Broad immunogenic spectrum of monovalent and trivalent foot-and-mouth disease virus vaccines containing O1 campos, A24 cruzeiro and A Argentina 2001 strains against circulating viral lineages in cattle and pigs

FMD remains endemic in many Asian and African countries where multiple variants of serotypes O and A, among others, currently circulate. Due to lack of cross-protection between serotypes and incomplete protection between some strains even within a serotype, an important challenge for the application of effective vaccination programs is to select highly immunogenic and widely cross-reactive vaccine strains. Adaptation of a candidate field virus for use as a vaccine can be quite complex, so that whenever possible, the use of well-established vaccine viruses could have enormous advantages. FMD vaccine strains harmonized for use in South America have shown excellent results in FMD control, not only in the region, where it is still used systematically as a preventive measure, but also more recently in some Asian countries. To gain further insight into the immunogenic spectrum of these strains, VN tests (VNT) were performed with sera from cattle and/or pigs vaccinated with monovalent (type O) or trivalent (types O and A) formulations against 122 type O and 32 type A field viruses isolated from 35 countries in Asia and Africa, belonging to different lineages. Almost all VNT titers obtained were within the expected protective level, indicating the wide immunogenic spectrum of high potency FMD vaccines formulated with O1 Campos, A24 Cruzeiro and A Argentina 2001 South American vaccine strains belonging to EURO-SA topotypes against currently active viruses from other topotypes. These in vitro results are in line with previously reported in vivo challenge tests in pigs against three A/ASIA/Sea-97 isolates and two isolates belonging to type O lineages O/SEA/Mya-98 and O/ME-SA/Ind-2001e.

Expression of recombinant dengue virus type 1 non-structural protein 1 in mammalian cells and preliminary assessment of its suitability to detect human IgG antibodies elicited by viral infection

In recent years dengue has become a rapidly growing public health problem worldwide, however, the availability of accurate and affordable diagnostic immunoassays is limited, partly due to the difficulty of producing large quantities of purified antigen. Non-structural protein 1 (NS1) has shown to be a good candidate for inclusion in diagnostic assays and for serosurveys, particularly in endemic countries as a prerequisite for vaccination. In this work the NS1 antigen derived from dengue virus type-1 (DENV1) was expressed in HEK293-T cells and purified by affinity chromatography. The recombinant protein was recovered properly folded as dimers, highly purified and with good yield (1.5 mg/L). It was applied as a serological probe in an indirect ELISA developed in this work to detect human IgG antibodies. Preliminary comparative performance values of 81.1% sensitivity and 83.0% specificity of the developed and preliminary validated iELISA, relative to a commercial kit were obtained, suggesting that the purified recombinant DENV1 NS1 antigen is suitable to detect IgG antibodies, indicative of past DENV infection.

Challenges in foot-and-mouth disease virus strain selection as an input to attain broad vaccine intraserotype cross-protection

Introduction: Vaccination against foot-and-mouth disease virus is regarded as the most effective way to prevent disease. Selection of appropriate vaccine strains is challenging due to lack of cross-protection between serotypes and incomplete protection between some strains within a serotype. Vaccine effectiveness can be affected by vaccine formulation, vaccination approaches, and also by emerging field variants. Therefore, a precise evaluation of the protective capacity of the selected vaccine virus is essential.Areas covered: This article discusses the limitations of currently in use in vitro methods to assess the protective capacity of vaccine strains. It includes the assessment of well-established South American vaccine strains, O₁/Campos and A₂₄/Cruzeiro, against outbreaks/emergencies in the continent, as well as against recent isolates from East and Southeast Asia.Expert opinion: In vitro methods, and particularly r₁ values, used to evaluate the protective capacity of vaccine strains are not conclusive and do not cover the variety of field scenarios. At present, an option when facing emergencies could be to use well-established vaccine strains with broad antigenic/immunogenic coverage, including conditions that lead to increased coverage such as vaccine formulations and vaccination schemes.

Thieno[2,3-b]pyridine derivatives: a new class of antiviral drugs against Mayaro virus

Mayaro virus (MAYV) is an arthropod-borne virus and a member of the family Togaviridae, genus Alphavirus. Its infection leads to an acute illness accompanied by long-lasting arthralgia. To date, there are no antiviral drugs or vaccines against infection with MAYV and resources for the prevention or treatment of other alphaviruses are very limited. MAYV has served as a model to study the antiviral potential of several substances on alphavirus replication. In this work we evaluated the antiviral effect of seven new derivatives of thieno[2,3-b]pyridine against MAYV replication in a mammalian cell line. All derivatives were able to reduce viral production effectively at concentrations that were non-toxic for Vero cells. Molecular modeling assays predicted low toxicity risk and good oral bioavailability of the substances in humans. One of the molecules, selected for further study, demonstrated a strong anti-MAYV effect at early stages of replication, as it protected pre-treated cells and also during the late stages, affecting virus morphogenesis. This study is the first to demonstrate the antiviral effect of thienopyridine derivatives on MAYV replication in vitro, suggesting the potential application of these substances as antiviral molecules against alphaviruses. Additional in vivo research will be needed to expand the putative therapeutic applications.

