Introduction

Cryptococcosis is a systemic mycosis distributed worldwide that can affect humans and animals. The causative agents are yeasts from the genus Cryptococcus, mainly the species C. neoformans and C. gattii [1]. These species present different ecological and microbiological patterns. C. neoformans presents a wide distribution in the environment and is associated mainly with avian droppings [2] and decaying wood [3], and most infections are linked to immunocompromised conditions [4]. However, C. gattii has a geographical distribution mainly in the tropical and subtropical regions of the world [5] and was first related to specific Eucalyptus species [6]. Moreover, isolates have been obtained from other tree species and also from indoor dust, showing a wider distribution and consequently more sources of infection [3, 7]. In contrast to C. neoformans, immunocompetent hosts are susceptible to C. gattii infection [5]. Although the disease aspects of cryptococcal infections are becoming more clearly understood, the life cycle of this yeast in the environment remains less well defined. The application of molecular epidemiology in clinical and environmental samples allows for a better understanding of the geographical distribution, ecological niches, epidemiology, clinical presentation and molecular characteristics of Cryptococcus. Different molecular technologies differentiate C. neoformans and C. gattii in eight molecular groups [8, 9].

Various domestic and wild mammals may be infected with Cryptococcus, including cats, dogs, ferrets, horses, camelids, goats, sheep, cattle, dolphins, koalas and other marsupials. Similar to human cryptococcosis, the most likely route of infection in dogs and cats is inhalation of basidiospores or desiccated yeast cells during environmental exposure. Therefore, the nasal cavity is potentially the initial site of infection [1]. Consequently, the most frequent clinical signs observed in veterinary medicine are associated with the upper and lower respiratory tracts. Mycotic rhinitis or bronchopneumonia can be demonstrated with imaging exams in most patients, even when typical signs of nasal cavity disease are absent. The known tropism of the genus Cryptococcus to the central nervous system results in a high prevalence of neurological signs in retrospective studies. Unlike other systemic mycoses, cryptococcosis is more common in cats than in dogs. However, dogs frequently develop disseminated disease, with the involvement of a variety of parenchymal organs. This propensity to disseminate early in canine cryptococcosis contrasts with the feline disease, where hematogenous spread occurs usually only in the immune-deficient host [10–12].

Despite the predisposing dissemination of canine cryptococcosis, gastrointestinal involvement is rare and few cases have been described. Some reports are summarized in Table 1 [13–16]. Even in human medicine, the reports refereeing to gastrointestinal symptoms associated with Cryptococcus infections remain rare [17, 18].

Table 1 Reports of gastrointestinal cryptococcosis in dogs
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The objective of this article is to report a case of gastrointestinal cryptococcosis in a dog apparently immunocompetent. Knowledge about an atypical presentation of this mycosis is of great importance for correct diagnosis of similar lesions and to determine the best therapy and prognosis.

Case

An 18-month-old unspayed female canine, English Bulldog was referred to a private veterinary practice due to episodes of diarrhea and progressive weight loss for the past 30 days. The owner went for veterinary assistance after the symptoms worsened and the animal started to present melena and prostration. A physical examination did not find any abnormalities. The hematological evaluation suggested an inflammatory process, without concurrent anemia. An empirical antimicrobial therapy was instituted with the association of co-trimoxazole (15 mg/kg orally every 12 h) and metronidazole (15 mg/kg orally every 24 h). A copro parasitological examination was also requested, but it was not authorized by the owner.

After four days, the patient was brought back to the clinic without any response to the prescribed drugs. The clinical signs had declined, with vomiting and subsequent anorexia. An abdominal ultrasound exam was performed to evaluate the gastrointestinal tract. A large mass was visualized in the small intestine with an irregular contour and heterogeneous parenchyma, resulting in a reduction of the intestinal lumen. There was also the absence of peristalsis. Neoplasia was suspected, and an exploratory laparotomy was indicated and performed with the owner’s consent.

The abdominal cavity was accessed by a medial longitudinal laparotomy. During the surgical procedure, severe thickening of the intestinal loops was observed, with a large area of small intestine adherence forming two granulomatous masses with a diameter of approximately 18 × 7 cm. Partial enterectomy was performed (Fig. 1). Because of the large area of the small intestine that had been removed and the impossibility of owner to provide intensive care, the owner’s consent for euthanasia was requested.

Fig. 1
figure 1

Granulomatous mass with a diameter of approximately 18 × 7 cm after partial enterectomy in a female canine English Bulldog

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The postmortem cytological analysis of the mass removed, by fine-needle aspiration, revealed the presence of ovoid to spherical yeast-like bodies surrounded by a capsule suggesting the involvement of Cryptococcus spp. (Fig. 2). Part of the granuloma was added to a sterile saline solution and sent to the Laboratory of Pathological and Environmental Yeasts—UFRRJ, Brazil. The solution was seeded in Sabouraud dextrose agar and Dopa medium. Plates were incubated at 30 °C and monitored daily. The yeast obtained was identified as Cryptococcus gattii by morphological analysis, biochemical and CGB tests [19].

Fig. 2
figure 2

Cytological analysis of the mass due by fine-needle aspiration showing the presence of ovoid to spherical yeast-like bodies surrounded by a capsule. Fuchsine stain—×1000

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Genotyping was performed according to Meyer et al. [8], and the URA5-RFLP pattern was assigned visually by comparison with patterns obtained from reference strains representing 8 molecular types.

