Epidemiological aspects and genotypic characterization of T.violaceum strains collected during a Belgian National survey on anthropophilic tinea

Objectives
The last two years, clinical cases of tinea capitis caused by Trichophyton violaceum (T. violaceum), have been identified in Belgium. To better understand the emergence of this species in the population, the Belgian National Reference Center (NRC Liège) launched a one-year national survey in 2013. Epidemiological aspects and genotypic characterization of the strains were included.
Methods
The study was conducted from March 2013 up to February 2014. All Belgian laboratories were asked to send M. audouinii and T. violaceum strains isolated from hair to the NRC with a form to fill in including epidemiological data. The fungal strains were identified by microscopy or ITS sequencing in case of doubtful identification. The genotypic analysis was performed by the DiversiLab® system (bioMérieux) for DNA fingerprinting and analysis. Epidemiological data were analyzed with the help of a biostatistician.
Results
Amongst the collected isolates, 23 strains were confirmed as T.violaceum (results concerning the 116 M. audouinii strains have already been reported). Analysis of the epidemiological characteristics of the infected population shows that the main age category concerns 0-4 year-old children (n=9, 39,1%) with a sex-ratio M/F of 1.875. Data concerning the geographic origin of the family were present in 82,6% of the cases and reveal that patients were mainly of Ethiopian origin (n=8, 57,9% of known cases). One patient was also from Burundi showing that T. violaceum strains probably circulate mainly in East Africa. The genotypic analysis led to the distinction of 2 variants of T. violaceum. The major group was composed of 17 strains which were mainly collected in the North of Belgium and included also the reference strain (18/23, 83,3%). The other group (6 strains) was close to the major group but the analysis of the spectral superposition showed some differences between these two groups, defining two distinct variants of T. violaceum in the Belgian population. This second variant was mainly recovered from South Belgium (5/6, 83,3%). No correlation could be made between the genotypic group and a particular ethnical origin as Ethiopian subjects were found in both groups.
Conclusion
The DiversiLab® system proved to be an efficient method to investigate the molecular epidemiology of dermatophytes infections as reported previously for M. audouinii. These results show that two distinct isolates co-exist in Belgium providing evidence of genetic heterogeneity and a possible spread of one genotypic variant in a restricted geographic area or the co-existence of two variants circulating in different African communities. However, no clear correlation could be established between the appartenance to a group and epidemiological factors, such as age or ethnical origin.