Authors' Reply

Sir,

We are grateful to Dr. Aline Elisa Santana from Brazil who responded to our article on the occurrence of the rare geophilic dermatophyte Nannizzia incurvata in Southeast Asia^1,2. N. incurvata belongs to the so-called Nannizzia gypsea (formerly Microsporum gypseum) complex. In addition to N. gypsea, one also counts Nannizzia fulva (formerly Microsporum fulvum) and N. incurvata described here. N. gypsea is perhaps the most prominent representative within the geophilic dermatophyte species. In a typical way, N. gypsea causes infection of the skin on the hands and arms, for example, in gardeners who have direct contact with the earth and the dust. Animals do not play a role in N. gypsea dermatophytoses. N. gypsea and also N. incurvata are per se not among the zoophilic dermatophytes. Of course, however, it is conceivable that especially in the rural environment at the village, ground living fur animals are surely capable of carrying spores or mycelia of primarily geophilic dermatophytes, thus also of N. incurvata. They may then also be indirect carriers for transmission of infections due to N. incurvata or N. gypsea to humans. However, data on this are not available. The boy we described in Cambodia with tinea capitis favosa and tinea faciei lives in a rural region and is surrounded by various animals in his village and in his parents’ house and farm. That is why, such an indirect transmission path from N. incurvata from the ground through the fur of animals (dogs, cats and rodents) would be conceivable and theoretically possible. There is no proof of this, however; it is purely speculative.

One further example of a transmission pathway of a primary geophilic dermatophyte from animals on humans is N. praecox, a geophilic dermatophyte present in soil and equine environments (saddles, straw and stables). N. praecox is rarely reported as a cause of human tinea, particularly after contact with horses. N. praecox can be isolated from horse hair in the absence of clinical lesions^3,4.

Interestingly, the colleagues from Brazil focused on the fact that the Translation Elongation Factor 1 α (TEF1α) gene sequence used in our investigation in Germany, was in theory, erroneously associated with N. gypsea¹. This is, indeed, right. We were able to show that by sequencing of the TEF1-α gene, for strain 213959/2017 isolated from the Vietnamese patient, no cluster to compare was available in the National Centre for Biotechnology Information (NCBI, Bethesda, Maryland, USA) database². On the other hand, strain 211859/2017, isolated from patient two, the Cambodian boy, clustered with KM678105.1 from the NCBI database. This sequence, however, was first assigned in the database as N. gypsea. Due to the new classification and nomenclature of dermatophytes from 2017, sequence of strain KM678105.1, now, has to be considered as N. incurvata⁵.

In addition to the two patients with N. incurvata dermatophytoses from Vietnam and Cambodia described in our IJDVL paper, in the meantime, we were able to isolate three other patients suffering from tinea corporis due to N. incurvata. These were a 33-year-old female with onychomycosis from Finland, a 29-year-old female with tinea corporis from Iraq and a 19-year-old German patient with tinea corporis after visiting Thailand. Interestingly, there was no background of any contact to animals in these patients. Despite the geophilic origin of the dermatophytosis, a human-to-human transmission of N. incurvata seems possible, too. Recently, in Russia, a new case report has been published on N. incurvata dermatophytosis in a 42-year-old man. The infection – tinea corporis of the forearm – due to this geophilic fungus occurred in Italy during a vacation on the seaside⁶.