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.

Selection of foot and mouth disease vaccine strains--a review

The choice of the most appropriate strains of foot and mouth disease (FMD) virus vaccines to use in FMD control programmes and to store in vaccine antigen reserves is based on the matching of representative field isolates from outbreaks around the world to available vaccine strains. However, those involved in FMD control at a national level do not always give this work a high priority, while in countries without effective control of FMD there is little incentive to collect samples or to overcome the constraints on submission to international reference laboratories. In the short term, specific initiatives for targeted collection can provide samples on a periodic basis, but a long-term solution requires the development of FMD control measures. This must be underpinned by the strengthening of local Veterinary Services and laboratories, and by demand-driven provision of sufficient amounts of high-quality vaccine. Difficulties may be increased by commercial constraints on disclosure of the strains used for vaccine production and on the supply of reagents needed for matching tests. Vaccine matching tests are mainly based on in vitro methods - such as virus neutralisation, enzyme-linked immunosorbent assay with polyclonal antibodies and complement fixation - and are performed in a relatively small number of laboratories around the world. In addition to the difficulties of gathering representative field and vaccine strains, neither the reagents nor the methods used for vaccine matching are fully harmonised. Consequently, there is no strict equivalence in the results obtained. Alternative approaches using monoclonal antibody panels and/or viral capsid gene sequencing are being developed and could complement the currently employed serological tests. However, there is limited in vivo cross-protection information, more of which is essential for future validation of the vaccine matching methods. In response to the funding and leadership deficit for vaccine strain selection, a network of World Organisation for Animal Health (OIE) and Food and Agriculture Organization FMD reference laboratories has been established; this gives these laboratories the potential to strengthen the coordination of their work and reporting and thereby improve recommendations on vaccine strain selection.

A global virtual network for foot-and-mouth disease in case of emergency

The use of emergency vaccination is considered in different contingency national plans as part of a foot-and-mouth disease (FMD) control strategy in countries whether vaccination is practised or not. The development of the inter-governmental and national FMD vaccine and antigen banks and some technical and operational problems that could affect their efficiency are analysed. The possibility of improving and implementing a more rational use of the antigen and vaccine banks through the creation of a Global Virtual Network of Vaccine and Antigen Banks is discussed.

Full length nucleotide sequence of foot-and-mouth disease virus strain O1 Campos/Bra/58. Brief report

The complete nucleotide sequence of foot-and-mouth disease virus (FMDV) South American strain O(1) Campos/Bra/58 was determined. The 8,168 Kb sequence and the deduced amino acid sequence were compared to published FMDV sequences. They showed the highest sequence homology with the O(1) Kaufbeuren/FRG/66 strain, but closer evolutionary relatedness to the Argentinean strains.

Phylogenetic analysis of foot-and-mouth disease viruses isolated in Argentina

We have analysed complete or partial VPI sequences of 31 foot-and-mouth disease (FMD) viruses belonging to serotypes A, O and C to determine the genetic relatedness of field strains of FMD virus (FMDV) that have circulated in Argentina between 1961 and 1994. Phylogenetic analysis, which also included 15 previously published Argentinean sequences and six reference strains, revealed that (i) FMD type A strains showed the highest genetic heterogeneity and could be divided into five lineages with a sequence divergence of 0.9-18.5% between strains (ii) most of the FMD type O viruses grouped in two clusters (within cluster sequence divergence ranging from 0.2% to 6.0%) circulating in Argentina since the early 1960s, and (iii) FMD type C viruses were grouped in two clusters with a 13.4% nucleotide sequence divergence between each cluster. The availability of sequence data for many more field isolates from the region will enable us to understand the genetic relationships between FMDV strains and to rapidly trace the source of an FMD outbreak for epidemiological surveillance.

