Control of foot-and-mouth disease during 2010-2011 epidemic, South Korea.

An outbreak of foot-and-mouth disease caused by serotype O virus occurred in cattle and pigs in South Korea during November 2010-April 2011. The highest rates of case and virus detection were observed 44 days after the first case was detected. Detection rates declined rapidly after culling and completion of a national vaccination program.

Evidence of recombination in a new isolate of foot-and-mouth disease virus serotype Asia 1.

Phylogenetic analysis of the nucleotide sequence of VP1 revealed that a new isolate of foot-and-mouth disease virus (FMDV) serotype Asia 1 identified in Mongolia in 2005 was related to Chinese and Russian strains isolated during the same year. In this study, these strains were defined as East Asian strains having a common geographical origin, and the complete genomic sequence of the Mongolian strain (As1/MOG/05) was determined and compared to other strains of serotype Asia 1. As1/MOG/05 showed 100% identity with an East Asian strain from China (As1/Qinghai/CHA/05) in terms of its VP1 nucleotide sequence. However, the Mongolian strain has a four-amino acid extension in 3D that is missing from all other strains of serotype Asia 1, and which is not due to an insertion. A full genomic scan revealed that the Mongolian strain is closer to the East Asian strain As1/JS/CHA/05 than to all other strains of serotype Asia 1 in nearly all genomic regions. Within the narrow region of low similarity between the two sequences, As1/JS/CHA/05 was found to have a mosaic structure with a partial 2C fragment supposedly transferred from Hong Kong strain As1/HNK/CHA/05. The genomic mosaicism and extension detected in non-structural protein-coding regions in this study may be used to trace the origins and evolution of problematic strains of serotype Asia 1 that have arisen in East Asia since 2005.

Development of an epitope-blocking-enzyme-linked immunosorbent assay to differentiate between animals infected with and vaccinated against foot-and-mouth disease virus.

An epitope-blocking ELISA (EB-ELISA) was developed to distinguish animals infected with foot-and-mouth-disease (FMDV) from those immunized with commercial vaccines. The assay used monoclonal antibodies to target the 3B core repeat motif (QKPLK) and purified recombinant 3AB proteins from the major B cell line epitopes of FMDV. Sera from uninfected and regularly vaccinated cattle, pigs, goats, and sheep (raised in FMDV free areas) were screened to evaluate the specificity of the EB-ELISA. The specificity scores of the assays were 99.8-100% and 100%, respectively. Reference sera from cattle, pigs, goats, and sheep experimentally infected with FMDV tested positive, with only a single exception. Antibodies formed in response to FMDV 3B appeared 1 week after infection and persisted at high levels for more than 8 weeks within the sera collected from serial bleeding of animals infected with FMDV O/SKR/2000. The EB-ELISA was used to differentiate between farms vaccinated against and those infected with FMDV (FMDV Asia serotype) during the 2005 epidemic in Mongolia by detecting antibodies against the FMDV Asia serotype in outbreak farms. This EB-ELISA method shows promise as an effective tool for FMDV control and eradication.

Enhanced immune response with foot and mouth disease virus VP1 and interleukin-1 fusion genes.

The capsid of the foot and mouth disease (FMD) virus carries the epitopes that are critical for inducing the immune response. In an attempt to enhance the specific immune response, plasmid DNA was constructed to express VP1/interleukin-1alpha (IL-1alpha) and precursor capsid (P1) in combination with 2A (P1-2A)/IL-1alpha under the control of the human cytomegalovirus (HCMV) immediateearly promoter and intron. After DNA transfection into MA104 (monkey kidney) cells, Western blotting and an immunofluorescence assay were used to confirm the expression of VP1 or P1-2A and IL-1alpha. Mice were inoculated with the encoding plasmids via the intradermal route, and the IgG1 and IgG2a levels were used to determine the immune responses. These results show that although the immunized groups did not carry a high level of neutralizing antibodies, the plasmids encoding the VP1/ IL-1alpha, and P1-2A /IL-1alpha fused genes were effective in inducing an enhanced immune response.

Development of a Lightcycler-based reverse transcription polymerase chain reaction for the detection of foot-and-mouth disease virus.

One step TaqMan real-time reverse transcription polymerase chain reaction (R/T RT-PCR) using a set of primers/probes was developed for the detection of foot-and-mouth disease (FMD) virus. The gene-specific probes labeled fluorogen for the internal ribosomal entry site, Leader sequence and 2B regions were used to detect FMD virus (FMDV). This assay specifically detected FMDV both in cell culture preparations and clinical samples, and was capable of distinguishing FMD from other viral diseases similar to clinical signs (swine vesicular disease, vesicular stomatitis and bovine viral diarrhea). This assay was shown to be 1000-fold more sensitive than the conventional RT-PCR method. The detection limits of this assay was 1 TCID(50)/ml of the FMDV RNA concentration. Quantification was obtained by a standard curves plotting threshold cycle values versus known infectivity titer. The assay was sensitive, specific and rapid enough to detect FMDV RNA genome in probang samples. As such, the described method is reliable and provides faster disease diagnostics than the conventional RT-PCR procedure to detect FMDV.

