Antibody responses after vaccination against equine influenza in Korea in 2016–2018 / 대한수의학회지

Equine influenza (EI) is the main cause of respiratory illness in equines across the globe and is caused by equine influenza A virus (EIV-A), which has impacted the equine industry internationally because of the marginal mortality and high morbidity. In the present study, the immune responses after equine influenza vaccination were evaluated in 4,144 horses in Korea using the hemagglutination inhibition (HI) assay. The equine influenza virus (EIV), A/equine/South Africa/4/03 (H3N8), was used as the antigen in the HI assay. The mean seropositive rates were 89.2% (97.4% in 2016, 77.6% in 2017, and 92.4% in 2018). This paper highlights the advances in understanding the effects of vaccines and control strategies for mitigating the emerging menace by EIV.

Antibody Response in Korean Raccoon Dogs Inoculated with Inactivated Rabies Vaccines

Since sylvatic rabies was first identified in South Korea in 1993, over three million bait vaccine doses have been distributed to rabies risk regions in order to block transmission of rabies among wild animals. New progressive strategy is needed to eliminate sylvatic rabies completely in rabies risk regions. Before applying the preventive program related to eradication, immunogenicity of inactivated rabies vaccines available in Korea has to be evaluated in Korean raccoon dogs (Nyctereutes procyonoides koreensis). Six groups of raccoon dogs in wild rescue center of Gyeonggi-do were vaccinated intramuscularly with single dose of six inactivated commercial rabies vaccines (designated A to F). Serum samples at the time of vaccination, and two and four weeks post vaccination were obtained and analyzed by virus neutralizing assay (VNA). All raccoon dogs inoculated with vaccines C, D, E or F, showed VN antibody titers ranging from 0.5 to 13.77 IU/ml. Half of four raccoon dogs immunized with vaccine B revealed VN titer over 0.5 IU/ml, and one of four raccoon dogs inoculated with vaccine A showed protective antibody titer. This finding suggests that most of the commercially available inactivated rabies vaccines could induce protective immunity in Korean raccoon dogs and be applicable to new rabies control program.

Molecular characterizations of phosphoprotein of rabies virus circulating in Korea / 대한수의학회지

Rabies is a major zoonotic disease that causes approximately 55,000 human deaths worldwide on an annual basis. The nucleocapsid protein and glycoprotein genes of the Korean rabies virus (RABV) have been subjected to molecular and phylogenetic analyses. Although the phosphoprotein (P) has several important functions in viral infection and pathogenicity, the genetic characterizations of the P of Korean RABV isolates have not yet been established. In the present study, we conducted genetic analyses of P genes of 24 RABV isolates circulating in the Republic of Korea (hereafter, Korea) from 2008 to 2011. This study revealed that the P genes of Korean RABVs are genetically similar to those of RABV strains of lyssavirus genotype I including V739 (dogs, Korea), NNV-RAB-H (humans, India), NeiMeng925 (raccoon dogs, China), and RU9.RD (raccoon dogs, Russia). Among Korean isolates, the RABV P genes showed low variability in the variable domains among Korean isolates; they had specific consensus sequences and amino acid substitutions capable of identifying geographic characteristics and retained specific sequences thought to be important for viral function. These results provide important genetic characteristics and epidemiological information pertaining to the P gene of the Korean RABV.

Molecular characterization of Korean rabies virus isolates

The nucleoprotein (N) and glycoprotein (G) of 11 Korean rabies virus (RABV) isolates collected from animals diagnosed with rabies between 2008 and 2009 were subjected to molecular and phylogenetic analyses. Six isolates originated from domestic animals (cattle and dogs) and five were obtained from wild free-ranging raccoon dogs. The similarities in the nucleotide sequences of the N gene among all Korean isolates ranged from 98.1 to 99.8%, while those of the G gene ranged from 97.9 to 99.3%. Based on the nucleotide analysis of the N and G genes, the Korean RABV isolates were confirmed as genotype I of Lyssavirus and classified into four distinct subgroups with high similarity. Phylogenetic analysis showed that the Korean isolates were most closely related to the non-Korean NeiMeng1025B and 857r strains, which were isolated from rabid raccoon dogs in Eastern China and Russia, respectively. These findings suggest that the Korean RABV isolates originated from a rabid raccoon dog in Northeastern Asia. Genetic analysis of the Korean RABV isolates revealed no substitutions at several antigenic sites, indicating that the isolates circulating in Korea may be pathogenic in several hosts.

