Intradermal DNA vaccination in ear pinnae is an efficient route to protect cats against rabies virus

A DNA vaccine against rabies (pGQH) was administrated to cats in order to examine different administration routes. Four groups of three cats each were inoculated with pGQH as follows: group A, intramuscularly (IM), 100 microg; group B, intranasally (IN), 100 microg; group C, intradermally into ear pinnae (ID-EP), 100 microg, and group D, IM, 200 microL of phosphate buffer solution (PBS) alone (control group). Blood was drawn on days 0, 30, 60, 90, 120, 150, and 180. Groups A, B, and C received a booster on day 30. At day 200 all animals were challenged. A passive transfer of cat sera, as well as a viral challenge, was performed in mice. The results displayed that neutralizing antibody titers were higher in cats of group C (ID-EP) showing high early titers (> 2 IU) and the highest titer was on day 120 (> 14 IU). In group B (IN), two out of three cats seroconverted on day 30 (> 0.5 IU), the third cat seroconverted until day 60 (> 0.5 IU). In contrast, the lowest levels of neutralizing antibodies were detected in group A (IM). The control group showed no anti-rabies antibodies. Groups A (IM) and D (control) succumbed after lethal challenge. All animals from the ID-EP group (C) survived, only one individual from the IN (B) group died. Mice that received cat sera from ID-EP, IM, and IN groups survived and were protected (30/30 survivors). Mice groups that received pre-immunization sera from cats were not protected (0/30 survivors). This study demonstrates that pGQH immunization was successful when it was administrated ID-EP, and acceptable through the IN route. The IM route, however, was not effective in cats. For vaccination, the IN route seems attractive due to its accessibility for application, but it seems to activate seroconversion slowly. The best route to promote anti-rabies antibody titers was the ID-EP route. This practical and efficient route should be further studied.