Intestinal Spirochetosis and Chronic Diarrhea: A Case Report and Literature Review

Spirochetosis is a rare condition characterized by the presence of spirochetes in the gastrointestinal tract. It is typically associated with immunodeficiency. We present a case of chronic watery diarrhea in a 48-year-old housewife who had a 12-week history of variable-volume bowel movements without blood or mucus, accompanied by a sense of urgency. Chronic diarrhea led to weight loss and fatigue, significantly impacting her quality of life. Despite the absence of known risk factors, a comprehensive clinical evaluation and exclusion of other potential causes prompted a rectosigmoid biopsy, which revealed distinctive histological findings of spirochetosis. This case underscores the significance of considering spirochetosis as a differential diagnosis in cases of chronic watery diarrhea, even in the absence of immunodeficiency. The utilization of rectosigmoid biopsy and careful histopathological examination played a pivotal role in establishing an accurate diagnosis.


Introduction
Diarrhea is defined as a change in stool consistency corresponding with types five to seven on the Bristol stool chart in addition to an increased stool frequency of greater than three stools daily [1]. If these symptoms last longer than four weeks, it is known as chronic diarrhea [2]. The differential diagnoses are broad and include (i) irritable bowel syndrome (IBS), (ii) inflammatory bowel disease such as Crohn's disease, (iii) microscopic colitis, (iv) systemic disorders such as hyperthyroidism, (v) medications including antibiotics, antacids, and chemotherapeutic agents, and (vi) malabsorptive syndromes such as celiac disease, chronic pancreatitis, and lactose intolerance [2]. Chronic infections of the gastrointestinal tract have been linked to diarrhea. Common microbial culprits include Clostridium difficile, Vibrio cholerae, Salmonella, Shigella, and Giardia [2]. However, in rare cases, spirochete colonization in the colon may lead to chronic diarrhea in addition to other symptoms, this is known as human intestinal spirochetosis (IS).
Human IS is a rare condition that is characterized by the presence of spirochetes within the apical membrane of the colorectal epithelium of the large intestines [3]. The most common microorganisms that cause IS include the anaerobic bacteria Brachyspira pilosicoli, which is an opportunistic pathogen, and Brachyspira aalborgi, which is a non-pathogenic commensal that is part of the intestinal tract of humans and animals [4]. The prevalence of IS is not well documented, but higher rates of spirochete colonization and subsequent infection ranging from 10.8% to 64.8% are found in developing countries in Asia, such as India and Indonesia, Australia, and Africa [4,5]. Over the years, the reported rates of IS in the Western world have been on the rise with an estimated prevalence of 1-5% [6]. A study in Chicago in the 1900s discovered intestinal spirochetes in the feces of 28% of healthy persons tested [3].
Habitation in unhygienic conditions with exposure to contaminated water and infected animals continues to be the most significant risk factor for IS in poorly developed areas [6]. In developed countries, immunocompromised states such as infection with human immunodeficiency virus (HIV) and persons who engage in homosexual intercourse, specifically men who have sex with men (MSM), are common risk factors and are associated with the highest prevalence with rates ranging between 20.6% and 62.5% [3,7]. This leads to the question of whether IS in the developed world can be classified as a sexually transmitted infection (STI) [8]. Although the risk is higher in these individuals, there are some cases of IS occurring in heterosexual and immunocompetent persons [9]. The presence of spirochetes in the colon or stool may not lead to the clinical manifestations of IS and symptoms of this condition do not reveal the exact location of the microorganisms in the intestine [6]. Colonization may occur in any portion of the colon with reported cases of isolated involvement of the rectum or proximal colon only or within the whole length of the large intestine [5]. This contributes to the heterogeneous nature of the symptomatic presentation of IS [5]. The severity of IS symptoms is broad and ranges from asymptomatic colonization to severe features, including abdominal pain, chronic diarrhea, meteorism, nausea and vomiting, hematochezia, and weight loss [10]. Severe cases of IS in critically ill patients may lead to spirochetemia, sepsis, and multiple organ failure [3].
In this report, we present the case of a previously healthy, 48-year-old female with a 12-week history of chronic diarrhea who was subsequently diagnosed with IS via rectosigmoid biopsy.

