Nasal Rhinosporidiosis in Two Dogs Native to the Upper Mississippi River Valley Region
Two dogs, 4 and 7 years of age, were presented for evaluation and treatment of excessive sneezing. Physical examinations in both cases were within acceptable limits except for the presence of a single mass in the left nasal passage in the first case and left-sided nasal discharge in the second case. Rhinoscopy was used to visualize the nasal masses, and in both cases a single mass was surgically removed. Impression smears and histopathology submitted from each mass revealed lymphoplasmacytic and neutrophilic inflammation with spores typical of Rhinosporidium seeberi. These are the first reported cases of nasal rhinosporidiosis in two dogs native to the Upper Mississippi River Valley area with no travel history outside the region.
Introduction
Rhinosporidium (R.) seeberi is the causative agent of rhinosporidiosis in humans and animals, and it is sporadically reported in parts of the world outside of India, Sri Lanka, and Argentina, where the disease is common.1–3 The organism has recently been classified in the Mesomycetozoea class, near the divergence of animal and fungal boundaries.4 The route of transmission and pathogenesis of rhinosporidiosis are poorly understood; however, the disease has been associated with exposure of moist mucous membranes to wet environments.1–3 The purpose of this case report is to document the diagnosis and treatment of two dogs with nasal polyps caused by rhinosporidiosis. The dogs were native to the Upper Mississippi River Valley area, and they had no travel history to regions in which the disease has previously been reported.
Case Reports
Case No. 1
A 4-year-old, intact male Labrador retriever was referred to the University of Minnesota Veterinary Teaching Hospital for further evaluation of sneezing and a possible nasal foreign body. Initially, the dog was presented to the referring veterinary clinic for sneezing of 5 to 6 weeks’ duration and a mass visible in the left nasal passageway. The dog had a minor episode of epistaxis that resolved spontaneously. Attempts to obtain samples of the nasal mass for cytological diagnosis were unsuccessful, and the dog did not respond to 10 days of treatment with cefpodoxime proxetil.a The dog lived near lakes and ponds in the Minneapolis-St. Paul metropolitan area. The owner’s property included a pond, and the dog spent a significant amount of time in and around the water. The dog had never traveled outside of the Upper Mississippi River Valley region.
Physical examination on presentation was normal except for the presence of a raised, pinkish-white, polypoid, proliferative mass arising from the left nasal septum 1 cm caudal to the nare. While the dog was awake, a cotton-tipped applicator was inserted into the nostril and rubbed against the nasal mass. The applicator was then rolled onto a glass slide, air-dried, and stained with a modified-Romanowsky stain. Cytology revealed a moderate to highly cellular sample with a background of small amounts of blood. Nucleated cells consisted predominately of nondegenerate neutrophils; well-differentiated, nucleated squamous epithelial cells; and occasional mature plasma cells. Numerous magenta-colored, spherical structures (consistent with endospores) were present. They were approximately 6 to 10 μ in diameter with a thick, refractile wall and several round eosinophilic structures inside. The cytological diagnosis was suppurative inflammation with spores typical of R. seeberi.
Four weeks after initial examination, the dog was returned for rhinoscopy and mass removal. Presurgical blood work was within normal limits. Rhinoscopy was performed with a 1.9-mm, 0°, rigid endoscope via a transnasal approach. Approximately 1 cm from the nare opening in the left nasal passage, a single, 5- to 7-mm mass was visualized. The mass was grasped with a small, curved, mosquito hemostatic forceps and retracted rostrally. An electrosurgical handpiece with a straight, fine, needlepoint tip was inserted alongside the endoscope, and the base of the mass was transected from the turbinate mucosa using electrocautery. The mass was removed, and the transected margin was further cauterized in an attempt to eliminate any remaining viable organisms associated with the mass. Hemorrhage was minimal, and the dog’s recovery from anesthesia was uneventful.
