Foot-and-mouth Disease Virus Infection Research Articles

Characterization of naturally occurring, new and persistent subclinical foot-and-mouth disease virus infection in vaccinated Asian buffalo in Islamabad Capital Territory, Pakistan.

The convalescent subclinical carrier state of foot-and-mouth disease virus (FMDV) infection has been thoroughly investigated; contrastingly, the subclinical form of new infections of vaccinated and naïve hosts is recognized, but poorly understood. To investigate the natural dynamics of subclinical FMDV infections, a prospective, 12-month, longitudinal study was conducted in vaccinated Asian buffalo (Bubalus bubalis) under natural conditions in Pakistan, where FMDV is hyperendemic. Oropharyngeal fluid (OPF) samples were obtained quarterly from 300 buffalo on 30 farms which reported no clinical FMD during the 12-month study period. At the start of the study, 77.7% of buffalo had FMDV anti-NSP antibodies, and all farms had at least one seropositive buffalo. Based upon the presence of viral RNA and viral VP1 sequences obtained, distinct subcategories of subclinical infections were documented, including new, persistent, and serial infections with different FMDV strains. Viral RNA was detected in at least one OPF sample from 180 (60%) of the 300 buffalo. Over the course of the study, FMDV was detected in OPF of 80 buffalo that had been FMDV-free in previous OPF samples, indicating the occurrence of new subclinical infections. Eight buffalo were confirmed to be persistently infected, and serial infection with different FMDVs was confirmed in 13 animals. The most prevalent serotype detected was Asia-1, followed by A, and O. Phylogenetic analysis indicated multiple distinct clusters of serotypes Asia-1 and A. This study indicates a high prevalence of subclinical FMDV infection in vaccinated buffalo in Pakistan and emphasizes the importance of clinically undetected infection in FMD dynamics in endemic regions.

Foot-and-Mouth Disease Infection Dynamics in Contact-Exposed Pigs Are Determined by the Estimated Exposure Dose

The quantitative relationship between the exposure dose of foot-and-mouth disease virus (FMDV) and subsequent infection dynamics has been demonstrated through controlled inoculation studies in various species. However, similar quantitation of viral doses has not been achieved during contact exposure experiments due to the intrinsic difficulty of measuring the virus quantities exchanged between animals. In the current study, novel modeling techniques were utilized to investigate FMDV infection dynamics in groups of pigs that had been contact-exposed to FMDV-infected donors shedding varying levels of virus, as well as in pigs inoculated via the intra-oropharyngeal (IOP) route. Estimated virus exposure doses were modeled and were found to be statistically significantly associated with the dynamics of FMDV RNA detection in serum and oropharyngeal fluid (OPF), and with the time to onset of clinical disease. The minimum estimated shedding quantity in OPF that defined infectiousness of donor pigs was 6.55 log10 genome copy numbers (GCN)/ml (95% CI 6.11, 6.98), which delineated the transition from the latent to infectious phase of disease which occurred during the incubation phase. This quantity corresponded to a minimum estimated exposure dose of 5.07 log10 GCN/ml (95% CI 4.25, 5.89) in contact-exposed pigs. Thus, we demonstrated that a threshold quantity of FMDV detection in donor pigs was necessary in order to achieve transmission by direct contact. The outcomes from this investigation demonstrate that variability of infection dynamics which occurs during the progression of FMD in naturally exposed pigs can be partially attributed to variations in exposure dose. Moreover, these modeling approaches for dose-quantitation may be retrospectively applied to contact-exposure experiments or field scenarios. Hence, robust information could be incorporated into models used to evaluate FMD spread and control.