[Molecular characterization of aphthous fever virus isolated during the years 1993-1994 in Argentina]

Nucleotide sequence and phylogenetic analysis of the VP1 structural protein have been used extensively as diagnostic and epidemiological tools for foot and mouth disease virus (FMDV). In this report we have applied this methodology to the analysis of the VP1 coding sequence from FMDV strains isolated in Argentina during 1993-1994. The results demonstrated that the field isolates were related to the vaccine strains used at that time. However the involvement of the vaccine virus appeared to be different for outbreaks caused by FMD viruses type O or C. These data provide a database essential for determining the origin of new epizootics.

Presentation of antigenic sites from foot-and-mouth disease virus on the surface of baculovirus and in the membrane of infected cells

We describe the construction of recombinant baculoviruses displaying on their surface and in the membrane of infected cells the small, immunodominant antigenic site (site A) or the large polyprotein (P1) coding for the four structural proteins of foot-and-mouth disease virus (FMDV). The coding sequences were inserted in the amino-terminus of gp64, the major glycoprotein of the baculovirus Autographa californica nuclear polyhedrosis virus (AcNPV). Following infection of insect cells with the recombinant baculoviruses, the cellular localization of the chimaeric proteins as well as their presence in the surface of extracellular viruses was assessed by immunofluorescence microscopy and Western blot. The antigenicity of the recombinant viruses was studied by competitive ELISAs, which showed that although both recombinant viruses were able to compete with FMDV-specific monoclonal antibodies (MAbs), their patterns of reactivity were different. The results suggest that this eukaryotic display system could be an alternative method of presentation of foreign antigens in a multimeric form as a new approach to biosynthetic vaccines.

[Expression and characterization of 2 bovine viral diarrhea virus structural proteins (]BVDV)]

The BVDV glycoproteins gp48 and gp53 were expressed in the baculovirus eukaryotic system. Both recombinant proteins were recognized in western blot analysis by monoclonal antibodies and polyclonal serum. Immunofluorescent test demonstrated that gp53 was localized on the cell surface whereas gp48 was in the cytoplasm. The expressed proteins were extracted by non-denaturing detergent treatment. Rabbit antiserum raised against gp53 recombinant protein efficiently neutralized the virus. These results demonstrate that the recombinant proteins have immunological properties similar to those of the native viral protein and that they can be useful as diagnostic reagents.

Identification of optimal regions for phylogenetic studies on VP1 gene of foot-and-mouth disease virus: analysis of types A and O Argentinean viruses

An analysis of the informative content of sequence stretches on the foot-and-mouth disease virus (FMDV) VPI gene was applied to two important viral serotypes: A and O. Several sequence regions were identified to allow the reconstruction of phylogenetic trees equivalent to those derived from the whole VPI gene. The optimal informative regions for sequence windows of 150 to 250 nt were predicted between positions 250 and 550 of the gene. The sequences spanning the 250 nt of the 3' end (positions 400 to 650), extensively used for FMDV phylogenetic analyses, showed a lower informative content. In spite of this, the use of sequences from this region allowed the derivation of phylogenetic trees for type A and type O FMDVs which showed topologies similar to those previously reported for the whole VP1 gene. When the sequences determined for viruses isolated in Argentina, between 1990 and 1993, were included in these analyses, the results obtained revealed features of the circulation of type A and type O viruses in the field, in the months that preceded the eradication of the disease in this country. Type A viruses were closely related to an Argentinean vaccine strain, and defined an independent cluster within this serotype. Among the type O viruses analysed, two groups were distinguished; one was closely related to the South American vaccine strains, while the other was grouped with viruses of the O3 subtype. In addition, a detailed phylogeny for type A FMDV is presented.

Association of bovine DRB3 alleles with immune response to FMDV peptides and protection against viral challenge

We have analysed the influence of bovine MHC (BoLA) polymorphism on the immune response and degree of protection induced by peptide vaccines against foot-and-mouth disease (FMD) in cattle. The peptides used for animal immunisation were: A (VP1(138-156)), AT (peptide A linked to VP1(21-40)) and ACT (peptide A, linked to VP1(196-209) and VP1(21-40)). Sixteen different DRB3 types were found among the 46 cattle analysed by PCR-RFLP typing. No absolute correlation was observed, for any type, with the serum neutralising titres (SNT) values and the protection induced. However, among the most common haplotypes present, associations were observed between expression of different types with the levels of SNT and/or protection induced by peptides A and ACT. Thus, types DRB3.2*1, 3 and 7 were associated with increased levels of protection. In contrast, types DRB3.2*12 and 18 were associated non-protection, and DRB3.2*12 was also associated with low SNT titres. Overall, the results indicate that the polymorphism in BoLA class II molecules affects both the immune response and protection induced by potential FMD peptide vaccines.

