Chronic intestinal inflammation and intestinal disease in dogs

Normal individuals maintain tolerance to the endogenous bacterial flora residing within their alimentary tract, a phenomenon mediated by the gastrointestinal lymphoid tissue. Loss of this tolerance is a key factor in the development of chronic intestinal inflammation. Manifestations of such uncontrolled inflammation in humans include inflammatory bowel disease and celiac disease. Dogs may similarly be affected, and although the etiopathogenesis is likely similar, the lesions differ. This review includes discussion of the factors involved in breakdown of mucosal tolerance, the immunologic basis of canine enteropathies, and the use of novel immunotherapies for these diseases.     

Immune cell populations in the duodenal mucosa of cats with inflammatory bowel disease

The aim of this study was to characterize the phenotype of leukocytes infiltrating the duodenal mucosa of cats with inflammatory bowel disease (IBD) by using immunohistochemistry and computer-aided morphometry to assess whether immunologic markers would aid in characterization of IBD. Frozen and formalin-fixed duodenal biopsies were collected from cats referred for investigation of chronic vomiting, diarrhea, or both (n = 34). Reference ranges were previously established by using duodenal samples from healthy cats (n = 16). No significant difference was found in the number of immunoglobulin G+ (IgG+) or IgA+ in either the villous lamina propria or the crypt lamina propria between cats with IBD and control cats. T cells (CD3+) increased in number from crypt to the tip of the villi in biopsies from both diseased (mean +/- SD for each group was 18.8 +/- 6.6 and 17.7 +/- 4.2 cells/ 10,000 m2 in cryptal areas to 25.2 +/- 9.5 and 29.1 +/- 13.3 cells/10,000m2 in villous areas) and healthy animals (17.9 +/- 3.9 cells/10,000 microm2 in cryptal areas to 24.1 +/- 9.3 cells/10,000 microm2 in villous areas) and no significant difference was found between diseased and control cats. By contrast, major histocompatibility complex (MHC) class II expression by leukocytes with dendritic cell or macrophage morphology in the lamina propria was significantly greater in cats with IBD (13.3 +/- 4.2 cells/10,000 microm2 in cryptal area; P = .016) than in healthy cats (11.9 +/- 3.0 cells/10,000 microm2) and MHC class II expression by enterocytes also was more pronounced in these cats showing an overall intensity of expression of 7.1 +/- 4.0 cells/10,000 microm2 in cats with IBD as opposed to 0.0 +/- 0.0 cells/10,000 microm2 to 0.3 +/- 0.7 cells/10,000 microm2 in healthy cats. These findings suggest that a subtle immunologic dysregulation occurs in spontaneously arising feline IBD.     

Upregulation of toll-like receptors in chronic enteropathies in dogs

BACKGROUND: Inflammatory bowel disease (IBD) is thought to result from a dysregulated interaction between the host immune system and commensal microflora. Toll-like receptors (TLRs) recognize microbe-associated molecular patterns (MAMPs), but their role in enteropathies in dogs is unknown. HYPOTHESIS: That there is a dysregulation of TLRs recognizing bacterial MAMPs in dogs with IBD. ANIMALS: Sixteen healthy beagles and 12 dogs with steroid-treated (ST) and 23 dogs with food-responsive (FR) diarrhea. METHODS: Prospective, observational study. mRNA expression of canine TLR2, 4, and 9 was evaluated by quantitative real-time RT-PCR in duodenal and colonic biopsies obtained before and after standard therapy. Samples from control dogs were taken at necropsy, with additional biopsies of stomach, jejunum, ileum, and mesenteric lymph node in 6 dogs. RESULTS: There were significant differences (P< or = .017) in expression of TLR2, 4, and 9 between the 6 sampled locations in healthy control dogs (lymph node > small intestine > or = colon). Before therapy, ST expressed more mRNA than control dogs for all 3 receptors (P < .05). There were no significant differences between pretreatment and posttreatment values, even though 32/35 dogs improved clinically. No associations were found when comparing receptor mRNA expression with either histology or clinical activity scores. CONCLUSIONS AND CLINICAL IMPORTANCE: Bacteria-responsive TLR2, 4, and 9 are upregulated in duodenal and colonic mucosa in IBD. This might lead to increased inflammation through interaction with the commensal flora. The absence of significant changes after therapy despite clinical improvement might point toward the existence of a genetic predisposition to IBD as described in human IBD.     

