Foot-and-mouth disease-associated myocarditis is age dependent in suckling calves

Myocarditis is considered a fatal form of foot-and-mouth disease (FMD) in suckling calves. In the present study, a total of 17 calves under 4 months of age and suspected clinically for FMD were examined for clinical lesions, respiratory rate, heart rate, and heart rhythm. Lesion samples, saliva, nasal swabs, and whole blood were collected from suspected calves and subjected to Sandwich ELISA and reverse transcription multiplex polymerase chain reaction (RT-mPCR) for detection and serotyping of FMD virus (FMDV). The samples were found to be positive for FMDV serotype "O". Myocarditis was suspected in 6 calves based on tachypnoea, tachycardia, and gallop rhythm. Serum aspartate aminotransferase (AST), creatinine kinase myocardial band (CK-MB) and lactate dehydrogenase (LDH), and cardiac troponins (cTnI) were measured. Mean serum AST, cTn-I and LDH were significantly higher (P < 0.001) in < 2 months old FMD-infected calves showing clinical signs suggestive of myocarditis (264.833 ± 4.16; 11.650 ± 0.34 and 1213.33 ± 29.06) than those without myocarditis (< 2 months old: 110.00 ± 0.00, 0.06 ± 0.00, 1050.00 ± 0.00; > 2 months < 4 months: 83.00 ± 3.00, 0.05 ± 0.02, 1159.00 ± 27.63) and healthy control groups (< 2 months old: 67.50 ± 3.10, 0.047 ± 0.01, 1120.00 ± 31.62; > 2 months < 4 months: 72.83 ± 2.09, 0.47 ± 0.00, 1160.00 ± 18.44). However, mean serum CK-MB did not differ significantly amongst the groups. Four calves under 2 months old died and a necropsy revealed the presence of a pathognomic gross lesion of the myocardial form of FMD known as "tigroid heart". Histopathology confirmed myocarditis. This study also reports the relevance of clinical and histopathological findings and biochemical markers in diagnosing FMD-related myocarditis in suckling calves.

Epidemiological study on foot-and-mouth disease in small ruminants: Sero-prevalence and risk factor assessment in Kenya

Foot-and-mouth disease (FMD) is endemic in Kenya affecting cloven-hoofed ruminants. The epidemiology of the disease in small ruminants (SR) in Kenya is not documented. We carried out a cross-sectional study, the first in Kenya, to estimate the sero-prevalence of FMD in SR and the associated risk factors nationally. Selection of animals to be sampled used a multistage cluster sampling approach. Serum samples totaling 7564 were screened for FMD antibodies of non-structural-proteins using ID Screen^® NSP Competition ELISA kit. To identify the risk factors, generalized linear mixed effects (GLMM) logistic regression analysis with county and villages as random effect variables was used. The country animal level sero-prevalence was 22.5% (95% CI: 22.3%-24.3%) while herd level sero-prevalence was 77.6% (95% CI: 73.9%-80.9%). The risk factor that was significantly positively associated with FMD sero-positivity in SR was multipurpose production type (OR = 1.307; p = 0.042). The risk factors that were significantly negatively associated with FMD sero-positivity were male sex (OR = 0.796; p = 0.007), young age (OR = 0.470; p = 0.010), and sedentary production zone (OR = 0.324; p<0.001). There were no statistically significant intra class correlations among the random effect variables but interactions between age and sex variables among the studied animals were statistically significant (p = 0.019). This study showed that there may be widespread undetected virus circulation in SR indicated by the near ubiquitous spatial distribution of significant FMD sero-positivity in the country. Strengthening of risk-based FMD surveillance in small ruminants is recommended. Adjustment of husbandry practices to control FMD in SR and in-contact species is suggested. Cross-transmission of FMD and more risk factors need to be researched.

Pathogenesis of non-epithelial foot-and-mouth disease in neonatal animals

Foot-and-mouth disease virus (FMDV), which causes a highly contagious viral disease of cloven-hoofed animals, is notable for epithelial cell tropism, resulting in the appearance of vesicles on the feet and in and around the mouth in infected animals, while FMDV infection in neonatal animals is also associated with not only epithelial lesions, but also muscle-associated lesions, which leads to myocarditis, resulting in high-mortality. However, critical knowledge about the non-epithelial tropism of FMDV is still lacking. In this paper, the current progress of the FMDV non-epithelial tropisms is summarized and the possible role of the key viral and cellular components involved is discussed.

Multilevel model for airborne transmission of foot-and-mouth disease applied to Swedish livestock

The foot-and-mouth disease is an ever-present hazard to the livestock industry due to the huge economic consequences following an outbreak that necessitates culling of possibly infected animals in vast numbers. The disease is highly contagious and previous epizootics have shown that it spreads by many routes. One such route is airborne transmission, which has been investigated in this study by means of a detailed multilevel model that includes all scales of an outbreak. Local spread within an infected farm is described by a stochastic compartment model while the spread between farms is quantified by atmospheric dispersion simulations using a network representation of the set of farms. The model was applied to the Swedish livestock industry and the risk for an epizootic outbreak in Sweden was estimated using the basic reproduction number of each individual livestock-holding farm as the endpoint metric. The study was based on comprehensive official data sets for both the current livestock holdings and regional meteorological conditions. Three species of farm animals are susceptible to the disease and are present in large numbers: cattle, pigs and sheep. These species are all included in this study using their individual responses and consequences to the disease. It was concluded that some parts of southern Sweden are indeed preconditioned to harbor an airborne epizootic, while the sparse farm population of the north renders such events unlikely to occur there. The distribution of the basic reproduction number spans over several orders of magnitudes with low risk of disease spread from the majority of the farms while some farms may act as very strong disease transmitters. The results may serve as basic data in the planning of the national preparedness for this type of events.

Virulence beneath the fleece; a tale of foot-and-mouth disease virus pathogenesis in sheep

Foot-and-mouth disease virus (FMDV) is capable of infecting all cloven-hoofed domestic livestock species, including cattle, pigs, goats, and sheep. However, in contrast to cattle and pigs, the pathogenesis of FMDV in small ruminants has been incompletely elucidated. The objective of the current investigation was to characterize tissue- and cellular tropism of early and late stages of FMDV infection in sheep following three different routes of simulated natural virus exposure. Extensive post-mortem harvest of tissue samples at pre-determined time points during early infection (24 and 48 hours post infection) demonstrated that tissues specifically susceptible to primary FMDV infection included the paraepiglottic- and palatine tonsils, as well as the nasopharyngeal mucosa. Additionally, experimental aerosol inoculation of sheep led to substantial virus replication in the lungs at 24-48 hours post-inoculation. During persistent infection (35 days post infection), the paraepiglottic- and palatine tonsils were the only tissues from which infectious FMDV was recovered. This is strikingly different from cattle, in which persistent FMDV infection has consistently been located to the nasopharyngeal mucosa. Analysis of tissue sections by immunomicroscopy revealed a strict epithelial tropism during both early and late phases of infection as FMDV was consistently localized to cytokeratin-expressing epithelial cells. This study expands upon previous knowledge of FMDV pathogenesis in sheep by providing detailed information on the temporo-anatomic distribution of FMDV in ovine tissues. Findings are discussed in relation to similar investigations previously performed in cattle and pigs, highlighting similarities and differences in FMDV pathogenesis across natural host species.

Thermostability of the Foot-and-Mouth Disease Virus Capsid Is Modulated by Lethal and Viability-Restoring Compensatory Amino Acid Substitutions

Infection by viruses depends on a balance between capsid stability and dynamics. This study investigated biologically and biotechnologically relevant aspects of the relationship in foot-and-mouth disease virus (FMDV) between capsid structure and thermostability and between thermostability and infectivity. In the FMDV capsid, a substantial number of amino acid side chains at the interfaces between pentameric subunits are charged at neutral pH. Here a mutational analysis revealed that the essential role for virus infection of most of the 8 tested charged groups is not related to substantial changes in capsid protein expression or processing or in capsid assembly or stability against a thermally induced dissociation into pentamers. However, the positively charged side chains of R2018 and H3141, located at the interpentamer interfaces close to the capsid 2-fold symmetry axes, were found to be critical both for virus infectivity and for keeping the capsid in a state of weak thermostability. A charge-restoring substitution (N2019H) that was repeatedly fixed during amplification of viral genomes carrying deleterious mutations reverted both the lethal and capsid-stabilizing effects of the substitution H3141A, leading to a double mutant virus with close to normal infectivity and thermolability. H3141A and other thermostabilizing substitutions had no detectable effect on capsid resistance to acid-induced dissociation into pentamers. The results suggest that FMDV infectivity requires limited local stability around the 2-fold axes at the interpentamer interfaces of the capsid. The implications for the mechanism of genome uncoating in FMDV and the development of thermostabilized vaccines against foot-and-mouth disease are discussed.IMPORTANCE This study provides novel insights into the little-known structural determinants of the balance between thermal stability and instability in the capsid of foot-and-mouth disease virus and into the relationship between capsid stability and virus infectivity. The results provide new guidelines for the development of thermostabilized empty capsid-based recombinant vaccines against foot-and-mouth disease, one of the economically most important animal diseases worldwide.