Case Presentation
A 48-year-old African housewife, previously healthy, presented to our gastroenterology clinic with a chief complaint of chronic watery diarrhea and vague abdominal pain persisting for the past 12 weeks. She complained of multiple loose and watery bowel movements per day, accompanied by a sense of urgency and abdominal pain. The volume of each bowel movement was variable, ranging from small to moderate. There were no reports of blood or mucus in the stool. The patient described a sense of urgency associated with bowel movements, and there were no specific triggers or exacerbating factors identified. The chronic watery diarrhea had significantly impacted the patient's daily life, resulting in weight loss (2-3 kg) and fatigue. The patient reported no recent history of travel and denies the use of any recent antibiotics or medications. However, in an attempt to alleviate her diarrhea, she resorted to over-the-counter (OTC) medications (bismuth and loperamide), but, unfortunately, there was no improvement in her condition. She was married and reported no history of multiple sexual partners. However, she admitted to engaging in anal intercourse with her husband in the past.
On physical examination, the patient appeared malnourished, and mild tenderness was elicited on abdominal palpation without any palpable masses or organomegaly. Vital signs were as follows: blood pressure was 100/70 mmHg, and heart rate was increased to 110 beats per minute with a normal body temperature. Stool samples were collected for microbiological analysis, including testing for bacterial, viral, and parasitic pathogens, as well as fecal calprotectin levels to assess for underlying inflammation. Additionally, blood tests were performed, including a complete blood count, liver and renal function tests, serum electrolytes, and inflammatory markers. The laboratory results showed no significant abnormalities, ruling out common causes such as infectious agents, inflammatory bowel disease, and malabsorption syndromes. The patient underwent further investigations, including celiac serology, and thyroid function tests, which did not reveal any specific abnormalities.  Considering the patient's sexual history, which involved anal intercourse with her husband, additional investigations were pursued to explore the possibility of an STI contributing to her symptoms. Specific laboratory tests were performed to screen for common STIs, including gonorrhea, chlamydia, syphilis, and HIV. However, these tests did not provide evidence of an STI.
Despite the extensive evaluation, the chronic watery diarrhea persisted, and the patient's quality of life continued to decline. To further investigate the underlying cause, a rectosigmoid biopsy was performed. The rectosigmoid biopsy specimens were subjected to histopathological examination. Microscopic analysis (light microscope) revealed the presence of spirochetes within the mucosal lining of the rectosigmoid colon. The histological analysis of spirochetosis demonstrated a notable, blurred blue line at the luminal border of the colonic mucosa upon examination with hematoxylin and eosin (H&E) staining. Additionally, the findings revealed the presence of non-specific inflammation characterized by lymphocytic, neutrophilic, or eosinophilic infiltration within the lamina propria or epithelium ( Figure 1).
A special silver stain, Warthin-Starry silver, was used to highlight the spirochetes, confirming the diagnosis of spirochetes ( Figure 2).

FIGURE 2: Histological section of the biopsy specimen showing spirochetosis using Warthin-Starry silver staining (arrowhead).
The presence of characteristic spiral-shaped organisms within the colon mucosa was consistent with gastrointestinal spirochetosis. Notably, the identified spirochetes were consistent with B. aalborgi infection.
To effectively manage the patient's condition, a course of metronidazole 500 mg four times daily for a duration of two weeks was initiated. Following the commencement of treatment, the patient reported a significant improvement in her symptoms, with a reduction in the frequency of bowel movements and an improvement in stool consistency. The patient was closely monitored during the treatment period, and no adverse effects were reported. The patient's energy levels improved, and she regained the weight she had lost during the illness.

