Human papillomaviruses (HPVs) are etiologically associated with various benign skin neoplasms, of which common warts (verrucae vulgares) are the most prevalent. The aim of our study was to reliably determine for the first time the etiological agent in at least 95% of common warts by a combination of different molecular methods. Within the established diagnostic protocol, we used broad-spectrum polymerase chain reactions (PCRs) followed by Sanger sequencing, two previously described and seven newly developed type-specific quantitative real-time PCRs (qPCRs) coupled with the human beta-globin gene qPCR to analyse 132 histologically confirmed common warts and to determine the etiologic role of all detected HPVs based on viral load estimation. A total of 12 different causative HPV types were determined in 126/130 (96.9%) HPV-positive common warts, with HPV27 (27.7%), HPV57 (26.1%), HPV4 (14.6%), HPV2 (13.1%), and HPV65 (7.7%) being the most prevalent. Metagenomic next-generation sequencing showed that HPV DNA was not present in any of the warts without a determined etiological agent. Using the type-specific digital PCRs, we confirmed the same etiologic agents previously identified by type-specific qPCRs in the warts tested, with higher precision in quantifying target HPV types and no statistically significant differences in viral loads, whereas the established diagnostic protocol had a wider dynamic range.
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