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The isolation of two enzyme-ribonucleic acid complexes involved in the synthesis of foot-and-mouth disease virus ribonucleic acid.

The foot-and-mouth disease virus-RNA polymerase complex was released from membrane particulates present in the cytoplasm of infected baby hamster kidney cells. The soluble polymerase complex was fractionated by zonal centrifugation in sucrose gradients. Two polymerase complexes (RNA and protein complex) active in the cell-free system were isolated and had S-rate ranges of 20-70S and 100-300S, respectively. The light polymerase complex contained 20S double-stranded RNA; and the heavy polymerase complex contained a polydisperse, partially RNase-resistant RNA. The cell-free product of these two polymerase complexes was analyzed by zonal centrifugation in sucrose gradients. The light polymerase complex synthesized only 20S double-stranded RNA. The product of the heavy polymerase complex contained no detectable 20S double-stranded RNA and only a peak of single-stranded RNA with S-rate corresponding to 37S viral RNA. A third polymerase complex was isolated with S-rate greater than 300S, and it contained a polydisperse, partially RNase-resistant RNA. This third polymerase complex synthesized both 37S viral RNA and 20S double-stranded RNA in the cell-free system, and it is probably the native polymerase complex still bound to cellular particulates.

Animals↗

Studies on the infectivity of foot-and-mouth disease virus RNA using microinjection.

Foot-and-mouth disease virus (FMDV) RNA, isolated as virion RNA from purified virus particles or as total RNA from infected cells, has been microinjected into nuclei and cytoplasms of BHK cells. When injected directly into the nucleus FMDV RNA was not infectious, whereas cytoplasmic injection resulted in a high proportion of productive infections. Infectivity microinjection assays on dilution series of various FMDV RNAs showed that both single-stranded positive sense 35S RNA and double-stranded replicative form (Rf) RNA have an infectivity close to 1 p.f.u. per molecule, although only a minor fraction of BHK cells appeared able to support plaque formation following microinjection of Rf FMDV RNA. The infectivity of Rf FMDV RNA was not sensitive to inhibition by actinomycin D. The results are discussed in relation to the high virus particle to p.f.u. ratios observed for FMDV.

Animals↗

Methods used in the structure determination of foot-and-mouth disease virus.

The structure of foot-and-mouth disease virus (FMDV) strain O1 BFS 1860 has been determined to 2.9 A resolution using the molecular-replacement method [Acharya, Fry, Stuart, Fox, Rowlands & Brown (1989). Nature (London), 337, 709-716]. Crystals of the virus with average dimensions 0.12 x 0.06 x 0.12 mm belong to space group I23, a = 345 A with 1/12 of the icosahedral particle per asymmetric unit giving fivefold noncrystallographic redundancy. Oscillation diffraction photographs were collected at the SERC Synchrotron Radiation Source at Daresbury in accordance with strict disease security regulations. The ambiguity in particle orientation was resolved using a self-rotation function and starting estimates of the phases to 8 A were derived from the known structures of two picornaviruses similarly oriented in the I23 unit cell. The phases were refined and extended using iterative averaging and solvent flattening with the implementation of a simple automatic envelope-determination procedure to increase the phasing power available.

Aphthovirus↗

Further characterization of a protein kinase from foot-and-mouth disease virus.

Acid disruption of foot-and-mouth disease virus released a protein kinase activity that sedimented at less than 7S. This enzyme was separated into three peaks of activity by ion-exchange and hydroxylapatite chromatography. Analysis of the various enzyme fractions by polyacrylamide gel electrophoresis and silver staining revealed that one of the fractions lacked the major virion structural proteins, but still contained two or three other polypeptides. This enzyme phosphorylated mainly one protein (P17) in an in vitro assay.

Animals↗

Dissecting the roles of VP0 cleavage and RNA packaging in picornavirus capsid stabilization: the structure of empty capsids of foot-and-mouth disease virus.

