Abstract
A study was carried out to examine the efficacy and safety of Nobivac rabies vaccine when administered after exposure to virulent rabies street virus under controlled conditions. Healthy, young dogs (n=40), seronegative for rabies antibody were challenged intramuscularly in the masseter muscle, following laceration to mimic the conditions of natural rabies exposure, with virulent challenge virus strain (104.4 LD50, 2 ml per dog). The dogs were vaccinated intramuscularly with Nobivac rabies vaccine (Intervet, n=20, groups A and C), Injectable Rabies Vaccine (Competitor, n=10, group B) and placebo (n=10, group D). Five vaccinations were administered on days 0 (day of challenge), 3, 7, 14 and 28 to dogs in groups A and B and three vaccinations on days 0, 5 and 28 to dogs in group C. The dogs in group D were administered placebo intramuscularly six times on days 0, 3, 5, 7, 14 and 28, to mimic the conditions in the other three groups. Sera samples were screened to measure the antibody titire of the vaccinated dogs by Rapid Fluorescent Flocculation Inhibition Test (RFFIT) and an Enzyme Linked Immunosorbent Assay (ELISA) tests. All of the dogs were observed for clinical signs of rabies. Brain impression smears were collected in duplicate from dogs that died of rabies to confirm the presence of the virus (Fluorescent antibody test (FAT)). The Rabies vaccine used in schedule A and B were showing similar immune responses. The Intervet interrupted schedule was showing higher protective antibody titres. The control group showed clear clinical illness. In the control group, out of 10 animals, 6 animals died and confirmed Rabies by FAT and demonstration of Negribodies. The Intervet vaccine is found to be potent and safe either as 0, 3, 7, 14 and 28 or 0, 5, 28 day post-bite vaccination schedule. But all the schedules were showing protective titres on the 7th day of the vaccination. Definite proof of the effectiveness of the vaccines used in the present study was provided by the antibody titres of the 30 dogs when tested on day 3, 7,14, 28 and 90 post-infections with rabies virus. Both the vaccines are found to be safe and potent. None of the vaccinated animals showed any clinical symptom as like control animals. The experimental studies confirmed the safety of the vaccine as well as high antigenic value with rapid development of antibodies, low reactogenicity and absence of neurological reactions.