Sporotrichosis is a subcutaneous mycosis with a worldwide distribution that is currently notable for areas of especially high endemicity in Latin America [1]–[3]. Some authors classify sporotrichosis as an implantation mycosis, because this infection may also involves other sites beyond the skin and the subcutaneous tissues, such as lymphatic vessels, muscles, fascia, cartilage, and bones [3]. Historically, sporotrichosis has been attributed to a single species, Sporothrix schenckii [1]. However, phenotypic and genotypic analyses by Marimon and coworkers [4] have led to the identification of four new species in the Sporothrix complex: (i) S. globosa, a globally distributed fungus [5]–[7]; (ii) S. brasiliensis, the species related to the zoonotic epidemic of sporotrichosis in Rio de Janeiro, Brazil [8]; (iii) S. mexicana, initially limited to Mexico [4], but with recent cases reported in other regions [9], [10]; and (iv) S. luriei, formerly S. schenckii var. luriei [11].

Classical infection is associated with traumatic subcutaneous inoculation of soil, plants, or organic matter contaminated with fungus, with rare cases of transmission occurring from infected animals [1]. However, in Rio de Janeiro state, Brazil, sporotrichosis is currently largely occurring via transmission from infected cats to humans [12]. Recently, our group performed a georeferencing survey of sporotrichosis cases that revealed a transmission belt along the border between Rio de Janeiro city and adjacent counties in the Greater Metropolitan Area [13]. Genotypic analyses have shown that isolates from the Rio de Janeiro epidemic have a high genetic similarity, which is suggestive of a common niche [14], [15].

Although some studies have described several clinical aspects of this epidemic [12], [16], [17], taxonomic analyses have not been correlated with disease presentations. Therefore, the main purpose of this study was to investigate a possible association between manifestations of sporotrichosis in Rio de Janeiro and the different genomic species of S. schenckii sensu lato.

The clinical presentations of sporotrichosis caused by Sporothrix spp are highly variable and poorly understood. Kong and collaborators [20] have demonstrated that S. schenckii genotypes can be correlated with clinical forms of disease, as mice challenged with S. schenckii isolates from patients with fixed cutaneous, lymphocutaneous or disseminated sporotrichosis developed more severe disease according to the severity of the manifestations in the originating patient. However, they did not define the relationships between genotype and treatment outcome or other unusual manifestations. In the present work, we show the direct association between unusual clinical presentations of human sporotrichosis with infection by S. brasiliensis. Although S. brasiliensis caused typical manifestations of fixed cutaneous and lymphocutaneous sporotrichosis, all 10 patients with hypersensitivity reactions and 6/7 patients with disseminated disease were infected with S. brasiliensis. To the best of our knowledge, this is the first work that demonstrates an association between genotypic identification of Sporothrix species and several clinical aspects of human sporotrichosis. Given the recent changes in the nomenclature and advances in the molecular taxonomy of Sporothrix, it is even more important to understand the clinical implications of these advances [21].

As expected, the majority of our isolates have been identified as S. brasiliensis by DNA analyses. Our group has previously characterized S. brasiliensis in 230 (93.5%) of 246 isolates obtained from this endemic zoonotic transmission area [8]. A study by Marimon and coworkers of 127 Sporothrix strains collected from several parts of the world reported only S. brasiliensis among the tested isolates from Rio de Janeiro [4]. There are also a few reports of S. brasiliensis in Brazilian states other than Rio de Janeiro [10], [22], [23], but, in these states, the frequency of S. brasiliensis appears to be lower than that for the other Sporothrix species, with S. schenckii predominating [22].

As noted above, S. brasiliensis genotype caused typical clinical forms of sporotrichosis (lymphocutaneous and fixed cutaneous). However, except for 1 case of disseminated S. schenckii in a patient with AIDS, all of the unusual clinical forms of sporotrichosis were attributed to infection with S. brasiliensis, including disseminated cutaneous sporotrichosis in the absence of an underlying immunosuppressive condition, mucosal involvement affecting nasal cavity or conjunctiva, and hypersensitivity reactions. Regarding the hypersensitivity manifestations, our finding are consistent with the previously reported cases of erythema nodosum and erythema multiforme associated with zoonotic sporotrichosis [24], [25] due to S. brasiliensis. Recently, Sweet syndrome has also described in 3 patients with sporotrichosis [26], and studies are underway to determine, by calmodulin sequencing, the species involved in these cases.

Another interesting finding for disease due to S. brasiliensis is the 32/13 female/male ratio, since there is a predominance of male over female patients with sporotrichosis caused by S. schenckii. This can be explained by the fact that the most affected group in the endemic area of sporotrichosis in Rio de Janeiro are housewives that interact with or take care of S. brasiliensis infected cats [1].