Empty capsids of foot-and-mouth disease virus (FMDV) type A22 Iraq 24/64, whose structure has been solved by X-ray crystallography, are unusual for picornaviruses since they contain VP2 and VP4, the cleavage products of the protein precursor VP0. Both the N terminus of VP1 and the C terminus of VP4, which pack together close to the icosahedral threefold symmetry axis where three pentamers associate, are more disordered in the empty capsid than they are in the RNA-containing virus. The ordering of these termini in the presence of RNA strengthens interactions within a single protomer and between protomers belonging to different pentamers. The disorder in the FMDV empty capsid forms a subset of that seen in the poliovirus empty capsid, which has VP0 intact. Thus, VP0 cleavage confers stability on the picornavirus capsid over and above that attributable to RNA encapsidation. In both FMDV and poliovirus empty capsids, the internal disordering uncovers a conserved histidine which has been proposed to be involved in the cleavage of VP0. A comparison of the putative active sites in FMDV and poliovirus suggests a structural explanation for the sequence specificity of the cleavage reaction.

Aphthovirus↗

Antibody response in mice inoculated with DNA expressing foot-and-mouth disease virus capsid proteins.

Candidate foot-and-mouth disease (FMD) DNA vaccines designed to produce viral capsids lacking infectious viral nucleic acid were evaluated. Plasmid DNAs containing a portion of the FMDV genome coding for the capsid precursor protein (P1-2A) and wild-type or mutant viral proteinase 3C (plasmids P12X3C or P12X3C-mut, respectively) were constructed. Cell-free translation reactions programmed with pP12X3C (wild-type 3C) and pP12X3C-mut produced a capsid precursor, but only the reactions programmed with the plasmid encoding the functional proteinase resulted in P1-2A processing and capsid formation. Baby hamster kidney (BHK) cells also produced viral capsid proteins when transfected with these plasmids. Plasmid P12X3C was administered to mice by intramuscular, intradermal, and epithelial (gene gun) inoculations. Anti-FMD virus (FMDV) antibodies were detected by radioimmunoprecipitation (RIP) and plaque reduction neutralization assays only in sera of mice inoculated by using a gene gun. When pP12X3C and pP12X3C-mut were inoculated into mice by using a gene gun, both plasmids elicited an antibody response detectable by RIP but only pP12X3C elicited a neutralizing antibody response. These results suggest that capsid formation in situ is required for effective immunization. Expression and stimulation of an immune response was enhanced by addition of an intron sequence upstream of the coding region, while addition of the FMDV internal ribosome entry site or leader proteinase (L) coding region either had no effect or reduced the immune response.

3C Viral Proteases↗

The epithelial integrin alphavbeta6 is a receptor for foot-and-mouth disease virus.

Field isolates of foot-and-mouth disease virus (FMDV) have been shown to use the RGD-dependent integrin alphavbeta3 as a cellular receptor on cultured cells. However, several other RGD-dependent integrins may have the potential to act as receptors for FMDV in vivo. Of these, alphavbeta6 is a likely candidate for use as a receptor by FMDV as it is expressed on epithelial cells, which correlates with the tissue tropism of the virus. In this report, we show that human colon carcinoma cells (SW480) that are normally nonpermissive for FMDV become susceptible to infection as a result of transfection with the integrin beta6 subunit and expression of alphavbeta6 at the cell surface. Integrin alphavbeta6 is the major site for virus attachment on the beta6-transfected cells, and binding to alphavbeta6 serves to increase the rate of virus entry into these cells. In addition, we show that virus binding and infection of the beta6-transfected cells is mediated through an RGD-dependent interaction that is specifically inhibited by a monoclonal antibody (10D5) that recognizes alphavbeta6. These studies establish a role for alphavbeta6 as a cellular receptor for FMDV.

Animals↗

Role of the cytoplasmic domain of the beta-subunit of integrin alpha(v)beta6 in infection by foot-and-mouth disease virus.

