Comparison of four diagnostic methods for detecting rabies viruses circulating in Korea

It is essential to rapidly and precisely diagnose rabies. In this study, we evaluated four diagnostic methods, indirect fluorescent antibody test (FAT), virus isolation (VI), reverse transcriptase polymerase chain reaction (RT-PCR), and rapid immunodiagnostic assay (RIDA), to detect rabies in animal brain homogenates. Out of the 110 animal brain samples tested, 20 (18.2%) were positive for rabies according to the FAT. Compared to the FAT, the sensitivities of VI, RT-PCR, and RIDA were 100, 100, and 95%, respectively. The specificities of VI, RT-PCR and RIDA were found to be 100, 100, and 98.9%, respectively. Rabies viruses circulating in Korea were isolated and propagated in murine neuroblastoma (NG108-15) cells with titers ranging from 101.5 to 104.5 TCID50/mL. Although the RIDA findings did not completely coincide with results obtained from FAT, VI, and RT-PCR, RIDA appears to be a fast and reliable assay that can be used to analyze brain samples. In summary, the results from our study showed that VI, RT-PCR, and RIDA can be used as supplementary diagnostic tools for detecting rabies viruses in both laboratory and field settings.

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.

Serosurveillance for Japanese encephalitis virus in wild birds captured in Korea

Climate change induced by recent global warming may have a significant impact on vector-borne and zoonotic diseases. For example, the distribution of Japanese encephalitis virus (JEV) has expanded into new regions. We surveyed the levels of hemagglutination-inhibition (HI) antibodies against JEV (Family Flaviviridae, genus Flavivirus) in wild birds captured in Korea. Blood samples were collected from 1,316 wild birds including the following migratory birds: Oceanodroma castro (n = 4), Anas formosa (n = 7), Anas penelope (n = 20), Fulica atra (n = 30), Anas acuta (n = 89), Anas crecca (n = 154), Anas platyrhynchos (n = 214), Aix galericulata (n = 310), and Anas poecilorhyncha (n = 488). All were captured in 16 locations in several Korea provinces between April 2007 and December 2009. Out of the 1,316 serum samples tested, 1,141 (86.7%) were positive for JEV. Wild birds captured in 2009 had a higher seroprevalence of ant-JEV antibodies than those captured in 2007. Wild birds with an HI antibody titer of 1 : 1,280 or higher accounted for 21.2% (280/1,316) of the animals tested. These findings indicated that wild birds from the region examined in our study have been exposed to JEV and may pose a high risk for introducing a new JEV genotype into 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.

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.

Serological Survey for Canine Parvovirus Type 2a (CPV-2a) in the Stray Dogs in South Korea

Canine parvovirus type-2 (CPV-2) is one of the major diarrhea-causing agents, inducing acute hemorrhagic gastroenteritis in puppies. In this study, we conducted a seroepidemiological survey of CPV-2a in stray dogs in South Korea. In total, 405 canine sera, collected between 2006 and 2007, were screened for the presence of antibodies against CPV-2a using a hemagglutination inhibition (HI) assay. The positive rate in stray dogs tested for CPV-2a was 93.8%. The regional CPV-2a prevalence was 100% (8/8) in Jeju, 95.1% (232/244) in Gyeonggi, 94.7% (36/38) in Jeonra, 92.9% (13/14) in Gangwon, 92.7% (38/41) in Chungcheong, and 88.3% (53/60) in Gyeungsang province. No significant difference in the seropositive rate was found between male (93.6%) and female (94.0%) dogs. Analysis of the distribution of HI titer against CPV-2a according to the age of the stray dogs showed a linear increase in seroprevalence with age, although the association with age was not statistically significant. The incidence of stray dogs showing an HI antibody titer above 1:5120 was estimated to be 26.2%. Thus, the presence of high HI antibody against CPV-2a may indicate circulation of CPV-2a in stray dogs.