equine sarcoid

Equine sarcoids are fibroblastic skin tumours affecting equids worldwide. While the pathogenesis is not entirely understood, infection with bovine papillomavirus (BPV) type 1 (and less commonly type 2) has been implicated as a major factor in the disease process. Sarcoids very seldom regress and in fact often recrudesce following therapy. Nothing is known about the immune response of the equine host to BPV. Given that the viral genes are expressed in sarcoids, it is reasonable to assume that vaccination of animals against the expressed viral proteins would lead to the induction of an immune response against the antigens and possible tumour rejection. To this end we vaccinated sarcoid-bearing donkeys in a placebo-controlled trial using chimeric virus-like particles (CVLPs) comprising BPV-1 L1 and E7 proteins. The results show a tendency towards enhanced tumour regression and reduced progression in the vaccinated group compared to control animals. Although promising, further studies are required with larger animal groups to definitely conclude that vaccination with CVLPs is a potential therapy for the induction of sarcoid regression.

BPVs are double stranded DNA viruses that can infect several species other than the natural host, cattle, including equids. In equids, BPV-1, and, less commonly BPV-2, infection gives rise to fibroblastic tumours of the skin. Whilst a causal relationship between BPV-1/2 and equine sarcoids is now well established, how the disease is transmitted is not known. In this study we show BPV-1 DNA can be detected in flies trapped in the proximity of sarcoid-affected animals. Sequence analysis of the BPV-1 LCR from flies indicates that flies harbour BPV-1 LCR sequence variants II and IV which are commonly detected in equine sarcoids. These data suggest that flies may be able to transmit BPV-1 between equids.

Logistic regression analysis was applied to data from a population of donkeys to obtain statistical models estimating the risk of equine sarcoid. Two models were constructed and compared. The group model was derived using the prevalence of animals with sarcoids in groups, classified according to the explanatory variables gender, age at first exposure (considered as age at entry to the population), duration of exposure, and gender by duration of exposure as an interaction. The subject model was derived from individual animal data and consisted of the factor gender with the covariates age at first exposure and duration of exposure. Age at first exposure was represented in the model by linear and quadratic terms, and as an interaction with duration of exposure. Both models provided a good approximation to the observed data. The analyses identified young male donkeys with short duration of exposure as being at highest risk. We concluded that risk assessment using the group model could be used effectively in the clinical management of sarcoids in the population of donkeys. Frequent examination of high risk groups might allow early diagnosis, therapeutic intervention and improved animal welfare.