Vaccines and companion diagnostic tests for foot-and-mouth disease virus. An overview of the experience in South America.

Vaccination constitutes an important control policy for foot-and-mouth disease (FMD) in affected areas with advanced eradication programmes, as well as in free regions that decide to use immunization as a control measure after a recent introduction of the disease. However, considering that vaccinated animals exposed to FMD virus can establish sub-clinical infection and eventually remain persistently infected, availability of tools to identify sub-clinical infection and its silent transmission within and between herds, regardless of their vaccination state, is of utmost importance. In response to the need for new diagnostic tools to support the eradication campaigns implemented in 1988 in South America, during the past decade we have developed, validated and applied a highly sensitive and specific immuno-enzymatic system for recognition of persistence at a herd level.

Rapid serological profiling by enzyme-linked immunosorbent assay and its use as an epidemiological indicator of foot-and-mouth disease viral activity.

Frequency distribution of reactivity levels of foot-and-mouth disease infection-specific antibodies in livestock populations was analysed. Specific antibody responses against non-capsid polyprotein 3ABC were assessed through a highly sensitive indirect enzyme-linked immonosorbent assay (I-ELISA 3ABC). A graphic display of data was designed based on three negative and three positive categories to illustrate reactivity patterns.

Use of the reverse transcription polymerase chain reaction (RT-PCR) for the rapid diagnosis of foot and mouth disease in South America.

Foot and mouth disease (FMD) is a limiting factor for the economic progress of the animal industry in South America. The presence of the disease results in the imposition of national and international sanitary barriers to animals and animal products, and, most especially, a reduction in the availability of protein from animal origin and in income. Rapid and accurate identification of infected animals, those with either clinical or subclinical disease as well as with persistent infection, is essential for maintaining an efficient eradication programme.

Control of foot and mouth disease: the experience of the Americas.

Foot and mouth disease (FMD) was first recognised in South America in 1870, almost simultaneously in the province of Buenos Aires (Argentina), in the central region of Chile, in Uruguay, in southern Brazil and coincidentally, on the northeastern coast of the United States of America. The epidemiology of the disease was unknown and no government action was taken following the initial outbreaks. This resulted in the disease spreading to other areas of Chile, as well as to Peru, Bolivia and Paraguay, reaching Venezuela and Colombia in the 1950s, and Ecuador in 1961.

Unapparent foot and mouth disease infection (sub-clinical infections and carriers): implications for control.

Unlike animals which are carriers of foot and mouth disease (FMD), sub-clinically infected animals may be highly contagious. The implications of sub-clinical infections for the control of FMD are serious because such animals are likely to disseminate the disease when in contact with susceptible livestock. Recent dissemination of FMD virus (FMDV) in Europe shows that sub-clinically infected animals render trade in animals or animal products a potential risk for importing countries.

International approach to eradication and surveillance for foot-and-mouth disease in the Americas.

Foot-and-mouth disease (FMD) was introduced into the Americas in 1870. At that time the disease was described simultaneously in the North coast of the United States of North America, the Province of Buenos Aires in Argentina, the central region of Chile, Uruguay, and South Brazil. At the beginning of the twentieth century the disease spread to the rest of Brazil, Bolivia, Paraguay, and Perú.

Improvement of a serodiagnostic strategy for foot-and-mouth disease virus surveillance in cattle under systematic vaccination: a combined system of an indirect ELISA-3ABC with an enzyme-linked immunoelectrotransfer blot assay.

Foot-and-mouth disease (FMD) recombinant non-capsideal viral antigens 3A, 3B, 2C, 3D and 3ABC were assessed individually in an indirect enzyme-linked immunosorbent assay (I-ELISA) for their ability to screen for persistent infection-specific antibodies in cattle, regardless of vaccination condition. Results of sequential serum samples from non-vaccinated animals with experimentally induced persistent infection, and their correlation with virus isolation, indicated that the polypeptides 3A, 3B and 3ABC showed the most adequate characteristics for further field studies. Reliable performance of the I-ELISA with the selected antigen 3ABC was indicated by the distinct patterns observed for the frequency distribution values of naive and true positive samples.

