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Comparative between-laboratory trials of the liquid-phase blocking sandwich ELISA for the detection of antibodies to foot-and-mouth disease virus.

Fifty bovine serum samples were tested for the presence or amounts of antibodies to foot-and-mouth disease (FMD) virus serotypes A, O and C by the liquid-phase blocking sandwich ELISA (lpb-ELISA) using reagents prepared by the World Reference Laboratory for Foot-and-Mouth Disease (WRL) in Pirbright, U.K. Twenty of the sera had been collected before extensive vaccination with a commercial inactivated trivalent FMD vaccine was ceased and the remaining thirty originated from animals which had not been vaccinated for more than one year. After the test had been completed, the samples were sent to another two laboratories to be examined by the same assay. Results obtained in the laboratories were compared to assess the degree of agreement in serological tests for FMD in cattle. Antibodies to at least one of the three FMD virus (FMDV) serotypes were demonstrated in 70% of the serum samples. Antibodies to the antigens A5, O1 and C1 were present in 58%, 66% and 58% of the sera, respectively. The overall between-laboratory agreement of the results of the lpb-ELISA for the detection of antibodies against all three serotypes was 96%. Discrepancies in terms of type specificity did not exceed 10%. Most discrepancies were recorded in sera with low antibody titres or optical densities (OD) around the cut-off point. An increase of concentration of C1 antigen in reaction mixture reduced the sensitivity of ELISA and results of screening tests became negative in sera with antibody titres of 1: 90 and lower.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

A solid-phase competition ELISA for measuring antibody to foot-and-mouth disease virus.

A solid-phase competition ELISA has been developed to measure antibodies to foot-and-mouth disease (FMD) virus and has been validated using an extensive range of sera from cattle. The assay uses polyclonal antisera and inactivated purified 146S antigens of FMD virus and was compared with the liquid-phase blocking ELISA and the virus neutralisation test on a range of serum sets. When examining test sera at a 1:5 dilution with a cut-off point of 30% inhibition of reaction, the solid-phase competition ELISA was as sensitive as the liquid-phase blocking ELISA for sera from infected or vaccinated animals. The limit of detection of the solid-phase ELISA was similar to that of the liquid-phase assay and both tests had lower limit of detection (i.e. were able to detect lower amounts of antibody) than the virus neutralisation test. The specificity of the solid-phase ELISA was considerably higher than that of the liquid-phase blocking ELISA and almost equivalent to that of the virus neutralisation test. The assay thus retains the sensitivity of the liquid-phase blocking ELISA whilst being easier to use, more robust and specific, and therefore offers an improvement for FMD virus antibody detection.

Animals↗

Biosensor characterization of antigenic site A of foot-and-mouth disease virus presented in different vector systems.

The region 141-160 of the VP1 protein of foot-and-mouth disease virus known as site A is an immunodominant region that has been extensively studied for the purpose of developing a synthetic vaccine. In the present study, site A of foot-and-mouth disease virus was inserted in three different loops of the maltose-binding protein and its antigenicity was compared with site A presented as a conjugated synthetic peptide or inserted in beta-galactosidase. The affinity of antibodies elicited against the site A synthetic peptide was also compared with that of antibodies raised against the site A inserted within the two carrier proteins. Using biosensor technology it was possible to estimate the concentration of site A antibodies present in the various antisera and to show that site A fused to maltose-binding protein was a slightly better mimic of the epitope present in the virus particle than the synthetic peptide or the beta-galactosidase recombinant construct.

Animals↗

Infectivity assays of foot-and-mouth disease virus: contact transmission between cattle and buffalo (Bubalus bubalis) in the early stages of infection.