Identification and antigenic site analysis of foot-and-mouth disease virus from pigs and cattle in Korea.

From May to June 2002, a total of 16 foot-and mouth disease (FMD) outbreaks due to the serotype O virus, Pan Asia strain, were recorded in Korea. The viruses were identified by antigen ELISA, RT-PCR and sequence analysis. The overall nucleotide sequence divergence of the VP1 region among the 4 isolates in 2002 was 0 to 1.4%, but between O/SKR/2002 and O/SKR/2000 isolates was 1.9-4.9%. Phylogenetic analysis with the some known strains from East Asian countries showed that the 4 Korean isolates in 2002 formed one distinct cluster, which different from clusters of Korean isolates in 2000, with in the same lineage of the ME-SA topotype strains. Deduced amino acid sequences around neutralizable antigenic site on VP1 site of O/SKR/2002 isolates were aligned and compared with other strains. At the antigenic site 1, the replacements of the critical amino acid residues at position 144 from V to L and at position 152 from A to T were observed in O/SKR/2002 viruses. For antigenic site 2 and 4, there were not significant variations in general. At the antigenic site 3, the substitutions of amino acid residues were present at positions 54 and 56 in O/SKR/2002 isolates and an alternative residue I at position 54 are observed only at the sequence of O/SKR/AS/2002 (cow) virus. And the substitution (L-->P) of significant residue at position 144 was detected at the amino acid sequence of the O/SKR/2002 (cow) virus.

A case of chronic wasting disease in an elk imported to Korea from Canada.

A seven-year-old male elk (Cervus elaphus nelsoni) was euthanized and necropsied after having a 3-week history of body weight loss, emaciation, excessive salivation, teeth grinding, fever, anorexia, and respiratory distress. The elk was imported into Korea from Canada on March 9, 1997. Gross pathologic findings were restricted to a diffuse fibrinous pneumonia. Microscopic lesions included mild neuronal vacuolation and spongiform change in the neuropil of selected brain stem nuclei and generalized astrocytosis. Immunohistochemistry for protease-resistant prion protein (PrP(res)) was positive in all brain sections but more pronounced in the section of the obex of the medulla. And the PrP(res) was also detected by western immunoblotting in the brain and spinal cord. All the remaining elk and deer that had been in contact with this elk were destroyed and negative for chronic wasting disease (CWD). To our knowledge, this is the first case of CWD occurring outside of the U.S.A. and Canada.

Molecular epidemiological investigation of foot-and-mouth disease virus in Korea in 2000.

The genetic relatedness of 7 Korean type O field strains of foot-and-mouth disease virus (FMDV) in clinical specimens collected from 5 different geographic locations in 2000 was investigated. The sequence of 162 nucleotides (nt 478-639) at the 3' end of the 1D (VP1) genes was determined from amplified cDNA fragments, and subjected to the analysis for the sequence identity/divergence and phylogenetic relationship. The overall nucleotide sequence divergence among the 7 field strains was 0 to 3.8%, suggesting that they are closely related to each other. Phylogenetic analysis with the known Middle East-South Asia (ME-SA) topotype strains showed that the 7 Korean field strains formed two distinct clusters within the same lineage of the ME-SA topotype strains. Cluster 1 consisted of the strains of the primary foci of infection (Paju and Hongseong), and closely related to the strains prevailed in the Far East. Cluster 2 comprised those of subsequently affected regions (Boryeong, Yongin, and Chungju), and was further diverged from the Cluster 1. The result of phylogenetic analysis indicated that the Korean strains may have evolved from a common ancestor of the Pan Asia strains, and that at least 2 phylogenetically clustered variants within the same lineage were prevalent during the epidemic. The potential origin and sources of the virus introduction to Korea were discussed.

Simple and rapid lateral-flow assay for the detection of foot-and-mouth disease virus.

A simple lateral-flow assay (LFA) based on a monoclonal antibody (MAb 70-17) was developed for the detection of foot-and-mouth disease virus (FMDV) under nonlaboratory conditions. The LFA was evaluated with epithelial suspensions (n = 704) prepared from current and historical field samples which had been submitted to the Pirbright Laboratory (United Kingdom) and from negative samples (n = 100) collected from naïve animals in Korea. Four FMDV serotypes (type O, A, Asia 1, and C) were detected in the LFA, but not the remaining three FMDV serotypes (SAT 1, SAT 2, and SAT 3). The diagnostic sensitivity of the LFA for FMDV types O, A, C, and Asia 1 was similar, at approximately 87.3%, to that of 87.7% obtained with antigen enzyme-linked immunosorbent assay (Ag-ELISA). The diagnostic specificity of the LFA was 98.8%, compared to 100% for the Ag-ELISA. These results demonstrate that the LFA using the FMDV MAb 70-17 to detect FMDV is a supportive method for taking rapid measurements at the site of a suspected foot-and-mouth disease outbreak in Asia before diagnosing the disease in the laboratory, thereby offering the possibility of implementing control procedures more rapidly.

Japanese encephalitis virus-based replicon RNAs/particles as an expression system for HIV-1 Pr55 Gag that is capable of producing virus-like particles.

