An Improved Protocol for Comprehensive Etiological Characterization of Skin Warts and Determining Causative Human Papillomavirus Types in 128 Histologically Confirmed Common Warts

Human papillomaviruses (HPVs) are etiologically associated with various benign and malignant neoplasms of cutaneous and mucosal epithelia. We describe an improved diagnostic protocol for comprehensive characterization of causative HPV types in common warts, in which broad-spectrum 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 qPCR were used for: (i) diagnosis of HPV infection in warts; (ii) estimation of cellular viral loads of all HPV types detected; and (iii) determination of their etiological role in 128 histologically confirmed fresh-frozen common wart tissue samples. A total of 12 different causative HPV types were determined in 122/126 (96.8%) HPV-positive warts, with HPV27 being most prevalent (27.0%), followed by HPV57 (26.2%), HPV4 (15.1%), HPV2 (13.5%), and HPV65 (7.9%). The cellular viral loads of HPV4 and HPV65 were estimated for the first time in common warts and were significantly higher than the viral loads of HPV2, HPV27, and HPV57. In addition, we showed for the first time that HPV65 is etiologically associated with the development of common warts in significantly older patients than HPV27 and HPV57, whereas HPV4-induced warts were significantly smaller than warts caused by HPV2, HPV27, HPV57, and HPV65.