Vaccination with Virus‐Like Particles Protects Horses from Experimental BPV‐1 Infection

Aims Bovine papillomavirus types 1 and 2 (BPV-1/-2) are chiefly involved in the pathogenesis of equine sarcoids. We have previously demonstrated that intramuscular immunisation of horses with BPV-1 L1 virus-like particles (VLPs) is safe and highly immunogenic, that BPV-1 and -2 are closely related serotypes, and that intradermal inoculation of horses with cow wart-derived BPV-1 virions reliably results in the development of transient pseudo-sarcoids. Based on these data, we next performed a virus challenge study. Methods Fourteen horses were immunised with 100 μg of BPV-1 L1 VLP in adjuvant on Days 1 and 28; 7 horses served as nonvaccinated controls. On Day 42, all 21 horses were intradermally inoculated on their neck with 5 x 107 BPV-1 virions per wheal (10 wheals per horse). The horses were monitored for adverse reactions and pseudo-sarcoid formation. Antibody titres were determined for Days 0 and 42. Results All 7 control horses developed pseudo-sarcoids at every inoculation site (10/10). Tumours reached sizes of up to 16 mm in diameter and persisted for a minimum of 20 weeks. Immunisation with BPV-1 L1 VLPs resulted in complete protection in 13 of 14 vaccinated horses, with serum antibody titres ranging between 6.400 and 25.600. One vaccinated horse developed 7 tumours, which reached a maximum size of 2 mm and completely regressed within 5 weeks, with antibody titres of 800. Conclusions and practical significance Immunisation of 14 horses with BPV-1 L1 VLPs conferred complete protection from experimental infection with BPV-1 virion in 13 cases, and partial protection in one horse. The old age of this individual may account for the poor response to vaccination. Provided that the upcoming BPV-2 challenge will yield similar results, BPV-1 L1 VLP may be used for routine immunisation of equids. Ethical animal research This work was approved by the institutional ethics committee and the national authority according to Austrian Law for Animal Experiments, Tierversuchsgesetz -TVG. Approval Number: BMWF-68.205/0236-II/3b/2011. Sources of funding: This project is funded by the Veterinary University of Vienna Austrian Science Fund (FWF). Competing interests: None.