Equine Hoof Canker: Bovine Papillomavirus Infection Is Not Associated With Impaired Keratinocyte Differentiation

Impaired keratinocyte differentiation has recently been suggested as a key event in equine hoof canker development. Koilocytotic appearance of keratinocytes, one of the most characteristic morphological alterations in hoof canker tissue, is also a common marker for papillomavirus (PV) infection, and bovine PV-1 and/or -2 (BPV-1/2) has previously been detected in equine canker patients. Therefore, the present study aimed to correlate the frequency and severity of koilocytotic keratinocytes with BPV detection in hoof canker samples. Hoof tissue of 5/18 canker-affected horses and 2/6 control horses tested positive for BPV-1/2 DNA using polymerase chain reaction. Thus, no association between the presence of BPV-1/2 papillomaviral DNA and koilocytotic appearance was found. Proteins associated with but not specific for PV infection were also investigated. Using immunohistochemistry, specific adhesion molecules (E-cadherin and β-catenin) and intermediate filaments (keratins 6 and 14) important for intact epidermal barrier function and keratinocyte differentiation were documented in control samples (n = 6) and in hoof canker tissue samples (n = 19). Altered expression patterns of intermediate filaments and adhesion molecules were demonstrated in canker tissue, confirming the importance of incomplete keratinocyte differentiation, as well as the crucial role of keratinocyte differentiation in hoof canker.