Discussion
B. aalborgi and B. pilosicoli belong to the Brachyspiraceae family, which is one of the three families of spirochetes [9]. The other two are Spirochaetaceae, comprising Borrelia, Spironema, Spirochaeta, and Treponema, and Leptospiraceae including the bacteria Leptonema and Leptospira [9]. Infections caused by bacteria from the Leptospiraceae and Spirochaetaceae families may also cause diarrhea and are more common, making the diagnosis of IS more difficult. For example, infection with Treponema pallidum may cause syphilitic proctitis, which is rare, and presents with diarrhea and lower abdominal pain with rectal biopsy histological findings of non-specific inflammation and spirochetes on silver stain [11]. Therefore, due to some overlapping symptoms, extensive patient history, lab work, and physical examination are required to differentiate between IS bacteria and other spirochetes.
The exact pathogenesis of IS and the mode of transmission in immunocompetent persons is unknown; however, some studies suggest that the bacteria can be transmitted via a fecal-oral route from contaminated water or poultry which may be the primary sources of infection in developing countries [9]. MSM regardless of HIV status have an increased risk of being colonized with B. pilosicoli and are more likely to be symptomatic when compared to IS in heterosexual persons which is commonly caused by B. aalborgi [12].
Studies have found that in MSM, some cases of IS are associated with gonococcal and/or Shigella flexneri coinfection indicating that a sexual route of transmission is possible [8]. It is theorized that the oro-anal sexual practices of MSM may alter the rectal microenvironment increasing the risk of colonization and infection [12]. Although patients with HIV and IS tend to be symptomatic, there appears to be no correlation between the degree of immunodeficiency and the extent of the disease [3].
These bacteria are slow growing with estimated growth times of six days ( B. pilosicoli) and two weeks (B. aalborgi), and because intestinal colonization is asymptomatic, the duration of the incubation period is unknown [3]. Due to the heterogeneous nature of IS, the clinical presentation varies. The most common symptom is chronic diarrhea which is usually watery in character [10]. These opportunistic anaerobes have a cytopathic effect by destroying the microvilli on the absorptive epithelial cells and inducing changes in the cellular cytoskeleton [8]. This may lead to chronic secretory diarrhea with associated symptoms of abdominal pain, nausea, vomiting, and weight loss due to nutrient loss [8]. In some cases, colonic invasion and inflammation may lead to hematochezia [7].
Diagnosis begins with a thorough patient history and laboratory tests to rule out the differential diagnoses of chronic diarrhea. Due to the rare nature of this condition, a high index of clinical suspicion is required to establish the diagnosis and begin appropriate treatment. An endoscopic view of the colon via colonoscopy commonly yields normal results with occasional cases of erythematous areas present [7]. A study by Alsaigh and Fogt evaluated the various clinical presentations of 15 patients with a confirmed diagnosis of IS [13]. Colonoscopy findings were described as normal in six patients, polyoid in seven patients, erythematous in one patient, and a lesion in one case [13]. This indicates that normal colonoscopy results are not sufficient to rule out the diagnosis of IS. The histological view of a biopsy sample is the gold standard diagnostic test, and this disease is characterized by the appearance of a 3-6 μm diffuse blue fringe along the intercryptal epithelial layer on the H&E stain [10]. Visualization of the spirochetes on Warthin-Starry or other silver stains confirms the diagnosis [10]. In some cases, organisms may be non-invasive and found on the cell surface; however, intraepithelial mast cell and IgE plasma cell infiltration may occur, leading to colonic inflammation [3]. Microvilli blunting, glycocalyx defects, and mitochondrial swelling may also occur [10]. The degree of cellular destruction positively correlates with the degree of spirochete invasion and severity of symptoms, with diarrhea being more pronounced in persons with severe microvilli destruction and higher spirochete attachment [3].
