12-year-old, female, Pigtail macaque, Macaca nemestrinaThe animal was part of a small research colony housed in outdoor/indoor gang cages. Following an outbreak of diarrhea, she had tested positive for fecal culture of Yersinia pseudotuberculosis and treated successfully with Enrofloxacin 8 years previously. During another diarrhea episode 2 years ago, she tested positive for Balantidium coli and was treated successfully with metronidazole. She recently developed diarrhea in which Balantidium coli was again identified. She was treated with metronidazole, but continued to have diarrhea that began to contain some fresh blood. Gentamycin and fluid therapy were quickly added to treatments, but she developed retching of food and continued to have diarrhea and dehydration until it was decided she should be euthanized approximately 10 day after onset of the initial signs.

Gross Description:  

At necropsy there was loose stool adhered to the perineal region and signs of dehydration based upon skin turgor and dryness of subcutaneous tissues. The stomach contained liquid contents, the small and large intestines contained pale greenish mucoid stool. There were petechial hemorrhages in the mucosa of the small intestine and paintbrush type hemorrhages on the mucosa and also serosa of the large intestines.

Morphologic Diagnosis:  

Acute hemorrhagic purulent colitis - Shigellosis

Lab Results:  

Shigella flexneri type IV was isolated from large intestines. 


Shigella flexneri type IV

Contributor Comment:  

Shigellosis represents a classic entity of nonhuman primates, an infection long associated with exposure to humans.2 For this reason, it is still a disease threat to captive primates and a good example of the need for employee health monitoring of the animal caretakers. This outbreak was associated with renovation of the gang cages by outside contractors. Pub MED currently lists over 12,500 citations for Shigella and 255 citations for Shigella and primates. 

Shigella flexneri, Yersinia enterocolitica, Strongyloides fulleborni, adenovirus, Campylobacter coli and C. jejuni were recently reported to be associated with chronic diarrhea in Rhesus macaques.7 Enteric agents not associated with chronic diarrhea within the same population included Balantidium coli, Giardia lamblia, Trichuris trichiura, Enterocytozoon bieneusi and enteropathogenic E. coli carrying the eaeA intimin or Stx2c Shiga toxin virulent genes. Chronic diarrhea was associated with increased CD69+ cells and CD4+ T lymphocytes as well as upregulation of IL-1-α, IL3, and TNF-α cytokine genes. Chronic diarrhea is the leading cause of morbidity requiring veterinary care in captive primates and is not currently a criterion of specific pathogen-free colonies. The enteric infections and associated modulation of the immune system is a complicating variable in the study of AIDS and SIV in the primate models. 

JPC Diagnosis:  

Colon: Colitis, fibrinonecrotic, subacute, diffuse, severe with edema and pseudomembrane (Fig. 2-1), Pigtail macaque (Macaca nemestrina), primate. 

Conference Comment:  

Shigellosis is a common disease in non-human primates, caused by a gram negative, nonmotile, nonspore forming, bacilli.2 The most common isolate is Shigella flexneri, although S. sonnei, S. dysenteriae and S. boydii have also been less frequently identified.2,3,5 Clinical signs of shigellosis may vary depending on the species of Old World monkey infected. Rhesus macaques generally present with either an acute foul-smelling, watery diarrhea with frank blood, or a more chronic intermittent semi-soft diarrhea with occasional episodes of frank blood. Tamarins and marmosets, on the other hand, will primarily demonstrate lethargy, depression, dehydration, and dried blood around the anus, rather than diarrhea.3

Infection and disease does not provide immunity. Animals with shigellosis may be chronically reinfected, and colonies endemically infected my not demonstrate overt clinical disease unless challenged by a stressful event or compromised immune system.3

Upon ingestion of the bacteria, it is proposed that invasion of the M cells overlaying lymphoid follicles within the colon, allows the bacteria to reach the basolateral pole of the epithelial cells, which is where they induce their entry.5

Shigellosis in humans is caused by both Shigella spp. and enteroinvasive Escherichia coli.5 These bacteria contain a virulence plasmid that encodes most proteins directly involved in host cell entry, bacterial dissemination, and induction of apoptosis in infected macrophages.4 This region encodes a type III secretion apparatus (Mxi-Spa TTS apparatus), translocators (IpaB and Ipa C), effectors (IpaD, IpgB1, IpgD and IcsB), their dedicated chaperones (IpgA, IpgC, IpgE and Spa15), and two transcriptional activators (VirB and MxiE). The current theory suggests that upon contact of the bacterium with the host cell, translocators are inserted into the host cell membrane which forms a pore, effectors are then transmitted through this pore and enter into the host cell cytoplasm.

Genes encoding a type III secretory apparatus have been identified in a number of mammalian and plant pathogens including enterohemorrhagic and enteropathogenic Escherichia coli, Shigella, Salmonella, Yersinia, Chlamydia, Bordetella, Pseudomonas, Xanthomonas, Ralstonia, and Erwinia spp.6


1. Adams MM, Allison GE, Verma NK: Type IV O antigen modification genes in the genome of Shigella flexneri NCTC 8296. Microbiol 147:851-860, 2001
2. Benirschke K, Garner FM, Jones TC: Pathology of Laboratory Animals, vol. II, pp 1449, 1978
3. Bernacky BJ, Gibson SV, Keeling ME, Abee CR: Nonhuman primates. In: Laboratory Animal Medicine, eds. Fox JG, Anderson LC, Loew FM, Quimby FW, 2nd ed., pp. 730-734. Elsevier Science, San Diego, CA, 2002
4. Gall TL, Mavris M, Martino MC, Bernardini ML, Denamur E, Parsot: Analysis of virulence plasmid gene expression defines three classes of effectors in the type III secretion system of Shigella flexneri. Microbiol 151:951-962, 2005
5. Parsot C: Shigella spp. and enteroinvasive Escherichia coli pathogenicity factors. FEMS Microbiol Let 252:11-18, 2005
6. Schuch R, Maurelli AT: The Mxi-Spa Type III secretory pathway of Shigella flexneri requires an outer membrane lipoprotein, MxiM, for invasion translocation. Infect Immun 67:1982-1991, 1999
7. Sestak K, Merritt CK, Borda J, Saylor E, Schwamberger SR, Cogswell F, Didier ES, Didier PJ, Plauche G, Bohm RP, Aye PP, Alexa P, Ward RL, Lackner AA: Infectious agent and immune response characteristics of chronic enterocolitis in captive rhesus macaques. Infect Immun 71:4079-4086, 2003

A virtual slide is not available for this case.

(Fig 2-1) Colon

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