Two-dimensional grayscale ultrasound and spectral Doppler waveform evaluation of dogs with chronic enteropathies

Sonography is an important diagnostic tool to examine the gastrointestinal tract of dogs with chronic diarrhea. Two-dimensional grayscale ultrasound parameters to assess for various enteropathies primarily focus on wall thickness and layering. Mild, generalized thickening of the intestinal wall with maintenance of the wall layering is common in inflammatory bowel disease. Quantitative and semi-quantitative spectral Doppler arterial waveform analysis can be utilized for various enteropathies, including inflammatory bowel disease and food allergies. Dogs with inflammatory bowel disease have inadequate hemodynamic responses during digestion of food. Dogs with food allergies have prolonged vasodilation and lower resistive and pulsatility indices after eating allergen-inducing foods.     

White spots on the mucosal surface of the duodenum in dogs with lymphocytic plasmacytic enteritis

Distended lacteals, described as expanded white villi in duodenum, are strongly indicative of primary intestinal lymphangiectasia. In the present study, we evaluated the significance of white spots present in the duodenal mucosa of dogs with lymphocytic plasmacytic enteritis (LPE). Fifty dogs with LPE were included in this study, and white spots were detected in the duodenal mucosa in 22 dogs during endoscopy. Hypoproteinemia was more frequent in dogs with white spots than in dogs without spots (p = 0.02). Serum protein and albumin concentration were significantly lower in LPE dogs with white spots (p = 0.038) compared to LPE dogs without white spots (p = 0.039). There was a significant correlation between white spots density and lymphatic dilatation histological scores (p = 0.023; ρ = 0.481). These results suggest that the presence of white spots in the duodenal mucosa of dogs is not a finding exclusive for intestinal lymphangiectasia. Low serum protein and albumin concentrations together with lymphatic dilatation seem to be related to the presence of white spots in the duodenal mucosa of LPE dogs.     

A randomized, open-label, positively-controlled field trial of a hydrolyzed protein diet in dogs with chronic small bowel enteropathy

Background: Hydrolyzed protein diets are commonly used to manage canine chronic enteropathies (CE), but their efficacy has not yet been critically evaluated. Hypothesis: A hydrolyzed protein diet is superior to that of a highly digestible (control) diet in the management of CE in dogs. Animals: Twenty‐six dogs (18 test diet, 8 control diet) referred for investigation and management of naturally occurring chronic small intestinal disease. Methods: Randomized, open‐label, positively controlled trial. After a full diagnostic investigation, which included endoscopy, dogs were assigned either to the test diet or control diet on a 2 : 1 basis (test : control). Cases were re‐evaluated 3 times (at approximately 3, 6–12 months, and 3 years). Outcome measures included response of clinical signs (complete, partial, none), change in severity of signs (based upon clinical disease activity index; canine inflammatory bowel disease activity index [CIBDAI]), change in body weight, and need for other therapy. Results: There were no significant differences in baseline characteristics (eg, signalment, body weight, and duration of clinical signs), and histopathologic severity between test and control diet groups. However, despite randomization, CIBDAI was significantly higher in the test diet group (P= .013). Most dogs had responded by first evaluation, with no difference between groups (P= .87). However, significantly more dogs on the test diet remained asymptomatic at both the second (P= .0012) and third (P < .001) re‐evaluation, and the decrease in CIBDAI was significantly greater (P= .010). Conclusions and Clinical Importance: A hydrolyzed protein diet can be highly effective for long‐term management of canine chronic small bowel enteropathy.     

Comparison of ultrasonographic findings with clinical activity index (CIBDAI) and diagnosis in dogs with chronic enteropathies.

