Answer: Intestinal spirochetosis. The condition was diagnosed as intestinal spirochetosis (IS). Histopathology of the colonic mucosa showed hematoxylin and eosin (H&E) and Warthin-Starry stains that were characteristic of intestinal spirochetosis. Intestinal spirochetosis is an uncommon disease in humans caused by Brachyspira spp. and is diagnosed when colorectal epithelial colonization by spirochetes is present. The highest rates of IS are reported in people living with HIV (PLWH) and men who have sex with men (MSM). The diagnosis is commonly made via random biopsies of samples from asymptomatic patients during routine colonoscopy; however, various gastrointestinal symptoms can occur. Although not clinically distinguishable, Brachyspira aalborgi is the most prevalent species overall and highest in Western countries, whereas Brachyspira pilosicoli incidence is highest in developing countries and among PLWH, particularly among MSM, given its fecal-oral proclivity (1). Brachyspira spp. do not stain well with Gram stain and require selective anaerobic media for growth: the spirochetes grow slowly (up to 2 weeks); the colonies form a thin film and are weakly hemolytic (2, 3). Characteristic appearance on H&E stain demonstrates a thickened brush border which appears dark brown with the Warthin-Starry stain. Electron microscopy demonstrates that B. pilosicoli is longer (4 to 20 μm), whereas B. aalborgi is shorter (2 to 6 μm) (4). The clinical differential diagnosis in MSM may include an infectious proctitis. In this regard, Brachyspira spp. may exhibit immunohistochemical cross-reactivity to Treponema pallidum antibodies, leading to a misdiagnosis of syphilis, however, syphilitic proctitis is characterized by active colitis (5). PCR amplification has proven useful, and DNA can be directly extracted from feces or biopsy specimens. The most commonly used PCR targets are the B. pilocisoli 16S rRNA gene, which contains a signature sequence for this species (2).The diagnosis of IS can be easily missed but should be considered in PLWH, especially MSM with gastrointestinal symptoms not explained by other etiologies. No evidence of bleeding was found on colonoscopy, and the patient’s hematochezia self-resolved. Metronidazole is generally recommended for symptomatic patients, and Brooke et al. found that in 123 human isolates, all were susceptible to metronidazole (MIC90 of 0.25) (6).
See https://doi.org/10.1128/JCM.00400-20 in this issue for photo quiz case presentation.
ACKNOWLEDGMENTS
This work was supported by the Infectious Diseases Service at Walter Reed National Military Medical Center. The cost of reproducing color figures is provided by Walter Reed National Military Medical Center.
None of the authors have conflicts of interest.
The views expressed are those of the authors and do not reflect the official views of the Department of Defense, or the Departments of the Army, Navy, or Air Force. Mention of trade names, commercial products, or organizations does not imply endorsement by the U.S. Government. The corresponding author had full access to all the data and had final responsibility for the decision to submit the article for publication.
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