A quantitative assessment of the risk of transmission of foot-and-mouth disease, bluetongue and vesicular stomatitis by embryo transfer in cattle.

This paper addresses the risks involved when bovine embryos are moved internationally and, specifically, the possibilities of transmitting foot-and-mouth disease, bluetongue and vesicular stomatitis by embryos originating from an area in South America. The risk scenario pathway was divided into three phases for analysis. The first phase dealt with the potential for embryo contamination which depends on the disease situation in the exporting country and/or region, the health status of the herds and the donor cows from which the embryos are collected, and the pathogenetic characteristics of the specified disease agent.

The risks of disease transmission by embryo transfer in cattle.

Guidelines for the safe international movement of livestock embryos are provided in the International Animal Health Code of the Office International des Epizooties, and recommendations for embryo processing, based on numerous research papers on embryo-pathogen interaction studies, are given in the Manual of the International Embryo Transfer Society. Risk assessment is the logical extension of these approaches, since it provides veterinary authorities with a complete package of information on which to base their import/export decisions. Risk assessment includes evaluation of disease prevalence, effectiveness of Veterinary Services and competence of the embryo collection team.

Risks of introducing foot and mouth disease through the importation of beef from South America.

The safety of beef with respect to foot and mouth disease (FMD) is determined by the level of risk which the exporting region poses through disease prevalence, the reliability of the surveillance system of the region, the efficacy of the prevention and control measures, the efficiency of the Veterinary Services and the support of the private sector. The South American continent has been regionalised in accordance with these criteria. Today there are approximately 90 million cattle in a territory of over 5 million km2 comprising regions classified as having a very low to low level risk for FMD with regard to the export of animals and animal products.

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.

Identification of foot-and-mouth disease virus-free regions by use of a standardized enzyme-linked immunoelectrotransfer blot assay.

Objective: To assess the potential of a highly sensitive enzyme-linked immunoelectrotransfer blot (EITB) assay to monitor persistent foot-and-mouth disease (FMD) viral activity in a livestock population.

Design: Cattle sera were obtained in Uruguay in 1992, 2 years after the last outbreaks of FMD. Prevalence of antibodies, as assessed by the EITB assay and by the conventional immunodiffusion in agarose gel method (virus infection-associated antigen [VIAA] test), was correlated with occurrence of FMD.

Detection of foot-and-mouth disease viral sequences in various fluids and tissues during persistence of the virus in cattle.

Objective: To assess whether foot-and-mouth disease virus (FMDV)-specific sequences could be identified in tissues from persistently virus-infected animals.

Design: Cattle with experimentally induced persistent FMDV infections were slaughtered at 750 days after viral exposure. Experimentally infected pigs were slaughtered at 28 days after FMDV inoculation.

Genetic variation of foot-and-mouth disease virus during persistent infection in cattle.

Genetic variation of foot-and-mouth disease virus O1 Campos has been analyzed in consecutive isolates recovered over a one- or two-year period from four cattle with experimental persistent infection. Comparisons of RNase T1 two-dimensional maps and nucleotide sequences of the VP1-coding region revealed a continual, although irregular, increase in the fixation of mutations as the infection progressed. Most changes were not conserved in consecutive isolates.

Application of monoclonal antibodies to quality control of foot-and-mouth disease vaccines.

Panels of monoclonal antibodies (mAbs) produced against foot-and-mouth disease (FMD) virus types O, A and C were selected for cell culture neutralization titre (NT), mouse protection index (MPI), trypsin sensitivity (TS) and avidity to different epitopes. The selected sets were used to assay the antigen concentration and the fit between FMDV vaccine and challenge strains. It was observed that FMD vaccines protect more than 75% of vaccinated cattle when manufactured with antigens characterized by (1) a high degree of fit with the potency control virus, and (2) mean ELISA 50% titres (T50) > 28 for O, > 18 for A and > 75 for C types, respectively, using the corresponding mAb set.

Comparison of virus neutralisation and enzyme-linked immunosorbent assay for the identification of antibodies against vesicular stomatitis (Indiana 3) virus.