Discussion

The genus Cryptococcus comprises yeast species of clinical interest to human and veterinary medicine [1]. The opportunistic characteristic has been closely associated with the species C. neoformans [4]. However, as we could see in the present report, C. gattii apparently affects healthy hosts and should be considered as a primary etiologic agent [5]. The causative agents of gastrointestinal cryptococcosis have been identified in three previous cases, showing the involvement of C. neoformans in two patients [14, 15] and C. gattii in one [14]. In a review study, the analysis of molecular typing data reported from Brazil using 1439 clinical and environmental strains of C. neoformans and C. gattii showed that the molecular type VGII is the second major type in this country [9]. A case of feline nasal granuloma involving C. gattii VGII was reported in the southeast region of Brazil, confirming the relevance of this molecular group in animal health [20]. Clinical samples of two dogs and two cats in Mato Grosso, Brazil, identified C. gattii through sequencing analysis. According to the sequence data, the four isolates showed identity with VGII genotype [21].

The respiratory tract is usually the primary system involved in the majority of cryptococcosis cases. An increase in respiratory effort and breath sounds, nasal discharge, coughing and sneezing are the most common symptoms observed in clinical practice. Neurological signs and cutaneous lesions also represent a high percentage of cases [1, 10, 12]. The symptoms in the present report were easily related to a wide range of gastrointestinal diseases, being also associated with previous reports of gastrointestinal cryptococcosis [13–16].

Studies on the environmental sources of the fungus demonstrated the correlation between specific Eucalyptus species and the presence of this yeast [5]. However, the isolation of C. gattii has also been obtained from Licania tomentosa, Cassia grandis and Ficus spp in the northeast of Brazil, showing a wider environmental distribution than was initially thought. The detection of C. gattii propagule in the air collected at the entrance of a hollow tree raises the possibility of dispersion from disturbance at sources by wind, animals or human activities, such as deforestation [3]. Another study demonstrated the presence of C. gatti VGII in indoor dust obtained in a human settlement formed in the Amazon rainforest in Brazil, thus, suggesting the possibility of exposure to those potential disease agents inside houses [7]. Furthermore, a previous study detected Cryptococcus spp DNA in the small intestine of both healthy dogs and those with chronic enteropathies, suggesting that the canine gastrointestinal tract may harbor opportunistic fungal pathogens. This research showed that different yeasts can be transitory or adhere to the intestinal mucosa [22]. C. neoformans can colonize and cause systemic cryptococcosis in mice, after alimentary tract introduction by swabbing the mouth with a Cryptococcus suspension [23]. In this report, the source of infection was not determined, but the characteristic of the lesion and the absence of clinical signs in other tracts suggest that the entry site of C. gattii was the gastrointestinal system.

In an endemic area, in Canada, for a period of four years (1999–2003) there were only 51 canine cases suspected of being C. gattii, with only 19 cases confirmed [10]. Also, a larger survey in California between 1988 and 2010 diagnosed only 31 dogs with cryptococcosis [12]. There are a higher number of infected cats in these retrospective case series, which demonstrates the different susceptibilities between these two animal species to this microorganism genus. As observed in our patient data, younger dogs seem to be more affected by Cryptococcus, in different body systems, and they are also more susceptible to gastrointestinal cryptococcosis [13–16]. Another evaluation from Australia, considering four reference institutes and one commercial laboratory from 2000 to 2012 showed that 24 dogs presented abdominal cryptococcosis, including 13 with small intestine lesions. The mean age was 2.2 years, suggesting again a higher susceptibility in younger dogs [24].

There have been described different methods to diagnose cryptococcosis, considering lesion location and possible routes of infection. The cytological examination is a good technique to reveal the involvement of Cryptococcus spp in clinical cases. Cryptococcal organisms were detected, by cytological examination, in 17 of 31 (55%) dogs in a previous study considering different sites of infection [12]. Fecal cytology stained with Wright-Giemsa [15] and ultrasound-guided fine-needle aspirates of the small intestine and mesenteric lymph nodes [15, 16] already demonstrated their potential to suggest Cryptococcus involvement in gastrointestinal lesions. The effectiveness of endoscopic evaluation has already been demonstrated in human medicine as well as veterinary medicine [13, 17]. Cryptococcus involvement was not suspected in the present case, and these less invasive technics were not applied, making diagnosis difficult to reach.

The entire resection of the masses in a previous report proved to be an important step for the treatment of one patient. Long-term association of flucytosine, itraconazole and amphotericin B on postoperative care resulted in no relapse [14]. The use of fluconazole [15] and terbinafine [16] were also associated with success in the treatment of gastrointestinal cryptococcosis. In the present report, the large extension of the masses added to the impossibility of the owner to provide intensive care to the patient resulted in the decision of euthanasia.

Conclusion

The gastrointestinal system is not usually affected by this fungus. The similarity of neoplastic lesions and the poor prognosis in these cases means that complementary tests are fundamental to achieve the correct diagnosis, as well as to implement the appropriate therapy and avoid mistakes. Aging in pets and the increase of immunosuppressed situations in small animal practice, like chemotherapy and chronic diseases, highlights the importance of opportunistic agents in the routine. Cryptococcosis and other mycoses must be considered as a possible differential diagnosis in uncommon clinical presentations. It is also important to notice that C. gattii causes predominantly primary infection in immunocompetent individuals in human and veterinary medicine.