Epidemiologic analysis of a sarcoid outbreak involving 12 of 111 donkeys in Northern Italy

Equine sarcoids develop upon bovine papillomavirus type 1 or 2 (BPV1, BPV2) infection in conjunction with trauma and represent the most common tumour disease in horses and other equids, including donkeys. In face of a sarcoid outbreak involving 12 of 111 donkeys and mules at the 'Rifugio degli Asinelli', a subsidiary charity organization of The Donkey Sanctuary, non-invasively collected sample material including crusts, dandruff, swabs and hair roots was collected from sarcoid-affected and 26 healthy donkeys, as well as dandruff from a grooming kit and tabanids caught from or in the vicinity of sarcoid patients. In addition five previously collected sarcoids stored in formalin were provided. DNA isolated from collected material was tested for the presence of the BPV1/2 E5 oncogene using PCR. Positive samples were further analysed by E2/E4 and LCR PCR and amplicon sequencing to determine a possible common source of infection via comparative alignment of intralesional BPV1/2 gene variants. IC/PCR was used to assess sample aliquots for the presence of BPV1/2 virions, and IHC to analyse five tumours for BPV1 E5 and L1 protein expression. All sarcoid-affected donkeys, two of 55 tabanids and dandruff from a curry comb tested positive for BPV1/2 E5, yet negative by IC/PCR. Healthy animals were BPV1/2-free. IHC revealed different levels of intralesional E5 and L1 expression. A series of BPV1 E5, E2, and LCR variants and BPV2 E5 were detected from donkeys, indicating that they had accidently developed sarcoids at about the same time rather than having acquired disease from each other.