Extensive antigenic and genetic variation among foot-and-mouth disease type A viruses isolated from the 1994 and 1995 foci in São Paulo, Brazil

Immunogenicity analysis of the E. coli expressed structural protein VP1 of persistent infection foot-and-mouth disease virus

The persistent infection of FMDV in cloven hoofed animals has made the epidemic prevention and control more difficult. VP1 is the main immunogenic protein and first candidate of vaccine development for FMDV prevention. However, the mutation of VP1 in host cell with persistent infection FMDV (PI-FMDV) caused the change of its immunogenicity. Hence, it is imperative to establish the expression system for VP1 of PI-FMDV (PI-VP1) and re-evaluate its immunogenicity. In this study, the PI-VP1 with His-tag was cloned into pET-28a vector. PI-VP1 protein was expressed and purified in E. coli, and further the antiserum of immunized mice was analyzed. Results showed that purified PI-VP1 protein produced a good humoral and cellular immune response after immunizing mice. Furthermore, our study showed that the antiserum could not only neutralize PI-FMDV, but also prevent the adsorption of WT-FMDV. In summarize, our work provides valuable implications for the FMDV vaccines and therapeutics development.

Silencing of the foot-and-mouth disease virus internal ribosomal entry site by targeting relatively conserved region among serotypes

Foot-and-mouth disease (FMD) is a host-restricted disease of cloven-hoofed animals, such as cattle and pigs. There are seven major serotypes of FMD virus that exhibit high antigenic variation, making vaccine strain selection difficult. However, there is an internal ribosomal entry site (IRES) element within the 5′ untranslated region of the FMD virus (FMDV) RNA genome that is relatively conserved among FMDV serotypes and could be used as a pan-serotype target for disease interventions. To determine the potential for targeting the IRES as promising drug target, we designed a short interfering RNA (siRNA) targeting a relatively conserved region in the FMDV-IRES. The siRNA affected FMDV-IRES expression but not the expression of the encephalomyocarditis virus or hepatitis C virus IRES. To evaluate the effects of siRNA-mediated silencing, we established cell lines expressing a bicistronic luciferase reporter plasmid, which contained an FMDV-IRES element between the Renilla and firefly luciferase genes. The designed siRNA inhibited FMDV-IRES-mediated translation in a concentration-dependent manner. In order to sustain this inhibitory effect, we designed a short hairpin RNA (shRNA)-expressing lentiviral vector. The results showed that the lenti-shRNA vector significantly suppressed FMDV-IRES activity for up to 2 weeks in cell culture. Thus, our findings in this study provided a basis for the development of effective pan-serotype FMDV inhibitors.

Unravelling Selection Shifts among Foot-and-Mouth Disease virus (FMDV) Serotypes

FMDV virus has been increasingly recognised as the most economically severe animal virus with a remarkable degree of antigenic diversity. Using an integrative evolutionary and computational approach we have compelling evidence for heterogeneity in the selection forces shaping the evolution of the seven different FMDV serotypes. Our results show that positive Darwinian selection has governed the evolution of the major antigenic regions of serotypes A, Asia1, O, SAT1 and SAT2, but not C or SAT3. Co-evolution between sites from antigenic regions under positive selection pinpoints their functional communication to generate immune-escape mutants while maintaining their ability to recognise the host-cell receptors. Neural network and functional divergence analyses strongly point to selection shifts between the different serotypes. Our results suggest that, unlike African FMDV serotypes, serotypes with wide geographical distribution have accumulated compensatory mutations as a strategy to ameliorate the effect of slightly deleterious mutations fixed by genetic drift. This strategy may have provided the virus by a flexibility to generate immune-escape mutants and yet recognise host-cell receptors. African serotypes presented no evidence for compensatory mutations. Our results support heterogeneous selective constraints affecting the different serotypes. This points to the possible accelerated rates of evolution diverging serotypes sharing geographical locations as to ameliorate the competition for the host.

FMD virus isolates: the candidate strains for polyvalent vaccine development in Ethiopia

The study was conducted on foot-and-mouth disease (FMD) viruses with the aim of selecting appropriate vaccinal strain to control of FMD in Ethiopia. The study was conducted in two-dimensional virus neutralization assay to determine the antigenic relationship 'r' value between the candidate vaccine strains and field isolates. A total of 21 serotype O, 7 serotype A, and 8 serotype SAT 2 FMD viruses, which were isolated from cattle and swine. A couple of isolates from each serotype were identified as vaccine candidates in the trial (O-ETH/38/2005, O-ETH/58/2008, A-ETH/7/2008, A-ETH/6/2000, SAT2-ETH/76/2009 and SAT2-ETH/64/2009). The finding revealed all the vaccine candidate depicted high antigenic similarity, above the mean "r" value, to their own serotypes in the studied serotype population except for one serotype A field isolate, A-ETH/13/1981, with "r" value=0.14 and 0.25) which is significantly lower than the minimum requirement. In general, the result indicated that these candidate vaccinal strains can be used for polyvalent vaccine production in the country.

