Introduction
Granulomatous colitis (GC) is also known as histiocytic ulcerative colitis (HUC) in the veterinary literature and afflicts both Boxer dogs but also non-Boxer dogs. This condition was first described in dogs in 1965 and is characterized by diffuse inflammation of the colon, cecum, and rectum with infiltration of periodic acid-Schiff (PAS) positive macrophages of the lamina propria and stroma of the submucosa with accompanying epithelial and submucosal ulceration (German et al.
2000; Van Kruiningen 1967). In human Crohn's disease and ulcerative colitis there is mounting evidence supporting the role of enteric microflora (Simpson et al. 2006). These conditions have increased number of bacteria but reduced diversity, and many patients will demonstrate clinical response to antimicrobial therapy. Host factors will also play a role, with individual susceptibility found in individuals with genetic defects in pathogen recognition receptors like toll-like receptors (TLR). Simpson and others proposed that an uncharacterized infectious agent or an abnormal mucosal flora is involved in the etiopathogenesis of GC (Simpson et al. 2006). Enteroinvasive E. coli was determined to be the invasive bacteria found in the mucosal biopsies, although the role of infectious diseases had been speculated on in prior studies, including culture of bacteria from regional lymph nodes and immunostaining for anti-E coli antibody, among other organisms in macrophages on formalin-fixed colon and colic lymph nodes (Van Kruiningen 1967; Van Kruiningen, Civco, and Cartun 2005). These strains of E. coli, adherent and invasive E. coli (AIEC), are similar to those found in Chrohn's disease (Craven et al. 2010). It is assumed that host mucosal immunity is compromised allowing opportunistic invasion by E. coli strains. This condition has been described to respond within 7 days and dogs remain in remission at a 21-month follow-up, after a prolonged course of antibiotics, either enrofloxacin on its own or in combination with metronidazole and amoxicillin (Hostutler et al. 2004).
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