Cyniclomyces guttulatus Infection in Dogs: 19 Cases (2006–2013)
Cyniclomyces guttulatus, a gastrointestinal yeast of rabbits, is considered an uncommon, nonpathogenic, “pass through” organism and possible opportunistic pathogen in dogs that consume rabbit feces. This retrospective study aimed to characterize the presenting complaint, clinical findings, location of organisms, and final diagnosis of dogs in which yeast morphologically consistent with C. guttulatus were identified at a veterinary teaching hospital from 2006–2013. The prevalence of C. guttulatus infection in a general population of dogs from a regional animal shelter was also determined. Nineteen dogs were retrospectively identified as diagnosed with C. guttulatus infection. Among these, 79% presented with a chief complaint and/or clinical signs consistent with gastrointestinal tract disease. The most common clinical sign was chronic diarrhea. The majority of dogs had C. guttulatus identified cytologically within samples obtained from the gastrointestinal tract; however, four dogs had C. guttulatus identified in non-gastrointestinal tract samples, including a nasal biopsy (one dog) and urine (three dogs). C. guttulatus was not identified in any of 105 shelter dogs evaluated, suggesting low prevalence of C. guttulatus in our region. These findings suggest that additional studies to determine if C. guttulatus is a potential cause or consequence of gastrointestinal illness in dogs may be warranted.
Introduction
Cyniclomyces guttulatus yeast have been infrequently described in fecal specimens from dogs.1–5 Recognition that C. guttulatus is also a commensal yeast of the rabbit gastrointestinal tract has led to the frequent presumption that dogs diagnosed with C. guttulatus infection must have ingested rabbit feces.6 In contrast, recent studies suggest that C. guttulatus may also be a normal inhabitant of the gastrointestinal tract in dogs.7 In published reports of C. guttulatus infection in dogs, however, clinical signs of gastrointestinal tract disease are common.4,5 Whether C. guttulatus is a normal inhabitant of the gastrointestinal tract, simply a pass-through organism associated with ingestion of rabbit feces, or a possible cause of gastrointestinal tract disease in dogs remains unclear.
As a foundation for further defining any relationship of C. guttulatus infection to clinical disease in dogs, the purpose of this study was to retrospectively characterize the presenting owner complaint, clinical findings, location of C. guttulatus, and final diagnosis of dogs identified with C. guttulatus infection at the North Carolina State University Veterinary Hospital (NCSU-VH). The prevalence of C. guttulatus infection in a general population of dogs from a regional animal shelter was also determined.
Materials and Methods
Case Selection and Review of Medical Records
The medical records of the NCSU-VH were searched for dogs and cats having a diagnosis of C. guttulatus recorded over the time interval from January 2006 to January 2013. Each medical record was retrospectively reviewed to obtain information pertaining to patient signalment, presenting complaint of the owner, historical information pertaining to clinical signs and current or prior administration of antimicrobial drugs or steroids, physical examination findings, diagnostic testing and results, sample type in which C. guttulatus was identified, treatments administered, and treatment outcome. Diarrhea was characterized as small bowel, small and large bowel (mixed), or large bowel in origin, based on fecal characteristics (e.g., volume and appearance) and clinical signs (defecation frequency, body condition, and appetite) recorded in the medical record.
Regional Prevalence of C. guttulatus in Feces of Shelter Dogs
Voided fecal samples were collected from dogs housed at a regional county animal shelter on three separate occasions between July 2011 and September 2011. For each dog, information pertaining to estimated age, sex, and breed were recorded. For each fecal specimen, a clean cotton-tipped swab was used to prepare a thin smear of feces on a clean glass microscopy slide. In instances in which feces were obtained from a run housing more than one dog, only a single fecal specimen was obtained. Following staining, each fecal smear was examined by a board-certified clinical pathologist (I.P.) for the presence of yeast morphologically consistent with C. guttulatus.
