Vaccine development against Squirrelpox virus (SQPV)
Funding was provided by the Wildlife Ark Trust for the Moredun Research Institute to explore the feasibility of producing a vaccine against SQPV that could be used in the field to protect red squirrels against disease. Initial efforts were directed at both a recombinant vaccine and an in vitro culture-attenuated vaccine as the most likely routes to success, but during the project we decided to concentrate on the in vitro culture-attenuated vaccine. Two in vitro-adapted viruses were used for this purpose. Each virus was passaged in culture over 70 times, with individual aliquots of virus being stored after each passage and with whole batches being stored after every 10th successive passage. This was to ensure that should the virus be lost during the passage process, or indeed if the resulting vaccine candidate proved to be too avirulent such that no protection was afforded by it, that sufficient virus stocks of lower passages would be available for continuation without needing to repeat the process from the beginning.
Both of the vaccine candidates provided protection against the wild-type virus.
Further development work may be required to ensure that the vaccine is as safe as possible for use in the field. Preliminary analyses of the results suggest this to be the case. Attenuation of poxvirus vaccines is not an exact science and it is probable that this work will take approximately a year.
Detailed discussions will be required with the Veterinary Medicines Directorate (VMD) to ensure that all appropriate steps are taken for purposes of licensing a vaccine. This is not a straightforward process as the aim is for the vaccine to be produced on a “not for profit” basis. Nevertheless, certain criteria will need to be satisfied.