No differences were observed between cattle and Indian buffalo (Bubalus bubalis) in terms of temperature, viraemia or virus replication in the pharyngeal area, during the acute phase of foot-and-mouth disease. Like cattle, the Indian buffalo became infected and excreted virus before any clinical signs of foot-and-mouth disease developed. The disease was transmitted from cattle to buffalo and vice versa, during the acute stage of infection, as if the animals had been of the same species, presumably because of their close phylogenetic relationship. There were more tongue lesions in the cattle than in the buffalo. Foot lesions in the buffalo at first had a scaley appearance, but later became vesicular. Anti-virus infection associated antigen and neutralising antibodies were synthesised at the same time in both species and reached similar titres in the same period. Persistent infection in the buffalo during the first 35 days after infection was similar to that in the cattle.

Animals↗

Patterns of spread and persistence of foot-and-mouth disease types A, O and Asia-1 in Turkey: a meta-population approach.

Despite significant control efforts, foot-and-mouth disease (FMD) persists in Turkey, and new strains of serotypes A, O and Asia-1 are periodically reported to enter the country from the east. The status of FMD in Turkey is important regionally because the country forms a natural bridge between Asia where the disease is endemic, and Europe which has disease-free status. This study analysed spatial and temporal patterns of FMD occurrence in Turkey to explore factors associated with the disease's persistence and spread. Annual records of FMD distribution in Turkish provinces throughout 1990-2002, grouped by serotype (O, A and Asia 1), were analysed using geostatistical techniques to explore their spatial and temporal patterns. A meta-population model was used to test how disease status, expressed in terms of presence/absence, extinction, and colonization, and measured at the province level throughout the periods 1990-1996 and 1997 2002, could be predicted using province-level data on: ruminant livestock numbers; meat production-demand discrepancy (as a surrogate measure of animal and animal products marketing, i.e. long-distance contagion through the traffic of mainly live animals to urban centres); and the disease prevalence distribution as recorded for the previous year. A drastic overall reduction in FMD occurrence was observed from the period 1990-1996 to 1997-2002 when the disease was shown to retract into persistence islands. FMD occurrence was associated with host abundance, short distance contagion from adjacent provinces, and meat production-demand discrepancies. With FMD retracting into identified provinces, a shift in predictors of FMD occurrence was observed with a lower contribution of short-distance contagion, and a relatively higher association with meat production-demand discrepancies leading to live animal transport over long distances, and hence presenting opportunities for identifying critical-control points. The pattern of persistence differed according to serotype groups and is discussed in relation to their differential affinity to cattle and small ruminant hosts.

Animals↗

Benefit-cost analysis of vaccination and preemptive slaughter as a means of eradicating foot-and-mouth disease.

OBJECTIVE: To assess relative costs and benefits of vaccination and preemptive herd slaughter to control transmission of foot-and-mouth disease (FMD) virus (FMDV). SAMPLE POPULATION: 2,238 herds and 5 sale yards located in Fresno, Kings, and Tulare counties of California. PROCEDURE: Direct costs associated with indemnity, slaughter, cleaning and disinfecting livestock premises, and vaccination were compared for various eradication strategies. Additional cost, total program cost, net benefit, and benefit-cost value (B/C) for each supplemental strategy were estimated, based in part on results of published model simulations for FMD. Sensitivity analyses were conducted. RESULTS: Mean herd indemnity payments were estimated to be dollars 2.6 million and dollars 110,359 for dairy and nondairy herds, respectively. Cost to clean and disinfect livestock premises ranged from dollars 18,062 to dollars 60,205. Mean vaccination cost was dollars 2,960/herd. Total eradication cost ranged from dollars 61 million to dollars 551 million. All supplemental strategies involving use of vaccination were economically efficient (B/C range, 5.0 to 10.1) and feasible, whereas supplemental strategies involving use of slaughter programs were not economically efficient (B-C, 0.05 to 0.8) or feasible. CONCLUSIONS AND CLINICAL RELEVANCE: Vaccination with a highly efficacious vaccine may be a cost-effective strategy for control of FMD if vaccinated animals are not subsequently slaughtered and there is no future adverse economic impact, such as trade restrictions. Although less preferable than the baseline eradication program, selective slaughter of highest-risk herds was preferable to other preemptive slaughter strategies. However, indirect costs can be expected to contribute substantially more than direct costs to the total cost of eradication programs.