Identification of C. guttulatus in Clinical Specimens
All cytological specimens were prepared as thin smears on glass microscope slides. Specimens of fecal origin were fixed in methanol and stained manuallya. Specimens of non-fecal origin were fixed in methanol and stained using modified Wright-Geimsab in an automated staining devicec. Samples of liquid urine sediment were prepared on glass microscope slides, cover-slipped, and examined unstained. Histological specimens were fixed in 10% neutral buffered formalin, paraffin-embedded, and sectioned at a thickness of 7 μm prior to mounting on glass slides and staining with a modified hematoxylin and eosin staind using an automated devicee. Identification of C. guttulatus in each clinical specimen was made by either a board-certified veterinary clinical or gross pathologist and determined on the basis of the unique light microscopic appearance of this yeast.1–5 The vegetative form of C. guttulatus is a 4.4–8 × 8.8–21 μm elongated cylindrical structure, usually with two basophilic nuclei that have an “eyeglass case” appearance6 (Figure 1). These structures can be found singly, in pairs, or branching.
Citation: Journal of the American Animal Hospital Association 52, 1; 10.5326/JAAHA-MS-6307
Results
Signalment of Dogs with C. guttulatus
A total of 19 dogs were identified as diagnosed with C. guttulatus at the NCSU-VH between January 2006 and January 2013. No cats were diagnosed with C. guttulatus over this time period. The dogs ranged in age from 1–16 yr (median, 9 yr) and consisted of 10 spayed female, 7 castrated male, and 2 intact male dogs. A variety of breeds were represented, including mixed breed (4 dogs); German shepherd dog, golden retriever, Labrador retriever, and dachshund (2 dogs each); Boston terrier, boxer, Boykin spaniel, cocker spaniel, rottweiler, Samoyed, and Swiss mountain dog (1 dog each).
Dogs with Gastrointestinal Tract Disease and C. guttulatus
Owners of 13 dogs diagnosed with C. guttulatus infection had presenting complaints consistent with clinical signs of gastrointestinal tract disease (cases 1–6, 8–13, 15; Table 1) while an additional 2 dogs had clinical signs of gastrointestinal disease that were not included as part of the presenting complaint (cases 7 and 14). The most common clinical signs of gastrointestinal disease reported in dogs with C. guttulatus were diarrhea (6 dogs) or both diarrhea and vomiting (7 dogs), followed by only vomiting (1 dog), or vomiting and regurgitation (1 dog). Based on characteristics reported in the medical record, diarrhea could be further classified as large bowel in 4 dogs, mixed bowel in 4 dogs and small bowel in 1 dog (Table 1). Classification of diarrhea could not be ascertained from the medical record of the remaining 4 dogs. The duration of gastrointestinal signs prior to presentation was documented as chronic (>2 wk duration) in 11 dogs, acute (≤1 wk duration) in 2 dogs, as an acute manifestation of chronic signs in 1 dog, and could not be determined from data in the medical record of the remaining dog.
All 15 dogs with clinical signs of gastrointestinal tract disease underwent testing pertinent to diagnosis of a gastrointestinal tract disorder as shown in Table 1. Cyniclomyces guttulatus was identified in specimens derived from the gastrointestinal tract in 14 dogs and in a urine sample collected by cystocentesis from the remaining dog (case 15). Sample types from the gastrointestinal tract in which C. guttulatus was identified included fecal or rectal smear (8 dogs), endoscopic gastric biopsy (3 dogs), fecal sedimentation (1 dog), endoscopic esophageal brushing (1 dog), and ultrasound-guided gastrointestinal mass aspirate (1 dog) (Table 1). Specific cytological or histological findings for each sample in which C. guttulatus was identified are shown in Table 2. Final diagnoses of the 15 dogs undergoing a specific diagnostic evaluation for gastrointestinal tract disease are shown in Table 1. Of these, 10 dogs had a definitive diagnosis of underlying inflammatory infiltrative disease (9 dogs) or infiltrative neoplasia (1 dog). The most common anatomical location of disease in these dogs was the small intestine (7 dogs), followed by the stomach (4 dogs), colon (2 dogs), and esophagus (1 dog). Five dogs had disease in more than one anatomical region of the gastrointestinal tract.