Animal-level risk factors associated with foot-and-mouth disease in cattle and buffalo in Egypt

There is a paucity of the investigation of risk factors associated with foot-and-mouth disease (FMD) in Egypt. Subsequently, in the present study the impact of risk factors associated with FMD infection was analyzed in cattle and buffalo reared in Qalyubia governorate, Egypt. Serum samples were collected from 288 animals (n = 90 water buffalo (Bubalus bubalis) and n = 198 cattle) and adapted for detection of FMD virus infection by ELISA assay with monoclonal antibody (MELISA) to type serotype O. Direct FMD virus serotype was detected in 115 animals (n = 82 cattle and n = 33 buffalo). Univariate analysis revealed a significant association between FMD infection and the fattening animals (P = 0.024; odds ratio (OR) 2.118; confidence interval (CI) 1.105–4.058). Multivariate statistics demonstrated that locality was the potential risk factors for infection by FMD virus (P = 0.001; OR 31.613; CI 13.791–72.466). The present investigation draws attention and gives the impression to the potential risk factors associated with FMD-infected cases in cattle and buffalo in Qalyubia governorate in Egypt. Recognition of the potential risk factors associated with FMD-infected cases offer a novel approach to construct the best preventive measures.

Transcript Profiling Identifies Early Response Genes against FMDV Infection in PK-15 Cells.

Foot-and-mouth disease (FMD) is a highly contagious disease that results in enormous economic loses worldwide. Although the protection provided by vaccination is limited during early infection, it is recognized as the best method to prevent FMD outbreaks. Furthermore, the mechanism of host early responses against foot-and-mouth disease virus (FMDV) infection remains unclear. In our study, a pig kidney cell line (PK-15) was used as a cell model to reveal the mechanism of early pig responses to FMDV infection. Four non-treated control and four FMDV-treated PK-15 cells were sequenced with RNA-seq technology, and the differentially expressed genes (DEGs) were analyzed. The results showed that 1212 DEGs were in the FMDV-infected PK-15 cells, including 914 up-regulated and 298 down-regulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were significantly enriched in the tumor necrosis factor (TNF), cytokine-cytokine receptor interaction, NOD-like receptor, toll-like receptor, NF-κB, and the chemokine signaling pathways. To verify the results of the DEGs, 30 immune-related DEGs (19 up-regulated and 11 down-regulated) were selected for Quantitative Reverse Transcriptase polymerase chain reaction (RT-qPCR) verification. The results showed that RT-qPCR-measured genes exhibited a similar pattern as the RNA-seq analyses. Based on bioinformatics analysis, during FMDV early infection, we found that a series of cytokines, such as interleukins (IL6), chemokines (CXCL2, CCL20 and CCL4), and transcription factors (ZFP36, FOS, NFKBIA, ZBTB3, ZNF503, ZNF283, dymeclin (DYM), and orthodenticle homeobox 1 (OTX1)) were involved in the battle between FMDV and the host. Combined with their features and functions, we propose inflammation as the main early mechanism by which the host responds to FMDV infection. These data provide an additional panel of candidate genes for deciphering the mechanisms of a host’s early response against FMDV infection.

Innate immune sensor LGP2 is cleaved by the Leader protease of foot-and-mouth disease virus.

The RNA helicase LGP2 (Laboratory of Genetics and Physiology 2) is a non-signaling member of the retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), whose pivotal role on innate immune responses against RNA viruses is being increasingly uncovered. LGP2 is known to work in synergy with melanoma differentiation-associated gene 5 (MDA5) to promote the antiviral response induced by picornavirus infection. Here, we describe the activity of the foot-and-mouth disease virus (FMDV) Leader protease (Lpro) targeting LGP2 for cleavage. When LGP2 and Lpro were co-expressed, cleavage products were observed in an Lpro dose-dependent manner while co-expression with a catalytically inactive Lpro mutant had no effect on LGP2 levels or pattern. We further show that Lpro localizes and immunoprecipitates with LGP2 in transfected cells supporting their interaction within the cytoplasm. Evidence of LGP2 proteolysis was also detected during FMDV infection. Moreover, the inhibitory effect of LGP2 overexpression on FMDV growth observed was reverted when Lpro was co-expressed, concomitant with lower levels of IFN-β mRNA and antiviral activity in those cells. The Lpro target site in LGP2 was identified as an RGRAR sequence in a conserved helicase motif whose replacement to EGEAE abrogated LGP2 cleavage by Lpro. Taken together, these data suggest that LGP2 cleavage by the Leader protease of aphthoviruses may represent a novel antagonistic mechanism for immune evasion.

