Transmission of avian viruses both bird-to-bird and from birds to non-avian species is a major health concern. Newcastle disease virus (NDV) is an economically important avian virus that poses substantial risks to the poultry industry. Rapid and sensitive diagnostic methods, such as the enzyme-linked immunosorbent assay (ELISA), are required to track such infections. To develop an ELISA for detecting anti-NDV antibody in avian sera, the nucleocapsid protein (NCP) gene of the NDV La Sota strain was cloned and expressed in Escherichia coli and the 513-amino acid recombinant NCP was purified by Ni-NTA affinity chromatography. To evaluate its ability to replace NDV whole virus antigen as a coating antigen, NCP-coated and whole NDV-coated ELISAs were tested and compared using a panel of NDV positive antisera from chickens. Results using purified NCP were highly correlated with those obtained using whole NDV (r=0.927), demonstrating that recombinant NCP expressed in Escherichia coli is a suitable substitute antigen for whole NDV in a diagnostic ELISA.

Paratuberculosis caused by Mycobacterium avium subspecies paratuberculosis (Mpt) is a chronic infectious enteric disease with deleterious impact on the performance in ruminants. In Korea, ELISA has been introduced to detect antibodies to Mpt in individual cattle. However, comparison study with ELISA has not been studied until now. In total, a panel of 899 serum samples obtained from dairy cattle was analyzed with two commercial ELISAs for Mpt to assess the performance. Two ELISAs employed in this study were both licensed worldwide. Two ELISAs applied onto same serum samples showed the morderate agreement (kappa value = 0.06). There was non-significant McNemar test (p=0.0614) between two ELISA results indicating that each proportion detected by two kits did not differ. In addition, the percent agreement between two ELISA results was turned out to be 96.8% which interpreted excellent reproducibility. It was shown from this study that two ELISAs revealed moderate kappa agreement performance. The implication raised is that when ELISAs as diagnostics are used to detect Mpt in individual cattle, positive reaction by either ELISA should be interpreted as serologically Mpt positive due to presumed low sensitivity of ELISAs and their test agreement being less than 100%.

The objective of this study was to investigate the use of extract from mesenteric lymph nodes as an alternative to serum for ELISA to detect Salmonella antibodies in slaughter pigs. Among 324 slaughter pigs, 65 (20.1%) were positive in the serum ELISA and 76 (23.5%) were positive in the ELISA with extract from lymph nodes. A total of 24 (7.4%) Salmonella representing 6 serotypes were isolated from mesenteric lymph nodes and 35 (10.8%) Salmonella belonging to 2 serotypes were also recovered from cecal contents of slaughter pig samples, respectively.

Newcastle disease (ND) is a highly contagious disease of poultry that can cause severe economic losses throughout the world. Vaccination has been used for a long time and proved as one of the most effective method to reduce the economic loss due to ND virus infection. The measurement of antibody titer such as hamagglutination-inhibition (HI) test with sera has been used as a useful method to evaluate the immunity leve of host. However, HI test is gradually being replaced by the enzyme linked-immunosorbent assay (ELISA).

Enzyme-linked immunosorbent assay (ELISA) for detection of antibodies to reticuloendotheliosis virus (REV) at single serum dilution was standardized. REV HI, one of the Korean field isolates, was inoculated into chicken embryo fibroblast (CEF) cells and was harvested from the culture fluids and cells after 10 to 12 days. Viruses were purified by centrifugation at the 107,000×g for 12 hours on 20, 30, 45% (W/V) sucrose gradient. Virus specific fraction was collected and used as ELISA antigen. To standardize ELISA, the optimal concentration of coating antigen (1 ㎍/well) and conjugate (1/1000) was determined by corrected OD (OD value of positive serum-OD value of negative serum) and P/N ratio (OD value of positive serum/OD value of negative serum).

Foot-and-mouth disease (FMD) is the most contagious disease of mammals. The use of inactivated vaccine can be chosen to prevent or control FMD. However, vaccination against one serotype of FMDV doses not cross-protect against other serotypes and may not protect fully against some strains of the same serotype. Appropriate selection of vaccine strain is an important element in the control of FMD. The immunity of vaccine antigens should be matched against newly circulating viruses. The phylogenetic analysis of serotype Asia1 reported from China, Mongolia, North Korea and Russia since 2005 shows that they are all classified into genetic group V, but the strain, Asia1/Shamir (ISR/89) which have been used as a vaccine strain in Korea, is clustered into different genetic group. So, in this study the serological relationship between the isolate (Asia1/MOG/05; MOG) and the Shamir stain was determined by ELISA and virus neutralization test. Even though the matching value of the virus (MOG) against the vaccinated sera in target animals was not so high, the vaccinated animals elicited antibodies enough for protection after vaccinated once or twice. Conclusively, we suggest that the vaccine containing Asia1/Shamir antigen could protect the genetic group V strains circulating in East Asia currently if vaccinated twice or the more.

