
2. Lymph node, mesenteric: Lymphadenitis, pyogranulomatous, diffuse, severe

Conference Comment:  

The abundant foamy material within macrophages was discussed during the conference. Dr. Nichols speculated that the foamy material within macrophages may be phagocytized mucus which the Klebseilla bacteria have produced. He also mentioned it is important to rule out mycobacterial causes when macrophages of this type are present in a lesion. In this case, an acid-fast stain was done and was negative. 

In domestic animals, Klesiella pneumonia is the cause of numerous maladies. In foals, K. pneumonia is a common cause of neonatal septicemia and pneumonia.(1,2) K. pneumonia has also been commonly implicated in equine abortions.(8)


1. Brown CC, Baker DC, Barker IK: Alimentary system. In: Jubb, Kennedy, and Palmer's Pathology of Domestic Animals, vol 3 ed. Maxie MG, pp. 507. Elsevier Limited, Philadelphia, PA, 2007
2. Caswell JL, Williams KJ: In: Jubb, Kennedy and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed., pp. 632. Elsevier, Philadelphia, Pennsylvania, 2007
3. Chuang YP, Fang CT, Lai SY, Chang SC, Wang JT: Genetic determinants of capsular serotype K1 of Klebsiella pneumoniae causing primary pyogenic liver abscess. J Infect Dis 193:645654, 2006
4. Fang CT, Chuang YP, Shun CT, Chang SC, Wang JT: A novel virulence gene in Klebsiella pneumoniae strains causing primary liver abscess and septic metastatic complications. J Exp Med 199:697705, 2004
5. Fang FC, Sandler N, Libby SJ: Liver abscess caused by magA+ Klebsiella pneumoniae in North America. J Clin Microbiol 43:991992, 2005
6. Kawai T: Hypermucoviscosity: an extremely sticky phenotype of Klebsiella pneumoniae associated with emerging destructive tissue abscess syndrome. Clin Infect Dis 42:13591361, 2006
7. Rahimian J and JT Wang: The Emerging Role of Klebsiellae in Liver Abscess. In: Emerging Infections, eds. Scheld WM, DC Hooper, and JM Hughes, pp. 199-211. ASM Press, Washington, DC, 2007
8. Schlafer DH, Miller RB: Female genital system. In: Jubb, Kennedy, and Palmer's Pathology of Domestic Animals, vol 3 ed. Maxie MG, pp. 507. Elsevier Limited, Philadelphia, PA, 2007
9. Twenhafel NA, Whitehouse CA, Stevens EL, Hottel HE, Foster CD, Gamble S, Abbott S, Janda JM, Kreiselmeier N, Steele KE: Multisystemic abscesses in African green monkeys (Chlorocebus aethiops) with invasive Klebsiella pneumoniae-identification of the hypermucoviscosity phenotype. Vet Pathol 45:2, 2008
10. Yu WL, Ko WC, Cheng KC, Lee HC, Ke DS, Lee CC, Fung CP, Chuang YC: Association between rmpA and magA genes and clinical syndromes caused by Klebsiella pneumoniae in Taiwan. Clin Infect Dis 42:13511358, 2006

Click the slide to view.

1-1. Mesentery, African Green Monkey

1-2. Lymph node, African Green Monkey

Back | VP Home | Contact Us |