Nucleotide sequence of the P1 region of foot-and-mouth disease virus strain O1 Caseros

It has been shown that variation of antigenic site I in VP1 of foot-and-mouth disease virus (FMDV) plays an important role in the antigenic diversification of this virus. However, the O1 Campos strain is able to efficiently cross-protect cattle against the O1 Caseros strain, despite having a different sequence in the site I. In this paper we report and compare the P1 coding region for the capsid proteins of FMDV O1 Caseros and O1 Campos. The deduced amino acid sequence showed a total of 31 amino acid differences. Eight of them are located in surface-exposed loops that have been implicated in antigenic sites. This study should help to identify additional sites to be considered in the development of a new generation of FMDV vaccines.

A large-scale evaluation of peptide vaccines against foot-and-mouth disease: lack of solid protection in cattle and isolation of escape mutants

A large-scale vaccination experiment involving a total of 138 cattle was carried out to evaluate the potential of synthetic peptides as vaccines against foot-and-mouth disease. Four types of peptides representing sequences of foot-and-mouth disease virus (FMDV) C3 Argentina 85 were tested: A, which includes the G-H loop of capsid protein VP1 (site A); AT, in which a T-cell epitope has been added to site A; AC, composed of site A and the carboxy-terminal region of VP1 (site C); and ACT, in which the three previous capsid motifs are colinearly represented. Induction of neutralizing antibodies, lymphoproliferation in response to viral antigens, and protection against challenge with homologous infectious virus were examined. None of the tested peptides, at several doses and vaccination schedules, afforded protection above 40%. Protection showed limited correlation with serum neutralization activity and lymphoproliferation in response to whole virus. In 12 of 29 lesions from vaccinated cattle that were challenged with homologous virus, mutant FMDVs with amino acid substitutions at antigenic site A were identified. This finding suggests the rapid generation and selection of FMDV antigenic variants in vivo. In contrast with previous studies, this large-scale vaccination experiment with an important FMDV host reveals considerable difficulties for vaccines based on synthetic peptides to achieve the required levels of efficacy. Possible modifications of the vaccine formulations to increase protective activity are discussed.

Emerging foot-and-mouth disease virus variants with antigenically critical amino acid substitutions predicted by model studies using reference viruses

One of the major obstacles to the design of effective antiviral vaccines is the frequent generation of antigenic viral variants in the field. The types of variants that will become dominant during disease outbreaks is often unpredictable. However, here we report the genetic and antigenic characterization of emerging foot-and-mouth disease virus (FMDV) variants with antigenically critical amino acid substitutions predicted by model studies using reference viruses and monoclonal antibodies. The new variants belong to serotype C and have caused a number of recent disease outbreaks in Argentina. The variants harbor antigenically drastic amino acid substitutions in each of the antigenic sites identified in FMDV. In particular, a substitution found at a major antigenic site (site A, the G-H loop of VP1) had been repeatedly selected in viruses resistant to neutralization by monoclonal and polyclonal antibodies. The association of critical amino acid replacements at predicted positions with new FMD outbreaks has a number of implications for FMD epidemiology and for the design of vaccines intended to control diseases caused by highly variable RNA viruses.

