Antibody responses of dogs inoculated with the inactivated rabies vaccine were investigated using the paired sera obtained from 125 dogs in Tokyo, Shizuoka, Gifu, Kyoto, Miyazaki and Kumamoto Prefectures, Japan, in 2005. Ninety of the 100 dogs that had been previously vaccinated within the past year possessed neutralizing antibodies with titers higher than 25 that are considered as being sufficient for protection. The antibody titers of dogs that were above 8 had geometric mean titers (GMT) of 251. Additional vaccination of those dogs resulted in all dogs acquiring neutralizing antibodies higher than 25, and their titers reached a GMT of 750 one month after the booster inoculation. On the other hand, 23 of 25 dogs having no history of rabies vaccination produced neutralizing antibodies with titers having a GMT of 43, ranging from below 8 to 256, one month after vaccination. Notably, no antibodies were detected in sera collected from two of those dogs even after vaccination. The results seem to suggest that the present vaccination regime in which dogs are vaccinated once a year is important in creating and maintaining consistent immunity in vaccinated dogs.
Test vaccines comprised of inactivated water-in-oil emulsions containing various antigen levels were prepared using a non-pathogenic H5N1 avian influenza (AI) virus, Alduck/Hokkaidol Vac-1/04 (H5N1). The potencies of these test vaccines were evaluated by two experiments. In the first experiment, the triangular relationship among the antigen levels of test vaccines, the hemagglutination inhibition (HI) antibody response, and the protective effect against challenge with a highly pathogenic avian influenza (HPAI) virus, A/chicken/Yamaguchi/7/04 (H5N1), was confirmed. Then lasting immunity of chickens after a single-shot vaccination was confirmed in the second experiment. As a result, complete protection after the challenge was observed in chickens immunized by test vaccines with an antigen level of 160 HA units/dose or higher. Thus, it was ascertained that the minimum antigen level in the AI vaccine was 160 HA units/dose, and the minimum HI antibody titer that could protect chickens from HPAI virus infection-related death was considered to be 1:16. Dose-dependent HI antibody responses were observed in chickens after the vaccination. Thus, 640 HA units/dose was thought to be similar to the optimal antigen level. Alternatively, the HI antibody titers of chickens, injected with the vaccine containing 640 HA units/dose, were maintained at 1:181 or higher for 100 weeks after the single-shot vaccination.
In order to produce an attenuated vaccine strain of infectious bursal disease (IBD) virus, we attempted to isolate the variants by plaque-cloning from chick embryo fibroblast (CEF) cultureadapted RF-1 strain of IBD virus.Two types of attenuated plaque variants (clones Lp and Sp) were established. The Lp clone formed large plaques with a uniform diameter of 5mm in CEF cultures, whereas the Sp clone produced only small plaques with a uniform diameter of 1mm. Distinct differences between the two clones were also observed in terms of pathogenicity for chick embryos and growth capability in CEFcultures. s Neither of the clones could be distinguished from the parent virus by a cross-neutralization test, and the clones possessed enough immunogenicity to protect chickens when challenged with virulent wild-type IBD virus. The minimum effective immunizing doses of Lp and Sp clones necessary for the protection were 104 and 105 TCID50, respectively. When Lp and Sp clones were tested for their pathogenic properties in one-day-and 4-week-old chickens with respect to clinical symptoms and lesions in the bursa of Fabri-cius, the two clones were found to be more attenuated than the parent virus. These clones had safety and immunogenic potency in accordance with the current “Minimum Requirement of Live Infectious Bursal Disease Virus Vaccine for Chicks”. The Lp clone had more immunogenic potency and higher growth capability in CEF cultures than the Sp clone, suggesting that the Lp clone promises to be useful as a live vaccine strain.
The efficacy and safety of Japanese rabies vaccine (inactivated) for veterinary use were investigated in dogs inoculated twice, as mandated by the Import-Export Quarantine Regulation for Dogs and Other Animals. The potency of these vaccines was 1.7-6.2IU/ml based on the National Institute of Health test. These values were more than the 1.0IU/ml potency recommended by OIE. A strong correlation (r=0.927) was found between the results of the fluorescent antibody virus neutralization (FAVN) test and those of the virus neutralization (VN) test. It was considered that the FAVN titer of 0.5IU/ml recommended by the Quarantine Regulations corresponded to a VN titer of 25. After two injections with a one month interval between them, the dogs had a VN titer of 1, 655 one month after the second injection and a VN titer of 176 one year after the second injec -tion. Moreover, after two injections with a one year interval between them, the VN titer increased to 3, 096 at one month after the second injection. There were no adverse reactions following vaccinations of dogs inject-ed once with five doses and three times with ten doses. Consequently, two vaccination methods for dogs with Japanese rabies vaccine as provided by the Quarantine Regulations were considered safe and effective.
Immunosuppressive potentials of attenuated variants (clones Lp and Sp) of infectious bursal disease (IBD) virus to the chickens were investigated comparing with those of virulent RF-1 strain (WT) and tissue culture-adapted RF-1 strain (the parent virus of the clones RF-1tc). After being orally inoculated with these viruses at one day or 21 days of age, the chickens were administered with either Newcastle disease B1 vaccine intranasally, Newcastle disease TCND vaccine intramuscularly or bivalent infectious coryza vaccine intramuscularly; these were administered at 7, 28 or 35 days of age, respectively. Hemagglutination-inhibition antibody titers were assayed at weekly intervals, and resistance to the challenge was tested 4-5 weeks later.Magnitude of immunosuppression due to the IBD virus varied depending on the virulence of IBD virus, the age of chickens at the time of IBD virus infection, and the sort of vaccine administered. The suppression was largest with WT, moderate with RF-1tc, and no suppression with clones Lp and Sp. Chickens inoculated with IBD virus at one day of age were remarkably suppressed, but those inoculated at 21 days were only slightly. Immunosuppressive effects against Newcastle disease B1 or bivalent infectious coryza vaccines were more severe than that against Newcastle disease TCND vaccine.The lack of immunosuppression after infection with clones Lp and Sp may reflect our previous results that the histopathological lesions due to the clones are less extensive than those produced by more virulent IBD strains. The results suggest complete attenuation of those clones.
To establish vaccine strains of H5 and H7 influenza viruses, A/duck/Hokkaido/Vac-1/04 (H5N1) [Vac-1/04 (H5N1)], A/duck/Hokkaido/Vac-3/07 (H5N1) [Vac-3/07 (H5N1)], and A/duck/Hokkaido/ Vac-2/04 (H7N7) [Vac-2/04 (H7N7)] were generated from non-pathogenic avian influenza viruses isolated from migratory ducks. Vac-1/04 (H5N1) and Vac-3/07 (H5N1) were generated by genetic reassortment between H5N2 or H5N3 virus as an HA gene provider and H7N1 or H6N1 viruses as an NA gene provider. Vac-2/04 (H7N7) was a genetic reassortant obtained using H7N7 and H9 N2 viruses to give high growth character of the H9N2 virus in chicken embryonated eggs. The results of sequence analyses and experimental infections revealed that these H5N1 and H7N7 reassortant viruses were non-pathogenic in chickens and embryos, and had good growth potential in embryonated eggs. These viruses should be useful to develop vaccines against H5 and H7 highly pathogenic avian influenza viruses.