A specific course of treatment for C. guttulatus was prescribed for only two dogs (case 1 and case 3, Table 1). Case 1 presented for evaluation of chronic vomiting and suspected intermittent regurgitation of 2 mo duration. Endoscopic examination of the upper gastrointestinal tract revealed a grossly abnormal esophageal mucosa principally in the region of the thoracic esophagus. The stomach and duodenum were visibly unremarkable. Cytological examination of an endoscopic esophageal brushing revealed large numbers of individual and pseudo-hyphal chains of C. guttulatus as well as a large, mixed population of extracellular cocci, rods, and Simonsiella. The presence of columnar epithelial cells was interpreted as representing esophageal mucosal metaplasia and there was no evidence of inflammation. Histopathologic examination of endoscopic mucosal biopsy specimens obtained from the stomach and duodenum revealed multiple spiral bacterial organisms in the stomach and minimal, multifocal, eosinophilic, and lymphoplasmacytic inflammation in the duodenal mucosa. C. guttulatus was not identified in either the stomach or duodenum. Based on clinical and cytological findings of esophageal dysfunction and C. guttulatus yeast, the dog was prescribed nystatin (100,000 IU per os q 8 hr) for a duration of 1 mo, in addition to famotidine. The nystatin therapy was tolerated without apparent adverse effects. However, there was no clinical resolution of regurgitation and the dog was presented to the referring veterinarian for euthanasia. A post-mortem examination was not performed. The second dog (case 3) was presented for evaluation of vomiting and chronic diarrhea. An upper gastrointestinal endoscopic examination of the gastric and duodenal mucosa was unremarkable for visible abnormalities. Histopathologic examination of endoscopically obtained gastric mucosal biopsy specimens revealed moderate, multifocal to coalescing fibrosis within the lamina propria and the presence of large numbers of C. guttulatus yeast in the gastric lumen (Figure 2). Specimens from the duodenum revealed a moderate eosinophilic granular cell infiltrate. Based on these findings, the attending clinician prescribed prednisone and a hypoallergenic diet for treatment of inflammatory bowel disease and nystatin (100,000 IU total per os q 8 hr for 1 mo) for treatment of the C. guttulatus infection. The dog's clinical signs were reported to improve and the patient was lost to further follow-up.
Citation: Journal of the American Animal Hospital Association 52, 1; 10.5326/JAAHA-MS-6307
Dogs with Non-gastrointestinal Tract Disease and C. guttulatus
Owners of four dogs diagnosed with C. guttulatus infection had presenting complaints that were unrelated to gastrointestinal tract disease (cases 16–19; Table 3) including intermittent epistaxis (two dogs), heart murmur evaluation (one dog), and evaluation of an adrenal mass (one dog). For the dogs presenting with intermittent epistaxis, a nasal mass was identified during rhinoscopy in case 18. The mass was biopsied and histopathology revealed marked multifocal neutrophilic rhinitis with intraluminal C. guttulatus (Figure 3). Several months later, this dog sneezed out a nasal turbinate that was submitted for histopathology by the primary veterinarian and yielded a diagnosis of nasal adenocarcinoma. A specific examination of the specimen for the presence of C. guttulatus was not noted. In case 19, an incidental pyloric mass was identified by abdominal ultrasound. Fine needle aspirates of the pyloric mass yielded cytologic findings of well-differentiated epithelial cells, rare immature round cells, and large numbers of C. guttulatus organisms. In the two dogs presenting for evaluation of a heart murmur and adrenal mass, C. guttulatus was identified in a urine sample that was collected by cytocentesis. Neither dog was showing clinical signs of lower urinary tract disease and the presence of C. guttulatus was considered to be an incidental finding. Urine cultures were performed in both dogs and yielded no growth (case 16) and recurrence of a previously documented Enterococcus faecalis and Escherichia coli infection (case 17). Definitive diagnoses of these four dogs are shown in Table 3.
Citation: Journal of the American Animal Hospital Association 52, 1; 10.5326/JAAHA-MS-6307
History of Antibiotic and Steroid Administration in Dogs Diagnosed with C. guttulatus
Sixty-three percent (12/19) of dogs diagnosed with C. guttulatus infection were either currently receiving or had a recent history of administration of an antimicrobial drug within the time span of their presenting problem. The most common antimicrobial drug administered was metronidazole (7 dogs), followed by amoxicillin clavulanate (3 dogs), doxycycline (3 dogs), cefpodoxime (2 dogs), enrofloxacin (2 dogs), cephalexin (1 dog), ciprofloxacin (1 dog), and marbofloxacin (1 dog). Five animals had received or were currently receiving multiple antibiotics. Forty-seven percent (9/19) of dogs diagnosed with C. guttulatus infection were identified as currently or having recently received steroids or immunosuppressive drugs within the time span of their presenting problem. Types of steroids administered included prednisone (6 dogs), cyclosporine (3 dogs), sulfasalazine (2 dogs), an unknown injectable steroid (1 dog), cytosine arabinoside (1 dog), and a product containing trimeprazine tartrate with prednisolonef (1 dog).