Field isolates of foot-and-mouth disease virus (FMDV) are believed to use RGD-dependent integrins as cellular receptors in vivo. Using SW480 cell transfectants, we have recently established that one such integrin, alpha(v)beta6, functions as a receptor for FMDV. This integrin was shown to function as a receptor for virus attachment. However, it was not known if the alpha(v)beta6 receptor itself participated in the events that follow virus binding to the host cell. In the present study, we investigated the effects of various deletion mutations in the beta6 cytoplasmic domain on infection. Our results show that although loss of the beta6 cytoplasmic domain has little effect on virus binding, this domain is essential for infection, indicating a critical role in postattachment events. The importance of endosomal acidification in alpha(v)beta6-mediated infection was confirmed by experiments showing that infection could be blocked by concanamycin A, a specific inhibitor of the vacuolar ATPase.

Acids↗

The N-terminal amino acid sequence is essential for foot-and-mouth disease virus replicase activity.

1. Foot-and-mouth disease virus replicase was expressed by fusing its cDNA to the OmpA signal peptide coding sequence present in the pIN-III ompA series vectors. 2. Two constructions were developed to express either a full-length or truncated enzyme lacking the 20 amino acids at the N-terminal end. Bacterial extracts expressing the recombinant proteins were submitted to SDS-PAGE and the presence of the replicase was revealed by immunoblotting. The truncated form exhibited a higher mobility and the relative positions of the proteins show that the signal peptide was removed. 3. The biological activity of these two molecules was tested using a poly(A)-dependent oligo(U)-primed poly(U)-polymerase assay. The full-length replicase is active. The aminoterminal truncated enzyme had 0.02% activity of the intact one. 4. This result indicates the importance of the twenty N-terminal amino acids for the activity of FMDV RNA-dependent RNA polymerase.

Amino Acid Sequence↗

[Studies on the influence of the host system on the result of the neutralization of monodispersed and untreated foot- and mouth disease virus (author's transl)].

Monodispersed foot- and mouth disease virus was obtained by filtration through membranes having a porosity only twice the diameter of the virus. This monodispersed virus was neutralized by immune sera in the same manner as not treated virus. This was shown by the inactivation curve comparing the amount of virus used for the test (calculated as ID50) with the neutralization titre (ND50) or comparing the reduction of infectivity (also calculated as ID50) with the dilution factor of the antiserum. When the virus was assayed by counting the plaque forming units, the monodispersed virus needed more antiserum to be neutralized than a not treated virus suspension. The same mixtures of virus and antiserum were inoculated into different host systems. Using suckling mice there was observed only about 1% of the infectivity measured in primary calf kidney cells. Primary calf kidney cells showed only a tenth of the infectivity seen in BHK-21 cells. The difference between the results in mice and calf kidney cells has been found to be caused by the existence of infectious virus in the mice, which does not cause illness or death in the presence of antibodies. Comparing the same size of cell sheet there is more virus absorbed by BHK-cells in the presence of antibodies than by calf kidney cells. The different results obtained in different hosts for the same virus antibody mixtures are discussed with respect to the detection of small amounts of antibodies and to the limits for the comparison of neutralization titres.

Animals↗

Co-replication of several isotypes of foot-and-mouth disease virus.

Genome segments of the foot-and-mouth disease virus isolates O1Lombardy and O3 Venezuela that encode, among other products, capsid protein VP1 were amplified using PCR, and the products were cloned and sequenced. The alignment of up to 11 O3-specific sequences revealed six silent nucleotide changes a well as six changes that cause amino acid substitutions in capsid protein VP1 at positions 45, 83, 141, 145, 170 and 178. The heterogeneity of three O1-specific sequences consisted of seven silent exchanges and amino acid changes at positions 85 and 134 on VP1. Amplification, subclonning and sequencing of cloned O3-specific cDNA was performed to examine the nature of the sequence heterogeneity. As no difference was found among five subcloned sequences, we conclude that the Taq polymerase copied the DNA correctly. The sequence heterogeneity observed with both virus isolates is, therefore, consistent with the quasispecies structure of foot-and-mouth disease virus. Furthermore, amino acid changes at a number of sites have been found to be involved in the formation or modulation of neutralizing epitopes. The novel aspect of this study is the ability to estimate, by cloning of PCR products, the number of virus isotypes, possibly varying in antigenicity, that are able to co-propagate. Seven isotypes of O3 Venezuela were identified. Some are of particular interest because they exhibit a change at VP1 codon 145 that causes the replacement of arginine, possibly essential for virus attachment to cells, by isoleucine.