Impression smears from the surgically removed tissue were of moderate to high cellularity with a background containing small amounts of blood and light eosinophilic, proteinaceous material. Small to moderate amounts of streaming nuclear material and free nuclei were seen. Intact nucleated cells consisted predominately of columnar respiratory epithelial cells that were occasionally hyperplastic in appearance, with plump or rounded cell margins and rare bi- or trinucleation. Moderate anisocytosis and anisokaryosis were present within this population. Also present were moderate numbers of plasma cells, small lymphocytes and nondegenerate neutrophils, and occasional vacuolated macrophages. Numerous magenta-colored spherical structures (endospores) approximately 6 to 10 μ in diameter were observed individually or in small aggregates. The structures were characterized by a thick, refractile wall and several internal, round eosinophilic globular bodies that were typical of R. seeberi endospores.
The cytological conclusion from the impression smear was nasal rhinosporidiosis with moderately reactive/dysplastic respiratory epithelial tissue, mixed lymphoplasmacytic and neutrophilic inflammation, and the presence of endospores typical of R. seeberi. The findings from the impression smear were similar to the initial cytology from the nasal swab, with minor differences in the types of inflammatory cells and epithelial cells. These differences were likely attributable to the superficial versus deep nature of the sample sources.
Histopathology of the mass demonstrated a proliferative polypoid mass covered by nasal mucosa with abundant, scattered, double-contoured, walled sporangia measuring between 30 and 250 μ in diameter. The larger, mature sporangia contained an abundant number of endospores. Moderate to marked infiltrates of neutrophils, lymphocytes, and plasma cells were also observed, similar to the cytological impression smear. The histological conclusion was a nasal polyp with regionally extensive, severe, subacute rhinitis secondary to R. seeberi infection [Figure 1]. Clinical signs resolved immediately after surgical removal of the mass, and the dog remained asymptomatic for over 21 months as of the time of this writing.
Case No. 2
A 7-year-old, neutered male Doberman pinscher was referred for treatment of a polyp located in the left nasal passage. Two weeks previously, the dog was presented to the referring veterinarian for a 4-month history of sneezing blood and mucus. Physical examination revealed unilateral left-side nasal discharge. Preanesthetic blood analyses revealed mild lymphopenia (0.5 × 103/μL, reference range 1.2 to 5.0 × 103/μL), occasional band neutrophils, mild toxic change in segmented neutrophils, and mildly elevated alkaline phosphatase activity (304 U/L, reference range 8 to 140 U/L). The dog was placed under general anesthesia, and radiographs and rhinoscopy were performed by the referring veterinarian. Radiographs showed a 2-cm2 soft-tissue opacity in the rostral left nasal cavity. Rhinoscopy was performed using a 2.5-mm, rigid handheld rhinoscope via a transnasal approach. A 1 × 3-cm, soft, pink, friable mass was visualized in the rostral left nasal passage. An alligator forceps was used to obtain a biopsy for cytology and histopathology.
A squash preparation made from the sample and stained with a quick stainb revealed mixed inflammation and spores consistent with R. seeberi. Histopathology revealed a polypoid structure diffusely infiltrated with inflammatory cells consisting of neutrophils, plasma cells, lymphocytes, macrophages, and numerous thick-walled sporangia and endospores consistent with R. seeberi. The dog was treated with 10 days of oral amoxicillin trihydrate/clavulanate potassiumc antibiotic (562 mg q 12 hours) and carprofend (100 mg q 12 hours) and was referred to the University of Minnesota Veterinary Teaching Hospital for further treatment. The dog lived on acreage with a marshy area in western Wisconsin, and it had never traveled outside of the Upper Mississippi River Valley region.
At the time of referral, physical examination was within normal limits, with notation of scars on the dog’s muzzle from a previous altercation with a wild animal. Preanesthetic blood work revealed a mildly elevated alkaline phosphatase activity (194 U/L, reference range 8 to 139 U/L) and a normal buccal mucosal bleeding time (3.5 minutes, reference range 1.7 to 4.2 minutes). Rhinoscopy was performed with a 3-mm, flexible endoscope via a transnasal approach. A solitary mass arising from the septum was found in the left nasal cavity approximately 2 cm from the opening of the nare and continuing approximately 2 to 3 cm caudally.