Molecular characterization of amino acid deletion in VP1 (1D) protein and novel amino acid substitutions in 3D polymerase protein of foot and mouth disease virus subtype A/Iran87

The nucleotide sequence of the VP1 (1D) and partial 3D polymerase (3D^pol) coding regions of the foot and mouth disease virus (FMDV) vaccine strain A/Iran87, a highly passaged isolate (~150 passages), was determined and aligned with previously published FMDV serotype A sequences. Overall analysis of the amino acid substitutions revealed that the partial 3D^pol coding region contained four amino acid alterations. Amino acid sequence comparison of the VP1 coding region of the field isolates revealed deletions in the highly passaged Iranian isolate (A/Iran87). The prominent G-H loop of the FMDV VP1 protein contains the conserved arginine-glycine-aspartic acid (RGD) tripeptide, which is a well-known ligand for a specific cell surface integrin. Despite losing the RGD sequence of the VP1 protein and an Asp₂₆→Glu substitution in a beta sheet located within a small groove of the 3D^pol protein, the virus grew in BHK 21 suspension cell cultures. Since this strain has been used as a vaccine strain, it may be inferred that the RGD deletion has no critical role in virus attachment to the cell during the initiation of infection. It is probable that this FMDV subtype can utilize other pathways for cell attachment.

Foot-and-mouth disease in pigs: current epidemiological situation and control methods

Foot-and-mouth disease (FMD) is the paradigm of a transboundary animal disease. Beyond any doubt, it is the most serious challenge for livestock's health. Official Veterinary Services from free countries invest considerable amount of money to prevent its introduction, whereas those from endemic countries invest most of their resources in the control of the disease. A very important volume of scientific production is developed every year in different aspects of FMD, and for that reason, the current knowledge makes the diagnosis of the disease easier to a great extent. However, FMD is still endemic in about two-thirds of the countries, and periodically re-emergent in several countries. This paper is a review of recent publications, focusing mainly on control measures and current world epidemiological situation, emphasizing primarily pigs.

Sequence and phylogenetic analysis of the non-structural 3A and 3B protein-coding regions of foot-and-mouth disease virus subtype A Iran 05

The A Iran 05 foot-and-mouth disease virus (FMDV) subtype was detected in Iran during 2005 and has proven to be highly virulent. This study was undertaken to focus on molecular and phylogenetic analysis of 3A and 3B coding-regions in the A Iran 05 field isolate. To assess the genetic relatedness of A Iran 05 isolate the nucleotide and predicted amino acid sequences of the 3AB region of type A FMDV isolates were compared with twenty previously described type A FMDV isolates. The phylogenetic tree based on the 672 bp 3AB gene sequences of type A FMDV from thirteen different locations clustered them into five distinct lineages. The A Iran 05 isolate clustered in lineage A along with four type A variants and was closely matched with viruses isolated in Turkey and Pakistan during 2005~2006. The number of protein sequence differences exhibited by each of the isolates revealed that A Iran 05 isolate contains three amino acid substitutions at positions 47 and 119 of 3A and 27 of the 3B coding region. The nucleotide identity between A Iran 05 and the other four isolates of lineage A was estimated to be 98%.

Genetic analysis of foot-and-mouth disease virus serotype A of Indian origin and detection of positive selection and recombination in leader protease-and capsid-coding regions

The leader protease (L pro) and capsid-coding sequences (P1) constitute approximately 3 kb of the foot-and-mouth disease virus (FMDV). We studied the phylogenetic relationship of 46 FMDV serotype A isolates of Indian origin collected during the period 1968-2005 and also eight vaccine strains using the neighbour-joining tree and Bayesian tree methods. The viruses were categorized under three major groups -Asian, Euro-South American and European. The Indian isolates formed a distinct genetic group among the Asian isolates. The Indian isolates were further classi?ed into different genetic subgroups (<5% divergence).Post-1995 isolates were divided into two subgroups while a few isolates which originated in the year 2005 from Andhra Pradesh formed a separate group. These isolates were closely related to the isolates of the 1970s. The FMDV isolates seem to undergo reverse mutation or convergent evolution wherein sequences identical to the ancestors are present in the isolates in circulation. The eight vaccine strains included in the study were not related to each other and belonged to different genetic groups. Recombination was detected in the L pro region in one isolate (A IND 20/82) and in the VP1 coding 1D region in another isolate (A RAJ 21/96). Positive selection was identi?ed at aa positions 23 in the L pro (P < 0.05; 0.046*) and at aa 171 in the capsid protein VP1 (P < 0.01; 0.003**).