Bovine, equine and swine sera from areas free from vesicular stomatitis virus (VSV) Indiana 3 (IND3)--namely Argentina, Chile, Italy and Uruguay--and endemic areas (in Brazil) were examined for anti-VSV IND3 virus antibodies in order to compare results obtained using the virus neutralisation (VN) test and liquid-phase blocking enzyme-linked immunosorbent assay (ELISA). Statistical analysis of the data showed close agreement between the two techniques (K = 0.92).

Diagnosis of persistent aphthovirus infection and its differentiation from vaccination response in cattle by use of enzyme-linked immunoelectrotransfer blot analysis with bioengineered nonstructural viral antigens.

A highly sensitive enzyme-linked immunoelectrotransfer blot (EITB) assay, capable of detecting aphthovirus-specific antibodies to replicating virus in sera from cattle with persistent infection, was developed. The assay uses a set of purified recombinant DNA-derived nonstructural viral antigens as serologic probes in lieu of the traditionally used virus infection-associated antigen(s) partially purified from baby hamster kidney-infected cells. Sera from cattle with experimentally induced aphthovirus infection were analyzed sequentially by EITB at various postinoculation days, and the results were compared with those obtained by currently used techniques.

Characterization of foot-and-mouth disease virus by monoclonal antibodies.

Monoclonal antibodies (MAbs) were produced against foot-and-mouth disease (FMD) virus types O1 Campos Br1/58, A24 Cruzeiro Br1/55, and C3 Indaial Br1/71, which are the strains used for production of FMD vaccines in the majority of South American countries. Within the library of MAbs produced, a group was selected on the basis of their neutralizing titer in cell culture, protective titer in suckling mice, sensitivity to trypsin, and specificity for virus structural proteins. The MAbs were utilized in an ELISA test format to compare European and South American representative field isolates with vaccine production strains in their r1 relationship as obtained by 50% complement fixation (CF50) with polyclonal antibodies (PAb) and their virus neutralization (VN) relationship obtained with sera from one-time-vaccinated and from revaccinated cattle, respectively.

Foot-and-mouth disease virus typing by complement fixation and enzyme-linked immunosorbent assay using monovalent and polyvalent antisera.

An indirect "sandwich" enzyme-linked immunosorbent assay (ELISA) using polyvalent and monovalent antisera was compared with the 50% complement fixation (CF50) test for the detection of foot-and-mouth disease (FMD) O, A, and C virus types. ELISA was more sensitive than CF50 tests when polyvalent antisera were used for detecting the 3 types of virus in epithelial samples, whereas ELISA using monovalent antisera was the least sensitive technique. The ELISA performed with polyvalent antisera was 9 times more sensitive for detecting FMD virus than that with monovalent antisera.

Development and evaluation of an enzyme-linked immunosorbent assay for detection, typing, and subtyping of vesicular stomatitis virus.

An indirect sandwich enzyme-linked immunosorbent assay (ELISA) has been used for vesicular stomatitis virus (VSV) typing using sets of monovalent and polyvalent rabbit/guinea pig antisera for identification of VSV types New Jersey (VNJ) and Indiana (VIND). The VIND polyvalent antiserum (VIND-P) detects any strain of the 3 subtypes of the VIND type (VIND-1, VIND-2, and VIND-3) with the same strong reactivity. It is also possible to subtype the VIND strains using VIND-P rabbit antiserum as capture antibody and monovalent VIND-1, VIND-2, or VIND-3 guinea pig antisera as detector.

Expression of the aphthovirus RNA polymerase gene in Escherichia coli and its use together with other bioengineered nonstructural antigens in detection of late persistent infections.

A plasmid has been constructed containing the DNA sequences that direct the expression of the aphthovirus RNA-dependent RNA polymerase (virus infection-associated antigen, VIAA) in its native form. The aphthovirus polypeptide was designed to contain only a single additional amino acid, the N-terminal methionine. The recombinant protein has been purified and used in enzyme-linked immunoelectrotransfer blots to detect aphthovirus-specific antibodies in the sera of persistently infected animals.