Complete Genome Sequence of O/VN1/2014, a Foot-and-Mouth Disease Virus of Serotype O Isolated in Vietnam in 2014

In this article, we report the complete genome sequence of foot-and-mouth disease virus (FMDV) strain O/VN1/2014 isolated in Vietnam (Lao Cai) in 2014. The virus belongs to serotype O, topotype South East Asia (SEA), and genotype Mya-98 (O/SEA/Mya-98).

The Pseudoknot Region of the 5′ Untranslated Region Is a Determinant of Viral Tropism and Virulence of Foot-and-Mouth Disease Virus

ABSTRACTFoot-and-mouth disease virus (FMDV) is the causative agent of foot-and-mouth disease. It is characterized by genetic instability and different antigenic properties. The nonstructural protein 3A is a primary determinant of the tropism and virulence of Cathay topotype FMDVs. However, several other determinants are also speculated to be involved in viral tropism and virulence. Deletion of 43 nucleotides (nt) in the pseudoknot (PK) region of the 5′ untranslated region (UTR) has been found to coexist with the identified 3A deletion in Cathay topotype FMDV genomes. In this study, we isolated an O/ME-SA/PanAsia lineage FMDV strain, O/GD/CHA/2015, that includes an 86-nt deletion in the PK region and shows a porcinophilic phenotype. To investigate the potential role of the PK region in viral pathogenicity, we generated a recombinant FMDV strain with an incomplete PK region and compared its virulence and pathogenesis to the intact FMDV strain in swine and bovines. Deletion of the 86 nt in the PKs had no major effects on the pathogenicity of the virus in swine but significantly attenuated its ability to infect bovine cells and cattle, indicating that the PK region is a newly discovered determinant of viral tropism and virulence. The role of the 43-nt deletion existing in the Cathay topotype FMDV was also investigated by evaluating the infection properties of genetically engineered viruses. Consistently, the 43-nt deletion in the PK region significantly decreased the pathogenicity of the virus in bovines. Overall, our findings suggest that the PK region deletion occurred naturally in the FMDV genome and that the PK region is highly associated with viral host range and functions as a novel determinant for FMDV pathogenesis.IMPORTANCEThis study demonstrates that the deletion in the PK region occurred naturally in the FMDV genome. The isolated O/ME-SA/PanAsia lineage FMDV with an 86-nt deletion in the PK region showed a pig-adapted characteristic that could cause clinical signs in swine but not bovines. Compared to the wild-type FMDV strain, which possesses full infection capacity in both swine and bovines, the recombinant virus with the 86-nt deletion in the PK region is deficient in causing disease in bovines. Deletion of the previously reported 43 nt in the PK region also led to significantly decreased pathogenicity of FMDV in bovines. This study indicates that the PK region is a novel determinant of the tropism and virulence of FMDV.

Identification of Foot-and-Mouth Disease Virus-Specific Linear B-Cell Epitopes To Differentiate between Infected and Vaccinated Cattle

ABSTRACT Foot-and-mouth disease (FMD) is a highly contagious viral disease of cloven-hoofed animals. For several years, vaccination of animals, which had proven to be successful for the eradication of the disease, has been forbidden in the United States and the European Community because of the difficulty of differentiating between vaccinated and infected animals. In this study, detailed investigations of the bovine humoral immune response against FMD virus (FMDV) were performed with the aim of identifying viral epitopes recognized specifically by sera derived from FMDV-infected animals. The use of overlapping 15-mer synthetic peptides, covering the whole open reading frame of FMDV strain O1K in a peptide enzyme-linked immunosorbent assay, allowed the identification of 12 FMDV strain O1K-specific linear B-cell epitopes. Six of these linear B-cell epitopes, located in the nonstructural proteins, were used in further assays to compare the reactivities of sera from vaccinated and infected cattle. Antibodies recognizing these peptides could be detected only in sera derived from infected cattle. In further experiments, the reactivity of the six peptides with sera from animals infected with different strains of FMDV was tested, and strain-independent infection-specific epitopes were identified. Thus, these results clearly demonstrate the ability of a simple peptide-based assay to discriminate between infected and conventionally FMD-vaccinated animals.

Natural aerosol transmission of foot-and-mouth disease virus to pigs: minimal infectious dose for strain O1 Lausanne

Foot-and-mouth disease virus (FMDV) can spread by a variety of mechanisms, including, under certain circumstances, by the wind. Simulation models have been developed to predict the risk of airborne spread of FMDV and have played an important part in decision making during emergencies. The minimal infectious dose of FMDV for different species by inhalation is an important determinant of airborne spread. Whereas the doses for cattle and sheep have been quantified, those for pigs are not known. The objective of the study was to obtain that data in order to enhance the capability of simulation models. Under experimental conditions, forty pigs were exposed individually to naturally generated aerosols of FMDV, strain O1 Lausanne. The results indicated that doses under 100 TCID50 failed to infect pigs but doses of approximately 300 TCID50 caused short-term sub-clinical infection. The calculations suggested that a dose of more than 800 TCID50 is required to cause infection and typical disease.

A comparison of some immunological methods for the differentiation of strains of foot-and-mouth disease virus

SUMMARYTwo FMDV strains which had been previously differentiated by complement-fixation were compared by guinea-pig protection test, kinetic neutralization and micro-neutralization tests. It was found that these tests, which have not been previously applied by the methods described, were all capable of FMDV strain differentiation. Similar differences were found by all methods, which suggests that comparisons made by cross-CF, cross-neutralization or cross-protection involve measurement of the same antigen/antibody interactions.

Electron Microscopy of Foot-and-Mouth Disease Virus Crystals and Ferritin-Tagged Antibodies

The interaction of ferritin-tagged antibodies with crystals of foot-and-mouth disease virus (FMDV) has been examined with a homologous and a heterologous antibody. Methods for crystal formation in primary swine kidney cells have been established on a more reproducible basis.The FMDV strain used in these experiments, A1, had been stored at -20°C as the sixth bovine kidney cell passage from the original bovine tongue tissue suspension. It was subsequently inoculated into primary swine kidney cultures for two more passages. The preparation used to inoculate cultures for the experiments reported here was therefore designated BK6PK2. Two-tenths ml of this virus passage was inoculated into each drained prescription bottle. After incubation at 37°C for 90 min, 5-10 ml of maintenance medium was added and the bottles returned to the incubator. Five to six hr after infection, the cell sheets were examined for cytopathic effect.