7 year and 346 day-old intact male rhesus macaque, Macaca mulatta.This animal had a history of ill thrift and intermittent diarrhea. Campylobacter coli and Campylobacter jejuni were isolated on fecal culture several months prior to euthanasia. Balantidium coli and eggs of Trichuris spp. were identified on fecal parasitology screens at the same time. Supportive and therapeutic care was provided. Euthanasia was performed due to the poor prognosis for long-term resolution of diarrhea.

Gross Description:  

The animal was thin with no visible subcutaneous or visceral adipose tissue stores. The mesenteric lymph nodes were multifocally enlarged up to five times the normal size. The large intestine was markedly and uniformly dilated and contained green liquid fecal material admixed with gas. Numerous 2 cm long slender nematodes were present in the lumens that are consistent with Trichuris sp. The mucosa of the cecum, ascending colon and transverse colon was diffusely thickened, edematous and red.

Histopathologic Description:

Colon: Diffusely, the colonic mucosa is thickened with a moderate inflammatory infiltrate composed of large numbers of neutrophils, plasma cells, lymphocytes and lesser numbers of eosinophils and macrophages that separate the crypts and often extend into the submucosa. Scattered within the mucosa are lesser numbers of large foamy macrophages measuring 8 - 20 μm in diameter and forming rare multinucleated giant cells containing up to 15 nuclei (muciphages). Crypt lumina multifocally contain intact and degenerate neutrophils admixed with cellular debris (crypt abscess) and affected crypts may be lined by attenuated epithelium. Occasionally the crypts are ruptured. Multifocally, there is mild loss of goblet cells. The remaining crypts are hypercellular and tall with moderate numbers of mitotic figures. The mucosal surface is multifocally eroded, irregular and attenuated with epithelial tags projecting into the lumen. Multifocally, the submucosal lymphatic vessels are dilated and contain eosinophilic flocculent fluid. Focally within the mucosa and within the lumen are 20-80 μm diameter protozoans with granular eosinophilic protoplasm containing variable numbers of vacuoles, a round to bean shaped nucleus and a cell membrane covered with cilia. There are cross and tangential sections of nematodes with irregularly spaced projections on the cuticle, a stichosome surrounding the esophagus, a single prominent bacillary band, coelomyarian/polymyarian musculature, pseudocoelom containing deeply eosinophilic fluid, digestive tract lined by uninucleate cells with a microvillous border, and ovary and uterus containing large numbers of thick shelled, oval unembryonated eggs with bipolar plugs. Multifocally, a wispy, basophilic mat of spirochetes is adhered to the microvillous border of the enteroocytes.

Morphologic Diagnosis:  

Colon: Colitis, proliferative, neutrophilic, lymphoplasmacytic, eosinophilic, chronic-active, moderate, diffuse, with crypt abscesses, intralesional protozoa consistent with Balantidium coli, and intraluminal nematodes consistent with Trichuris spp. 
Colon: Spirochetes, apical cytoplasm, moderate numbers, multifocal. Microscopic findings of tissues not submitted:
Duodenum, jejunum and ileum: Enteritis, lymphoplasmacytic and eosinophilic, mild, multifocal with moderate deposits of amyloid in the lamina propria. 
Spleen: Amyloid deposition, multifocal, mild.
Liver, space of Disse: Amyloid deposition, multifocal, minimal. Adrenal gland, corticomedullary junction: Amyloid deposition, multifocal, minimal.

Lab Results:  

Normal ranges are given in parentheses.
Albumin (g/dl): 2.4 (3.4 - 4.70)
Protein (g/dl): 5.5 (5.8 7.5)


Chronic colitis of rhesus macaques

Contributor Comment:  

The primary findings in this case are proliferative, neutrophilic, lymphoplasmacytic typhlocolitis with mesenteric lymphoid hyperplasia, and systemic amyloidosis. Chronic colitis in rhesus macaques is a complex syndrome with a prolonged clinical course of intermittent diarrhea, dehydration and poor growth rate. Juvenile to young animals are usually affected. The initiating and perpetuating cause of the chronic colitis is unknown and is most likely multifactorial. Microbial infection, stress, exposure to dietary antigens and inappropriate immune response are all thought to play a role in its pathogenesis.

Numerous enteric pathogens have been examined for their role in the development of chronic colitis. C. coli and C. jejuni were identified to be strongly associated with chronic colitis in rhesus macaques(5). In a recent study, significant differences in the gastrointestinal tract microbial population have been reported between healthy animals and animals with chronic colitis(5). In group housed colonies at ONPRC, Campylobacter spp. or Shigella spp. have been associated with initial episodes of diarrhea followed by presence of normal flora(4). Virulent shiga toxin/eaeA intimin expressing Escherichia coli, Balantidium coli, Giardia lamblia, Enterocytozoon bieneusi and Trichuris trichiura have all been isolated in animals with and without diarrhea(5).

Grossly, most of the animals with chronic idiopathic colitis are emaciated with no subcutaneous or visceral adipose tissue stores, and mild to severe thymic atrophy(1). The large intestine may be dilated and contain liquid fecal material. The cecum, ascending colon, and transverse colon are consistently affected. In severe cases, most of the large intestine may be involved; however, the rectum is seldom affected. The affected mucosa is thickened and may have a rugose appearance(1) with or without erosions or ulcerations. The mesenteric lymph nodes, ileocecal lymph nodes and colonic lymph nodes are usually hyperplastic. In severely affected animals, serous atrophy of visceral adipose tissue may be seen. Gastritis is not a consistent finding in animals with chronic idiopathic colitis(6).