Redefining the "carrier" state for foot-and-mouth disease from the dynamics of virus persistence in endemically affected cattle populations

The foot-and-mouth disease virus (FMDV) "carrier" state was defined by van Bekkum in 1959. It was based on the recovery of infectious virus 28 days or more post infection and has been a useful construct for experimental studies. Using historic data from 1,107 cattle, collected as part of a population based study of endemic FMD in 2000, we developed a mixed effects logistic regression model to predict the probability of recovering viable FMDV by probang and culture, conditional on the animal's age and time since last reported outbreak. We constructed a second set of models to predict the probability of an animal being probang positive given its antibody response in three common non-structural protein (NSP) ELISAs and its age. We argue that, in natural ecological settings, the current definition of a "carrier" fails to capture the dynamics of either persistence of the virus (as measured by recovery using probangs) or the uncertainty in transmission from such animals that the term implies. In these respects it is not particularly useful. We therefore propose the first predictive statistical models for identifying persistently infected cattle in an endemic setting that captures some of the dynamics of the probability of persistence. Furthermore, we provide a set of predictive tools to use alongside NSP ELISAs to help target persistently infected cattle.

Accuracy of herdsmen reporting versus serologic testing for estimating foot-and-mouth disease prevalence

Herdsman-reported disease prevalence is widely used in veterinary epidemiologic studies, especially for diseases with visible external lesions; however, the accuracy of such reports is rarely validated. Thus, we used latent class analysis in a Bayesian framework to compare sensitivity and specificity of herdsman reporting with virus neutralization testing and use of 3 nonstructural protein ELISAs for estimates of foot-and-mouth disease (FMD) prevalence on the Adamawa plateau of Cameroon in 2000. Herdsman-reported estimates in this FMD-endemic area were comparable to those obtained from serologic testing. To harness to this cost-effective resource of monitoring emerging infectious diseases, we suggest that estimates of the sensitivity and specificity of herdsmen reporting should be done in parallel with serologic surveys of other animal diseases.

Evolving perception on the benefits of vaccination as a foot and mouth disease control policy: contributions of South America

Within the past decade, changes in perceptions on the benefits of vaccination as an appropriate tool to achieve complete foot and mouth disease eradication have become evident. The former negative view was derived from misconceptions, resulting mainly from the belief that vaccines are not entirely effective and that vaccination masks asymptomatic viral circulation. The advent in the 1990s of vaccination policies implemented within a strategic eradication plan in South America, and during recurrence of the disease in disease-free regions contributed towards generating more reliable and visible outcomes of vaccination programs, paving the way towards a new perception. Particularly relevant was the development and application of novel serodiagnostic approaches to assess silent viral circulation, irrespective of vaccination. The use in South America of vaccination allied to serosurveys to accompany viral clarification during eradication campaigns and after emergencies clearly established the importance of this control tool to stop the spread of viral infection. This alliance gave input to break many myths associated with the use of vaccines, including the belief that immunized carrier animals pose an epidemiologic risk. This experience launched new concepts that supported the internationally recognized status of foot and mouth disease-free regions with vaccination and the 'vaccination to live' policy as an alternative to 'stamping out'.

First full-length genomic sequence of a hepatitis A virus isolated in Argentina shows recombination between subgenotypes IA and IB

A hepatitis A virus (HAV) recovered in Argentina from a stool sample of a sick child in the year 2006 (HAV-Arg/06) was entirely sequenced. Phylogenetic analysis included the HAV-Arg/06 sequence in subgenotype IA, either considering the usual VP1-2A variable junction fragment or the full length nucleotide sequence. Interestingly, a recombination event with subgenotype IB, involving a portion of the 2C-3A nonstructural proteins coding region (nucleotides 4961-5140) was detected using specific software. Only subgenotype IA strains have been detected in Argentina or Uruguay, whereas subgenotype IA and IB strains have been reported to circulate in Brazil. Although recombination has been given an important role in the evolution of picornaviruses, there have been only a few reports of its involvement in the evolution of HAV, probably due to the limited number of complete HAV sequences available. This study constitutes the first report of a full-length HAV sequence in Argentina and the third in South America, after the sequence of the IA isolate HAV5 from Uruguay and the IB isolate HAF-203 from Brazil. The availability of new sequence data covering the complete HAV genome will help establish a more consistent genetic relatedness among HAV isolates and the role of recombination in its evolution.