Large deletions in the 5'-untranslated region of foot-and-mouth disease virus of serotype C

Nucleotide sequences of the 5'-untranslated region (5'-UTR), at the 3'-side of the poly C tract, have been compared for 21 isolates of foot-and-mouth disease virus (FMDV) of serotype C from Europe, South America and The Philippines. A deletion of 43 nucleotides is present in the European isolates as compared with most American isolates. A larger deletion of 86 nucleotides is present in some viruses from South America and The Philippines. These deletions include the loss of one or two pseudoknot structures predicted in this region of the 5'-UTR. In addition, multiple point mutations have allowed the derivation of a phylogenetic tree which defines a grouping of isolates very similar to that derived from the capsid gene sequences of the same viruses. The study provides evidence that deletion (or addition) events must be very frequent during evolution of FMDV type C, since viruses which are phylogenetically very closely related (they belong to the same tree branch) may differ in the presence or absence of these deletions. Implications for FMDV evolution are discussed.

Antigenic heterogeneity of a foot-and-mouth disease virus serotype in the field is mediated by very limited sequence variation at several antigenic sites

Antigenic variation in a major discontinuous site (site D) of foot-and-mouth disease virus (FMDV) of serotype C has been evaluated with neutralizing monoclonal antibodies. Isolates representing the major evolutionary sublines previously defined for serotype C were compared. Extensive variation, comparable to that of continuous epitopes within the hypervariable immunodominant site A (the VP1 G-H loop), was found. The amino acid sequences of the complete capsids of three antigenically highly divergent FMDVs (C1 Haute Loire-Fr/69, C5 Argentina/69, and C3 Argentina/85) have been determined and compared with the corresponding sequences previously determined for seven additional type C viruses. Differences in antigenicity are due to a very limited number of substitutions of surface amino acids accessible to antibodies and located within antigenic sites previously identified on FMDV. A significant number of residues at these positions were also replaced in monoclonal antibody escape mutants. Depending on the variants compared, replacements within site A or at site D, or at both sites, contributed significantly to their antigenic differences. Examples of divergence mediated by a few amino acid replacements were found among FMDVs of Europe and South America. The results suggest that within a serotype of FMDV, antigenically highly divergent viruses can arise in the field by very limited sequence variation at exposed key residues of each of several antigenic sites.

Extensive antigenic diversification of foot-and-mouth disease virus by amino acid substitutions outside the major antigenic site

The antigenic sites A and C (the G-H loop and the C terminus, respectively) in VP1 of foot-and-mouth disease virus (FMDV) have been considered the immunodominant regions of the virus involved in the induction of protection. Other antigenic sites have been described but their involvement in protection has not been established. Here we report that two closely related but serologically different FMDVs (the field isolate C3 Argentina/84 and the vaccine strain C3 Resende Br/55) have identical A and C sites but differ as other antigenic sites. Such differences have been documented by reactivity with a panel of 28 monoclonal antibodies (MAbs). The two viruses reacted to the same extent with each of 13 MAbs which recognized epitopes within sites A or C, but reacted differently with six out of 15 MAbs that recognized other sites. Accordingly, sequencing of the entire region coding for the capsid proteins, for both viruses, revealed four amino acid substitutions at three antigenic sites other than A and C. The results suggest that identity of sites A and C may not be sufficient to induce cross-protection, and provide the first evidence of significant antigenic diversification of FMDV in the field mediated by amino acid substitutions outside sites A or C.

Two mechanisms of antigenic diversification of foot-and-mouth disease virus

The amino acid replacements that underlay the diversification of the main antigenic site A (VP1 residues 138 to 150) of foot-and-mouth disease virus (FMDV) of serotype C have been identified. Sixteen new VP1 sequences of isolates from 1926 until 1989 belonging to subtypes C1, C2, C3, C4, C5, and unclassified are reported. The reactivities in enzyme-linked immunoelectrotransfer blot assays of capsid protein VP1 with a panel of neutralizing monoclonal antibodies that recognize sites A or C (the VP1 carboxy-terminus) have been correlated with the amino acid sequence at the relevant epitopes. The analyses involving the immunodominant site A reveal two mechanisms of antigenic change. One is a gradual increase in antigenic distance brought about by accumulation of amino acid replacements at two hypervariable segments within site A. A second mechanism consists of an abrupt antigenic change manifested by loss of many epitopes, caused by one replacement at a critical position (particularly Ala (145)----Val or His (146)----Gln). The identification of the amino acid substitutions responsible for such large antigenic changes provides new information for the design of synthetic anti-FMD vaccines. However, the screening of isolates from six decades suggests that the virus, even within the confines of a single serotype, has exploited a minimum of its potential for antigenic variation.