Animals↗

Expression of the VP3-VP1 sequence of foot-and-mouth disease virus in Escherichia coli.

1. cDNA recombinants containing the VP3 and VP1 sequences of foot-and-mouth disease virus were isolated and the VP3-VP1 sequence was reconstructed. 2. The reconstructed VP3-VP1 sequence was subcloned into expression vector pEX31b and a fusion protein of about 62,000 Da was expressed. 3. When injected into mice, the fusion protein was able to elicit the production of antibodies that recognized viral VP1 and VP3. 4. Antibodies present in sera from mice immunized with VP3-VP1 protein did not neutralize the foot-and-mouth disease virus in vitro.

Animals↗

Effect of pasteurization and evaporation on foot-and-mouth disease virus in whole milk from infected cows.

The effects of pasteurization and evaporation on foot-and-mouth disease virus in whole milk from infected cows obtained one day postinoculation were studied. Virus survived the heating of milk at high temperature-short time pasteurization at 75 degrees C for 15-17 seconds. In addition, virus from infected milk survived heating at 80 degrees C for the same time. Infective virus also survived in the pasteurized milk after evaporation at 65 degrees C to 50% of the original volume. The bovine udder was found to be highly susceptible to foot-and-mouth disease virus replication. Seven log10 plaque-forming units/ml of virus were recovered in whole milk 24 hours postinoculation, and decreasing titers were recovered for as long as seven days postinoculation.

Animals↗

Identification of a fifth neutralizable site on type O foot-and-mouth disease virus following characterization of single and quintuple monoclonal antibody escape mutants.

A monoclonal antibody (C3) produced against foot-and-mouth disease virus type O1Caseros was found to neutralize quadrivalent monoclonal antibody escape mutant (G67) of foot-and-mouth disease virus type O1Kaufbeuren. This mutant had been characterized at the sequence level as having distinct changes affecting four non-overlapping neutralizable sites. The C3 monoclonal antibody was used to prepare a quintuple escape mutant from the G67 and a single escape mutant from the parental O1Kaufbeuren viruses. Polyclonal post-vaccinated and infected cattle sera as well as polyclonal mouse and guinea-pig sera, which neutralized the quadrivalent mutant, no longer neutralized the quintuple mutant, indicating that a fifth site had been identified and that changing the fifth site eliminated all neutralization. The site was characterized using serological techniques and found to be conformationally dependent, trypsin-sensitive and independent of sites previously characterized by monoclonal antibodies. Amino acid sequencing comparing parental, single C3 and quintuple mutants showed that a single change from a glutamine to a histidine, at amino acid 149 in the structural protein VP1, (1D) characterized the C3 mutation. The fifth site probably represents a conformational epitope which is formed due to the interaction of the VP1 loop region with other surface amino acids.

Amino Acid Sequence↗

Identification and isolation of foot-and-mouth disease virus from primary suspect cases in Korea in 2000.

The Republic of Korea had been free from foot and mouth disease (FMD) since 1934, until a recent outbreak in 2000. From March to April 2000, a total of 15 FMD outbreaks due to the serotype O virus were recorded. Coincidental outbreaks of FMD in cattle or pigs by the serotype O virus were reported in the region, including Taiwan, China, Japan, Russia and Mongolia. In this report, the results of emergency investigations of FMD cases on a dairy farm located approximately 5-km from the demilitarized zone in Korea are described. The causative agent of the disease was identified as the FMD virus O by reverse transcription-polymerase chain reaction (RT-PCR) assays using primers derived from the 3D polymerase, internal ribosome entry site (IRES), 1D/2B regions, enzyme-linked immunosorbent assay (ELISA) for antigen detection and typing. Sequence data of the partial 1D/2B region obtained from vesicular fluid showed close similarity (98% sequence identity) to the Kinmen isolate of the FMD virus O in Taiwan. The causative virus was isolated using black goat fetal lung cells following propagation in unweaned mice.

