Digital droplet PCR for the detection and quantification of circulating
bovine Deltapapillomavirus
Abstract
In this study, the digital droplet polymerase chain reaction (ddPCR) was
used to quantify circulating bovine papillomavirus (BPV; genus:
Deltapapillomavirus) levels in blood samples from 25 healthy cows and 15
cows with chronic enzootic hematuria due to papillomavirus-associated
bladder tumors. ddPCR detected the BPV DNA in 95% of all the samples
(i.e., in 24 of the healthy cows and 14 of the diseased animals),
whereas quantitative real time PCR (qPCR) detected it in only 57.5% of
the same blood samples, with the percentage differences between ddPCR
and qPCR being statistically significant (P value 0.05), according to
the 2 test of Campbell and Richardson. Furthermore, ddPCR detected BPV
infections by a single genotype and by multiple genotypes in 37% and
63% of the cows, respectively, whereas qPCR detected these in 16% and
16%, respectively. Of the two assays, ddPCR was the more sensitive and
accurate clinical diagnostic tool, allowing the detection of otherwise
undetectable BPV genotypes, and consequently, a higher number of BPV
co-infections. qPCR failed to detect many BPV co-infections by multiple
genotypes. Therefore, ddPCR may be an essential tool for improving
diagnostic procedures, allowing the identification of the genotypic
distribution of BPV and a better understanding about the territorial
divergence, if any, of the BPV prevalence in different areas. No
significant differences in the blood viral load estimations were
observed between the two animal groups, suggesting that the bloodstream
could be a site of primary infection. Finally, as BPV DNA was detected
in cows affected by noninvasive urothelial tumors, including papilloma
and papillary urothelial neoplasms of low malignant potential, the
circulating BPVs appeared to be independent of the status of urothelial
neoplasms. Therefore, unlike in humans, circulating BPVs cannot be an
actual prognostic marker of urothelial tumors in cows.