Search for a command to run...
This report describes a rare case of acute gastric mucosal lesion associated with H. felis infection. Numerous bacilli were identified within the mucopurulent exudate. The microorganisms were larger, longer, and more tightly coiled than H. pylori. Low vacuum-SEM reveals the spiral microorganisms with characteristic two or three periplasmic fibrils on the surface. RT-PCR detected the presence of H. felis urease B gene. Non-Helicobacter pylori Helicobacter (NHPH) species have been regarded as a group of Helicobacter organisms that are primarily found in animals and can be present in gastric lesions, including chronic gastritis and gastric mucosa-associated lymphoid tissue (MALT) lymphoma. Helicobacter felis (H. felis), one of the NHPH species, colonizes the gastric mucosa of dogs and cats. In 2012, Wüppenhorst et al. [1] described the first isolation of H. felis from a human case with mild chronic gastritis. However, studies on gastric mucosal lesions associated with H. felis infection remain extremely limited. Scanning electron microscopy (SEM) allows the visualization of ultrastructural cellular details but requires specialized processing and complex specimen preparation. Low-vacuum scanning electron microscopy (LV-SEM) enables the direct, high-magnification, three-dimensional observation of routine histological paraffin-embedded tissue sections. In the present study, we report a rare case of acute gastric mucosal lesions (AGML) in which H. felis infection was confirmed by LV-SEM and reverse transcription polymerase chain reaction (RT-PCR). A woman in her 40 s, who had a cat, developed upper abdominal pain after traveling to Thailand. Her past medical history was unremarkable. She denied any direct exposure to feline vomitus or other gastric contents preceding her travel, and had no contact with animals, including cats or dogs, in Thailand. Blood test results, including complete blood count and renal and liver profiles, were within normal ranges. The rapid urease test showed weak and delayed positivity compared with a typical H. pylori infection. IgG antibodies against H. pylori were confirmed to be negative. Upper gastrointestinal endoscopy revealed an AGML characterized by multiple hemorrhagic erosions without evidence of atrophic gastritis (Figure 1a). Histologically, the nonatrophic fundic mucosa demonstrated erosive changes with hemorrhage and fibrinopurulent exudate (Figure 1b), accompanied by dense neutrophilic infiltration extending into the fundic glands (Figure S1). Numerous bacilli were identified within the mucopurulent exudate and glands using hematoxylin and eosin and Giemsa staining (Figure 1c and Figure S2). These microorganisms were larger, longer, and more tightly coiled than H. pylori (Figure 1d). LV-SEM was performed on paraffin-embedded sections, revealing several spiral microorganisms measuring approximately 5–6 μm in length (Figure 1e). Two or three periplasmic fibrils running along the external aspect of the helix were regularly observed. These spiral bacilli exhibited moderately coiled bodies with five to seven turns (Figure S3). Based on the electron micrographs of Helicobacter species published by Stoffel et al. [2], the ultrastructural features were considered consistent with H. felis. Gastric Helicobacter species–specific RT-PCR was performed using primers for the urease A and B genes (Table S1). The analysis detected H. felis–specific amplicons of 350 and 241 bp, confirming the presence of H. felis (Figure 1f and Figure S4). Her symptoms resolved 1 week after triple therapy consisting of rabeprazole, amoxicillin, and clarithromycin, without recurrence of AGML. Three months after the eradication therapy, the rapid urease test was negative. Differentiating Helicobacter species using routine light microscopy is difficult and may contribute to the underdiagnosis of NHPH infection. In the present case, Giemsa-stained sections clearly demonstrated long, large bacilli that were more elongated than H. pylori and exhibited a tightly coiled spiral morphology, suggestive of NHPH [3]. Unlike H. pylori, which typically adheres to the surface of the gastric foveolar epithelium, these organisms float within the surface mucus layer, which is another distinguishing feature from H. pylori [3]. Furthermore, H. felis has characteristic periplasmic fibrils in SEM, while Helicobacter heilmannii (H. heilmannii) shows a more tightly coiled morphology and a lack of periplasmic fibrils [2]. NHPH, particularly H. heilmannii, have been reported to be associated mainly with chronic gastritis, and H. heilmannii-associated gastritis shows less severe neutrophilic and mononuclear cell infiltration than H. pylori-associated