Gene expression, viral load, and bovine papillomavirus coinfection in blood and cutaneous warts of cattle.

This study characterized the biology of Bovine Papillomavirus (BPV) in cattle from Pernambuco, Brazil, comparing viral load and gene expression between papillomas (warts) and blood. A total of 89 samples (46 for viral load, 43 for gene expression) were analyzed, all previously positive for BPV-1, -2, or -6. After simultaneous DNA/RNA extraction and cDNA synthesis, viral load was quantified via qPCR targeting the L1 gene, while expression of regulatory (E5/E7) and structural (L1) genes was assessed by RT-PCR. BPV-2 exhibited significantly higher viral load in warts (15.20 ± 45.50 log₁₀ copies/µL) versus blood (3.45 ± 6.20; p < 0.01), with greater presence in adult cows (p = 0.02) and symptomatic animals (p = 0.03). Expression of the structural gene L1 (BPV-2) was more frequent in lesions (47.8%) than in blood (25%), and a strong correlation existed between BPV-1 presence and E5 expression (φ = 0.65; p < 0.001). Warts showed higher genetic diversity (Shannon index H = 1.25 vs. 0.78 in blood) and a 4.3-fold higher probability of coinfection by multiple viral types (OR = 4.3; 95% CI 1.2-15.8), with clonal predominance of BPV-2 (84.6% of samples). The absence of negative correlations suggests viral coexistence without mutual inhibition. It is concluded that papillomas are the primary site of active BPV replication and expression, especially for type 2. Viral coexistence may promote infection persistence and lesion chronicity.