Protection conferred by TrpE fusion proteins containing portions of the C-terminal region of capsid protein VP1 of foot-and-mouth disease virus

Major immunogenic sites of foot-and-mouth disease virus (FMDV) have been mapped to the C-terminal third of capsid protein VP1; we studied the immunogenicity of a series of TrpE-FMDV fusion proteins containing this region of FMDV strain O1 Campos. Fusion protein TrpE-dCN, which contains a dimer of VP1 amino acid sequences consisting of amino acids 200 to 213 linked by a diproline spacer to amino acids 141 to 158 (200-213 approximately P-P-G approximately 141-158), induced the best response. A single inoculation of guinea-pigs with 100 micrograms TrpE-dCN elicited high levels of neutralizing antibodies and protected all the animals against challenge infection with homologous virus. Although the closely related FMDV strains O1 Campos and O1 Caseros induced high levels of cross-protection, TrpE-dCN-vaccinated guinea-pigs were poorly protected against challenge infection with heterologous FMDV strain O1 Caseros. Nucleotide sequence analysis revealed that amino acid differences at residues 149 and 152 were critical for the induction of cross-protection and that neutralizing epitopes not present in TrpE-dCN are likely to be responsible for conferring a high level of cross-protection between FMDV strains O1 Campos and O1 Caseros.

Gene encoding capsid protein VP1 of foot-and-mouth disease virus: a quasispecies model of molecular evolution

A phylogenetic tree relating the VP1 gene of 15 isolates of foot-and-mouth disease virus (FMDV) of serotypes A, C, and O has been constructed. The most parsimonious tree shows that FMDV subtypes and isolates within subtypes constitute sets of related, nonidentical genomes, in agreement with a quasispecies mode of evolution of this virus. The average number of nucleotide replacements per site for all possible pairs of VP1 coding segments is higher among representatives of serotype A than serotype C or O. In comparing amino acid sequences, the values of dispersion index (variance/mean value) are greater than 1, with the highest values scored when all sequences are considered. This indicates an accumulation of mutations at a limited number of residues, suggesting that distributions of sequences fluctuate around points of high stability. Evolution of FMDV follows a path very distant from that of a star phylogeny, and it has not been possible to derive conclusions on constancy of evolutionary rates with the test applied to the analysis. FMDVs, as other RNA viruses, are of limited genetic complexity and their population sizes are extremely large. Their evolution concerns complex, indeterminate mixtures of genomes rather than a single, determinate species.

[Neutralization of foot-and-mouth disease virus O1 Campos by antibodies induced by a synthetic peptide]

Foot-and-Mouth disease virus (FMDV), contains a positive single-stranded RNA enclosed in a protein capsid. Previous studies have shown that a synthetic peptide located at the carboxyterminal end of VP1 of FMDV strain O1 Kaufbeuren (O1K) at the amino acid positions 144-159, and coupled to KLH was able to elicit high titers of neutralizing antibodies in guinea pigs and protected them against challenge with the homologous virus (8, 15). FMDV strain O1 Campos (O1 Ca) has a similar amino acid sequence to O1K, differing in amino acid 144 (leucin instead valine). We report that the O1K synthetic peptide 144-159 protects adult mice against challenge with FMDV O1Ca when the peptide is coupled to KLH with glutaraldehyde as coupling agent (Table 2) whereas protection is very low when other carrier proteins are used.

VP1 of serotype C foot-and-mouth disease viruses: long-term conservation of sequences

The nucleotide sequences of the VP1-coding regions of several isolates of serotype C3 foot-and-mouth disease virus (FMDV) were determined. The deduced amino acid sequences were compared with those of serotype C1 FMDV. The results provide evidence for two different lineages of FMDV C3 and document the potential for both long-term conservation and rapid evolution of FMDV.