Protection of guinea pigs and swine by a recombinant adenovirus expressing O serotype of foot-and-mouth disease virus whole capsid and 3C protease

Two recombinant adenoviruses were constructed expressing foot-and-mouth disease virus (FMDV) capsid and 3C/3CD proteins in replicative deficient human adenovirus type 5 vector. Guinea pigs vaccinated with 1-3 x 10(8)TCID(50) Ad-P12x3C recombinant adenovirus were completely protected against 10,000GID(50) homologous virulent FMDV challenge 25 days post vaccination (dpv). Ad-P12x3CD vaccinated guinea pigs were only partially protected. Swine were vaccinated once with 1x10(9)TCID(50) Ad-P12x3C hybrid virus and challenged 28 days later. Three of four vaccinated swine were completely protected against 200 pig 50% infectious doses (ID(50)) of homologous FMDV challenge, and vaccinated pigs developed specific cellular and humoral immune responses. The immune effect of Ad-P12x3C in swine further indicated that the recombinant adenovirus was highly efficient in transferring the foreign gene. This approach may thus be a very hopeful tool for developing FMD live virus vector vaccine.

Molecular epidemiology of foot-and-mouth disease virus types A and O isolated in Argentina during the 2000–2002 epizootic

During 2000-2002 a foot-and-mouth disease (FMD) epizootic affected Argentina and spread across the country resulting in more than 2500 outbreaks. In order to study the evolution of the FMD viruses (FMDV) and help with disease control measures, a genetic characterization and phylogenetic analysis was performed of 43 field isolates representative of the epizootic. The nucleotide sequence of the VP1-coding region was determined for the viruses and used in this study. Two serotype A lineages, A/Arg/00 and A/Arg/01 (1000/1000 bootstrap value) and two different serotype O/Arg/00 lineages (848/1000 bootstrap value) were identified. Phylogenetic analysis showed that viruses A/Arg/01 and O/Arg/00 could be related with former South American isolates, while the origin of A Argentina 2000 viruses remains unclear. Comparison of the amino acid sequences with vaccine reference strains revealed differences at critical antigenic sites for emergent strains A/Arg/00 and A/Arg/01, leading to a change in the current vaccine formulation.

Phylogenetic analysis of foot-and-mouth disease virus type O re-emerging in free areas of South America

The nucleotide sequences of the complete VP(1)-coding region of foot-and-mouth disease viruses (FMDV), type O, isolated during the recent emergencies of the disease in free areas of South America (Mato Grosso do Sul, Brazil, October 2005, and Corrientes, Argentina, February 2006), were determined. Also established were the complete VP(1)-coding sequences of viruses occurring in neighbouring locations between the years 2000 and 2003. A phylogenetic analysis was performed based on comparison with continental relevant field and vaccine strains, as well as with extra-continental representative viruses. The results show that the emergencies in Argentina and Brazil were caused by viruses presenting 93% genetic relatedness. Both variants are endogenous to South America, as they were placed within the Europe-South America topotype. When compared with the continental viruses available for the phylogenetic studies, they show the closest relationship with viruses responsible for previous emergencies in neighbouring free areas, or for sporadic outbreaks in the adjacent places with advanced eradication stages, presenting similarity values of at least 90% among them, and clustering together in a unique lineage. This lineage represents the only one sporadically appearing in the Southern Cone and differs from those including viruses presently circulating in the Andean region, reflecting the different livestock circuits and epidemiological scenarios.

Reintroduction of foot-and-mouth disease in Argentina: characterisation of the isolates and development of tools for the control and eradication of the disease

This paper describes the antigenic and molecular characterisation of foot-and-mouth disease virus (FMDV) strains isolated during the 2000-2002 epidemic in Argentina, and the strategy implemented for disease control. Two different FMDV serotypes, O and A, were involved. Of the various field isolates studied, two distinct O1 lineages (strains Corrientes/00 and Misiones/00) and two serotype A lineages (A/Argentina/00 and A/Argentina/01 prototypes) were identified. The genome sequences of these strains were compared with sequences of previous regional isolates and sequences of vaccine strains. O1 strains were found to be related to regional strains while serotype A strains were found to be more distanced from them. The updating of the antigenic composition of the vaccines used in the emergency was a key issue, since the outbreaks stopped shortly after the implementation of the vaccination programs. The O1 strains quickly disappeared from the field following strict control measures and the use of vaccines containing O1/Campos strain. However, in the case of the A serotype strains, the situation was different, since the use of a vaccine containing strain A24/Cruzeiro yielded acceptable levels of protection only after re-vaccination. Therefore, the new field strains A/Argentina/00 and A/Argentina/01 were incorporated into the vaccine, leading to an effective control of the disease. Viral circulation greatly diminished, as indicated by the significant reduction in the number of outbreaks and in the number of animals with antibodies against non-structural proteins. Satisfactory levels of protective antibodies were subsequently detected in the cattle population (above 75% protection). The absence of outbreaks after January 2002 indicated that the epidemic was controlled.