Ectopic expression of the structural protein Pr55(Gag) of HIV-1 has been limited by the presence of inhibitory sequences in the gag coding region that must normally be counteracted by HIV-1 Rev and RRE. Here, we describe a cytoplasmic RNA replicon based on the RNA genome of Japanese encephalitis virus (JEV) that is capable of expressing HIV-1 gag without requiring Rev/RRE. This replicon system was constructed by deleting all three JEV structural protein-coding regions (C, prM, and E) from the 5'-proximal region of the genome and simultaneously inserting an HIV-1 gag expression cassette driven by the internal ribosome entry site of encephalomyocarditis virus into the 3'-proximal noncoding region of the genome. Transfection of this JEV replicon RNA led to expression of Pr55(Gag) in the absence of Rev/RRE in the cytoplasm of hamster BHK-21, human HeLa, and mouse NIH/3T3 cells. Production of the Pr55(Gag) derived from this JEV replicon RNA appeared to be increased by approximately 3-fold when compared to that based on an alphavirus replicon RNA. Biochemical and morphological analyses demonstrated that the Pr55(Gag) proteins were released into the culture medium in the form of virus-like particles. We also observed that the JEV replicon RNAs expressing the Pr55(Gag) could be encapsidated into single-round infectious JEV replicon particles when transfected into a stable packaging cell line that provided the three JEV structural proteins in trans. This ectopic expression of the HIV-1 Pr55(Gag) by JEV-based replicon RNAs/particles in diverse cell types may represent a useful molecular platform for various biological applications in medicine and industry.

Therapeutic application of RNA interference against foot-and-mouth disease virus in vitro and in vivo.

Foot-and-mouth disease (FMD) is an economically important animal disease because of the speed of its transmission. Routine vaccination may not be effective for early protection in an outbreak situation. Small interfering RNA (siRNA) can be used in a rapid and effective antiviral approach. However, siRNA has limitations when used in disease prevention, such as a short duration of action. In this study, we have demonstrated that treatment with siRNA after FMD virus (FMDV) infection has an antiviral effect and could be effective in control of FMDV. We applied adenoviruses expressing siRNA both before and after FMDV infection in vitro and in vivo. Treatment after FMDV infection gave effective viral inhibition, but a combination of treatment before and after FMDV infection gave the best results in IBRS-2 cells. We obtained high survival rates in suckling mice by the use of therapeutic injections following challenge. The results of this study suggest that treatment with siRNA could enhance antiviral effects and may be helpful in the control of FMDV in an outbreak.

Comparison and analysis of the complete nucleotide sequence of foot-and-mouth disease viruses from animals in Korea and other PanAsia strains.

During the last 3 years, foot-and-mouth disease virus serotype O, named PanAsia, caused two outbreaks in the Republic of Korea. To determine if there was an obvious genetic relationship between the virus isolated in 2002 (O/SKR/2002) and the O/SKR/2000, and to further analyze the epidemiological relationships between the PanAsia viruses and the viruses identified in Korea, the complete nucleotide sequence of the O/SKR/2002 and the O/SKR/2000 were determined by automatic cycling sequencing and primer walking. The nucleotides and the deduced amino acid (aa) sequences of the strains identified in Korea were compared with each other and also those enrolled in the GenBank database. In comparison and analysis of the viruses identified in Korea, any deletions or insertions in the specific fragment gene of both the O/SKR/2002 and O/SKR/2000 were not identified. However, comparison of the aa sequence of the identified virus in 2002 from pigs with those of other PanAsia strains revealed significant substitutions of 4 aa in the VPI region and 8 aa in the 3A region. In phylogenetic analysis based on the translated region, the identified virus in 2002 appeared to be the divergence of approximately 1% degree with other PanAsia viruses. Also, animal experiments indicated that O/SKR/2000 is not host-restricted and develop the clinical signs in the main susceptible livestock species (cattle and pigs). However, O/SKR/2002 did not develop the clinical signs in cattle and showed severe clinical signs only in pigs. These analytic data suggest that 2002 outbreaks in Korea is not re-occurred but re-introduced from nowhere.

Development of a foot-and-mouth disease NSP ELISA and its comparison with differential diagnostic methods.

The gene encoding the nonstructural protein (NSP) of O/SKR/2000 foot-and-mouth disease virus (FMDV) was constructed to express under the polyhedron promoter of baculovirus. The expression of NSP was confirmed by indirect immunofluorescence assay (IFA) and Western blotting. The expressed NSP was applied as a diagnostic antigen for indirect-trapping ELISA (I-ELISA). An I-ELISA using monoclonal antibody (Mab) against 3A as trapping antibody was developed to differentiate infected from vaccinated cattle. The diagnostic efficiency of Mab linked I-ELISA was compared and evaluated with baculovirus expressed 3ABC I-ELISA from USDA and Mab (3A) linked E. coli expressed 3ABC I-ELISA from IZSLE through retrospective sero-surveillance. Compared with the two different I-ELISA methods, Mab (3A) linked I-ELISA using baculovirus expressed NSP showed the same level of sensitivity and specificity, indicating that this method is suitable for a differential diagnostic method in cattle.