gastritis [3]. A pediatric case of H. felis-associated gastritis presented with persistent epigastric pain and histologically mild chronic gastritis [1]. These histological findings were comparable to those of H. heilmannii-associated gastritis. Yakoob et al. [4] reported the prevalence of H. pylori (57%), H. heilmannii (6%), and H. felis (4%) in the gastric mucosa of 250 patients with dyspepsia. The prevalence of H. felis infection was lower than that of H. heilmannii. The histological findings in the gastric mucosa infected with H. felis indicated chronic inflammation or chronic active inflammation without lymphoid follicles [4]. A recent study suggested that NHPH infection contributes to the development of MALT lymphoma and its response to eradication therapy. NHPH infection was more common in 182 cases of H. pylori–negative gastric MALT lymphoma, and NHPH-positive tumors responded favorably to eradication therapy [5]. H. felis was not detected by PCR in this study. Collectively, the present case suggests that H. felis infection may exert pathogenic effects on the human stomach and represents a potential cause of acute gastric mucosal injury and chronic gastritis; however, its association with gastric MALT lymphoma remains unclear. Gastric infections caused by H. felis are commonly observed in dogs and cats. Two of the ten H. felis-positive patients with dyspepsia were exposed to cats or dogs [4]. Identical NHPH species were detected in both patients and their companion animals. In the present case, transmission from a domestic cat was suspected. However, there was no history of close contact with the patient's domestic cat before symptom onset, or contact with animals or animal waste during travel to Thailand. Moreover, colonization of domestic cats with H. felis could not be confirmed. In this case, the transmission route remained undetermined. LV-SEM is a valuable technique that enables direct three-dimensional observation of paraffin-embedded tissue sections at high magnification. This case report is notable as a rare case in which H. felis was identified in human gastric mucosa affected by AGML. Furthermore, it may be the first report to demonstrate the identification of H. felis based on the characteristic ultrastructures in paraffin-embedded tissue using LV-SEM. In conclusion, we report a rare case of AGML associated with H. felis infection. This case suggests that H. felis can colonize the human stomach and may be pathogenic, leading to AGML. Furthermore, LV-SEM was shown to be a useful tool for the detailed morphological evaluation of Helicobacter species in paraffin-embedded tissues. This report highlights the importance of considering NHPH infections during routine pathological diagnosis. Murasaki Aman: histopathological evaluation, conceptualization, investigation, data analysis, figure preparation, manuscript writing – original draft. Toshihiro Gi: histopathological evaluation, investigation, data analysis. Kazunari Maekawa: histopathological evaluation, figure preparation. Tomoaki Kimura: clinical data collection, manuscript writing – review and editing. Akira Sawaguchi: manuscript writing – review and editing, supervision. Atsushi Yamashita: histopathological evaluation, conceptualization, manuscript writing – review and editing, supervision. All authors have read and approved the manuscript before submission. The authors thank Prof. Ryoji Kushima (Department of Pathology, Shiga University of Medical Science, Japan) for his valuable comments on the pathological diagnosis and Nahoko Udatsu and Kyoko Ohashi for their excellent technical support. Atsushi Yamashita is an Editorial Board member of Pathology International and co-author of this article. To minimize bias, the author was excluded from all editorial decision-making related to the acceptance of this article for publication. The remaining authors declare no conflicts of interest. The case study was conducted in accordance with the principles of the Declaration of Helsinki (1975). Written informed consent was obtained from the patient. Ethics committee approval was not required for this single case report according to the institutional policy. Figure S1: Fundic glands show dense infiltration of neutrophils. Figure S2: Giemsa staining demonstrates numerous spiral bacilli within the mucus layer. Figure S3: High magnification image shows characteristic features of spiral bacillus exhibiting a moderately coiled body with five to seven turns and periplasmic fibrils. Figure S4: Reverse transcription polymerase chain reaction detected amplicon corresponding to Helicobacter felis urease A and B genes at the 241-bp position. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.