Quantitative impacts of incubation phase transmission of foot-and-mouth disease virus

The current investigation applied a Bayesian modeling approach to a unique experimental transmission study to estimate the occurrence of transmission of foot-and-mouth disease (FMD) during the incubation phase amongst group-housed pigs. The primary outcome was that transmission occurred approximately one day prior to development of visible signs of disease (posterior median 21 hours, 95% CI: 1.1-45.0). Updated disease state durations were incorporated into a simulation model to examine the importance of addressing preclinical transmission in the face of robust response measures. Simulation of FMD outbreaks in the US pig production sector demonstrated that including a preclinical infectious period of one day would result in a 40% increase in the median number of farms affected (166 additional farms and 664,912 pigs euthanized) compared to the scenario of no preclinical transmission, assuming suboptimal outbreak response. These findings emphasize the importance of considering transmission of FMD during the incubation phase in modeling and response planning.

Genetic stability of foot-and-mouth disease virus during long-term infections in natural hosts

Foot-and-mouth disease (FMD) is a severe infection caused by a picornavirus that affects livestock and wildlife. Persistence in ruminants is a well-documented feature of Foot-and-mouth disease virus (FMDV) pathogenesis and a major concern for disease control. Persistently infected animals harbor virus for extended periods, providing a unique opportunity to study within-host virus evolution. This study investigated the genetic dynamics of FMDV during persistent infections of naturally infected Asian buffalo. Using next-generation sequencing (NGS) we obtained 21 near complete FMDV genome sequences from 12 sub-clinically infected buffalo over a period of one year. Four animals yielded only one virus isolate and one yielded two isolates of different serotype suggesting a serial infection. Seven persistently infected animals yielded more than one virus of the same serotype showing a long-term intra-host viral genetic divergence at the consensus level of less than 2.5%. Quasi-species analysis showed few nucleotide variants and non-synonymous substitutions of progeny virus despite intra-host persistence of up to 152 days. Phylogenetic analyses of serotype Asia-1 VP1 sequences clustered all viruses from persistent animals with Group VII viruses circulating in Pakistan in 2011, but distinct from those circulating on 2008–2009. Furthermore, signature amino acid (aa) substitutions were found in the antigenically relevant VP1 of persistent viruses compared with viruses from 2008–2009. Intra-host purifying selective pressure was observed, with few codons in structural proteins undergoing positive selection. However, FMD persistent viruses did not show a clear pattern of antigenic selection. Our findings provide insight into the evolutionary dynamics of FMDV populations within naturally occurring subclinical and persistent infections that may have implications to vaccination strategies in the region.

Quantitative Assessment of the Risk of Release of Foot-and-Mouth Disease Virus via Export of Bull Semen from Israel

Various foot-and-mouth disease (FMD) virus strains circulate in the Middle East, causing frequent episodes of FMD outbreaks among Israeli livestock. Since the virus is highly resistant in semen, artificial insemination with contaminated bull semen may lead to the infection of the receiver cow. As a non-FMD-free country with vaccination, Israel is currently engaged in trading bull semen only with countries of the same status. The purpose of this study was to assess the risk of release of FMD virus through export of bull semen in order to estimate the risk for FMD-free countries considering purchasing Israeli bull semen. A stochastic risk assessment model was used to estimate this risk, defined as the annual likelihood of exporting at least one ejaculate of bull semen contaminated with viable FMD virus. A total of 45 scenarios were assessed to account for uncertainty and variability around specific parameter estimates and to evaluate the effect of various mitigation measures, such as performing a preexport test on semen ejaculates. Under the most plausible scenario, the annual likelihood of exporting bull semen contaminated with FMD virus had a median of 1.3 * 10^-7 for an export of 100 ejaculates per year. This corresponds to one infected ejaculate exported every 7 million years. Under the worst-case scenario, the median of the risk rose to 7.9 * 10^-5 , which is equivalent to the export of one infected ejaculate every 12,000 years. Sensitivity analysis indicated that the most influential parameter is the probability of viral excretion in infected bulls.

Evaluation of cytotoxic and antiviral activities of aqueous leaves extracts of different plants against foot and mouth disease virus infection in farming animals

Cytotoxic and antiviral activity of aqueous leaves extracts of three plants: Azadirachta indica, Moringa oleifera and Morus alba against Foot and Mouth disease virus (FMDV) were determined using MTT assay (3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide). Eight different concentrations of each plant were evaluated. Cytotoxic and antiviral activity of each extract was evaluated as cell survival percentage and results were expressed as Means ± S.D. From the tested plant extracts, Azadirachta indica & Moringa oleifera exhibited cytotoxicity at 200 & 100 μ/ml respectively. In case of antiviral assay, Moringa oleifera showed potent antiviral activity (p<0.05) while Azadirachta indica showed significant antiviral activity in the range of 12.5-50 μ/ml & 50-100 μ/ml respectively. In contrast no anti-FMDV activity in the present study was observed with Morus alba, although all the tested concentrations were found to be safe.

Foot-and-mouth disease virus induces lysosomal degradation of host protein kinase PKR by 3C proteinase to facilitate virus replication

The interferon-induced double-strand RNA activated protein kinase (PKR) plays important roles in host defense against viral infection. Here we demonstrate the significant antiviral role of PKR against foot-and-mouth disease virus (FMDV) and report that FMDV infection inhibits PKR expression and activation in porcine kidney (PK-15) cells. The viral nonstructural protein 3C proteinase (3Cpro) is identified to be responsible for this inhibition. However, it is independent of the well-known proteinase activity of 3Cpro or 3Cpro-induced shutoff of host protein synthesis. We show that 3Cpro induces PKR degradation by lysosomal pathway and no interaction is determined between 3Cpro and PKR. Together, our results indicate that PKR acts an important antiviral factor during FMDV infection, and FMDV has evolved a strategy to overcome PKR-mediated antiviral role by downregulation of PKR protein.

Attenuation of Foot-and-Mouth Disease Virus by Engineered Viral Polymerase Fidelity

Foot-and-mouth disease virus (FMDV) RNA-dependent RNA polymerase (RdRp) (3Dpol) catalyzes viral RNA synthesis. Its characteristic low fidelity and absence of proofreading activity allow FMDV to rapidly mutate and adapt to dynamic environments. In this study, we used the structure of FMDV 3Dpol in combination with previously reported results from similar picornaviral polymerases to design point mutations that would alter replication fidelity. In particular, we targeted Trp237 within conserved polymerase motif A because of the low reversion potential inherent in the single UGG codon. Using biochemical and genetic tools, we show that the replacement of tryptophan 237 with phenylalanine imparts higher fidelity, but replacements with isoleucine and leucine resulted in lower-fidelity phenotypes. Viruses containing these W237 substitutions show in vitro growth kinetics and plaque morphologies similar to those of the wild-type (WT) A24 Cruzeiro strain in BHK cells, and both high- and low-fidelity variants retained fitness during coinfection with the wild-type virus. The higher-fidelity W237F (W237FHF) mutant virus was more resistant to the mutagenic nucleoside analogs ribavirin and 5-fluorouracil than the WT virus, whereas the lower-fidelity W237I (W237ILF) and W237LLF mutant viruses exhibited lower ribavirin resistance. Interestingly, the variant viruses showed heterogeneous and slightly delayed growth kinetics in primary porcine kidney cells, and they were significantly attenuated in mouse infection experiments. These data demonstrate, for a single virus, that either increased or decreased RdRp fidelity attenuates virus growth in animals, which is a desirable feature for the development of safer and genetically more stable vaccine candidates.IMPORTANCE Foot-and-mouth disease (FMD) is the most devastating disease affecting livestock worldwide. Here, using structural and biochemical analyses, we have identified FMDV 3Dpol mutations that affect polymerase fidelity. Recombinant FMDVs containing substitutions at 3Dpol tryptophan residue 237 were genetically stable and displayed plaque phenotypes and growth kinetics similar to those of the wild-type virus in cell culture. We further demonstrate that viruses harboring either a W237FHF substitution or W237ILF and W237LLF mutations were highly attenuated in animals. Our study shows that obtaining 3Dpol fidelity variants by protein engineering based on polymerase structure and function could be exploited for the development of attenuated FMDV vaccine candidates that are safer and more stable than strains obtained by selective pressure via mutagenic nucleotides or adaptation approaches.