Detection of foot-and-mouth disease virus with DNA probes in bovine esophageal-pharyngeal fluids

Infectivity and dot-blot hybridization techniques were compared for the detection of FMDV in esophageal-pharyngeal fluids from experimentally infected cows. The probe used includes the viral polymerase sequence which allows the detection of the three types of virus (A, O, and C) with equivalent sensitivity. Virus was detected by dot-blot hybridization as well as by infectivity, according to sample analysis of esophageal-pharyngeal fluids extracted seven days post-infection. It was not possible to recover infective virus from some samples extracted at 180 and 560 days post-infection, although specific viral RNA was detected by dot-blot hybridization. This could indicate the presence of a high ratio of non-infective viral mutants in FMDV carrier cattle. These results emphasize the usefulness of molecular hybridization techniques for FMDV carrier-state detection.

Genetic and immunogenic variations among closely related isolates of foot-and-mouth disease virus

Genetic heterogeneity among closely related isolates of foot-and-mouth disease virus (FMDV) has been measured by direct sequencing of the VP1-coding-region RNA for three new FMDVs of serotype C1 and by additional sequences of RNA from previously reported isolates, all belonging to a single episode of disease [Sobrino et al., Gene 50 (1986) 149-159]. In the ten viruses compared, eight different VP1 are represented. The changes include amino acid substitutions at a critical antigenic determinant of VP1. We document that variations present in such natural isolates result in changes of the immunogenic properties of the viruses. Vaccines prepared with two of the FMDV C1 analyzed induce complete protection against an homologous virus but only partial protection against an heterologous virus in swine, the host from which these viruses were isolated.

Detection of bovine herpesvirus-1 nucleic acid sequences, using a dot-blot hybridization procedure

A sensitive and specific procedure for the detection of Argentine isolates of bovine herpesvirus-1 was developed. The procedure was based on a dot-blot, nucleic acid hybridization, using 32P, nick-translated, plasmidic probes. The probes contained cloned Bam H1 restriction fragments in the left half of the viral genome. The detection limit of the procedure was 10 pg of viral DNA.

Host cell modulation of foot-and-mouth disease virus procapsid synthesis

BHK21 (clone 13S) cells of high (BHK-SH) and low (BHK-SL) passage number were infected with foot-and-mouth disease virus (FMDV) subtypes A24, A25 and C3. While the amount of virus specific RNA produced in BHK-SH cells was 25% of that in BHK-SL cells and the virion production was 27% (C3) to 53% (A24) lower, the synthesis of viral proteins was comparable, associated with an accumulation of procapsids in BHK-SH cells. The results suggest that changes in viral infection pattern with increasing BHK21 cell passage number should be considered in FMDV vaccine production.

Biochemical characterization of a foot-and-mouth disease virus strain attenuated for cattle. Brief report

Wild-type, virulent (A-24 Cruzeiro subtype) foot-and-mouth disease virus (FMDV), a related attenuated strain and revertants of the attenuated strain were examined by titration on primary bovine kidney (PBK) and baby hamster kidney (BHK-21) cells, as well as, by infection of unweaned mice. Wild type virus grew equally well in all three systems, whereas the attenuated strain had a titer 2-3 log lower in PBK cells than in the other 2 assays. Within 9 successive passages in BHK-21 cells the attenuated strain gave rise to revertants that had regained the growth properties of wild-type virus in PBK cells. After cloning of the attenuated strain by plaque isolations, the same revertant phenotype was obtained within 9 successive passages. Oligonucleotide mapping indicated that the attenuated strain differed from the wild-type and revertants by at least one additional oligonucleotide. Differences in poly(C) length were not found among any of the three strains of FMDV. These results correlate attenuation and virulence with point mutation(s) and not with deletions. Possible reversions in nature with this attenuated strain may be anticipated.