Intestinal wall thickness is neither a specific nor sensitive ultrasound parameter for detecting intestinal inflammation. We hypothesize that mucosal echogenicity, lymphadenomegaly, and secondary findings of the gastrointestinal tract would be more sensitive and specific markers for detecting and differentiating causes of chronic inflammatory bowel disease in dogs. Fifty-six client-owned dogs with chronic diarrhea and 10 control dogs were examined with two-dimensional, gray-scale ultrasound (time 0, 4, and 10 weeks post therapy) and small intestinal mucosal biopsies were performed at the 0- and 4-week time points. The clinical activity was assessed at each time point using the canine inflammatory bowel disease activity index (CIBDAI). Fifty-one dogs had inflammatory infiltration of the duodenal mucosa and were divided into three groups, food-responsive disease, idiopathic inflammatory bowel disease, and protein-losing enteropathy, based on their response to the different treatments and histology. Two different patterns of increased echogenicity of the mucosa were detected: hyperechoic speckles and hyperechoic striations. A normal, hypoechoic bowel mucosa in dogs with chronic diarrhea had a sensitivity of 80% and a specificity of 81% for the diagnosis of food-responsive disease. Hyperechoic striations had a sensitivity of 75% and a specificity of 96% for dogs with protein-losing enteropathy. Hyperechoic speckles were non-specific for diagnosing inflammatory bowel disease. There was a significant relationship between ultrasound score and CIBDAI at t0, but not following therapy. Mucosal echogenicity may be a better parameter for detecting inflammatory bowel disease than bowel wall thickness in dogs with chronic diarrhea.     

Comparison of direct and indirect tests for small intestinal bacterial overgrowth and antibiotic-responsive diarrhea in dogs

Controversy exists over the diagnosis of idiopathic small intestinal bacterial overgrowth (SIBO) in dogs and some clinicians use the term antibiotic-responsive diarrhea (ARD) in preference. However, whether such terms are interchangeable is not clear. To examine the relationship between duodenal bacterial numbers and a clinical response to antibiotics, SIBO and ARD were defined by nonoverlapping criteria. Quantitative duodenal juice bacteriology and indirect serum biochemical tests were used to assess small intestinal bacterial populations in 30 dogs with gastrointestinal disorders, including 9 with ARD. Serum total unconjugated bile acid (TUBA) concentrations were measured in all dogs, serum folate and cobalamin concentrations were measured in 29 of 30 dogs, and quantitative culture of duodenal juice was performed in 22 of 30 dogs. Serum TUBA concentrations also were measured in samples from 38 control dogs. Twenty of 22 affected (clinical) dogs in which quantitative bacteriology was performed were classified as having SIBO (>10(5) colony-forming units of total bacteria per milliliter of duodenal juice), but bacterial numbers did not differ significantly between dogs with ARD and dogs with other disorders. Increased folate (19/29), decreased cobalamin (16/ 29), or a combination (9/29) were common, but increased TUBA concentrations were documented in only 5 of 30 clinical dogs. Again, no significant differences were observed between dogs with ARD and those with other disorders, and a similar proportion (5/38) of controls had abnormally high TUBA concentrations. Finally, no significant differences were noted when duodenal bacteriology and TUBA concentrations were assessed before and during antibiotic therapy. These results question the utility of quantitative duodenal juice bacteriology and indirect biochemical marker tests for SIBO in the investigation of canine gastrointestinal disorders.     

Structural and functional changes of neuronal and glial components of the feline enteric nervous system in cats with chronic inflammatory and non-inflammatory diseases of the gastrointestinal tract

Immunohistochemical examinations of the enteric nervous system (ENS) were performed on biopsies of healthy cats and compared to findings in cats suffering from inflammatory bowel disease or intestinal lymphoma. In lymphocytic–plasmacytic enterocolitis all affected samples had significant reductions in glial fibrillary acidic protein and vasoactive intestinal peptide (VIP) and mostly of neuron-specific enolase (NSE) possibly reflecting alterations in enteric glial cells and neurons. In cases with eosinophilic gastroenterocolitis significantly reduced phosphorylated neurofilament (PN) expression was present suggesting a disturbance in neuronal cytoskeleton, whereas cats with fibrosing enteropathy had reduced expression of NSE, non-phosphorylated neurofilaments (NPN), PN and VIP, possibly reflecting neuronal disturbances. In cases with intestinal lymphoma only the reduction in PN and the increase in NPN were obvious suggesting direct damage or interference of neoplastic cells with enteric neurons. In conclusion, structural and functional alterations of the ENS may contribute to clinically evident signs of vomiting and/or diarrhea.     