Foot-and-mouth disease virus infection suppresses autophagy and NF-кB antiviral responses via degradation of ATG5-ATG12 by 3Cpro

Autophagy-related protein ATG5-ATG12 is an essential complex for the autophagophore elongation in autophagy, which has been reported to be involved in foot-and-mouth disease virus (FMDV) replication. Previous reports show that ATG5-ATG12 positively or negatively regulates type I interferon (IFN-α/β) pathway during virus infection. In this study, we found that FMDV infection rapidly induced LC3 lipidation and GFP-LC3 subcellular redistribution at the early infection stage in PK-15 cells. Along with infection time course to 2-5 h.p.i., the levels of LC3II and ATG5-ATG12 were gradually reduced. Further study showed that ATG5-ATG12 was degraded by viral protein 3Cpro, demonstrating that FMDV suppresses autophagy along with viral protein production. Depletion of ATG5-ATG12 by siRNA knock down significantly increased the FMDV yields, whereas overexpression of ATG5-ATG12 had the opposite effects, suggesting that degradation of ATG5-ATG12 benefits virus growth. Further experiment showed that overexpression of ATG5-ATG12 positively regulated NF-кB pathway during FMDV infection, marked with promotion of IKKα/β phosphorylation and IκBα degradation, inhibition of p65 degradation, and facilitation of p65 nuclear translocation. Meanwhile, ATG5-ATG12 also promoted the phosphorylation of TBK1 and activation of IRF3 via preventing TRAF3 degradation. The positive regulation of NF-кB and IRF3 pathway by ATG5-ATG12 resulted in enhanced expression of IFN-β, chemokines/cytokines, and IFN stimulated genes, including anti-viral protein PKR. Altogether, above findings suggest that ATG5-ATG12 positively regulate anti-viral NF-κB and IRF3 signaling during FMDV infection, thereby limiting FMDV proliferation. FMDV has evolved mechanisms to counteract the antiviral function of ATG5-ATG12, via degradation of them by viral protein 3Cpro.

Investigating intra-host and intra-herd sequence diversity of foot-and-mouth disease virus

Due to the poor-fidelity of the enzymes involved in RNA genome replication, foot-and-mouth disease (FMD) virus samples comprise of unique polymorphic populations. In this study, deep sequencing was utilised to characterise the diversity of FMD virus (FMDV) populations in 6 infected cattle present on a single farm during the series of outbreaks in the UK in 2007. A novel RT–PCR method was developed to amplify a 7.6 kb nucleotide fragment encompassing the polyprotein coding region of the FMDV genome. Illumina sequencing of each sample identified the fine polymorphic structures at each nucleotide position, from consensus level changes to variants present at a 0.24% frequency. These data were used to investigate population dynamics of FMDV at both herd and host levels, evaluate the impact of host on the viral swarm structure and to identify transmission links with viruses recovered from other farms in the same series of outbreaks. In 7 samples, from 6 different animals, a total of 5 consensus level variants were identified, in addition to 104 sub-consensus variants of which 22 were shared between 2 or more animals. Further analysis revealed differences in swarm structures from samples derived from the same animal suggesting the presence of distinct viral populations evolving independently at different lesion sites within the same infected animal.

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NGS was used to characterise FMD viruses in clinical samples from cattle.

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5 consensus and 104 sub-consensus level substitutions were identified.

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Distinct virus swarms were found in different lesions within the same host.

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Only 22 sub-consensus substitutions were shared between 2 or more animals.

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Data suggest that FMDV evolves independently at different lesion sites.

[SYNTHETIC PEPTIDE VACCINES]

An update on the development and trials of synthetic peptide vaccines is reviewed. The review considers the successful examples of specific protection as a result of immunization with synthetic peptides using various protocols. The importance of conformation for the immunogenicity of the peptide is pointed out. An alternative strategy of the protection of the organism against the infection using synthetic peptides is suggested.

Pathogenesis of Primary Foot-and-Mouth Disease Virus Infection in the Nasopharynx of Vaccinated and Non-Vaccinated Cattle

A time-course pathogenesis study was performed to compare and contrast primary foot-and-mouth disease virus (FMDV) infection following simulated-natural (intra-nasopharyngeal) virus exposure of cattle that were non-vaccinated or vaccinated using a recombinant adenovirus-vectored FMDV vaccine. FMDV genome and infectious virus were detected during the initial phase of infection in both categories of animals with consistent predilection for the nasopharyngeal mucosa. A rapid progression of infection with viremia and widespread dissemination of virus occurred in non-vaccinated animals whilst vaccinated cattle were protected from viremia and clinical FMD. Analysis of micro-anatomic distribution of virus during early infection by lasercapture microdissection localized FMDV RNA to follicle-associated epithelium of the nasopharyngeal mucosa in both groups of animals, with concurrent detection of viral genome in nasopharyngeal MALT follicles in vaccinated cattle only. FMDV structural and non-structural proteins were detected in epithelial cells of the nasopharyngeal mucosa by immunomicroscopy 24 hours after inoculation in both non-vaccinated and vaccinated steers. Co-localization of CD11c+/MHC II+ cells with viral protein occurred early at primary infection sites in vaccinated steers while similar host-virus interactions were observed at later time points in non-vaccinated steers. Additionally, numerous CD8+/CD3- host cells, representing presumptive natural killer cells, were observed in association with foci of primary FMDV infection in the nasopharyngeal mucosa of vaccinated steers but were absent in non-vaccinated steers. Immunomicroscopic evidence of an activated antiviral response at primary infection sites of vaccinated cattle was corroborated by a relative induction of interferon -α, -β, -γ and -λ mRNA in micro-dissected samples of nasopharyngeal mucosa. Although vaccination protected cattle from viremia and clinical FMD, there was subclinical infection of epithelial cells of the nasopharyngeal mucosa that could enable shedding and long-term persistence of infectious virus. Additionally, these data indicate different mechanisms within the immediate host response to infection between non-vaccinated and vaccinated cattle.

Using Mathematical Modelling to Explore Hypotheses about the Role of Bovine Epithelium Structure in Foot-And-Mouth Disease Virus-Induced Cell Lysis

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. FMD virus (FMDV) shows a strong tropism for epithelial cells, and FMD is characterised by cell lysis and the development of vesicular lesions in certain epithelial tissues (for example, the tongue). By contrast, other epithelial tissues do not develop lesions, despite being sites of viral replication (for example, the dorsal soft palate). The reasons for this difference are poorly understood, but hypotheses are difficult to test experimentally. In order to identify the factors which drive cell lysis, and consequently determine the development of lesions, we developed a partial differential equation model of FMDV infection in bovine epithelial tissues and used it to explore a range of hypotheses about epithelium structure which could be driving differences in lytic behaviour observed in different tissues. Our results demonstrate that, based on current parameter estimates, epithelial tissue thickness and cell layer structure are unlikely to be determinants of FMDV-induced cell lysis. However, differences in receptor distribution or viral replication amongst cell layers could influence the development of lesions, but only if viral replication rates are much lower than current estimates.