Foot-and-mouth disease virus nonstructural protein 2B interacts with cyclophilin A, modulating virus replication.

Foot-and-mouth disease (FMD) is a highly contagious virus that affects cloven-hoofed animals. To understand better the role of nonstructural protein 2B of the causative agent FMD virus (FMDV) in the process of virus replication, we identified a porcine host protein, cyclophilin A (CypA), which interacts with FMDV 2B. The 2B-CypA interaction was confirmed by coimmunoprecipitation and GST pull-down assays. CypA showed antiviral functions during FMDV infection. Overexpression of CypA decreased FMDV leader protein (Lpro) and 3A at protein levels. CypA-induced reduction of Lpro enhanced the synthesis of host proteins and increased the integrality of host eukaryotic translation initiation factor (eIF)-4γ (eIF4G). The reduction of Lpro and 3A was dependent on the proteasome pathway. No interaction was identified between CypA and Lpro or 3A. However, CypA-induced reduction of Lpro and 3A was suppressed by 2B, and disruption of 2B-CypA interaction impaired this inhibitive effect induced by 2B. In summary, our findings identify the antiviral role of CypA against FMDV and provide key insights into how FMDV antagonizes host antiviral response by 2B protein.-Liu, H., Xue, Q., Cao, W., Yang, F., Ma, L., Liu, W., Zhang, K., Liu, X., Zhu, Z., Zheng, H. Foot-and-mouth disease virus nonstructural protein 2B interacts with cyclophilin A, modulating virus replication.

Foot-and-Mouth Disease Virus Counteracts on Internal Ribosome Entry Site Suppression by G3BP1 and Inhibits G3BP1-Mediated Stress Granule Assembly via Post-Translational Mechanisms.

Foot-and-mouth disease (FMD) is a highly contagious, severe viral illness notifiable to the World Organization for Animal Health. The causative agent, FMD virus (FMDV), replicates rapidly and efficiently inhibits host translation and the innate immune response for it has developed multiple tactics to evade host defenses and takes over gene expression machinery in the host cell. Here, we report a systemic analysis of the proteome and phosphoproteome of FMDV-infected cells. Bioinformatics analysis suggested that FMDV infection shuts off host cap-dependent translation, but leaves intact internal ribosome entry site (IRES)-mediated translation for viral proteins. Interestingly, several FMDV IRES-transacting factors, including G3BP stress granule assembly factor 1 (G3BP1), were dephosphorylated during FMDV infection. Ectopic expression of G3BP1 inhibited FMDV IRES activity, promoted assembly of stress granules, and activated innate immune responses, collectively suppressing FMDV replication. To counteract these host protective responses, FMDV-induced dephosphorylation of G3BP1, compromising its inhibitory effect on viral IRES. In addition, FMDV also proteolytically cleaved G3BP1 by its 3C protease (3Cpro). G3BP1 was cleaved at glutamic acid-284 (E284) by FMDV 3Cpro, and this cleavage completely lost the abilities of G3BP1 to activate innate immunity and to inhibit FMDV replication. Together, these data provide new insights into the post-translational mechanisms by which FMDV limits host stress and antiviral responses and indicate that G3BP1 dephosphorylation and its proteolysis by viral protease are important factors in the failure of host defense against FMDV infection.

Single-Cell Analysis of the Impact of Host Cell Heterogeneity on Infection with Foot-and-Mouth Disease Virus.

