The small bowel shows alteration of the mucosal architecture due to massive lymphoid infiltration.

Many of the lymphoid follicles show suppurative lymphadenopathy. Suppurative inflammation may be mixed with granulomatous inflammation as well (not shown here).

The massive lymphoid inflammation includes back to back follicles which undermine the mucosa.

Surface ulceration and injured mucosal pattern mimics Crohn's. Yersinia has the potential to cause apthous ulcers and fissures and in some cases, appear indistinguishable from Crohn's disease on histology.

Yersinia enterocolitica and Yersinia pseudotuberculosis are gram-negative anaerobic bacilli that are pathogenic toward humans. These bacteria infect Peyer's patches and mesenteric lymph nodes resulting in the potential to cause systemic infection. There is preferential involvement of the appendix, ileum, and right colon. Nodes may be markedly enlarged and necrotic.

Infection occurs through the fecal-oral route, by hand-to-mouth transfer after handling of contaminated animals or animal products, or by ingestion of contaminated food or water. The organism can grow at 4 degrees C, so refrigerated meats are a potential source.

Typical symptoms include fever, diarrhea, and abdominal pain of 1 to 3 weeks duration. Nausea and vomiting occur in some. Stool specimens are often positive for fecal leukocytes, blood, or mucus may be present in stool specimens. Often the clinical impression is that of acute appendicitis. If the patient were to undergo colonoscopy, the findings may suggest Crohn's disease, with the presence of elevations with or without ulceration in the ileum and yellow oval aphthae of the colon.

Infections are usually self-limited, but in those with prolonged enteritis, extraintestinal manifestations, or increased risk of septicemia, antibiotics such as aminoglycosides, TMP-SMX, doxycycline, or fluoroquinolones are employed.

Usually self limited and complete recovery is the rule. However, septicemic patients have mortality rates in the 50% to 75% range despite appropriate antibiotic therapy.