Papillomavirus role in dog transmissible venereal tumors

Abstract

Transmissible venereal tumors (TVT) are malignant (cancerous) round cell tumors. Unlike other cancers, TVTs are transferrable sexually between dogs through direct skin-to-skin contact with the tumor. Although the exact source of TVT cells remains unclear, the presence of inclusion bodies in tumor cell cytoplasm indicates the involvement of a viral agent. However, this hypothesis has not been fully revealed. Considering that, the papillomaviruses, which can cause cancer in many animal species, may play a role as an etiological agent in TVT cases. In this study, the presence of papillomaviruses in samples taken from dogs with TVT was investigated by PCR using different primer pairs. All samples were analyzed with FAP59/64, MY09/11, PVF/FAP64 primer sets targeting the L1 gene of PVs, and CP4/5 primer sets targeting the E1 gene of CPV. PV DNA was detected in 33 (45.20%) of 73 dogs with TVT. After carrying out PCR, positive samples were used for typing using sequence analysis. The MY09/11 primers amplified a 450 bp band in 27 out of 33 positive dogs (81.81%) as single. The MY09/11-CP4/5, PVF/FAP64, and PVF/FAP64-FAP59/64-CP4/5 primer sets showed positivity in 4, 1, and 1 of the animals, respectively. After molecular studies, only the oral biopsy sample of one dog showed 98-99% nucleotide sequence similarity with the L1 and E2 genes of canine PV type 1 for three primer sets but not for MY09/11. The other sequenced samples showed 70-73% similarity to Leptoncychotes weddellii papillomavirus 6 and 7. This therefore represents a novel PV, indicating that papillomaviruses belonging to different genera may cause TVT cases. These results suggest that PV infection may be involved in TVT pathogenesis in sampled dogs with TVT. Comprehensive studies on this subject can both clarify the etiology of these case and also indicate effective practices for controlling the disease, such as treatment and vaccination.