Because of the extent and depth of the mass, a dorsal rhinotomy to the nasal cavity was deemed necessary to ensure adequate excision [Figure 2]. A mosquito hemostatic forceps was inserted in the nasal cavity to the level of the mass to define the appropriate level of exposure. A rostrodorsal, left-lateral approach to the nasal cavity was made, just rostral to the nasal incisive bone and extending through the left dorsolateral nasal cartilage. The mass was visualized and measured approximately 5 cm long × 1 cm2. The mass and all nasal mucosa in the area of the mass were excised using a rongeurs and curette. The area was lavaged and closed in three layers. Hemorrhage was minimal, and the dog’s recovery from anesthesia was uneventful.
Impression smears from the surgically removed tissue were of marked cellularity with a light eosinophilic background containing small numbers of erythrocytes and broken cells [Figure 3A]. The nucleated cell population was predominated by ciliated columnar to plump respiratory epithelial cells. Also present were moderately increased numbers of mixed inflammatory cells consisting mostly of mild to moderately degenerate neutrophils and well-differentiated plasma cells with lower numbers of small mature lymphocytes and occasional vacuolated macrophages. Abundant numbers of deeply basophilic to magenta spherical structures (mature endospores) approximately 4 to 11 μ in diameter were observed, often in small aggregates. The structures had a thick refractile wall, and some endospores had several internal, round eosinophilic structures (eosinophilic globular bodies) arranged concentrically just inside the cell wall [Figure 3A inset]. Some endospores appeared surrounded by a variably thick, clear halo; a thinner cell wall; and eosinophilic globular bodies (consistent with intermediate endospores). Also present were occasional large mats of small (1 to 3 μ), spherical structures. These structures had round, lightly basophilic, stippled centers and a small, deeply basophilic to magenta form, consistent with immature endospores [Figure 3B]. Rare, large (20 to 40 μ), round, deeply basophilic spherical structures with disorganized material within (consistent with immature sporangia) were seen [Figure 3B inset]. All of the forms of endospores and sporangia were consistent with R. seeberi.
The cytological conclusion from the impression smear was nasal rhinosporidiosis with mildly reactive/dysplastic respiratory epithelial tissue, mixed lymphoplasmacytic and neutrophilic inflammation, and the presence of immature, intermediate, and mature endospores and immature sporangia typical of R. seeberi. The sample was also submitted for histopathology, and lymphoplasmacytic and neutrophilic rhinitis with R. seeberi sporangia was diagnosed. Clinical signs resolved after surgical removal of the mass, and the dog remained asymptomatic for 14 months as of this writing.
Discussion
These cases present an unusual diagnosis for nasal polyps in two dogs native to the Upper Mississippi River Valley area. Rhinosporidiosis, caused by R. seeberi, is a condition typically found in tropical areas such as India and Sri Lanka, Argentina, and sporadically in other areas.1–3 In the United States, the majority of the cases are reported in the southeastern and south central states and as far north as Missouri.2,5–13 One case of a dog in Ontario, Canada, has been reported.14
After years of controversy on the taxonomy of R. seeberi, the organism has been placed in the Mesomycetozoea class, near the divergence of animal and fungal boundaries.1,3,4 Rhinosporidium seeberi is the only member of Mesomycetozoea that is pathogenic to mammals and birds.4 In tissues, endospores develop progressively from juvenile, or trophocyte, to intermediate states and finally form mature sporangia with thousands of endospores, which are then released to reinitiate the cycle.1,4 The release of endospores from sporangia occurs after exposure to water; therefore, the disease is associated with wet environments.1–3 However, the natural host, route of transmission, and pathogenesis of rhinosporidiosis are poorly understood.1–3
Recent evidence using 18S rRNA gene sequences suggests multiple host-specific strains of R. seeberi.15 No cases of zoonotic transmission have been reported, although humans are susceptible to disease, as well as dogs, cats, cattle, waterfowl, and horses.1 In humans, the majority of cases occur in the upper respiratory tract, with lower numbers of cases observed in the skin, subcutaneous tissues, and eyes.1 Lesions of rhinosporidiosis in dogs and cats in the United States have only been reported in the nasal cavity.2,5–11
