Equine sarcoids. Part 1: the aetiopathogenesis of equine sarcoid disease

Equine sarcoids are the most common neoplastic skin tumors in equids, and despite being histologically benign, they can become locally invasive, recurrent and compromise animal welfare, use and value. Although bovine papillomavirus types 1 and 2 are widely accepted as key extrinsic factors in sarcoid development, equids appear to be dead-end hosts in which infectious virions are not produced, leaving questions regarding disease transmission unresolved. Experimental and field observations have generated conflicting evidence about the potential for equid-to-equid spread. Host-related susceptibility, likely passed on as a polygenic trait and influenced by environmental cofactors, plays a critical role in disease expression. The unpredictable clinical course of sarcoids, their high recurrence rate and limited availability of effective, tissue-sparing therapies further challenge management. Moreover, limited recognition of sarcoids as a significant health problem has hindered the implementation of breeding-based prevention strategies. Collectively, these biological uncertainties and practical barriers explain why progress in developing effective and durable disease prevention strategies has remained slow, despite decades of research.