Characteristics of a foot-and-mouth disease virus with a partial VP1 G-H loop deletion in experimentally infected cattle

Previous work in cattle illustrated the protective efficacy and negative marker potential of a A serotype foot-and-mouth disease virus (FMDV) vaccine prepared from a virus lacking a significant portion of the VP1 G-H loop (termed A(-)). Since this deletion also includes the arginine-glycine-aspartate (RGD) motif required for virus attachment to the host cell in vivo, it was hypothesised that this virus would be attentuated in naturally susceptible animals. The A(-) virus was passaged three times in cattle via needle inoculation of virus suspension delivered into the intradermal space of the tongue (intradermolingual: IDL). Included in the study were three direct contact cattle, two of which were used for the third cattle passage (by inoculation) after direct contact exposure for three days. Cattle were monitored for clinical signs and samples were collected for sequencing as well as antibody and viral genome detection by ELISA and qRT-PCR. Following needle inoculation with the A(-) virus, naïve cattle developed typical clinical signs of FMDV infection, diagnostic assays also provided positive serological and virological results. However, the contact cattle did not develop clinical signs or generate serological or virological markers indicative of FMDV infection even when the cattle were subsequently needle inoculated with 10(5) TCID50 A(-) FMDV delivered IDL following three days of direct contact exposure. The results suggest that the A(-) virus is not attentuated in cattle when inoculated IDL. This virus could be useful as a tool to understand further the natural pathogenesis, receptor usage and internalisation pathways of FMDV.

Foot-and-mouth disease virus 3C protease induces fragmentation of the Golgi compartment and blocks intra-Golgi transport

Picornavirus infection can cause Golgi fragmentation and impose a block in the secretory pathway which reduces expression of major histocompatibility antigens at the plasma membrane and slows secretion of proinflammatory cytokines. In this study, we show that Golgi fragmentation and a block in secretion are induced by expression of foot-and-mouth disease virus (FMDV) 3C(pro) and that this requires the protease activity of 3C(pro). 3C(pro) caused fragmentation of early, medial, and late Golgi compartments, but the most marked effect was on early Golgi compartments, indicated by redistribution of ERGIC53 and membrin. Golgi fragments were dispersed in the cytoplasm and were able to receive a model membrane protein exported from the endoplasmic reticulum (ER). Golgi fragments were, however, unable to transfer the protein to the plasma membrane, indicating a block in intra-Golgi transport. Golgi fragmentation was coincident with a loss of microtubule organization resulting from an inhibition of microtubule regrowth from the centrosome. Inhibition of microtubule regrowth also required 3C(pro) protease activity. The loss of microtubule organization induced by 3C(pro) caused Golgi fragmentation, but loss of microtubule organization does not block intra-Golgi transport. It is likely that the block of intra-Golgi transport is imposed by separate actions of 3C(pro), possibly through degradation of proteins required for intra-Golgi transport.

An increased replication fidelity mutant of foot-and-mouth disease virus retains fitness in vitro and virulence in vivo

In a screen for RNA mutagen-resistant foot-and-mouth disease virus (FMDV) strains, we isolated an FMDV mutant with RNA-dependent RNA polymerase (RdRp) R84H substitution. This mutant, selected under the mutagenic pressure of 5-fluorouracil (5-FU), is resistant not only to 5-FU but also to other two RNA mutagens, 5-azacytidine and ribavirin, suggesting that the RdRp R84H mutant is a high fidelity variant. Subsequently, the increased fidelity of this mutant was verified through analysis of mutation frequency, which revealed a 1.4-fold enhancement in RdRp fidelity compared with the wild-type virus. Further studies indicated that the R84H mutant exhibited slightly increased fitness in vitro, and its virulence was not reduced in suckling mice. These results indicated that an increase in RdRp fidelity does not always correlate with reduced virus fitness and virus attenuation. Thus, this isolated R84H mutant provides a new platform to examine the evolutionary dynamics of fidelity-changing RNA viruses, such as mutagen resistance, fitness and virulence.

Mutagenesis-mediated decrease of pathogenicity as a feature of the mutant spectrum of a viral population

BACKGROUND

RNA virus populations are heterogeneous ensembles of closely related genomes termed quasispecies. This highly complex distribution of variants confers important properties to RNA viruses and influences their pathogenic behavior. It has been hypothesized that increased mutagenesis of viral populations, by treatment with mutagenic agents, can induce alterations in the pathogenic potential of a virus population. In this work we investigate whether mutagenized foot-and-mouth disease virus (FMDV) populations display changes in their virulence in mice.

METHODOLOGY AND PRINCIPAL FINDINGS

FMDV C-S8c1 was passaged in BHK cells in the presence of the mutagenic agent ribavirin. Decline in viral titer and viral RNA progeny was observed in the first passage, fluctuating around a constant value thereafter. Hence, the specific infectivity remained stable during the passages. The viral population harvested from passage 9 (P9 R) showed decreased virulence in mice, with a lethal dose 50 (LD(50)) >10(4) PFU, as compared with LD(50) of 50 PFU of the parental population FMDV C-S8c1. This decrease in virulence was associated to a 20-fold increase in the mutation frequency of the P9 R population with respect to C-S8c1. Interestingly, individual biological clones isolated from the attenuated population P9 R were as virulent as the parental virus C-S8c1. Furthermore, a mixed population of C-S8c1 and P9 R was inoculated into mice and showed decreased virulence as compared to C-S8c1, suggesting that population P9 R is able to suppress the virulent phenotype of C-S8c1.

CONCLUSION

Ribavirin-mediated mutagenesis of an FMDV population resulted in attenuation in vivo, albeit a large proportion of its biological clones displayed a highly virulent phenotype. These results, together with the suppression of C-S8c1 by mutagenized P9 R population, document a suppressive effect of mutagenized viral quasispecies in vivo, and suggest novel approaches to the treatment and prevention of viral diseases.

The nuclear protein Sam68 is cleaved by the FMDV 3C protease redistributing Sam68 to the cytoplasm during FMDV infection of host cells

Picornavirus infection can lead to disruption of nuclear pore traffic, shut-off of cell translation machinery, and cleavage of proteins involved in cellular signal transduction and the innate response to infection. Here, we demonstrated that the FMDV 3C(pro) induced the cleavage of nuclear RNA-binding protein Sam68 C-terminus containing the nuclear localization sequence (NLS). Consequently, it stimulated the redistribution of Sam68 to the cytoplasm. The siRNA knockdown of Sam68 resulted in a 1000-fold reduction in viral titers, which prompted us to study the effect of Sam68 on FMDV post-entry events. Interestingly, Sam68 interacts with the internal ribosomal entry site within the 5' non-translated region of the FMDV genome, and Sam68 knockdown decreased FMDV IRES-driven activity in vitro suggesting that it could modulate translation of the viral genome. The results uncover a novel role for Sam68 in the context of picornaviruses and the proteolysis of a new cellular target of the FMDV 3C(pro).

[Construction of a full-length infectious cDNA clone of inter-genotypic chimeric foot-and-mouth disease virus]

OBJECTIVE

A series of type O foot-and-mouth disease (FMD) outbreaks occurred in China seriously affect development of Chinese husbandry. Its causative agent-type O foot-and-mouth disease virus (FMDV) has been evolved three topotypes: Cathay, Middle East-South Asia and Southeast Asia, specifically, the viruses of Cathay topotype are highly adapted to pig, representing the biggest threat on Chinese pig industry. The available FMD vaccine in China provides insufficient protection against some arising viruses of Chathay topotype, which exert important obstacle to control porcinophilic FMD epidemics in China. To develop vaccine candidate with characteristics of good immunogenicity and broad spectrotype, a full-length infectious cDNA clone of inter-genotypic chimeric FMDV was constructed, which replaced part VP3 and VP1 gene of O/HN/93 strain with the corresponding to the variants of Cathay topotype (mainly replaced the B-C and G-H loop of structure protein VP1).

METHODS

Linearized recombinant plasmid and plasmid expressing T7 RNA polymerase were cotransfected into BHK-21 cells to rescue the chimeric virus in vivo.

RESULT

The transfected cells showed apparent cytopathic effects (CPE) after 36 h post-transfection. The rescued virus was checked by RT-PCR, indirect immunofluorescence, electron microscope. Results show that chimeric FMDV was successfully rescued in vivo. The study of sulk mice pathogenicity show chimeric FMDV has attenuated pathogenicity for suckling mice compared with its parental virus.

CONCLUSION

The construction of inter-genotypic chimeric FMDV will lay the basis for developing novel vaccine against FMD.

The infectivity and pathogenicity of a foot-and-mouth disease virus persistent infection strain from oesophageal-pharyngeal fluid of a Chinese cattle in 2010

BACKGROUND

Foot-and mouth disease (FMD) is an acute, febrile, and contagious vesicular disease affecting cloven-hoofed animals. Some animals may become persistent infected carriers when they contact FMD virus (FMDV), and persistent infected animals are a dangerous factor to cause FMD outbreak.