Detection of Mycobacterium avium subspecies paratuberculosis-specific DNA by PCR in intestinal biopsies of dogs

Background: Mycobacterium avium subspecies paratuberculosis (MAP) is the cause of paratuberculosis. MAP infections have not been reliably detected in dogs, but a reemerging debate about the link between MAP and Crohn's disease has renewed interest about the occurrence of MAP in pets.
Hypothesis: This study was undertaken to examine canine intestinal biopsies for the presence of MAP-specific DNA.
Animals: Forty-two dogs with chronic vomiting, diarrhea, or both; and 14 dogs with no gastrointestinal disease.
Methods: All dogs with signs of gastrointestinal disease had a standard work-up for chronic gastrointestinal disease. Endoscopically obtained intestinal biopsies were submitted for histopathologic and molecular investigations. Biopsies were screened for MAP-specific DNA by 3 polymerase chain reaction (PCR) methods (nested, seminested, and triplex real-time PCR). Samples from control dogs were obtained during necropsy.
Results: Histopathology of the biopsies was indicative of inflammatory bowel disease (IBD) in 17 and neoplasia in 6 dogs. Six dogs showing nonspecific changes responded to diet and were classified as having food-responsive enteropathy. In 13 dogs a final diagnosis was not established. MAP-specific DNA was detected and confirmed by sequencing in 8 dogs (19%). These dogs were diagnosed with food-responsive enteropathy (n = 3), IBD (n = 2), and open diagnosis (n = 3). MAP-specific DNA was not detected in dogs with no gastrointestinal disease.
Conclusions and clinical importance: MAP-specific DNA was detected in approximately one fifth of dogs with chronic gastrointestinal disease and might play a role as a pathogenic agent. Apart from animal welfare, the zoonotic aspect warrants further studies addressing the viability of MAP organism in canine intestinal biopsies by culture.     

Endoscopic Assessment of the Duodenum in Dogs with Inflammatory Bowel Disease

Background

Endoscopy is performed for direct inspection of the mucosa and acquisition of biopsies in dogs with inflammatory bowel disease (IBD).

Aim

To evaluate the interobserver agreement in the endoscopic assessment of duodenal mucosa in dogs with IBD.

Methods

Thirty‐five archived endoscopic images of grossly normal (n = 6) and inflamed (n = 29) duodenal mucosa were displayed to 3 expert and 5 trainee endoscopists. Each image was assessed independently by endoscopists for mucosal abnormalities using established indices (of hyperemia, granularity, friability, lymphatic dilatation, and erosions) or interpreted as normal mucosa (trial 1). A repeated trial (trial 2) was performed with the same images presented in random order 1 month later, and accompanied by a visual template.

Results

There was slight interobserver agreement in initial mucosal assessment for expert and trainee endoscopists in trial 1 (kappa ≤ 0.02, P > .05). Interobserver agreement improved in trial 2 for both expert and trainee endoscopists (kappa = 0.2, P > .05) for experts and (P < .05) for trainees. There was a significant (P < .01) improvement in trainee endoscopy scores of lesions from trial 1 to trial 2. Regression analysis showed a significant (P < .01) difference between expert versus trainee endoscopy scores in trial 1. Repeat lesion assessment aided by use of a visual template (trial 2) improved the overall scores of trainee endoscopists to near that of expert endoscopists (P = .06).

Conclusions and Clinical Importance

Interobserver agreement of IBD mucosal appearance from endoscopic findings benefitted from operator experience.