Colonization varies from patient to patient and may be isolated or affect the entire colon including the rectum [5]. Studies have found that intestinal spirochetes have a tendency to affect the right side and ascending colon; however, in some cases like this one, isolated rectosigmoid involvement may occur [10]. Biopsies in the ascending colon have a success rate of diagnosis of 56%, followed by the transverse colon (54%), descending colon (48%), sigmoid colon (47%), cecum (40%), and, lastly, the rectum (38%) [4]. In this case, the colonoscopy with biopsy of the ascending, transverse, and descending colon yielded normal results while the rectosigmoid biopsy aided in confirming the diagnosis. This signifies that isolated colonic biopsies may lead to missing the diagnosis, therefore, a biopsy from each segment of the colon will confirm or completely rule out IS. Research by Tanahashi et al. discovered that immunostaining with anti-T. pallidum and anti-M. bovis antibodies cross-react with spirochetes and aids in the visualization of spirochetes on the epithelial surface [14]. They are easily available and have been found to provide clear staining [14]. Newer methods of identifying IS bacteria are being explored. Fecal polymerase chain reaction (PCR) targeting the 16S ribosomal ribonucleic acid (rRNA) subunit and reduced nicotinamide adenine dinucleotide (NADH) oxidase genes specific for B. pilosicoli and B. aalborgi show promising results [15]. PCR techniques are useful for specifically detecting the presence of B. aalborgi or B. pilosicoli DNA in biopsied tissue samples; however, they do not provide information about the distribution or extension of the organisms in the sample [15].
Antimicrobial therapy, specifically metronidazole monotherapy, is the most effective treatment modality for IS [4]. Its efficiency surpasses macrolide, clindamycin, and macrolide plus metronidazole use [10]. In cases of coinfection, combination antibiotic therapy may be required. Treatment dosage and duration may differ and depend on factors such as age and weight; however, patients are normally given metronidazole for 10 days [10]. Although capable of symptom resolution, some patients treated with metronidazole have reported symptomatic relapse when following up. This may be due to incomplete eradication or re-infection from environmental sources [4]. A study by Jabbar et al. found that metronidazole treatment paradoxically promoted Brachyspira relocation into the colonic crypts and goblet cell granules representing a possible bacterial strategy to elude antibiotic exposure [16]. This may also be a possible cause of symptom continuance and relapse; therefore, further research on spirochete antibiotic sensitivity and alternative modes of treatment is required for more effective management. Some cases of IS have been reported to spontaneously resolve [10].
IS has been reported in the literature with new discoveries surfacing every few years. Table 2 summarizes various reports highlighting the patients' presentations, significant diagnostic findings, and the treatment and prognosis [8][9][10]13,14,[17][18][19][20]. In addition to the cases mentioned, our case aims to increase physician awareness about the heterogeneous nature of intestinal spirochetosis and the importance of considering it as a differential diagnosis in patients presenting with chronic diarrhea.

Conclusions
Human IS is a rare gastrointestinal condition that remains poorly understood. IS manifests with a wide range of symptoms, with chronic diarrhea being the most common presentation. Given the extensive list of potential causes for chronic watery diarrhea, IS often goes unnoticed and undiagnosed in many individuals. This case underscores the importance of considering spirochetosis as a potential differential diagnosis in cases of chronic watery diarrhea, even in individuals without immunodeficiency or predisposing factors. Therefore, maintaining a high index of clinical suspicion and employing appropriate diagnostic measures, such as colonic biopsy with Warthin-Starry silver staining, along with targeted treatment using metronidazole for symptomatic patients, are crucial.
While spirochetes typically colonize the ascending colon, there have been instances of isolated rectal involvement, underscoring the importance of conducting rectosigmoid biopsies to effectively rule out the diagnosis. Additionally, PCR testing for B. aalborgi and B. pilosicoli, as well as anti-treponemal and anti-M. bovis antibody testing, has shown promise in aiding the diagnosis of IS. Physicians should be aware of this condition and its diverse range of symptoms, particularly in endemic areas, to facilitate timely management and enhance patients' quality of life.

Additional Information Disclosures
Human subjects: Consent was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.