FINDINGS

300 OP (oesophageal-pharyngeal) fluid samples were collected from cattle without clinic symptom after one month FMD circulated in 2010 in China. A FMDV strain was isolated when a positive OP sample was passed in BHK21 cell line. The strain, named O/CHN/2010/33-OP, was detected to be O/Myanmar/1998 lineage with VP1 DNA sequence comparison. In order to testify its infectivity, two cattle were challenged with OP fluid and three pigs were put into the same pen for direct contact infection. The result showed that one of the cattle and one of the pigs appeared FMD clinic symptoms respectively. Furthermore, two cattle (three pigs were also put into the same pen for direct contact infection) and three pigs were inoculated with O/CHN/2010/33-OP cell passaged strain. The result showed that one of the challenged pigs appeared FMD clinic symptoms. Two cattle and three pigs in the same pen did not appeared FMD clinic symptoms, but the sera antibody and their OP fluid of two cattle were positive. Meanwhile, the spinal cords of three pigs in the same pen with two cattle were positive detected with multiplex- RT-PCR.

CONCLUSION

The persistent infection strain O/CHN/2010/33-OP has infectivity and pathogenicity to cattle and pigs, and infected cattle may transmit the virus to pigs although its virulence was lower than the circulated strain O/CHN/Mya98/2010.

Recombinant non-structural polyprotein 3AB-based serodiagnostic strategy for FMD surveillance in bovines irrespective of vaccination

In India, the proportion of bovines vaccinated against foot-and-mouth disease (FMD) is increasing since the implementation of the Government supported 'FMD Control Programme', and non-structural protein (NSP)-based serological assays for discriminating between antibodies induced by infection or vaccination (DIVA) could be useful. The FMD virus NSP 3AB was expressed in a prokaryotic system and an indirect ELISA (r3AB(3) I-ELISA) was developed and validated as a screening assay for detecting virus in vaccinated bovines. The diagnostic sensitivity of the assay was estimated to be 96%, while the diagnostic specificity varied between the naïve and vaccinates as 99.1% and 96.4%, respectively. This assay could detect antibodies to 3AB (3AB-Ab) from 10 to as late as 900 days post-infection in cattle infected experimentally. The "in-house" assay demonstrated higher sensitivity than a commercial 3ABC ELISA kit particularly with samples obtained from the late stages of infection. Transient post-vaccinal 3AB-Ab response could be detected in one of the three commercial vaccines during the six-month vaccination regimen, which emphasizes the fact that for a DIVA-compatible diagnostic strategy to be a realistic option, all vaccines need to be quality checked for the NSP content.

Viral genome segmentation can result from a trade-off between genetic content and particle stability

The evolutionary benefit of viral genome segmentation is a classical, yet unsolved question in evolutionary biology and RNA genetics. Theoretical studies anticipated that replication of shorter RNA segments could provide a replicative advantage over standard size genomes. However, this question has remained elusive to experimentalists because of the lack of a proper viral model system. Here we present a study with a stable segmented bipartite RNA virus and its ancestor non-segmented counterpart, in an identical genomic nucleotide sequence context. Results of RNA replication, protein expression, competition experiments, and inactivation of infectious particles point to a non-replicative trait, the particle stability, as the main driver of fitness gain of segmented genomes. Accordingly, measurements of the volume occupation of the genome inside viral capsids indicate that packaging shorter genomes involves a relaxation of the packaging density that is energetically favourable. The empirical observations are used to design a computational model that predicts the existence of a critical multiplicity of infection for domination of segmented over standard types. Our experiments suggest that viral segmented genomes may have arisen as a molecular solution for the trade-off between genome length and particle stability. Genome segmentation allows maximizing the genetic content without the detrimental effect in stability derived from incresing genome length.

Genome segmentation, the splitting of a linear genome into two or more segments, is a major evolutionary transition from independent towards complementing transmission of genetic information. Many viruses with RNA as genetic material have segmented genomes, but the molecular forces behind genome segmentation are unknown. We have used foot-and-mouth disease virus to address this question, because this non-segmented RNA virus became segmented into two RNAs when it was extensively propagated in cell culture. This made possible a comparison of the segmented form (with two shorter RNAs enclosed into separate viral particles) with its exactly matching non-segmented counterpart. The results show that the advantage of the segmented form lies in the higher stability of the particles that enclose the shorter RNA, and not in any difference in the rate of RNA synthesis or expression of the genetic material. Genome segmentation may have arisen as a molecular mechanism to overcome the trade-off between genomic content and particle stability. It allows optimizing the amount of genetic information while relaxing packaging density.

Effects of macromolecular crowding on the inhibition of virus assembly and virus-cell receptor recognition

Biological fluids contain a very high total concentration of macromolecules that leads to volume exclusion by one molecule to another. Theory and experiment have shown that this condition, termed macromolecular crowding, can have significant effects on molecular recognition. However, the influence of molecular crowding on recognition events involving virus particles, and their inhibition by antiviral compounds, is virtually unexplored. Among these processes, capsid self-assembly during viral morphogenesis and capsid-cell receptor recognition during virus entry into cells are receiving increasing attention as targets for the development of new antiviral drugs. In this study, we have analyzed the effect of macromolecular crowding on the inhibition of these two processes by peptides. Macromolecular crowding led to a significant reduction in the inhibitory activity of: 1), a capsid-binding peptide and a small capsid protein domain that interfere with assembly of the human immunodeficiency virus capsid, and 2), a RGD-containing peptide able to block the interaction between foot-and-mouth disease virus and receptor molecules on the host cell membrane (in this case, the effect was dependent on the conditions used). The results, discussed in the light of macromolecular crowding theory, are relevant for a quantitative understanding of molecular recognition processes during virus infection and its inhibition.

Effect of the route of foot-and-mouth disease virus infection of piglets on the course of disease

Three different routes of Foot-and-mouth disease virus (FMDV) infection of piglets, namely intranasal (i.n.) through drops, intradermal (i.d.) into the foot, and intramuscular (i.m.) were compared regarding the onset and severity of the disease. The results showed that the i.d. injection of the virus resulted in the fastest onset of the disease. The i.m. injection led to a delayed onset, but the final effect was identical with i.d. injection. Moreover, the i.m. injection was simpler to perform and easier to evaluate. Therefore, the i.m. injection of piglets is recommended as the optimal infection route for evaluation of the FMDV vaccine potency.

[Current situation and future preventive measures of foot-and-mouth disease in Japan]

Foot-and-mouth disease caused by Foot-and-mouth disease virus (FMDV) is a severe and acute vesicular disease of cloven-hoofed animals including cattle, pigs, sheep and goats. As FMDV is highly contagious and causes productivity losses among infected animals, outbreaks of the disease are a primary animal health concern worldwide. In April, 2010, the disease reoccurred in Miyazaki prefecture in 10 years. Compared to the outbreak in 2000 in which no infection among pigs was observed, a total of 292 infected farms have been involved in this outbreak, and infected animals (37,412 cattle, 42 water buffalos, 174,132 pigs, 14 goats, and 8 sheep) were culled and buried. Vaccination was decided to reduce the speed of virus spreading. Finally a total of 76,756 heads of vaccinated animals were also slaughtered. The outbreak has continued for 2.5 months, and the ban on animal movements have been eased 3 months after the first occurrence. As several factors for disease spreading have been rumored, I would like to note this point and discuss future preventive measures.

Domain disruptions of individual 3B proteins of foot-and-mouth disease virus do not alter growth in cell culture or virulence in cattle

Picornavirus RNA replication is initiated by a small viral protein primer, 3B (also known as VPg), that is covalently linked to the 5' terminus of the viral genome. In contrast to other picornaviruses that encode a single copy of 3B, foot-and-mouth disease virus (FMDV) encodes three copies of 3B. Viruses containing disrupted native sequence or deletion of one of their three 3B proteins were derived from a FMDV A24 Cruzeiro full-length cDNA infectious clone. Mutant viruses had growth characteristics similar to the parental virus in cells. RNA synthesis and protein cleavage processes were not significantly affected in these mutant viruses. Cattle infected by aerosol exposure with mutant viruses developed clinical disease similar to that caused by the parental A24 Cruzeiro. Therefore, severe domain disruption or deletion of individual 3B proteins in FMDV do not affect the virus' ability to replicate in vitro and cause clinical disease in cattle.

