Letter in response to the article: “Nannizzia incurvata as a rare cause of favus and tinea corporis in Cambodia and Vietnam”

Sir,

We read with great interest the recently published work entitled “Nannizzia incurvata as a rare cause of favus and tinea corporis in Cambodia and Vietnam” by Uhrlaß et al.¹ The authors describe, for the first time, the isolation of Nannizzia incurvata from humans in Cambodia and the description of favus in a child due to this dermatophyte. In this article, the authors have identified N. incurvata from a 6-year-old Cambodian boy presenting with symptoms of the favus-like tinea capitis and tinea faciei. Diagnosis was performed using culture and DNA sequencing. The authors performed an excellent clinical investigation; however, we are concerned about epidemiological aspects and would like to discuss some points that would benefit the readers of your esteemed journal.

The authors reported that the patient had previous contact with animals (i.e., chicken, dogs, and cattle). However, we feel that these interactions were not described in detail. In our opinion, it is relevant to elucidate the transmission mechanism of this new dermatophyte species. Did the animals have access to the household? Any animals with clinical signs? Although the genus Nannizzia has been assigned as geophilic and humans infections are commonly associated with contaminated soil, it is important to emphasize that animals may play an important role in the persistence and dissemination of these fungi. A study carried out in Tunisia investigated 141 soil samples for the presence of keratinophilic fungi. The authors found that 69% of keratinophilic fungi were isolated from soils where animals were present.² The authors also mentioned that residual animal fur and skin debris could act as soil enricher by providing organic matter for keratinophilic fungi. It is noteworthy that infected materials can maintain viable fungi for years, and therefore the presence of animals can significantly contribute to fungal shedding and persistence in the environment.

In another recent study, Dukik et al. evaluated the molecular and phenotypic aspects of Nannizzia spp. The authors speculated on the direct association between geophilic members of the genus Nannizzia and animal hosts.³ The authors mentioned that animals might act as carriers, contributing to the maintenance and shedding of these fungi to the environment and humans. As a matter of fact, the direct association between geophilic species and animals has already been demonstrated. Bonifaz et al. identified N. nana in a man that had worked in a pig farm in Mexico, whereas Soankasina et al. demonstrated the epidemiological role of cats in the transmission of N. gypsea to humans in an African island.^4,5 Thus, the ecological classification of the genus Nannizzia remains unclear, since species classified as geophilic may be associated with animals. Recent phylogenetic analyses suggested that Nannizzia spp. are derived from an ancestry located between Trichophyton spp. and Microsporum spp. (a largely zoophilic genus).³

We would also like to discuss the fact that the TEF-1 α gene sequence used by the authors was, in theory, erroneously associated with N. gypsea. A BLAST search using the same database (NCBI) and accession (KM678069) the authors used as query matched to three N. incurvata strains. Two of which were >99% similar (MT497551 and MH512804), but one that was only 96% similar (MH706756). This was significantly higher than the percent identity to other N. gypsea strains (90.3%, KM678161 and KM678057). Finally, accessions associated with N. duboisii (KM678089) and N. fulva (KM678079) were 93% and 91% similar to the query sequence. While it is not our goal here to question the recent taxonomic changes related to these species, it does raise concerns to the use of this gene for speciation.

Considering that animals may represent a potential source of infection for humans through direct contact or shedding in the environment, we would like to suggest to the medical mycology community to pay special attention to the involvement of animals in this topic. In fact, it seems that the human-animal interface may significantly contribute to recurrent infections, which is one of the leading causes of treatment failure.

To conclude, we would like to congratulate Uhrlaß et al. for their work. ¹ This is a step further towards better understanding the clinical aspects and therapeutic challenges of N. incurvata, a pathogen with potential to emerge as a threat to in human, pets and livestock. In our perspective, the findings by Uhrlaß et al. turn the spotlight on the importance of this new fungal species, possibly leading to the identification of new cases in other countries. Finally, we hope that our discussion may add relevant information regarding the epidemiological aspects of animals as carriers and disseminators of Nannizzia spp.