Foot-and-mouth disease

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. The disease was initially described in the 16th century and was the first animal pathogen identified as a virus. Recent FMD outbreaks in developed countries and their significant economic impact have increased the concern of governments worldwide. This review describes the reemergence of FMD in developed countries that had been disease free for many years and the effect that this has had on disease control strategies. The etiologic agent, FMD virus (FMDV), a member of the Picornaviridae family, is examined in detail at the genetic, structural, and biochemical levels and in terms of its antigenic diversity. The virus replication cycle, including virus-receptor interactions as well as unique aspects of virus translation and shutoff of host macromolecular synthesis, is discussed. This information has been the basis for the development of improved protocols to rapidly identify disease outbreaks, to differentiate vaccinated from infected animals, and to begin to identify and test novel vaccine candidates. Furthermore, this knowledge, coupled with the ability to manipulate FMDV genomes at the molecular level, has provided the framework for examination of disease pathogenesis and the development of a more complete understanding of the virus and host factors involved.

Molecular epidemiology of SAT3-type foot-and-mouth disease

VP1 gene nucleotide sequences of 51 SAT3-type foot-and-mouth disease (FMD) viruses from seven southern and eastern African countries were used to infer a gene phylogeny. Results obtained by phylogenetic analysis of the homologous 405 nt region corresponding to the C-terminal 128 amino acids of 1D and adjacent 7 amino acids of 2A indicate that there are six distinct virus lineages evolving independently in different geographical localities in accordance with the FMD topotype concept. Topotypes I-IV occur in southern Africa, whilst topotypes V and VI are unique to East Africa. Viruses of different topotypes differ from each other at 20% or more of the nucleotide sites, specified in this study. Despite the limited geographical distribution of this serotype, the level of intratypic variation is intermediate between that of SAT1 and SAT2, both of which are widely distributed in sub-Saharan Africa. Within SAT3, 37.3% and 47.4% of sites were completely conserved on nucleotide and amino acid levels, respectively. The locality-specific grouping of viruses permits accurate determination of the sources of outbreaks, whilst the high levels of variation within the immunodominant 1D protein has implications for the control of the disease through vaccination.

The implications of virus diversity within the SAT 2 serotype for control of foot-and-mouth disease in sub-Saharan Africa

SAT 2 is the serotype most often associated with outbreaks of foot-and-mouth disease (FMD) in livestock in southern and western Africa and is the only SAT type to have been recorded outside the African continent in the last decade. Its epidemiology is complicated by the presence of African buffalo (Syncerus caffer), which play an important role in virus maintenance and transmission. To assess the level of genetic complexity of this serotype among viruses associated with both domestic livestock and wildlife, complete VP1 gene sequences of 53 viruses from 17 countries and three different host species were analysed. Phylogenetic analysis revealed eleven virus lineages, differing from each other by at least 20 % in pairwise nucleotide comparisons, four of which fall within the southern African region, two in West Africa and the remaining five in central and East Africa. No evidence of recombination between these lineages was detected, and thus we conclude that these are independently evolving virus lineages which occur primarily in discrete geographical localities in accordance with the FMD virus topotype concept. Applied to the whole phylogeny, rates of nucleotide substitution are significantly different between topotypes, but most individual topotypes evolve in accordance with a molecular clock at an average rate of approximately 0.002 substitutions per site per year. This study provides an indication of the intratypic complexity of the SAT 2 serotype at the continental level and emphasizes the value of molecular characterization of diverse FMD field strains for tracing the origin of outbreaks.

Molecular epidemiology of foot-and-mouth disease virus

Foot-and-mouth disease (FMD) is the most economically important veterinary pathogen due to its highly infectious nature, ability to cause persistent infections and long term effects on the condition and productivity of the many animal species it affects. Countries which have the disease have many trade restrictions placed upon them. In the last 15 years there have been significant advances in the understanding of FMD epidemiology. These have largely been due to the application of the molecular biological techniques of polymerase chain-reaction amplification and nucleotide sequencing. In the World Reference Laboratory for FMD (Pirbright, UK), a large sequence database has been built up. This database has been used to aid in the global tracing of virus movements. It has been possible to genetically group many FMDV's based on their geographic origin and this has led to their being referred to as topotypes. The implications of this are that inter-regional spread of viruses can often be easily recognised and any evolutionary changes which subsequently occur can be monitored. Using these techniques, for the first time, we have been able to unequivocally show the recent pandemic spread of a FMDV type O strain through the whole of Asia and into Africa and Europe. This type of surveillance will become increasingly important as further globalisation of markets occurs. An increased understanding of how FMDV strains move between geographic regions will play a pivotal role in the development of future disease control strategies.