Regional Prevalence of C. guttulatus in Feces of Shelter Dogs
A total of 90 voided fecal samples were obtained from 105 dogs housed at a regional county animal shelter between July 2011 and September 2011. The distribution in estimated age of the dogs sampled was <6 mo (39 dogs), 6–12 mo (32 dogs), 1–5 yr (31 dogs), and >5 yr (3 dogs). Sexes of the dogs were 47 intact females, 31 intact males, 11 spayed females, and 16 castrated males. A variety of breeds were represented; however, Pit bull terrier mixed breed dogs were the most common (39 dogs). Of the 90 fecal smears undergoing cytological examination by a board-certified clinical pathologist (I.P.), none were identified as containing C. guttulatus.
Discussion
The purpose of this study was to retrospectively characterize the presenting owner complaint, clinical findings, location of C. guttulatus yeast, and final diagnosis of dogs identified with C. guttulatus infection at the NCSU-VH. Although we originally intended to also include cats in this retrospective study, no cats were identified with C. guttulatus infection at our institution over the study interval. Only one case of C. guttulatus infection in a cat has been reported in the literature,3 suggesting that the infection in cats may be rare.
Among the 19 dogs identified with C. guttulatus infection in this study, 79% presented with a chief complaint and/or clinical signs consistent with gastrointestinal tract disease, with chronic diarrhea being the most commonly reported. In all but one dog that presented with gastrointestinal tract disease, C. guttulatus was identified in a sample that was derived from the gastrointestinal tract. Few dogs had C. guttulatus identified in a non-gastrointestinal tract sample, namely, a nasal biopsy specimen (1 dog) and urine (3 dogs). To the authors' knowledge C. guttulatus has not previously been documented in urine. Contamination of the urine sample with gastrointestinal content is possible in these latter dogs. However, the facts that the urine samples were obtained by cytocentesis and urine sediment and culture results were concurrently negative or consistent with a recurrent bacterial infection make fecal contamination seem unlikely.
Based on the population of dogs diagnosed with C. guttulatus in this study, it would appear that the yeast are found most commonly in samples derived from the gastrointestinal tract; perhaps reflecting the proclivity of C. guttulatus for also colonizing the gastrointestinal tract of rabbits6,8–12 and other small rodents such as guinea pigs, chinchillas, rats, and mice.6 In rabbits, C. guttulatus forms a loose barrier between the mucosal surface and luminal contents of the stomach, where it proliferates and then passes through the intestinal tract to be excreted in the feces.6 Recognition that C. guttulatus is a commensal yeast of the rabbit gastrointestinal tract has led to the frequent presumption that dogs with C. guttulatus must have ingested rabbit feces. In only one dog was a history of exposure to rabbit feces solicited from the owner and positively documented in the medical record in our study. Consequently, little can be concluded regarding the origin of C. guttulatus in these dogs. It was of interest that the dog with documented rabbit exposure had C. guttulatus identified in a gastric biopsy specimen. The C. guttulatus was described in this dog as intraluminal and forming a loose barrier between the gastric mucosa and lumen contents, in a manner similar to that described in rabbits.6
While C. guttulatus was initially implicated as a pathologic cause of rabbit enteropathies, it is currently considered to be a normal inhabitant of the rabbit gastrointestinal tract.6,9,10,12,13 Importantly, any association of C. guttulatus with gastrointestinal disease in the dogs reported here may merely reflect bias, in that fecal examinations were more likely to be performed in dogs with clinical signs of gastrointestinal illness. On the other hand, C. guttulatus may have been a contributing cause of diarrhea or an opportunistic consequence of the gastrointestinal diseases ultimately documented in these dogs. Many dogs were currently or had previously received antibiotics and/or steroids that may have predisposed the gastrointestinal environment to colonization by C. guttulatus. Additional studies are warranted to ascertain any direct pathogenic role of C. guttulatus infection in dogs with gastrointestinal disease.
