One-time intradermal DNA vaccination in ear pinnae one year prior to infection protects dogs against rabies virus.

Rabid dog exposures result in > 99% of human rabies deaths worldwide. Ninety-eight percent of these cases occur in developing countries. Thus, the best protection against human rabies would be prevention through adequate vaccination of the reservoir population. The difficulty in re-locating ownerless, freely roaming dogs for booster vaccinations, in addition to poor coverage with inadequate vaccines, suggests that a potentially inexpensive vaccine that elicits long-term protection after a single-dose could improve control of canine rabies in developing countries. One solution could be a DNA vaccine. We have previously determined that dogs vaccinated intradermally (i.d.) in ear pinnae with a rabies DNA vaccine expressing a rabies virus glycoprotein (G) produce high levels of neutralizing antibody that persist for at least 6 months. In the present study, we determined whether a one-time i.d. rabies DNA vaccination into ear pinnae 1 year before viral challenge would protect dogs against rabies virus. The dogs did not receive a booster vaccination. All dogs (100%) vaccinated i.d. in each ear pinna with 50 microg of rabies DNA vaccine, or intramuscular (i.m.) with a commercial canine rabies vaccine survived a lethal dose of rabies virus. In contrast, 100% of dogs vaccinated i.m. with 100 microg of rabies DNA developed rabies, as did 100% of negative control dogs that were vaccinated i.d. in each ear pinna or i.m. with DNA that did not express the rabies virus G. The data suggest that a one-time i.d. rabies DNA vaccination into ear pinnae offers a new approach to facilitate control of endemic canine rabies in developing countries.