[Morphological observation of bovine kidney (MDBK) cells effected by foot-and-mouth disease virus L(pro)]

In order to explore the morphological changes of Bovine Kidney (MDBK) cells induced by foot-and-mouth disease virus (FMDV) L protease, we induced the expression of FMDV L protease in bovine kidney cells (MDBK) artificially. All work is carried out on the basis of a stable MDBK cell line inducibly expresses the Lab gene under the control of tetracycline. We use cell morphology, Hoechst 33258 staining, AO-EB staining, and DNA Ladder abstraction to research the morphological changes of MDBK cells. 24 hours after FMDV L protease were induced and expressed in MDBK cells, cells shown the diminish of cell size, nuclear enrichment and the appearance of transparency circle under the light microscope. Apoptosis characteristics of nuclear condensation, fragmentation, accompanied by apoptotic bodies formation (Hoechst 33258 staining). 36 hours after the expression, nuclear staining of early lesions showed bright green plaque or debris-like dense, and advanced lesions showed Orange and dense plaques (AO-EB staining). 48 hours after the expression, DNA gel electrophoresis showed visible DNA ladder. Results indicate that FMDV L protease can induce apoptosis of MDBK and apoptosis plays an important role in the cytopathogenicity effect of FMDV.

[Construction of an infectious cDNA clone derived from foot-and-mouth disease virus O/QYYS/s/06]

After sequencing, we amplified and cloned foot-and-mouth disease virus (FMDV) O/QYYS/s/06 whole genome by three fragments. These three fragments were cloned into vector P43 one by one to construct recombinant plasmid P43C, which carried the full-length cDNA of FMDV O/QYYS/s/06. Then, plasmid P43C and plasmid T7 expressing T7 RNA polymerase were co-transfected into BHK-21 cells. After 48 h, we harvested the culture broth from transfected BHK-21 cells and inoculated into 2-3 day-old sucking mice. After four generation passage, the virus harvested from sucking mice was confirmed to be type O FMDV by the indirect hemagglutination test, sucking mice's neutralization test and sequencing. The results showed that we have successfully constructed the full-length cDNA clone of FMDV O/QYYS/s/06 strain.

[Rescue and identification foot-and-mouth disease virus Asia1/JS/China/2005 strain with Arg-Gly-Asp RGD receptor recognition site]

OBJECTIVE

To construct an infectious full-length cDNA clone of Asial/JS/China/2005 strain with Arg-Gly-Asp (RGD) receptor recognition site.

METHODS

We constructed foot-and-mouth disease virus type Asial full-length cDNA clone pFMDV-RGD by using site-directed mutagenesis. The plasmid pFMDV-RGD contained the desired mutation. The plasmids pFMDV-RGD were linearized with NotI enzyme. Linearized plasmid and pcDNAT7P plasmids expressing T7 RNA polymerase cotransfected into BHK-21 cells to rescue FMDV-RGD.

RESULTS

We constructed FMDV Asial/JS/China/2005 strain full-length cDNA clone with Arg-Gly-Asp receptor recognition site by sequence. We obtained rescued virus by plasmid cotransfection. The results of sequencing, indirect immunofluorescence, electron microscope and sulk mice pathogenicity analysis showed foot-and-mouth disease virus containing Arg-Gly-Asp receptor recognition site was successfully rescued.

CONCLUSION

The results lay a foundation for further study of biology characteristic diversity of rescued virus with Arg-Gly-Asp and Arg-Asp-Asp (RDD) receptor recognition site.

Influence of exposure intensity on the efficiency and speed of transmission of Foot-and-mouth disease

Foot-and-mouth disease virus (FMDV) can be spread by direct animal-to-animal contact, indirect contact facilitated by contaminated materials or by airborne spread. The rate of spread and the incubation period, as well as the severity of disease, depends on many variables including the dose received, the route of introduction, the virus strain, the animal species and the conditions under which the animals are kept. Quantitative data related to these variables are needed if model predictions are to be used in practical disease control. This experimental study quantifies the risk of transmission of FMDV in pigs exposed by contact, sheep exposed by indirect contact with pigs and sheep exposed to airborne FMDV. Groups of pigs were inoculated with the FMDV O UKG 34/2001 strain and susceptible pigs were then exposed to the inoculated animals at different stages of the infection cycle. The mean incubation period in the susceptible pigs ranged from 1 to 10 days. The length of the incubation period, severity of clinical disease and efficiency of spread were related to dose (i.e. infectiousness of source and intensity of contact). Low intensity transmission increased the proportion of subclinical or abortive infections. Local conditions are important in the efficiency and speed of transmission of FMDV. The results of the experiments described above suggest that transmission is frequency dependent rather than density dependent. The sheep experiments provided further evidence that development of infection and clinical disease is dependent upon local conditions. Dose, infectiousness, intensity of contact and local factors are thus important determinants for the outcome of an initial outbreak and must be truthfully accounted for in mathematical models of epidemiological spread.

Airborne spread of foot-and-mouth disease--model intercomparison

Foot-and-mouth disease virus (FMDV) spreads by direct contact between animals, by animal products (milk, meat and semen), by mechanical transfer on people or fomites and by the airborne route, with the relative importance of each mechanism depending on the particular outbreak characteristics. Atmospheric dispersion models have been developed to assess airborne spread of FMDV in a number of countries, including the UK, Denmark, Australia, New Zealand, USA and Canada. These models were compared at a Workshop hosted by the Institute for Animal Health/Met Office in 2008. Each modeller was provided with data relating to the 1967 outbreak of FMD in Hampshire, UK, and asked to predict the spread of FMDV by the airborne route. A number of key issues emerged from the Workshop and subsequent modelling work: (1) in general all models predicted similar directions for livestock at risk, with much of the remaining differences strongly related to differences in the meteorological data used; (2) determination of an accurate sequence of events on the infected premises is highly important, especially if the meteorological conditions vary substantially during the virus emission period; (3) differences in assumptions made about virus release, environmental fate and susceptibility to airborne infection can substantially modify the size and location of the downwind risk area. All of the atmospheric dispersion models compared at the Workshop can be used to assess windborne spread of FMDV and provide scientific advice to those responsible for making control and eradication decisions in the event of an outbreak of disease.

[Construction and identification of infectious molecular clone of foot-and-mouth disease virus strain O/CHINA/99]

Nine primers were designed for the full-length genome of O/CHINA/99 and each sequence fragment was obtained by RT-PCR, and cloned into pOK12 vecter, the full-length genome cDNA clone of O/CHINA/99 was identified by restriction enzymes digestion, PCR, and the whole genome sequencing. The results showed that the O/CHINA/99 whole genome was formed with the length of 8200 nt. The nucleotide sequence of the full-length cDNA shared 99.1% homology with its prototype. RNA synthesized in vitro by means of a bacteriophage T7 promter inserted in front of the cDNA led to the production of infectious particle upon transfection of BHK-21 cell using lipofectamine reagent, as shown by cytopathic effects. The rescued virus had high pathogenicity in mice by endermic infection too. All the results showed that an infectious molecular clone was successfully constructed and rescued virus could be obtained.

[Virulence comparison of genetic engineering virus containing different length poly(C) tract of foot-and-mouth disease virus]

OBJECTIVE

Study the association of the length of poly(C) tract with virulence of foot-and-mouth disease virus.

METHODS

The recombinant plasmids pGEM-XJ/AKT/69 containing the full-length cDNA of FMDV were linearized by Nhe I /Not I and transcribed by T7 RNA polymerase. The in vitro transcripts were transfected into BHK-21 cells using Lipofectamine 2000 reagent. Then, the genetic engineering virus was rescued from BHK-21 cells. The poly(C) tracts were sequenced at different passages of rescued virus, and the pathogenicities were evaluated with 3-day-old mice and BHK-21 cells by detection of LD50 and TCID50.

RESULTS

After six passages in BHK-21 cells, cytopathic effect was observed by microscopy. The rescued virus was rejuvenated once in unweaned mice, and then came back to cell passage. We found that the poly(C) tract of rescued virus was shortened when the virus was passaged twice in BHK-21 cells. Although the data of LD50 in mice and TCID50 in BHK-21 cells showed that the virulence and infectivity of genetic engineering viruses were lower than its parental virus, no significant difference was observed between the genetic engineering viruses with the different length poly(C) tract.

CONCLUSION

The length of poly(C) tract ranged from 12 to 17 nucleotides did not cause significant influence on the virulence and infectivity of genetic engineering virus.