Amino Acid Sequence↗

Managing an animal health emergency in Taipei China: foot and mouth disease.

Taipei China had been free from foot and mouth disease (FMD) over 68 years before the disease occurred in March 1997. The first suspected case was recorded on a pig farm in the Hsinchu Prefecture on 14 March 1997. Based on clinical signs, gross histopathological findings, and results of enzyme-linked immunosorbent assays and reverse-transcriptase polymerase chain reaction tests, diagnosis of FMD was confirmed by the Taiwan Animal Health Research Institute on 19 March 1997 and was reconfirmed by the FMD World Reference Laboratory in Pirbright (United Kingdom), on 25 March 1997. By the end of July 1997, 6,147 pig farms (about a quarter of the pig farms in Taipei China), were affected. The disease was well under control within two months by means of stamping-out and blanket vaccination. The Government purchased 21 million doses of inactivated oil-adjuvant FMD vaccine, which allowed for two injections per pig and one injection of other cloven-hoofed animals. Before the vaccine was used, the stamping-out policy was implemented, ensuring that all pigs in the affected farms were destroyed. After blanket vaccination, a partial stamping-out policy was adopted, i.e. only pigs showing clinical signs were destroyed.

Animals↗

Kinetics of humoral immune response in pigs vaccinated against foot and mouth disease.

The present investigation was conducted to study the foot and mouth disease virus (FMDV)-specific humoral immune response (HIR) in pigs, following vaccination with oil adjuvanted foot and mouth disease (FMD) vaccine, upto 90 days post vaccination (dpv). For this, 40 Large White Yorkshire (LWY) pigs (20; one-year old female (gilts) and 20; three-month old piglets) were vaccinated @ 2 ml/animal, subcutaneously. Sera samples were collected at fortnight interval from all the animals. The log10 SN50 antibody titres against all the serotypes (Type O, A and Asia-1) were detected in both gilts and piglets from day 7 to 90 dpv indicating the persistence of HIR up to the last day of sampling. The maximum antibody titres were observed on 28 dpv, thereafter, titres started declining, but were present till 90 dpv against all the three FMDV serotypes. HIR was more pronounced in piglets in comparison to gilts, as group mean SN antibody titres against all the three FMDV serotypes were found to be more maintained and significantly higher in piglets.

Animals↗

Molecular epidemiology of foot-and-mouth disease viruses in the Adamawa province of Cameroon.

Foot-and-mouth disease virus (FMDV) causes a highly contagious viral disease of even-toed ungulates and is one of the most important economic diseases of livestock. Most studies of FMDV are done in countries where control measures are being implemented. In contrast, in areas such as sub-Saharan Africa, where FMDV is endemic and new strains are likely to emerge, there are only sporadic submissions to the World Reference Laboratory, Pirbright, United Kingdom. This paper describes the molecular epidemiology of FMDV in the Adamawa province of Cameroon based on a population sample of cattle herds. Serotypes SAT2 and A were isolated in the cross-sectional study. SAT2 isolates were all similar, with phylogenetic distances of <6%, and were most closely related to published sequences of isolates from Eritrea and Saudi Arabia. Serotype A isolates were more variable, with phylogenetic distances of 0 to 11%, and were most closely related to historic isolates from Cameroon. Use of a population-based sample gives a representative sample of virus diversity and will improve our understanding of the evolution of FMDV and its epidemiology. A supplementary study of pigs passing through the railhead collection yard at Ngaoundere detected a serotype O virus. A third pilot longitudinal study monitored viral persistence in three cattle herds over 12 months, and serotype O and A viruses were recovered from a herd 12 months after it was first recorded as being infected with SAT2 virus. The pig type O isolate was not closely related to that recovered from the cattle, suggesting that the pigs had not introduced the O virus into the cattle herds.

Animals↗