Viral infection and replication are affected by host cell heterogeneity, but the mechanisms underlying the effects remain unclear. Using single-cell analysis, we investigated the effects of host cell heterogeneity, including cell size, inclusion, and cell cycle, on foot-and-mouth disease virus (FMDV) infection (acute and persistent infections) and replication. We detected various viral genome replication levels in FMDV-infected cells. Large cells and cells with a high number of inclusions generated more viral RNA copies and viral protein and a higher proportion of infectious cells than other cells. Additionally, we found that the viral titer was 10- to 100-fold higher in cells in G2/M than those in other cell cycle phases and identified a strong correlation between cell size, inclusion, and cell cycle heterogeneity, which all affected the infection and replication of FMDV. Furthermore, we demonstrated that host cell heterogeneity influenced the adsorption of FMDV due to differences in the levels of FMDV integrin receptors expression. Collectively, these results further our understanding of the evolution of a virus in a single host cell.IMPORTANCE It is important to understand how host cell heterogeneity affects viral infection and replication. Using single-cell analysis, we found that viral genome replication levels exhibited dramatic variability in foot-and-mouth disease virus (FMDV)-infected cells. We also found a strong correlation between heterogeneity in cell size, inclusion number, and cell cycle status and that all of these characteristics affect the infection and replication of FMDV. Moreover, we found that host cell heterogeneity influenced the viral adsorption as differences in the levels of FMDV integrin receptors' expression. This study provided new ideas for the studies of correlation between FMDV infection mechanisms and host cells.

Host serum microRNA profiling during the early stage of foot-and-mouth disease virus infection.

Foot-and-mouth disease virus (FMDV) causes a highly contagious infection in cloven-hoofed animals, with many outbreaks in the developing world. MicroRNAs (miRNAs) are non-coding RNAs that regulate antiviral defence by post-transcriptional regulation of gene expression. In this study, the host miRNA response following FMDV infection was investigated in cattle, a natural host for FMDV. A significant alteration in serum miRNA expression was detected at early stages of infection. Compared to prior to infection, on day 2 postinfection (PI), 119 miRNAs were upregulated, of which 39 were significantly upregulated (P < 0.05). Gene target prediction and pathway enrichment analysis suggested that upregulated miRNAs target innate immune signalling pathways, suggesting a homeostasis effect, possibly to limit inappropriate immune responses. Further, for the significantly upregulated miRNAs, nine miRNA recognition elements were identified in the genome sequence of FMDV serotype O, which was used for infection. The antiviral effect of four of these miRNAs was confirmed in a cell culture system. These data demonstrate that changes in miRNA expression occur during early pathogenesis, and the identification of possible miRNA targets genes could help in elucidating molecular events involved in virus-host interaction and thus could be useful in developing therapeutic strategies.

Isolation and identification of bovine nasopharyngeal mucosal epithelial cells and establishment of cell models of acute infection by foot-and-mouth disease virus.

Foot-and-mouth disease (FMD) commonly occurs via the respiratory tract, and bovine nasopharyngeal mucosal epithelial cells are the primary infection cells in cattle. The aim of the present study was to isolate and culture epithelial cells from the bovine nasopharyngeal mucosa in vitro using a mechanical separation method. The cells were expanded, established in continuous cell culture, and used for immunofluorescence cytochemistry and establishment of infection models. We detected pan-cytokeratin markers of bovine nasopharyngeal mucosal epithelial cells by immunofluorescence. Bovine nasopharyngeal mucosal epithelial cells were then infected with foot-and-mouth disease virus (FMDV) serum type O. RT-PCR demonstrated the successful establishment of acute FMDV infection in the cell models. This infection model provides the basis for clarification of the interaction between FMDV and host bovine nasopharyngeal mucosal epithelial cells in vitro.

Evidence of subclinical foot-and-mouth disease virus infection in young calves born from clinically recovered cow under natural condition.