Epidemiological Characteristics of Rabies in South Korea from January 2004 to March 2011

Over the seven years from January 2004 to March 2011, 105 rabies cases in three different animal species and one case in human were recorded in South Korea. Forty three (40.6%) cattle and 33 (31.1%) dogs, 29 (27.4%) raccoon dogs were affected and one (0.9%) death in human was reported. The highest annual incidence of rabies was recorded with 27 cases in 2004, and then decreased to a median of 14 cases per year. Eighty cases (76.2%) occurred in Gangwon and 24 cases (22.9%) in Gyeonggi and one case in Seoul Province. All rabies cases occurred in the northern part of the country, namely, Seoul, Gyeonggi and Gangwon Provinces. Since 2007, rabies cases were not reported in Gyeonggi Province, but continued to occur and move eastward in Gangwon Province. The monthly distribution of animal rabies during the seven year period peaked in January, and the incidence was the highest during winter, from December to February, and the least common in summer, from June to September. The epidemiological study indicated that preventive measures including distribution of bait vaccine for the control of rabies in wild animals was helpful to a substantial decrease in number of rabies cases in South Korea.

Sero-surveillance of Transmissible Gastroenteritis Virus (TGEV) and Porcine Respiratory Coronavirus (PRCV) in South Korea

Transmissible gastroenteritis (TGE) is sporadic in South Korea. Since porcine respiratory coronavirus (PRCV) infection was identified in South Korea in 1996, the TGE infection has decreased with the PRCV occurrence. In this study, we described the sero-surveillance of TGE/PRCV infection by using a commercially available ELISA kit. A total of 1,295 sera from slaughtered pigs and 69 sera from wild boars were collected in years 2009 and 2010 throughout the country and tested for antibodies against TGE and PRCV. Although there was no clinical sign observed for TGE and vaccination had not been done for TGEV, 4.9% of sera showed positive for antibody against TGEV. Furthermore, 63.7% of finisher and 8.7% of wild boars were positive for antibody against PRCV. Our result suggests that the TGEV infection might still be present in some farms in South Korea.

Molecular Identification of the Vaccine Strain from the Inactivated Rabies Vaccine

Since 1994, several different inactivated rabies vaccines have been used to immunize domestic animals such as dogs, cats, and cattle in South Korea. The Korean Veterinary Authority has conducted safety and efficacy testes of inactivated vaccines using laboratory animals. In this study, we applied a molecular method to investigate the genetic characterization of the rabies virus (RABV) genes in six commercial inactivated rabies vaccines, and determined the efficiency of two extraction reagents (i.e., sodium citrate or isopropyl myristate) to separate the vaccine antigens from the antigen/adjuvant complexes. Six partial nucleocapsid (N: 181 bp) and five partial glycoprotein (G: 306 bp) genes were successfully amplified with specific primer sets, which demonstrated that sodium citrate is more efficient than isopropyl myristate in extracting viral RNA from inactivated gel vaccines. In addition, we identified the viral strain of the vaccine by analyzing the nucleotide sequences of the N and the G genes. The nucleotide similarity of the partial N and G genes ranged from 97.1 to 99.4% and from 91.8 to 100% among rabies vaccine strains, respectively, indicating that each manufacturer used different rabies virus strains to produce their vaccines. The molecular method used in this study could also be used to identify viral strains in other inactivated vaccines.