No evidence of bovine papillomavirus type 1 or 2 infection in healthy equids.

Abstract

There is a large body of evidence supporting bovine papillomavirus types 1 and 2 (BPV1; BPV2) as aetiological agents of equine sarcoids. However, there is conflicting data regarding BPV1/2 infection in sarcoid-free equids. Data obtained between 2007 and 2017 by BPV1/2 screening of sarcoids and nonsarcoid tumours vs. samples from healthy equids are presented to help clarify this issue. Cross-sectional study. Tumour material obtained from horses, donkeys and mules with confirmed sarcoids (n=130), suspected sarcoids (n=120), or nonsarcoid lesions (n=70), skin biopsies from 102 tumour-free horses and dandruff/hair roots from 35 tumour-free donkeys and mules were screened for BPV1/2 infection. Sample DNA was extracted and validated by equine β-actin PCR. BPV1/2 screening was performed by BPV1/2 E5-specific PCR allowing for the detection of less than 10 viral DNA molecules. Twenty-six amplicons were bidirectionally sequenced and compared to known E5 variants using BLAST program. BPV1/2 E5 PCR scored positive for 130/130 diagnosed sarcoids, 63/120 suspected sarcoids and 13/70 nonsarcoid lesions, whereas 137/137 DNA aliquots derived from tumour-free equids tested negative. On predicted E5 protein level, six different BPV1 E5 variants were identified. The diagnosis of equine sarcoid was not confirmed in 120 lesions. Lack of BPV1/2 E5 DNA in tumour-free equids and the prevalence of sarcoid disease in young adult individuals suggest that the time span between initial infection and sarcoid development is short. This contrasts with the long phase of virus latency characterising infection of humans by carcinogenic papillomaviruses. Presence of BPV1/2 DNA in several cases of poor wound healing/hypergranulation and dermatitis points to these skin disorders being possibly co-induced by BPV1/2. PCR screening of tumour tissue/scrapings for BPV1/2 DNA represents a reliable tool for the rapid validation of a clinical diagnosis of equine sarcoid.