Diagnosis of rhinosporidiosis is typically accomplished using histopathology or cytology, both of which show typical morphological features of R. seeberi, as culture of the organism has been unsuccessful.1–3 A polymerase chain reaction assay using R. seeberi-specific primers for the 18S rRNA sequence has been developed; however, the assay remains largely used in research settings.4 Rhinosporidium spp. organisms can be stained with a variety of stains including hematoxylin and eosin, Wright, toluidine blue, methenamine, and periodic acid-Schiff.1,2,16,17
In cytological samples, sporangia and immature forms of endospores are infrequently found.2,16,18 Cytological descriptions of mature endospores include round eosinophilic to magenta to basophilic structures, 5 to 15 μm in diameter, with internal eosinophilic globules and thick walls.2,16,18 Immature endospores have also been described cytologically as lightly basophilic, spherical structures that are 2 to 4 μm in diameter, with a paracentral light pink-purple area and one to two smaller, spherical, dark-purple structures.2 A mixed inflammatory response of plasma cells, small lymphocytes, and neutrophils is typical.16
Histopathological features include fibrous tissue, granulomatous inflammation, and sporangia. These are further classified as juvenile (15 to 75 μm with a single nucleus) or mature (100 to 400 μm with numerous endospores).3 Differential diagnoses on cytological and histological samples include Coccidioides immitis and Cryptococcus neoformans, based on slight morphological similarities and staining characteristics. However, diagnosis of rhinosporidiosis typically only requires cytological or histological identification.1,2,17
Clinical signs of rhinosporidiosis in animals relate to single or multiple polyps in the nasal cavity and associated inflammation. White-yellowish foci can be observed on the surface of the polyp, and they represent sporangia.1 The treatment of choice is surgical excision, preferably with electrocautery, because antifungal and antibacterial agents are not effective.1,2 Dapsone, a sulfone anti-infective drug that appears to stop the maturation of the sporangia, has been used in humans as an adjunct to surgical removal.1,2 However, recurrence of disease is not uncommon.1,2
Conclusion
This is the first case report of nasal rhinosporidiosis in two dogs in the Upper Mississippi River Valley region. Diagnoses were made based on cytological samples and were confirmed with histopathology. Treatment consisted of surgical removal of the masses, and the dogs have been free of clinical signs of the disease for 21 and 14 months, respectively. Although rare, rhinosporidiosis should be included on differential lists for a nasal polyp, especially if the animal is commonly exposed to wet environments.
Simplicef; Pfizer Animal Health, Exton, PA 19341
Quick III Solution; Astral Diagnostics, Inc., West Deptford, NJ 08066
Clavamox; Pfizer Animal Health, Exton, PA 19341
Rimadyl; Pfizer Animal Health, Exton, PA 19341
Citation: Journal of the American Animal Hospital Association 46, 2; 10.5326/0460127
Citation: Journal of the American Animal Hospital Association 46, 2; 10.5326/0460127
Citation: Journal of the American Animal Hospital Association 46, 2; 10.5326/0460127
Case no. 1: Histopathology showing mature sporangia (arrow), immature sporangia (asterisk) with mature endospores (arrowhead), and surrounding inflammation (Hematoxylin and eosin stain, bar=200 μm).
Case no. 2: Intraoperative photo of a large rhinosporidiosis lesion in the left nasal cavity of a dog. White foci are visible on the surface of the lesion, which equate to mature sporangia.
Case no. 2: Cytology samples of an impression smear made from a nasal polyp in a dog (Modified-Romanowsky stain). (A) Mature Rhinosporidium seeberi endospores (arrow) with intermediate endospores (arrowhead) (50× objective, bar=10 μm). Inset: Eosinophilic globular bodies (arrow) inside mature endospores (100× objective, bar=5 μm). (B) A large mat of immature endospores (top) is present, along with mature endospores (arrow) (100× objective, bar=10 μm). Inset: Intermediate sporangia (50× objective, bar=10 μm).