Barros and coworkers [27] studied the effects of itraconaozle treatment on cutaneous sporotrichosis in 645 patients from the Rio de Janeiro epidemic, including 87 patients with erythema nodosum or erythema multiforme. Interestingly, they observed that of the patients with hypersensitivity reactions resolved their disease more rapidly compared with patients without these conditions. Although our current study did not find differences regarding treatment between these groups, we did determine that most patients with hypersensitivity reactions presented with fixed cutaneous sporotrichosis. Hence, we believe that hypersensitivity reactions may indicate a robust host response to the S. brasiliensis yeast cells and play a protective role in sporotrichosis, as observed in coccidioidomycosis [28].

The small number of S. schenckii cases in our study calls our attention to the infection caused by this species in Rio de Janeiro. The majority of these cases occurred in rural counties where inhabitants are engaged in agricultural activities, and, therefore, they have frequent and protracted contact with soil. Moreover, in two of these cases, patients denied cat contact. However, S. schenckii was identified in one case from the endemic zoonotic transmission area. Our results suggest that S. schenckii also circulates, in minor proportions, in this endemic area. New studies with a large number of S. schenckii infected patients are necessary to verify the clinical meaningful of sporotrichosis caused by this species.

Several factors could influence the different outcomes of sporotrichosis, such as the size of initial inoculum, the host immune response status, depth of traumatic inoculation and fungal virulence [29]. Virulence studies in a mouse infection model have shown that S. brasiliensis is significantly more lethal and results in higher fungal burdens compared to S. schenckii as well as other examined Sporothrix spp. [30]. This same study concludes that lesional mechanisms could be species-specific, which supports our results. Zoonotic transmission of sporotrichosis by cats results in high Sporothrix inoculums for humans, since these animals have high fungal burdens [31]. In some of the endemic sporotrichosis cases, fungal inoculation is presumably repetitive, due to constant bites and scratches suffered by owners [32]. These factors, coupled with the purported higher virulence of S. brasiliensis [30], could account for the unusual and more severe clinical manifestations observed with this species.

Itraconazole is the drug of choice for sporotrichosis treatment [27]. It is interesting to note that, regardless the clinical form, there was a trend toward shorter treatment durations in patients with sporotrichosis caused by S. brasiliensis, (median = 16 weeks) than the cases due to S. schenckii (median = 24 weeks), for our study. Although we are comparing 46 cases of S. brasiliensis to only 4 infections due to S. schenckii, we propose that our finding might have a therapeutic implication. The response of S. brasiliensis to treatment is consistent with the fact that S. brasiliensis is more susceptible to antifungal drugs, such as itraconazole, posaconazole, and ravuconazole, than S. schenckii [33]. Moreover, previous results of our group, which included eight S. brasiliensis from this study, showed that strains from the zoonotic endemic area were highly susceptible to itraconazole [14]. Nevertheless, clinical, randomized studies should be performed to confirm these findings.

Since different Sporothrix species appear to be related to distinct clinical manifestations and treatment responses, we propose that speciation should become standard laboratory practice. However, it will require a significant effort to make this recommendation a reality in most clinical laboratories. Phenotypic fungal identification is easier than molecular methods to routinely apply. However, in the present work as well as in a previous study from our team [8] and studies from other groups [10], phenotypic description too often fails to be corroborated by genotypic results. Since the differences between the species of the S. schenckii complex were observed at the molecular level [18], we considered DNA sequencing as the gold standard on species identification for the present study. Unfortunately, at present, DNA sequencing is not a suitable methodology for routine clinical laboratories. We recently described a simple and reliable T3B DNA fingerprinting methodology to identify the S. schenckii species complex at the DNA level [34], making it an alternative identification methodology for clinical microbiology laboratories.

Our study intended to perform a molecular analysis of the most peculiar clinical cases that we observed in this epidemic as well as typical cases, and also patients presenting from areas outside the sporotrichosis belt of zoonotic transmission, which corresponds to almost 20% of our stored samples. We have checked the medical data from the other 196 patients and they were very similar to the cases we included here. The small size of genotyped strains is a weakness of this study, but in our opinion, these cases illustrate the association of S. brasiliensis to the unusual presentations of sporotrichosis. Also, molecular genotyping with sequencing of the calmodulin gene is laborious and expensive (at present), with significant financial impact in our severely limited funding situation.

In conclusion, we have used molecular analysis to clearly demonstrate that S. brasiliensis is the primary cause of endemic sporotrichosis in Rio de Janeiro state. Moreover, S. brasiliensis causes both classic and unusual manifestations of sporotrichosis, including severe disease in otherwise immunocompetent individuals. We also have documented that local and invasive S. brasiliensis disease responds well to itraconazole therapy, with shorter durations of therapy compared to the patients studied with sporotrichosis caused by S. schenckii. This study adds new information to our knowledge base on S. brasiliensis disease and supports the careful speciation of Sporothrix isolates to guide clinical care.