[Preparation and characterization of the polyclonal antibody against pig integrin beta6 subunit LBD as FMDV receptor]

AIM

To induce the expression of FMDV receptor integrin beta6 subunit ligand-binding domain in E.coli and prepare the rabbit polyclonal antibody against it.

METHODS

The fragment coding beta6 ligand-binding domain was amplified by PCR and doubly digested with BamH Iand Xho I. Then it was cloned into expression vector pGEX-4T-1 to obtain recombinant plasmid pGEX-4T-1-beta6LBD. After pGEX-4T-1-beta6LBD was transformed into E.coli BL21(DE3) and induced by IPTG, the expression of fusion proteins was identified by SDS-PAGE, with inclusion body prepared and fusion protein purified. Then new Zealand rabbits were immunized to prepare polyclonal antibody against beta6LBD. GST-beta6LBD antiserum was obtained and the specificity of polyclonal antibody was detected by Western blot.

RESULTS

SDS-PAGE demonstrated that the fusion protein GST-beta6LBD was expressed with the expected molecular weight at 42 000. A single clear band of GST-beta6LBD fusion protein appeared in SDS-PAGE gel after purification. The titer of the polyclonal antibody was above 1:12 800 and it is of high specificity.

CONCLUSION

The successful preparation of rabbit anti pig beta6LBD polyclonal antibody with high affinity and specificity will lay a foundation for further research into the function of integrin beta6 in FMDV infection.

Susceptibility to viral infection is enhanced by stable expression of 3A or 3AB proteins from foot-and-mouth disease virus

The foot-and-mouth disease virus (FMDV) 3A protein is involved in virulence and host range. A distinguishing feature of FMDV 3B among picornaviruses is that three non-identical copies are encoded in the viral RNA and required for optimal replication in cell culture. Here, we have studied the involvement of the 3AB region on viral infection using constitutive and transient expression systems. BHK-21 stably transformed clones expressed low levels of FMDV 3A or 3A(B) proteins in the cell cytoplasm. Transformed cells stably expressing these proteins did not exhibit inner cellular rearrangements detectable by electron microscope analysis. Upon FMDV infection, clones expressing either 3A alone or 3A(B) proteins showed a significant increase in the percentage of infected cells, the number of plaque forming units and the virus yield. The 3A-enhancing effect was specific for FMDV as no increase in viral multiplication was observed in transformed clones infected with another picornavirus, encephalomyocarditis virus, or the negative-strand RNA virus vesicular stomatitis virus. A potential role of 3A protein in viral RNA translation was discarded by the lack of effect on FMDV IRES-dependent translation. Increased viral susceptibility was not caused by a released factor; neither the supernatant of transformed clones nor the addition of purified 3A protein to the infection medium was responsible for this effect. Unlike stable expression, high levels of 3A or 3A(B) protein transient expression led to unspecific inhibition of viral infection. Therefore, the effect observed on viral yield, which inversely correlated with the intracellular levels of 3A protein, suggests a transacting role operating on the FMDV multiplication cycle.

Experimental transmission of foot-and-mouth disease among Indian buffalo (Bubalus bubalis) and from buffalo to cattle

Indian buffalo and cattle were infected experimentally with a serotype O strain of foot-and-mouth disease virus of buffalo origin. Whereas intradermolingual inoculation of buffalo produced largely sub-clinical infection, inoculation in the dental pad produced vesicles in the mouth and on the feet. A buffalo infected via the dental pad transmitted infection to cattle and buffalo by direct contact with them for 24h. The contact-exposed buffalo developed (1) delayed-onset clinical signs, and (2) shedding of virus from the nose, commencing before the appearance of vesicles and continuing until the experiment was terminated 10 weeks after exposure. The covert nature of the disease in Indian buffalo, coupled with the prolonged shedding of virus, suggests that this species represents a host of epidemiological importance.

Pathogenic characteristics of the Korean 2002 isolate of foot-and-mouth disease virus serotype O in pigs and cattle

Experimental infection of susceptible cattle and pigs showed that the O/SKR/AS/2002 pig strain of foot-and-mouth disease virus (FMDV) causes an infection that is highly virulent and contagious in pigs but very limited in cattle. Pigs directly inoculated with, or exposed to swine infected with, strain O/SKR/AS/2002 showed typical clinical signs, including gross vesicular lesions in mouth and pedal sites. In addition, FMDV was isolated from, and FMDV genomic RNA was detected in, blood, serum, nasal swabs and oesophageal-pharyngeal (OP) fluid early in the course of infection. Antibodies against the non-structural protein (NSP) 3ABC were detected in both directly inoculated and contact pigs, indicating active virus replication. In contrast, the disease in cattle was atypical. After inoculation, lesions were confined to the infection site. A transient viraemia occurred 1 and 2 days after inoculation, and this was followed by the production of antibodies to NSP 3ABC, indicating subclinical infection. No clinical disease was seen, and no antibodies to NSP 3ABC were present in contact cattle. Additionally, no virus or viral nucleic acid was detected in blood, nasal swab and OP fluid samples from contact cattle. Thus, the virus appeared not to be transmitted from infected cattle to contact cattle. In its behaviour in pigs and cattle, strain O/SKR/AS/2002 resembled the porcinophilic FMDV strain of Cathay origin, O/TAW/97. However, the latter, unlike O/SKR/AS/2002, has reduced ability to grow in bovine-derived cells. The porcinophilic character of O/TAW/97 has been attributed to a deletion in the 3A coding region of the viral genome. However, O/SKR/AS/2002 has an intact 3A coding region.

Induction of immature dendritic cell apoptosis by foot and mouth disease virus is an integrin receptor mediated event before viral infection

Foot and mouth disease virus (FMDV) has been demonstrated to infect dendritic cells (DC) and reduced its ability to stimulate host immune responses. This study aimed to determine whether non‐replicating FMDV could induce apoptosis of the host immune cells. In this study, we have demonstrated that bone morrow derived dendritic cells (BMDCs) were induced to undergo apoptosis in a dose‐dependent manner, which was determined by the annexin‐V staining, DNA fragmentation, and TUNEL staining methods, after they were treated with the chemically inactivated FMDV in vitro. The initiation of apoptosis was apparently via an interaction of the integrin receptor on BMDCs and the RGD motif within the VP1 capsid protein of FMDV. The initiation activated a cascade of apoptotic pathway including reduced expression of Bcl‐2, activation of caspases, and release of cytochrome c from mitochondria. Pretreatment with BMDCs with LPS prevented the inactivated FMDV induced apoptosis, suggesting immature BMDCs are susceptible to such apoptosis. Taken together, the data demonstrate that the inactivated FMDV induces the apoptosis in BMDCs via the integrin receptor and subsequently triggers the apoptosis signal, suggesting that such induction of apoptosis is likely to impair immune responses against FMDV infection. J. Cell. Biochem. 102: 980–991, 2007. © 2007 Wiley‐Liss, Inc.

Subcellular distribution of swine vesicular disease virus proteins and alterations induced in infected cells: a comparative study with foot-and-mouth disease virus and vesicular stomatitis virus

The intracellular distribution of swine vesicular disease virus (SVDV) proteins and the induced reorganization of endomembranes in IBRS-2 cells were analyzed. Fluorescence to new SVDV capsids appeared first upon infection, concentrated in perinuclear circular structures and colocalized to dsRNA. As in foot-and-mouth disease virus (FMDV)-infected cells, a vesicular pattern was predominantly found in later stages of SVDV capsid morphogenesis that colocalized with those of non-structural proteins 2C, 2BC and 3A. These results suggest that assembly of capsid proteins is associated to the replication complex. Confocal microscopy showed a decreased fluorescence to ER markers (calreticulin and protein disulfide isomerase), and disorganization of cis-Golgi gp74 and trans-Golgi caveolin-1 markers in SVDV- and FMDV-, but not in vesicular stomatitis virus (VSV)-infected cells. Electron microscopy of SVDV-infected cells at an early stage of infection revealed fragmented ER cisternae with expanded lumen and accumulation of large Golgi vesicles, suggesting alterations of vesicle traffic through Golgi compartments. At this early stage, FMDV induced different patterns of ER fragmentation and Golgi alterations. At later stages of SVDV cytopathology, cells showed a completely vacuolated cytoplasm containing vesicles of different sizes. Cell treatment with brefeldin A, which disrupts the Golgi complex, reduced SVDV (approximately 5 log) and VSV (approximately 4 log) titers, but did not affect FMDV growth. Thus, three viruses, which share target tissues and clinical signs in natural hosts, induce different intracellular effects in cultured cells.

