Rabies DNA vaccination by the intranasal route in dogs

A DNA vaccine, using a pCl-neo plasmid encoding the glycoprotein gene of a Mexican isolate of rabies virus, was developed to induce long-lasting protective immunity against rabies virus in dogs. The aim of this work was to evaluate the intranasal (IN) vaccination route in mice and dogs. Mice and dogs were immunized via the intramuscular (IM) and IN routes. Mice received 50 microg of DNA vaccine, a booster on day 30, using the same doses and routes, and on day 90 they were challenged. Dogs received 100 microg of DNA vaccine, with a booster on day 180, and immune responses were studied on day 210. Virus-neutralizing antibodies were detected in blood sera (up to 0.5 IU) in animals immunized via the IN route and when the animals were submitted to a booster, the levels of neutralizing antibodies increased. Animals vaccinated via the IM route presented higher neutralizing antibody titres than those vaccinated IN. Control groups lacked anti-rabies antibodies. On day 90, mice were challenged. From these, a 100 % of the IM vaccinated mice, and an 80 % of the IN vaccinated mice survived the challenge. No animals from the control group survived. Dogs revealed significant virus-neutralizing antibody titres (up to 0.5 IU) on day 30 and, after booster, on day 210 neutralizing antibody titre was higher than 1.8 IU. The main advantage of using DNA vaccines over traditional live ones is that there is no contamination with viruses that could be disseminated in the environment and reproduced in susceptible animals. This study demonstrated that pGQH was succesful when administrated via the IN route. IN vaccination seems attractive due to its easy application and mucosal protection. This form of vaccination could also be advantageous in domestic animal vaccination campaigns, for it is less stressful than the parenteral route (no painful shots).