Acyclovir for Equine Sarcoids?

Reports that acyclovir could have some favorable effect on equine sarcoids have been tested by a recent study at the Ghent University’s College of Veterinary Medicine. While the exact pathogenesis of equine sarcoids is not known, in some cases, bovine papilloma virus (BPV) might be involved [Haspeslagh, M.; Garcia, M.J.; Vlaminck, L.E.M.; and Martens, M. Topical use of 5% acyclovir cream for the treatment of occult and verrucous equine sarcoids: a double- blinded placebo-controlled study. BMC Veterinary Research (2017) 13:296].

Other studies have suggested that use of an anti-viral cream can achieve resolution. 

In this placebo-controlled and double-blinded study of 28 horses and three ponies, a 5% topical acyclovir cream was applied for up to six months to sarcoid tumors. Each lesion was assessed via measurements and photographs, and swabs were taken to obtain DNA to confirm or rule out the presence of BPV. Roughly 16% of the acyclovir-treated lesions lacked BPV DNA, as did 23% of the placebo-treated lesions.

In both treated and placebo groups, the mean surface area of the lesions increased while also becoming less verrucous. It was noted that some of these changes could be attributable to hydration effects of the cream such that it prevents formation of the verrucous layer, much in the same way as an antikeratotic cream would. However, these changes were statistically insignificant.

There is some question as to how an anti-viral medication could work on BPV-containing sarcoids, since BPV “lacks the presence of thymidine kinase that is necessary to activate acyclovir.” While earlier studies reported 68% success (Stadler, S., et al., 2011) and 53% success (Baker, C.C., et al., 2016) with acyclovir cream, the conclusion here was that: “None of the results presented in this study indicated that topical treatment of occult or partly verrucous equine sarcoids with acyclovir yields any better results compared to treatment with placebo cream.”