Immunization of DNA vaccine encoding C3d-VP1 fusion enhanced protective immune response against foot-and-mouth disease virus

Because foot-and-mouth disease virus (FMDV) remains a great problem to many livestock of agricultural importance, safe, effective vaccines are in great need. DNA vaccine would be a promising candidate but the design remains to be optimized. VP1 gene of FMDV strain O/ES/2001 was linked to three copies of either porcine or murine C3d or four copies of a 28-aa fragment of murine C3d containing the CR2 receptor binding domain (M28). The resultant plasmids encoding C3d/M28-VP1 fusion or only VP1 as control were immunized guinea pigs. Both cellular and humoral immune responses were evaluated and protection was observed after virus challenge. As a result, although the plasmid encoding only VP1 could elicit virus-binding antibody detected by ELISA, splenocyte proliferation, IL-4 and IFN-gamma production, the levels were significantly less than C3d/M28-VP1 fusion. Furthermore, VP1 failed to induce neutralization antibody and protect animals against virus challenge, while murine C3d-VP1 fusion efficiently induced neutralization antibody response and provided 87.50% of the animals with complete protection and 12.50% with partial protection. Among murine C3d, M28, and porcine C3d, the adjuvant effect of murine C3d is strongest, followed by porcine C3d, and last murine M28. In conclusion, the fact that C3d genes, when coupled to VP1 gene, are able to greatly enhance the protective immune response of VP1 DNA in guinea pigs suggests that C3d-VP1 DNA chimera has a significant potential for use as a novel DNA vaccine against FMDV.

Foot-and-mouth disease virus infection in young lambs: pathogenesis and tissue tropism

Foot-and-mouth disease (FMD) in adult sheep usually causes milder clinical signs than in cattle or pigs, and is often subtle enough to go undiagnosed. In contrast, FMD in lambs has been reported to cause high mortality during field outbreaks. In order to investigate the pathogenesis of FMD in lambs, two groups, aged 10-14 days, were infected with foot-and-mouth disease virus (FMDV) type O UKG. One group of lambs (n=8) was inoculated with FMDV in the coronary band, while the other (n=4) was infected by direct contact with FMDV-inoculated ewes. Daily serum samples and temperature measurements were taken. Lambs were killed sequentially and tissue samples taken for analysis. Using real-time RT-PCR, viral RNA levels in tissue samples and serum were measured, and a novel strand-specific real-time RT-PCR assay was used to quantify viral replication levels in tissues. Tissue sections were examined for histopathological lesions, and in situ hybridisation (ISH) was used to localise viral RNA within histological sections. The contact-infected lambs became infected approximately 24h after the ewes were inoculated. Vesicular lesions developed on the feet of all lambs and on the caudo-lateral part of the tongues of six of the eight inoculated lambs and three of the four contact-infected lambs. Although no lambs developed severe clinical signs, one of the contact-infected lambs died acutely at 5 days post-exposure. Histological examination of the heart from this lamb showed multi-focal areas of lymphocytic-plasmacytic myocarditis; similar lesions were also observed in the hearts of three of the inoculated lambs. Using ISH, viral RNA was localised within cardiac and skeletal muscle cells from the lamb which had died, and also from vesicular lesions on the coronary band and tongue of inoculated lambs. These results provide a detailed description of the pathogenesis of the disease in lambs.

Foot-and-mouth disease: measurements of aerosol emission from pigs as a function of virus strain and initial dose

Measurements of airborne foot-and-mouth disease virus have been made using 20 pigs that had either O UKG or C Noville injected into their heel-pads to determine if the kinetics of virus emission are related to the virus strain and dose administered in the challenge inoculum. Viable virus was detected in aerosol emissions for 3 days regardless of the strain or dose of virus given. No correlation was found between the peak level of virus emission and dose, but pigs infected with a lower dose of virus had a delayed onset of aerosol emission and emitted a greater total amount of aerosolised virus. Irrespective of the dose, both the total amount and the peak level of virus emission were higher from pigs infected with C Noville compared to those infected with O UKG. The results suggest that care should be taken when extrapolating from laboratory derived data to the field; this is particularly the case in the early days of an outbreak when the aerosol characteristics of the virus involved may be unknown and the amount of virus that an individual animal has been challenged with remains uncertain.

[Molecular cloning and characteristics of cDNA encoding pig beta6 subunit for FMDV receptor]

In order to study the roles of integrin beta6 in Foot-and-Mouth Disease Virus infection, pig integrin beta6 was firstly molecularly cloned from RNA of the tongue and lung of recovered pig infected experimentally with foot-and-mouth-disease virus (FMDV), and was compared with the beta6 gene of other animals available in GenBank at nucleotide and amino acid leves. GeneBank association number of the beta6 gene is EF432729. Pig integrin beta6 gene (2367bp) encodes a polypeptide of 788 amino acids consisting of 9 potential N-linked glycosylation sites, 3 Glycosaminoglycan attachment sites, a cGMP-dependent protein kinase phosphorylation site, 10 Protein kinase C phosphorylation sites, 2 EGF-like domains and 2 cysteine-rich regions. Pig integrin beta6 subunit has a 26-residue putative signal peptide, a 681-residue ectodomain, a 29-residue transmembrane domain, and a 52-residue cytoplasmic domain. 11 mutant nucleotides were found in beta6 gene coding region and 9 amino acids were changed. The nucleotide sequence similarity of integrin beta6 gene between rheses monkey, mouse, Norway rat, dog, guinea pig, human, bovine, sheep is 79.5%, 84.9%, 85.4%, 85.2%, 88.7%, 90.1%, 91.9% and 91.9%, and the amino acid sequence similarity is 93.5%, 88.2%, 88.5%, 88.3%, 91.0%, 92.8%, 93.3% and 93.4% respectively. This study will lay a foundation for understanding the interactions of FMDV with receptors.

Genetic and phenotypic variation of foot-and-mouth disease virus during serial passages in a natural host

Foot-and-mouth disease virus (FMDV), like other RNA viruses, exhibits high mutation rates during replication that have been suggested to be of adaptive value. However, even though genetic variation in RNA viruses and, more specifically, FMDV has been extensively examined during virus replication in a wide variety of in vitro cell cultures, very little is known regarding the generation and effects of genetic variability of virus replication in the natural host under experimental conditions and no genetic data are available regarding the effects of serial passage in natural hosts. Here, we present the results of 20 serial contact transmissions of the highly pathogenic, pig-adapted O Taiwan 97 (O Tw97) isolate of FMDV in swine. We examined the virus genomic consensus sequences for a total of 37 full-length viral genomes recovered from 20 in vivo passages. The characteristics and distributions of changes in the sequences during the series of pig infections were analyzed in comparison to the O Tw97 genomes recovered from serially infected BHK-21 cell cultures. Unexpectedly, a significant reduction of virulence upon pig passages was observed, and finally, interruption of the viral transmission chain occurred after the14th pig passage (T14). Virus was, however, isolated from the tonsils and nasal swabs of the asymptomatic T15 pigs at 26 days postcontact, consistent with a natural establishment of the carrier state previously described only for ruminants. Surprisingly, the region encoding the capsid protein VP1 (1D) did not show amino acid changes during in vivo passages. These data demonstrate that contact transmission of FMDV O Tw97 in pigs mimics the fitness loss induced by the bottleneck effect, which was previously observed by others during plaque-to-plaque FMDV passage in vitro, suggesting that unknown mechanisms of virulence recovery might be necessary during the evolution and perpetuation of FMDV in nature.

Foot-and-mouth disease virus (O/UKG/2001) is poorly transmitted between sheep by the airborne route

Foot-and-mouth disease virus (FMDV) can be spread by the airborne route and therefore atmospheric dispersion models have been developed to predict where the virus might spread during a disease outbreak. Airborne transmission between sheep of the FMDV strain involved in the outbreak in Europe in 2001 (O/UKG/2001) was studied experimentally. Recipient animals were exposed to two donor sheep excreting virus for 2, 4, 6, 8 or 24 h. Although FMDV was detected in air samples collected during challenge, none of the recipient sheep became infected. These data suggest that O/UKG/2001 is not efficiently transmitted by the airborne route between sheep.