Foot-and-mouth disease (FMD) is a highly contagious and economically important, transboundary viral disease of cloven-hoofed animals. It is known that an asymptomatic, persistent FMD virus (FMDV) infection may occur subsequent to acute or subclinical FMDV infection in adult ruminants. However, virus persistence in young calves has not been studied. In the current investigation, FMDV infection parameters were examined for calves born to FMD-clinically recovered cows (CRC), asymptomatic cows from infected herds (ASC) and cows from with no history of FMD (NHF). The study was conducted in natural condition after FMD outbreaks in two dairy herds in India. No calves described herein had any clinical signs of FMD. Six out of 12 calves born to CRC had detectable FMDV RNA in oesophageal-pharyngeal fluid consistent with asymptomatic FMDV infection. Three of the 12 calves of CRC group had seroreactivity against FMDV non-structural proteins. One calf had detectable FMDV RNA at two consecutive samplings at 2months apart. However, infectious FMDV was not isolated from any calf in the study. None of the calves in the ASC or NHF groups had any evidence of FMDV infection. Overall, these data are consistent with earlier report on calves having been infected in utero. Further investigation of FMDV persistence in calves under controlled conditions may lead to greater understanding of the viral pathogenesis.

Interplay of foot and mouth disease virus with cell-mediated and humoral immunity of host.

Foot and mouth disease virus (FMDV) causes a communicable disease of cloven hoofed animals, resulting in major economic losses during disease outbreaks. Like other members of the Picornaviridae FMDV has a relatively short infectious cycle; initiation of infection and dissemination, with production of infectious virions occurs in less than a week. The components of innate immunity as well as cell-mediated and humoral immunity play a crucial role in control of FMDV. However, it has been shown in vitro using a mouse model that FMDV has evolved certain mechanisms to counteract host immune responses ensuring its survival and spread. The viral leader proteinase, L pro, deters interferon beta (IFN-β) mRNA synthesis, thus, inhibiting host cell translation. Another viral proteinase, 3C pro, disrupts host cell transcription by cleaving histone H3. A transient lymphopenia in swine as a consequence of FMDV infection has also been observed, but the mechanism involved and viral protein(s) associated with this process are not clearly understood. In this review, we have covered the interaction of FMDV with different immune cells including lymphocytes and antigen presenting cells and their consequences.

Foot-and-mouth disease virus infection stimulates innate immune signaling in the mouse macrophage RAW 264.7 cells.

The innate immune system acts as the first line of defense against invasion by bacterial and viral pathogens. The role of macrophages in innate immune responses to foot-and-mouth disease virus (FMDV) is poorly understood. To determine the mechanism underlying activation of innate immunity after FMDV infection in macrophages, we performed FMDV infection in mouse macrophage RAW 264.7 cells and found that FMDV serotype O infection induced a cytopathic effect. We then evaluated the gene expression profile in macrophage RAW 264.7 cells after FMDV infection using systematic microarray analysis. Gene ontology annotation and enrichment analysis revealed that FMDV promoted expression in a group of genes that are enriched in innate immune response and inflammatory response processes. Further research demonstrated that FMDV serotype O infection enhanced NF-κB, Toll-like, and RIG-I-like receptor signaling pathways and proteins expression and increased transcription and expression of a series of cytokines and interferons, as proved by qRT-PCR, Western blot, ELISA, and dual-luciferase reporter assay. Our study concluded that FMDV infection triggers the innate immune response in macrophages after activation of multiple innate immune pathway receptors and proteins by FMDV serotype O, resulting in activation and secretion of a series of cytokines and interferons.

