Experimental infections using the foot-and-mouth disease virus O/JPN/2010 in animals administered a vaccine preserved for emergency use in Japan

Effect of doubled dose administration of foot-and-mouth disease vaccine against heterologous virus infection in cattle

Vaccination is a feasible approach for controlling foot-and-mouth disease (FMD). In FMD-free countries, vaccines are stored as a precautionary measure to control potential outbreaks. However, the challenge lies in pre-stocking optimal vaccines against the newly emerging strains. This study examined the potency of pre-stocked vaccines administered at elevated doses during emergencies. We vaccinated the cows with either a single or double trivalent vaccine dose containing two serotype O and one serotype A strains. Subsequently, vaccinated and unvaccinated cows were exposed to virulent strains of serotype O (O/JPN/2010; topotype Southeast Asia/Mya-98 lineage) or A (A/IRN/2016; topotype ASIA/G-VII lineage), which were genetically and antigenically distinct from the vaccine strains. Following challenge infections, all cows that received a single dose vaccination exhibited vesicular lesions with excreted viruses in the oral and nasal discharges. However, a substantial reduction was observed in the total clinical scores and virus titers in the sera and nasal discharges compared to those in the unvaccinated group. Cows receiving a doubled dose vaccination were completely protected from infection with O/JPN/2010 or demonstrated a significant decrease in viral shedding and clinical scores against A/IRN/2016. To note, vesicular lesions harbor significant amounts of viruses; thus, by mitigating their formation, viral transmission can be impeded, thereby slowing viral spread in the field. Furthermore, increasing the vaccine dose induced higher neutralizing antibody titers against heterologous strains. These findings suggest an alternative strategy for the effective management of future epidemics using pre-stocked vaccines.

Pathogenesis of the attenuated foot-and-mouth disease virus O/JPN/2000 in experimentally infected pigs

We examined the pathogenesis of the attenuated foot-and-mouth disease virus (FMDV) O/JPN/2000 in pigs. The virus used in this study was passaged three times in primary bovine kidney (BK) cells and once in baby hamster kidney-21 (BHK-21) cells after isolation. A plaque assay demonstrated that this virus exhibited the small plaque (SP) phenotype. There was no clinical or histological evidence of vesicular lesions in pigs intraorally inoculated with 10⁶ 50% tissue culture infectious dose (TCID₅₀)/ml of the SP virus (SPV) of FMDV O/JPN/2000. Although fever was detected from 2 or 3 days post inoculation (dpi), there was no other prominent clinical sign up to 6 dpi. Virus shedding from saliva and nasal swab samples was not observed in any pigs inoculated with the SPV of FMDV O/JPN/2000. In the foot, mild lamellar degeneration of prickle cells in the upper layer of the stratum spinosum was histologically observed without development into vesicular or necrotic lesions. Immunohistochemical virus antigen- and terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL)-positive reactions observed in the foot at 1 dpi seemed to disappear after 3 and 6 dpi. Our findings suggest that the SPV of FMDV O/JPN/2000 had low pathogenicity against pigs by intraoral inoculation.

Comparative evaluation of two ELISA kits for detecting antibodies to a nonstructural protein of foot-and-mouth disease virus using serum samples collected from naturally and experimentally infected cows

When foot-and-mouth disease (FMD) occurs and a “vaccination-to-live” policy is adopted in a country, the country must perform serological surveillance of a nonstructural protein (NSP) of FMD virus. The NCPanaftosa kit is the only kit for detecting antibodies to NSPs that is officially recognized as the reference regent by the World Organization for Animal Health; however, it is only used in South American countries. In this study, the specificity and sensitivity of the NCPanaftosa kit were compared with those of the PrioCHECK kit sold by an international company. Results in this study suggest that the PrioCHECK kit performs similarly to the NCPanaftosa kit in detecting antibodies to the NSP in the cattle population.

Genetic identification and serological evaluation of commercial inactivated foot-and-mouth disease virus vaccine in pigs

Vaccination is considered a frequently used tool to prevent and control foot-and-mouth disease (FMD). However, the effectiveness of conventional FMD virus (FMDV) vaccines in pigs has been controversial because the massive prophylactic vaccination could not elicit proper immune response nor prevent the broad spread of FMD outbreak, mainly in pig farms, in South Korea during outbreaks of 2014. In addition, there has been little information on the efficacy of inactivated, high potency, multivalent, oil-based FMDV vaccine in pigs, because an evaluation of FMDV vaccines had been mainly carried out using cattle. In this study, we evaluated the genetic identification of commercial inactivated FMDV vaccine and monitored the immune responses in pigs under the field condition. Results implied that it contained three different serotypes with a high level of antigen payload. However, serological results showed low mean percentage of inhibition, and positive rate reached its peak at 6-week post-vaccination, indicating current FMDV vaccine need to improve for a prophylactic vaccination policy in pigs. Therefore, there is an imperative need to develop FMDV vaccine that can provide rapid and long-lasting protective immunity in pigs.

Early pathogenesis of the foot-and-mouth disease virus O/JPN/2010 in experimentally infected pigs

We examined the histological distribution of the lesions and the viral antigen associated with the virus and virus RNA in multisystemic organs in the early stages of foot-and-mouth disease virus (FMDV) O/JPN/2010 infection in pigs. Characteristic lesions commonly observed in pigs with FMD arise following inoculation with 10⁶ tissue culture infectious dose (TCID)₅₀/ml of FMDV O/JPN/2010 in pigs at 3 days post inoculation (dpi) by a natural infectious route. However, none of the six pigs inoculated with 10³ TCID₅₀/ml of FMDV O/JPN/2010 showed any evidence of infection up to 6 dpi. Immunohistochemical detection for the FMDV antigen and terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL) showed that FMDV predominantly infected prickle cells in the stratum spinosum in the tongue, coronet and bulb of the heel, and caused these infected cells to undergo cell death by apoptosis. However, there was no evidence that FMDV O/JPN/2010 infected epithelial/epidermal basal cells in the basal layer. Epithelial lesions with viral antigen in the tongue were distributed in the dorsal surface but not in the papillae, corpus linguae or inferior surface of the tongue. Non-suppurative myocarditis and epithelial lesions in the esophagus with FMDV antigen were observed in all three pigs examined at 3 dpi.