Fixation of mutations in the viral genome during an outbreak of foot-and-mouth disease: heterogeneity and rate variations

Rates of fixation of mutations during the evolution of the foot-and-mouth disease virus (FMDV) C1 in nature have been estimated by hybridization of viral RNA to cloned cDNAs representing defined FMDV genome segments, and comparison of the selected RNAs by T1 RNase oligonucleotide fingerprinting. Values ranged from less than 0.04 X 10(-2) to 4.5 X 10(-2) substitutions per nucleotide per year (s/nt/yr), depending on the time period and the genomic segment considered. Rates for viral structural protein genes were up to sixfold higher than for nonstructural protein genes. Values in excess of 10(-2) s/nt/yr have been measured for the RNA region that encodes VP1-VP3. The nucleotide sequences of the major immunogenic region of capsid protein VP1 have been determined for six new FMDV C1 isolates, and they are compared with the two previously known sequences of FMDV C1 (C-S8 and C1-O). Both oligonucleotide fingerprinting of selected RNA fragments and direct nucleotide sequencing demonstrate that genetic heterogeneity exists among three viruses isolated on the same day, introducing a significant indetermination in the evaluation of fixation rates of mutations. During the FMDV C1 outbreak, amino acid substitutions did occur that are known to affect the immunological properties of the virus. The proportion of mutations between two viral RNAs does not increase significantly with the time elapsed between the two isolations, suggesting a cocirculation of multiple, related, nonidentical FMDVs ('evolving quasispecies') as the mode of evolution of this agent.

Detection of vesicular stomatitis virus RNA and its defective-interfering particles in individual mouse brains

To develop a highly sensitive and direct assay for defective interfering (DI) particles of vesicular stomatitis virus (VSV), we reverse transcribed RNA from DI particles and cloned the DNA in pBR322 and used it as hybridization probes. At the lower limit, cDNA of about 850 nucleotides detected 150 pg of VSV RNA. For differentiation of hybridizable sequences found in the RNA of DI particles from complementary or identical sequences in the L mRNA or standard genomic RNA of VSV, RNA obtained from mouse brains was first separated by size, blotted onto nitrocellulose, and then hybridized to in vitro-labeled cDNA probe. Genomic VSV, DI, or L mRNA sequences from one-half of the brain of an infected mouse were detectable, whereas uninfected mice failed to react with this specific probe. When mice were infected intranasally with 10(8) PFU of standard VSV, most of them died between days 6 and 7, and the detection of standard genomic RNA correlated with paralysis and death. DI RNA was not detected in these mice. When mice were infected with 10(8) PFU of standard VSV together with an equivalent amount of DI particles, similar results were obtained. When fewer DI particles were inoculated together with standard virus, significant protection of mice occurred together with the detection of DI RNA. These results indicate that DI particles are protective in vivo and that the details of the virus-host interaction may resemble the cyclic growth patterns in cell cultures for standard VSV and its DI particles.

Morphogenesis of foot-and-mouth disease virus. I. Role of procapsids as virion Precursors

The role of procapsids during foot-and-mouth disease virus multiplication was studied on infected BHK-21 cells. Purified virus and procapsids were obtained by treating the infected cytoplasmic extracts with RNase and EDTA. The synthesis of virus, procapsids, and total particles was determined in pulse-chase experiments. A precursor-product relationship between procapsids and virions was obtained. The results show that the rate of synthesis of total particles (virus + procapsids) was linear from the addition of the label and was identical to that corresponding to virions. Therefore, the speed of the morphogenetic process as well as the existence of a precursor pool of structural proteins was established. Furthermore, the rate of virus synthesis from procapsids was identical to the rate of synthesis of procapsids from their structural precursors. A quantitative recovery of label from procapsids into virions was obtained by the use of cycloheximide or tosyl-lysine chloromethyl ketone. Under these conditions, virus synthesis proceeds, indicating that these drugs do not affect the morphogenetic step studied in this paper.

Inhibition of foot and mouth disease virus and procapsid synthesis by zinc ions. Brief report

Zinc ions inhibit virus production and viral RNA synthesis in FMDV infected-BHK 21 cells. The degree of inhibition depends upon the zinc concentration and the time of addition of the drug. A differential inhibition on virus and procapsids synthesis was observed.