Microscopically, the colonic mucosa is thickened variably with neutrophils, lymphocytes, plasma cells that often separate the crypts. Crypt abscesses and crypt ruptures are common in acute infections(1). In chronic cases, the mucosa is proliferative; the crypts may be distorted, tortuous with karyomegaly, hyperchromicity, pseudostratification, frequent mitotic figures and presence of mitotic figures in the upper 1/3 of the mucosal glands. Goblet cell loss is common. The epithelial changes include micro-erosions, attenuation, irregularities of cell shape and size, disparity of nuclear size and hyperchromicity. Mucosal herniation into the submucosal lymphoid tissue is common. The ileum may be involved variably. Other associated histological changes include lymphoid hyperplasia of mesenteric lymph nodes, chronic cholecystitis, mild portal lymphocytic hepatitis and thymic atrophy(1). Chronic inflammation is a risk factor for developing reactive amyloidosis and chronic colitis is a common underlying inflammatory condition leading to the development of amyloidosis in this species. Amyloid deposition may be present in the lamina propria of small intestine, spleen, liver, adrenal gland and kidney(2).

This case exhibits all the classic gross and histologic features of chronic colitis in macaques but has some additional features. Numerous protozoa are present within the mucosa as well as in the lumen and the nematodes are present within the lumen. Additionally, moderate numbers of foamy macrophages (muciphages) and multinucleated giant cells are present. Their significance is unknown. (Acid fast stains were performed to rule out possible Mycobacteria. sp.) The filamentous spriochetes visible in some portions of the section are relatively uncommonly seen in macaques with chronic diarrhea but are typically found in animals with normal colons. Spirochetes in the large intestine of rhesus macaques have not been associated with disease processes and are generally considered benign. In addition, Congophilic amyloid deposits were present in the lamina propria of duodenum, jejunum and, ileum as well as spleen, liver and adrenal glands. The gross and microscopic findings suggest that the severity of chronic diarrhea in this animal could be multifactorial, ie the presence of chronic colitis, balantidiasis, trichuriasis and enteric amyloidosis. Enteric amyloid deposition leading to protein-losing enteropathy accounts for the laboratory finding of panhypoproteinemia.

JPC Diagnosis:  

Colon: Colitis, proliferative, lymphoplasmacytic, chronic, diffuse, moderate, with crypt abscesses, luminal and intramucosal ciliates, and luminal adult aphasmid nematodes.

Conference Comment:  

The contributor has provided a comprehensive overview of chronic colitis in macaques. Chronic colitis of juvenile rhesus macaques, which typically occurs in animals from 10 months to three years of age, must be distinguished from chronic diarrhea from opportunistic infections associated with simian acquired immunodeficiency syndrome. Colonic neoplasia has not been associated with chronic colitis of juvenile rhesus macaques1. Conference participants also discussed the differential diagnosis of ulcerative cicatrizing colitis, which is also seen in rhesus macaques. In this disease, there is deep linear mucosal ulceration in the cecum and proximal colon, and resultant bands of reactive fibrosis cause colonic strictures(4). This disease must be distinguished from colonic adenocarcinoma, a very common malignancy in older rhesus macaques, which often arises in the same location. 

Muciphages are present in the superficial and deep mucosa and may be a response to damaged goblet cells. In the human, muciphages are seen in both normal and diseased large intestine and rectum, and are not considered predictive of disease. 

The contributor mentioned the presence of mitotic figures in the upper 1/3 of the mucosal glands, and conference participants discussed this finding as a way to differentiate significant proliferative disease from normal mucosal epithelium turnover. Another helpful indicator of proliferative colitis is the relative paucity of goblet cells, as they are terminally differentiated cells and will not be present in newly regenerated epithelium. Chronic colitis of juvenile rhesus macaques differs from proliferative enteritides in other species in that severe ulceration and hematochezia, as well as the preneoplastic crypt mucosal dysplasia seen in the ulcerative diseases, are not present. 

The spirochetes observed in some sections may be Helicobacter cinaedi, which has been associated with chronic colitis in a rhesus macaque, and has been shown to induce diarrhea and bacteremia in pigtail macaques(3).  There is superficial necrotizing colitis multifocally throughout this section, with neutrophilic and histiocytic inflammation, which is an indicator of active disease and is likely due to Campylobacter jejuni and C. coli overgrowth. These are usually seen in initial episodes, but Campylobacter and protozoans may be absent in subsequent episodes of the disease(4). 


1. Alder RR, Moore PF, Scmucker DL and Lowemstein LJ. In Jones TC, Mohr U and Hunt, RD (eds). Monographs on Pathology of Laboratory Animals: Nonhuman Primates II. Berlin and New York: Springer-Verlag, 1993; 81-86.
2. Blanchard JL, Baskin GB, Watson EA. Generalized amyloidosis in rhesus monkeys. Vet Pathol. 1986 Jul;23(4):425-30.
3.  Fox JG, et al. Isolation of Helicobacter cinaedi from the Colon, Liver, and Mesenteric Lymph Node of a Rhesus Monkey with Chronic Colitis and Hepatitis. J Clin Microbiol. 2001; 39:1580-5.
4. Lewis AD, Colgin LMA: Pathology of noninfectious diseases of the laboratory primate. In: The Laboratory Primate. San Diego: Elsevier, 2005; 4774. 
5. McKenna P, Hoffmann C, Minkah N, Aye PP, Lackner A, Liu Z, Lozupone CA, Hamady M, Knight R, Bushman FD. The macaque gut microbiome in health, lentiviral infection, and chronic enterocolitis. PLoS Pathog. 2008 Feb 8;4(2):e20.
6. Sonnenberg A, Melton SD, Genta RM, Lewis AD. Absence of focally enhanced gastritis in macaques with idiopathic colitis. Inflamm Bowel Dis. 2011 Mar 18. doi: 10.1002/ibd.21696. 

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