Clearance of a persistent picornavirus infection is associated with enhanced pro-apoptotic and cellular immune responses

Long-term persistent viral infections cause substantial morbidity and associated economic losses in human and veterinary contexts. Yet, the mechanisms associated with establishment of persistent infections are poorly elucidated. We investigated immunomodulatory mechanisms associated with clearance versus persistence of foot-and-mouth disease virus (FMDV) in micro-dissected compartments of the bovine nasopharynx by microarray. The use of laser-capture microdissection allowed elucidation of differential gene regulation within distinct anatomic compartments critical to FMDV infection. Analysis of samples from transitional and persistent phases of infection demonstrated significant differences in transcriptome profiles of animals that cleared infection versus those that became persistently infected carriers. Specifically, it was demonstrated that clearance of FMDV from the nasopharyngeal mucosa was associated with upregulation of targets associated with activation of T cell-mediated immunity. Contrastingly, gene regulation in FMDV carriers suggested inhibition of T cell activation and promotion of Th2 polarization. These findings were corroborated by immunofluorescence microscopy which demonstrated relative abundance of CD8+ T cells in the nasopharyngeal mucosa in association with clearance of FMDV. The findings presented herein emphasize that a critical balance between Th1 and Th2 -mediated immunity is essential for successful clearance of FMDV infection and should be considered for development of next-generation vaccines and antiviral products.

EEF1G interaction with foot-and-mouth disease virus nonstructural protein 2B: Identification by yeast two-hybrid system

Foot-and-mouth disease virus (FMDV) is a picornavirus that causes an economically significant disease in cattle and swine. Replication of FMDV is dependent on both viral proteins and cellular factors. Nonstructural protein 2B of FMDV plays multiple roles during viral infection and replication. We investigated the roles of 2B in virus–host interactions by constructing a cDNA library obtained from FMDV-infected swine tissues, and used a split-ubiquitin-based yeast two-hybrid system to identify host proteins that interacted with 2B. We found that 2B interacted with amino acids 208–437 in the C-terminal region of the eEF1G subunit of eukaryotic elongation factor 1, which is essential for protein synthesis. The 2B–eEF1G interaction was confirmed by co-immunoprecipitation of 2B and eEF1G in HEK293T cells. Collectively, our results suggest that eEF1G interacts with the 2B protein of FMDV. The identified 2B interaction partner may help to elucidate the mechanisms of FMDV infection and replication.

G3BP1 interacts directly with the FMDV IRES and negatively regulates translation.

RNA-protein interactions play a pivotal role in the function of picornavirus internal ribosome entry site (IRES) elements. Here we analysed the impact of Ras GTPase SH3 domain binding protein 1 (G3BP1) in the IRES activity of foot-and-mouth disease virus (FMDV). We found that G3BP1 interacts directly with three distinct sequences of the IRES element using RNA electrophoretic mobility-shift assays. Analysis of the interaction with domain 5 indicated that the G3BP1 binding-site is placed at the single-stranded region although it allows large sequence heterogeneity and the hairpin located upstream of this region enhances retarded complex formation. In addition, G3BP1 interacts directly with the polypyrimidine tract-binding protein and the translation initiation factor 4B (eIF4B) through the C-terminal region. Moreover, G3BP1 is cleaved during FMDV infection yielding two fragments, Ct-G3BP1 and Nt-G3BP1. Both fragments inhibit cap- and IRES-dependent translation, but the Ct-G3BP1 fragment shows a stronger effect on IRES-dependent translation. Assembly of complexes with G3BP1 results in a significantly reduced local flexibility of the IRES element, consistent with the negative effect of this protein. Our results highlight the IRES-binding capacity of G3BP1 and illustrate its function as a translation inhibitor.

Lithium chloride inhibits early stages of foot-and-mouth disease virus (FMDV) replication in vitro.