Animals↗

Further investigations on the airborne excretion of foot-and-mouth disease virus.

Calf thyroid tissue cultures were found to be the most sensitive system in detecting virus collected in a large volume air sampler from boxes, where cattle, sheep and pigs infected with A and C strains of foot-and-mouth disease (FMD) virus were housed. It was confirmed with all strains of FMD virus tested that pigs excreted the most virus followed by cattle and sheep, but there was variation between strains, the highest virus recoveries being obtained from animals infected with O(1) and C Noville viruses. The results are discussed in relation to outbreaks of foot-and-mouth disease in Great Britain since 1954.

Air Microbiology↗

Carcass disposal: lessons from The Netherlands after the foot and mouth disease outbreak of 2001.

The main logistical problems of the foot and mouth disease (FMD) outbreak that occurred in the Netherlands in 2001 were a lack of culling and rendering capacity. Suppressive vaccination formed the basis for the solution to both problems and was primarily used to halt the possible spread of the virus. This allowed culls to take place on vaccinated farms when sufficient culling capacity eventually became available. In addition, the vaccinated cloven-hoofed animals could be removed alive and then killed in central culling places fourteen or more days after vaccination. Using slaughterhouses as central culling places meant that parts of carcasses could be deep-frozen, which solved the lack of rendering capacity. The deep-frozen carcass parts were destroyed later, when rendering capacity became available. To guarantee that all vaccinated, culled and temporarily deep-frozen cloven-hoofed animals were eventually destroyed, a balanced audit trail, partly based on kilogram records, was vital in this situation.

Abattoirs↗

The macro-economic impact of a foot-and-mouth disease incursion in New Zealand.

The 2001 outbreak of Foot-and-Mouth Disease (FMD) in the United Kingdom heightened public concern in New Zealand about the economic consequences of an outbreak of FMD, and resulted in the Reserve Bank and Treasury conducting an assessment of the macro-economic impact of a small FMD outbreak in New Zealand. The study was based on a relatively small outbreak in which 50 properties were infected over a period of two months. Cumulative losses calculated over two years from the beginning of the hypothetical outbreak were estimated at around NZ dollars 10 billion, a figure twice as large as the initial Ministry of Agriculture and Forestry estimate. The main reason for this difference is that the Reserve Bank study included the additional macro-economic effects of a slump in domestic demand. The study also demonstrated that in New Zealand under the conditions of the current OIE Terrestrial Animal Health Code for FMD, the economic impact of any programme to control FMD by vaccination in which vaccinated animals are not slaughtered, is significantly worse than rapid eradication by stamping out.

Animals↗

Molecular cloning and expression of the VP1 gene of foot-and-mouth disease virus C1 in E. coli: effect on bacterial cell viability.

The VP1 gene of foot-and-mouth disease virus (serotype C1) has been cloned in Escherichia coli Clts cells, under the control of the bacteriophage lambda pL promoter. The expressed VP1 protein was complete and non-fused, and its molecular weight was indistinguishable from that of the VP1 obtained from virions. Cells harbouring the recombinant vectors exhibited symptoms of plasmid instability and toxicity and died in a few weeks even when never exposed to inducing conditions. A new plasmid clone in which a segment of the VP1 gene was fused with contiguous genes of the viral genome was very stable. The expressed partial VP1 protein contains the two major immunogenic domains of the virion. This system can be used as a tool to design an immunogenic VP1, and to explore possible synthetic vaccines against foot-and-mouth disease.

Animals↗

Structure and immunogenicity of experimental foot-and-mouth disease and poliomyelitis vaccines.