In most cases, in addition to those presented here, diagnosis of C. guttulatus infection is based on the unique light microscopic appearance of this yeast.1–5 In the current age of molecular biology, such an approach appears rudimentary and reflects our current lack of knowledge about this organism. This is confounded by limited data on how to culture the organisms6 and molecular data that are confined to several partial 26S ribosomal DNA sequences reported in GenBank. Despite the morphological similarity between C. guttulatus observed in rabbit feces and that observed in companion animals, recent studies based on sequence analysis of 26S ribosomal DNA suggest that C. guttulatus isolated from dogs may represent a different strain than the one infecting rabbits.4 Further validation of this finding will have important implications regarding the origin, microbial ecology, and the possible pathogenicity of C. guttulatus in dogs.
A major limitation of this retrospective study is the absence of a control group of dogs without gastrointestinal disease that underwent similar diagnostic testing. Such testing is generally not performed on dogs that do not have clinical signs of gastrointestinal tract disease. Consequently, we chose to examine fecal samples collected from a large group of dogs housed at a high-turnover regional animal shelter. Our rationale was that stray dogs were likely to have an increased exposure to rabbits and ingestion of rabbit feces and, therefore, presumed increased risk for C. guttulatus infection. The fact that C. guttulatus was not found in any of these dogs suggests that the prevalence of the infection in apparently healthy stray dogs in our region is low. While greater numbers of dogs tested would lend more power to this conclusion, these results suggest there is an association between the presence of C. guttulatus and gastrointestinal tract disease in dogs. These findings are inconsistent with the report of Flausino et al., who detected C. guttulatus in 14/63 (22.2%) of dogs in Brazil that did not have clinical signs of gastrointestinal illness.7
Specific treatment of C. guttulatus infection using the anti-fungal drug nystatin was prescribed to two dogs in this study. Evidence for the use of nystatin to treat C. guttulatus infection in dogs is limited to several case reports, and the recommended dosage varies from 20,000 IU/kg body weight orally once a day for three days1 to 1,666 IU/kg body weight orally twice a day for 4 wk.4 Dogs with C. guttulatus in this study were treated with 3,333 and 8,130 IU/kg body weight (exactly 100,000 IU per dose per dog) of nystatin orally three times a day for 4 wk without apparent adverse effect. As C. guttulatus was diagnosed in both dogs using samples obtained via endoscopy and post-treatment samples were not obtained, efficacy of nystatin in eliminating C. guttulatus infection in these dogs is unknown.
Conclusion
Overall, this retrospective study identified that C. guttulatus infection is most commonly documented in samples derived from the gastrointestinal tract of dogs having clinical signs of gastrointestinal illness. The majority of dogs diagnosed with C. guttulatus had chronic diarrhea at presentation and final diagnoses consistent with inflammatory bowel disease. A low prevalence of C. guttulatus in feces of dogs at a regional animal shelter suggests that a causal or opportunistic association of C. guttulatus infection with gastrointestinal illness is worthy of further investigation.
Cyniclomyces guttulatus in a fecal wet mount from a dog. The vegetative form of C. guttulatus is a 4.4–8 × 8.8–21 μm elongated cylindrical yeast usually with two basophilic nuclei that have an “eyeglass case” appearance. Magnification, 40X.
Gastric Histopathology from dog diagnosed with C. guttulatus via endoscopic biopsy (Case 3). This patient was diagnosed with moderate, multifocal to coalescing laminal proprial fibrosis with luminal yeast most consistent with C. guttulatus. This patient was treated for C. guttulatus with nystatin as well as a hypoallergenic diet and steroids. Resolution of clinical signs was noted with these therapeutics. Magnification, 200X with Hematoxylin and eosin (H&E) staining.
Nasal Histopathology from dog diagnosed with C. guttulatus via rhinoscopic biopsy (Case 18). This patient was diagnosed with neutrophilic rhinitis within intraluminal yeast suggestive of Cyniclomyces spp. Ultimately, the patient was diagnosed with a nasal adenocarcinoma and euthanized. The significance of C. guttulatus in this patient is unknown. Magnification, 200X with Periodic Acid Schiff (PAS) staining.
Contributor Notes