Foot‐and‐mouth disease virus (FMDV) causes an economically important and highly contagious disease of cloven‐hoofed animals such as cattle, swine, and sheep. FMD vaccine is the traditional way to protect against the disease, which can greatly reduce its occurrence. However, the use of FMD vaccines to protect early infection is limited. Therefore, the alternative strategy of applying antiviral agents is required to control the spread of FMDV in outbreak situations. As previously reported, LiCl has obviously inhibition effects on a variety of viruses such as transmissible gastroenteritis virus (TGEV), infectious bronchitis coronavirus (IBV), and pseudorabies herpesvirus and EV‐A71 virus. In this study, our findings were the first to demonstrate that LiCl inhibition of the FMDV replication. In this study, BHK‐21 cell was dose‐dependent with LiCl at various stages of FMDV. Virus titration assay was calculated by the 50% tissue culture infected dose (TCID50) with the Reed and Muench method. The cytotoxicity assay of LiCl was performed by the CCK8 kit. The expression level of viral mRNA was measured by RT‐qPCR. The results revealed LiCl can inhibit FMDV replication, but it cannot affect FMDV attachment stage and entry stage in the course of FMDV life cycle. Further studies confirmed that the LiCl affect the replication stage of FMDV, especially the early stages of FMDV replication. So LiCl has potential as an effective anti‐FMDV drug. Therefore, LiCl may be an effective drug for the control of FMDV. Based on that, the mechanism of the antiviral effect of LiCl on FMDV infection is need to in‐depth research in vivo.

Chemiluminescence Immunoassay for the Detection of Antibodies against the 2C and 3ABC Nonstructural Proteins Induced by Infecting Pigs with Foot-and-Mouth Disease Virus.

The potential diagnostic value of chemiluminescence immunoassays (CLIAs) has been accepted in recent years, although their use for foot-and-mouth disease (FMD) diagnostics has not been reported. Full-length 3ABC and 2C proteins were expressed in bacteria and purified by affinity chromatography to develop a rapid and accurate approach to distinguish pigs infected with foot-and-mouth disease virus (FMDV) from vaccinated pigs. The recombinant proteins were then used as antigens to develop two CLIAs for the detection of antibodies against nonstructural viral proteins. The diagnostic performance of the two assays was compared by analyzing serum from pigs (naive pigs, n = 63; vaccinated, uninfected pigs, n = 532; naive, infected pigs, n = 117) with a known infection status. The 3ABC-2C CLIA had a higher accuracy rate, with a diagnostic sensitivity of 100% and a diagnostic specificity of 96.5%, than the 3ABC CLIA, which had a diagnostic sensitivity of 95.7% and a diagnostic specificity of 96.0%. The results of the 3ABC-2C CLIA also had a high rate of concordance with those of two commercial FMDV enzyme-linked immunosorbent assay (ELISA) kits used to assess serum collected from 962 pigs in the field (96.2% and 97.8%, respectively). The 3ABC-2C CLIA detected infection in serum samples from infected pigs earlier than the commercial ELISA kits. In addition, the 3ABC-2C CLIA produced results within 15 min. On the basis of these findings, the 3ABC-2C CLIA could serve as the foundation for the development of penside FMD diagnostics and offers an alternative method to detect FMDV infections.

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.

Molecular Mechanisms of Foot-and-Mouth Disease Virus Targeting the Host Antiviral Response.

Foot-and-mouth disease virus (FMDV) is the causative agent of an acute vesicular disease affecting pigs, cattle and other domestic, and wild animals worldwide. The aim of the host interferon (IFN) response is to limit viral replication and spread. Detection of the viral genome and products by specialized cellular sensors initiates a signaling cascade that leads to a rapid antiviral response involving the secretion of type I- and type III-IFNs and other antiviral cytokines with antiproliferative and immunomodulatory functions. During co-evolution with their hosts, viruses have acquired strategies to actively counteract host antiviral responses and the balance between innate response and viral antagonism may determine the outcome of disease and pathogenesis. FMDV proteases Lpro and 3C have been found to antagonize the host IFN response by a repertoire of mechanisms. Moreover, the putative role of other viral proteins in IFN antagonism is being recently unveiled, uncovering sophisticated immune evasion strategies different to those reported to date for other members of the Picornaviridae family. Here, we review the interplay between antiviral responses induced by FMDV infection and viral countermeasures to block them. Research on strategies used by viruses to modulate immunity will provide insights into the function of host pathways involved in defense against pathogens and will also lead to development of new therapeutic strategies to fight virus infections.