Abstract
Ovine papillomavirus (OaPV) comprises four genotypes; OaPV1, OaPV2, and
OaPV4 are fibropapillomaviruses within the genus
Delta-papillomavirus ( Delta-PV ), whereas OaPV3 is
an epitheliotropic virus that belongs to the genus
Dyokappa-papillomavirus ( Dyokappa-PV ). To date,
all of them have been known to infect sheep only. OaPV1, OaPV2, and
OaPV4 have been associated with ovine cutaneous and mucosal
fibropapillomas, while OaPV3 is a key factor in the squamous cell
carcinoma (SCC) pathway of the sheep skin. Peripheral blood mononuclear
cell (PBMC) samples obtained from 128 cattle at public slaughterhouses
were investigated using droplet digital polymerase chain reaction
(ddPCR). ddPCR is a new-generation PCR technique that enables accurate
and absolute quantification of target molecules with high sensitivity
and specificity. All OaPVs were detected by identification and
quantification of nucleic acids using specific fluorescent probes. Of
128 PBMC samples, 100 (~78%) showed OaPV infections.
Further, 42, 35, and 23 PBMC samples showed single, double, and triple
OaPV infections, respectively. OaPV1 was responsible for 22 single
infections, OaPV2 caused 16 single infections, and OaPV3 and OaPV4
caused two single infections each. OaPV1 and OaPV2 were the most
frequent ovine viruses in dual and triple infections. In many PBMC
samples, both ovine Delta-PV and Dyokappa-PV were found to
be transcriptionally active, as shown by the detection and
quantification of E5 oncogene transcripts for OaPV1, L1 transcripts for
OaPV2, E6 and E7 transcripts for OaPV3, and E6 for OaPV4. OaPVs were
found in the blood samples from cattle that shared grasslands rich in
bracken ferns known to contain immunosuppressant substances.
Furthermore, OaPVs were also found in cattle from intensive livestock
farming without any contact with sheep. Because OaPV DNA was detected in
both grass hay and corn silage, it is conceivable that these feed may be
the viral sources.