The physico-chemical properties and immunogenicity of experimental vaccines against foot-and-mouth disease (FMD) and poliomyelitis, prepared by treatment of the viruses with N-acetylethyleneimine (AEI), formaldehyde or neutral red, have been studied. None of these reagents affects the rate of sedimentation of the particles or their reaction with antibody against the major immunogenic sites. FMD vaccines prepared by inactivation with AEI or neutral red, behaved like the untreated virus, in that they were disrupted on lowering the pH below 7. The RNA of the AEI-inactivated virus was degraded into slowly sedimenting molecules. Unlike AEI-inactivated virus, from which all the RNA could be extracted with phenol-SDS, the recovery from the neutral red inactivated virus was variable and was sometimes as low as 40%; this RNA gave a heterogenous profile in sucrose gradients. The capsid proteins in the AEI preparation migrated in SDS-PAGE to the same positions as those of untreated virus, but in the neutral red preparation there was evidence of cross-linking. In contrast, the formaldehyde-inactivated vaccine was stable below pH 7 and the RNA could not be released by extraction with phenol-SDS at pH 5, because the capsid proteins had become cross-linked and/or linked to the RNA. As with foot-and-mouth disease virus (FMDV), poliovirus which had been inactivated with formaldehyde did not release its RNA on extraction with phenol-SDS and the capsid proteins were also cross-linked. Surprisingly, although AEI cleaved the viral RNA slowly in situ, the virus was no longer infectious after 6 h. Neutral red did not reduce the infectivity of the virus. All of the preparations gave similar levels of neutralizing antibody after a single inoculation. The high levels obtained with the formaldehyde-inactivated vaccines have implications for the processing of fixed particles by the antigen-presenting cells.

Animals↗

Comparison of SAT-1 foot-and-mouth disease virus isolates obtained from East Africa between 1971 and 2000 with viruses from the rest of sub-Saharan Africa.

Foot-and-mouth disease serotype SAT-1 seems to be endemic in many sub-Saharan African countries. Phylogenetic analysis using the 1D gene of 51 SAT-1 isolates from East, West and southern Africa indicated the presence of at least 6 lineages and 11 genotypes with linkages between various geographical regions of the subcontinent. Differences were observed between countries in East Africa, the main focus of this study, with individual countries suffering outbreaks from isolates belonging to various genotypes, which is evidence of reintroduction of strains and long-term circulation of outbreak viruses. The amount of variation observed has significant implications for disease control on the subcontinent.

Africa South of the Sahara↗

Validation of a LightCycler-based reverse transcription polymerase chain reaction for the detection of foot-and-mouth disease virus.

A specific reverse transcription polymerase chain reaction (RT-PCR) for the detection of the polymerase gene (3D) of foot-and-mouth disease virus (FMDV) was developed and validated with an analytical sensitivity of equal to, to 1,000 times higher than that of a single passage virus isolation. The performance of the RT-PCR was determined in 180 runs. After implementation, 5.3% of the tests had to be rejected due to invalid controls (e.g. cross-contamination of negative controls). The diagnostic sensitivity, determined using 124 samples from experimentally infected animals, was 91.9% for RT-PCR and 84.7% for virus isolation. Diagnostic specificity, determined by testing 258 samples from uninfected animals, was 100% by both tests. Of the 627 samples tested by RT-PCR and virus isolation, 85 reacted positively in both tests (13.5%) and 447 negatively in both tests (71.3%). One sample was positive by virus isolation and negative by RT-PCR (0.2%), 94 samples were positive by RT-PCR and negative by virus isolation (15%). The majority (84 of 94) of the 15% RT-PCR positive and virus isolation negative samples were among other samples from farms that reacted positively by both tests. The new RT-PCR is a robust, reliable and sensitive test, provided that adequate measures are taken to prevent cross-contamination. A possible preventive measure is to exclude ELISA positive samples from the RT-PCR testing.

Animals↗