A genetically modified rabies vaccine (ERAGS) induces protective immunity in dogs and cattle

PURPOSE: The current live attenuated rabies vaccine must be replaced with a safer vaccine based on the ERAGS strain to prevent rabies in South Korea. We evaluated the safety and immunogenicity of a new strain in dogs and cattle. MATERIALS AND METHODS: The ERAGS strain, featuring two mutations altering two amino acids in a glycoprotein of rabies virus, was propagated in NG108-15 cells. We lyophilized the virus in the presence of two different stabilizers to evaluate the utilities of such preparations as novel rabies vaccines for animals. To explore safety and immunogenicity, dogs and cattle were inoculated with the vaccine at various doses via different routes and observed daily for 8 weeks post-inoculation (WPI). Immunogenicity was evaluated using a fluorescent antibody virus neutralization test or enzyme-linked immunosorbent assay. RESULTS: The two different stabilizers did not differ greatly in terms of maintenance of virus viability in accelerated stability testing. No clinical signs of rabies developed in dogs or cattle inoculated with the vaccines (10(7.0) FAID₅₀/mL). Dogs and cattle inoculated intramuscularly with 10(5.0) FAID₅₀/mL exhibited virus neutralization assay titers of 4.6 IU/mL and 1.5 to 0.87 IU/mL at 4 WPI, respectively. All control animals remained rabies virus–seronegative throughout, confirming that no contact transmission occurred between vaccinated and control animals. CONCLUSION: Our findings indicate that the new rabies vaccine is safe and immunogenic in dogs and cattle.

Oral immunization of mice with recombinant rabies vaccine strain (ERAG3G) induces complete protection

PURPOSE: New rabies vaccine bait for both pets and raccoon dogs residing in Korea is needed to eradicate rabies infection among animals. In this study, we constructed a recombinant rabies virus (RABV), the ERAG3G strain, using a reverse genetics system. Then we investigated the efficacy of this strain in mice after oral administration and the safety of this strain in cats after intramuscular administration. MATERIALS AND METHODS: The ERAG3G strain was rescued in BHK/T7-9 cells using the full-length genome mutated at the amino acid position 333 of the glycoprotein gene of RABV and helper plasmids. Four-week-old mice underwent one or two oral administrations of the ERAG3G strain and were challenged with the highly virulent RABV strain CVSN2c 14 days after the second administration. Clinical symptoms were observed and body weights were measured every day after the challenge. RESULTS: All mice showed complete protection against virulent RABV. In addition, cats intramuscularly inoculated with the ERAG3G strain showed high antibody titers ranging from 2.62 to 23.9 IU/mL at 28-day postinoculation. CONCLUSION: The oral immunization of the ERAG3G strain plays an important role in conferring complete protection in mice, and intramuscular inoculation of the ERAG3G strain induces the formation of anti-rabies neutralizing antibody in cats.

Antibody Response in Cattle and Guinea Pigs Inoculated with Rabies Vaccines

One hundred ninety-five rabies cases in cattle were identified in South Korea since 1993. As most of rabies cases have a relation to rabid Korean raccoon dogs (Nyctereutes procyonoides koreensis), vaccination to animals including cattle is mandatory in rabies risk region. In order to minimize fatal rabies in animals, eradication policy of the disease has been achieved by controlling reservoirs and by mass vaccination. In this study, we compared the antibody response in cattle and guinea pigs inoculated with rabies vaccines commercially available in Korea. Each group of cattle in Gangwon-do was vaccinated intramuscularly with either one of five commercial inactivated vaccines or a live attenuated rabies vaccine (designated as A to F). Serum samples at the time of vaccination and four weeks post vaccination were obtained from the cattle and guinea pigs and were analyzed with virus neutralizing assay (VNA). Each group of cattle inoculating rabies vaccines showed significant virus neutralizing antibody titers (p < 0.05) ranging from 1.55 to 17.8 mean IU/ml compared with the non-vaccinated cattle and guinea pigs inoculated with 1/20 dose of vaccine showed relatively low VN antibody titers ranging from 0.23 to 6.1 mean IU/ml. All cattle immunized with A, C and F showed high VN antibody titers over 0.5 IU/ml and 62.5% and 37.5% of cattle inoculated with D and E showed protective antibody titer, respectively. This finding suggests that the inactivated or live attenuated rabies vaccination commercially available in Korea could induce protective antibody response in Korean cattle, but sero-conversion rate and sero-positive rate showing VN antibody titer over 0.5 IU/ml depend on vaccines.

Serologic Survey of Rabies Virus, Canine Distemper Virus and Parvovirus in Wild Raccoon Dogs (Nyctereutes procyonoides koreensis) in Korea

Oral rabies vaccination (ORV) program for the wild animals in rabies risk regions of Korea has been conducted since 2000. Evaluation of ORV program under field condition and information concerning the incidence of exposure to canine distemper and canine parvovirus (CPV) are needed in wild raccoon dogs (Nyctereutes procyonoides koreensis). Ninety four sera of wild raccoon dogs were screened for antibodies against rabies, canine distemper virus (CDV) and CPV in Korea. The overall prevalence of antibodies against rabies virus (RABV), CDV and CPV in wild raccoon dogs was 35.1%, 89.4% and 24.5%, respectively. Comparisons of sero-prevalences of RABV, CDV and CPV were assayed in two regions (Gyeonggi-do and Gangwon-do). The Gyeonggi-do (36.4%) showed higher sero-positive rate against CPV than Gangwon-do (20.8%). In contrast, Gangwon-do (41.7% and 97.2%) showed higher sero-positive rates against RABV and CDV than Gyeonggi-do (13.6% and 63.6%). These results indicate that there was severe circulation of CDV and CPV among wild raccoon dogs in the two regions of Korea. Furthermore, raccoon dogs showing a protective antibody titer (0.5 IU/ml) were 15.9%, suggesting that new rabies control program such as trap-vaccination-release (TVR) should be launched urgently in rabies risk regions.