Porcine reproductive and respiratory syndrome (PRRS) is the most economically important viral infectious disease in pig populations worldwide. This study was conducted to better understand the epidemic and dynamics of PRRS virus (PRRSV) on each farm and to evaluate the risk of PRRSV infection in Korea. Interviews with pig farmers were carried out to obtain PRRS vaccination programmes in 60 pig farms throughout Korea. Blood samples were also collected from the 59 pig farms to investigate outbreak patterns of each farm. Vaccination against PRRS was performed in 16.7% farms for breeding pigs and 8.3% of farm for nursery pigs. According to the seroepidemiological analysis, 56 (94.9%) out of 59 farms were considered to be affected by PRRSV infection. The results revealed that 68.9% of sows tested were seroconverted and interestingly, gilt herds had the highest seropositive rate (73%), suggesting that gilts may play a key role in PRRSV transmission in sow herds. Among the PRRS-affected piglet herds, 33 (55.9%), 14 (23.7%) and 6 (10.2%) farms were initially infected with PRRSV during the weaning, suckling and nursery period, respectively. It seems likely, therefore, that PRRSV infection predominantly occurs around the weaning period in piglet herds. Based on antibody seroprevalence levels in both sow and piglet groups, we were able to classify patterns of PRRSV infection per farm unit into 4 categories; category 1 (stable sow groups and non-infected piglet groups), category 2 (unstable sow groups and non-infected piglet groups), category 3 (stable sow groups and infected piglet groups), and category 4 (unstable sow groups and infected piglet groups). Our data suggested that 43 (72.9%) farms were analysed to belong to category 4, which is considered to be at high-risk for PRRS outbreak. Taken together, our information from this study will provide insight into the establishment of an effective control strategy for PRRS on the field.

Iridovirus is an icosahedral cytoplasmic double-stranded DNA virus with a genome size of 170-200kb. Outbreaks of fish iridovirus infection are characterized by their wide geographic distribution and broad host spectrum, especially in water temperatures of 22-27℃ Recently, the causative agent of high mortalities in flounder (Paralichthys olivaceus) was identified as fish iridovirus in Korea. Iridoviral infection repeatedly occurs in the same area for long periods, suggesting the possibility of viral infection in nursery.

Serum samples of 1,175 pigs from 148 Korean swine farms not using Mycoplasma hyopneumoniae (M. hyo) vaccines were collected for seroepidemiological study of M. hyo infection by indirect ELISA method. Informations of each farm were provided about province where the farm was located and season when blood samples were collected. Then, the selected farms were divided into farm units which had 5 serum samples according to production stages : sow, suckling piglet (less than 30 days old), nursery pig (30-70 days old), and growing pig (greater than 70 days old).

Brucellosis is one of the most important zoonosis in worldwide. As one of the control measures, attempts have been made to develop new diagnostic methods using filed isolates as a national policy in many countries. Currently, bovine brucellosis in Korea have been received attention in both public health and economical aspects due to sudden increase of outbreak. Based on the situation, we compared standard strain (B. abortus 1119-3) with field isolates to reveal the differences among them. Biological and biochemical charateristics, antibiotic resistance profiles, outer membrane proteins (OMPs) and lipopolysaccharide analysis of the strains were included in this study. For the diagnostic purpose, an attempt was made to find out a novel antigen from the Korean isolates by serological analysis. There were differences about 55 kDa, 36-38 kDa and 20 kDa in analysis of OMPs by SDS-PAGE and Western blot with positive sera (greater-than or equal to 1:400 in SAT titer). Also, a serological diagnostic method, ELISA was conducted using OMPs of the strains as novel antigen. Relationships between O.D. and SAT titer were analyzed using field sera showing different SAT titer. High correlation coefficient was observed between SAT titer and ELISA. Results from this study suggested that a new diagnsotic method should be developed using their own field isolates in each country.