Comparative evaluation of six ELISAs for the detection of antibodies to the non-structural proteins of foot-and-mouth disease virus

To validate the use of serology in substantiating freedom from infection after foot-and-mouth disease (FMD) outbreaks have been controlled by measures that include vaccination, 3551 sera were tested with six assays that detect antibodies to the non-structural proteins of FMD virus. The sera came from naïve, vaccinated, infected and vaccinated-and-infected animals; two-thirds from cattle, the remainder from sheep and pigs. The assays were covariant for sensitivity, but not necessarily for specificity. A commercial kit from Cedi-diagnostics and an in-house assay from IZS-Brescia were comparable to the NCPanaftosa-screening index method described in the Diagnostic Manual of the World Animal Health Organisation. Using these three tests the specificity and sensitivity for the detection of carriers in vaccinated cattle approaches or exceeds 99% and 90%, respectively.

Genetic variation of foot-and-mouth disease virus isolates recovered from persistently infected water buffalo (Bubalus bubalis)

Genetic variation of foot-and-mouth disease virus (FMDV) isolates, serotype O, recovered serially over a 1-year period from persistently infected buffalos was assessed. The persistent state was established experimentally with plaque-purified FMDV, strain O(1)Campos, in five buffalos (Bubalus bubalis). Viral isolates collected from esophageal-pharyngeal (EP) fluids for up to 71 weeks after infection were analyzed at different times by nucleotide sequencing and T(1) RNase oligonucleotide fingerprinting to assess variability in the VP1-coding region and in the complete genome, respectively. Genetic variation increased, although irregularly, with time after infection. The highest values observed for the VP1-coding region and for the whole genome were 2.5% and 1.8%, respectively. High rates of fixation of mutations were observed using both methodologies, reaching values of 0.65 substitutions per nucleotide per year (s/nt/y) and 0.44s/nt/y for nucleotide sequencing and oligonucleotide fingerprinting, respectively, when selected samples recovered at close time periods were analyzed. The data herein indicate that complex mixtures of genotypes may arise during FMDV type O persistent infection in water buffalos, which can act as viral reservoirs and also represent a potential source of viral variants. These results fit within the quasi-species dynamics described for FMDV, in which viral populations are constituted by related, non-identical genomes that evolve independently from each other, and may predominate at a given time.

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.

Development of an inhibition ELISA test for the detection of non-capsid polyprotein 3ABC in viral suspensions destined for inactivated foot-and-mouth disease vaccines

The use during the last decade of immuno-enzymatic tests based on the detection of antibodies to the non-capsid proteins (NCPs) of foot-and-mouth disease virus (FMDV) to assess viral circulation, irrespective of vaccination, supported the incorporation into the OIE code of the 'free from FMDV with vaccination' category and opened the way to a 'vaccination to live' policy. Eradication programmes in South America include systematic vaccination accompanied by large serosurveys through NCP antibody testing to ensure the absence of residual viral activity. For correct interpretation of serosurveys, a major prerequisite is that vaccines made of semi-purified preparations of inactivated virions do not contain levels of NCPs, which upon proper presentation conditions, could induce an antibody response under the conditions for field immunization. This work describes the development of an inhibition ELISA to detect NCP polyprotein 3ABC in viral suspensions destined for vaccine production as an in-process control during vaccine manufacture. Antibody responses against NCP 3ABC in vaccinated and revaccinated cattle, induced by vaccines with different purification processes and formulations, are discussed.

Non-capsid proteins to identify foot-and-mouth disease viral circulation in cattle irrespective of vaccination

The ability of foot-and-mouth disease virus (FMDV) to establish subclinical and even persistent infection, the so called carrier state, imposes the need to reliably demonstrate absence of viral circulation, to monitor the progress of control measures, either during eradication programs or after reintroduction of virus in free areas. This demonstration becomes critical in immunized populations, because of the concern that silent viral circulation could be hidden by immunization. This concern originates from the fact that vaccination against foot-and-mouth disease (FMD) protects against clinical disease, but not necessarily against subclinical infection or establishment of the carrier state in cattle. A novel approach, developed and validated at PANAFTOSA during the 1990s, based on an immunoenzymatic system for detection of antibodies against non-capsid proteins (NCP) has proven valuable for monitoring viral circulation within and between herds, irrespective of the vaccination status. Antibodies against NCP are induced during infection but, in principle, not upon vaccination. The validation of this system led to its international recognition as the OIE index test. The fitness of this serosurvey tool to assess viral circulation in systematically vaccinated populations was demonstrated through its extensive application in most regions in South America. The experience attained in these regions supported the incorporation of the "free of FMD with vaccination" provisions into the OIE code. Likewise, it opened the way to alternatives to the "stamping out" policy. The results gave input to an old controversy related to the real epidemiological significance, if any, of carrier animals under the vaccination conditions in South America, and supported the development of recommendations and guidelines that are being implemented for serosurveys that go with control measures in vaccinated populations.

Vaccination: foot-and-mouth disease experience in South America

Vaccination against foot-and-mouth disease (FMD) constitutes an important component of the policy for its control and eradication in South America. Considering that immunization may not impair subclinical infection, it became advisable to ally to vaccination campaigns a surveillance instrument to monitor silent viral circulation. Novel approaches for the evaluation of antibodies to FMD non-capsid proteins (NCPs), developed and validated at PANAFTOSA proved valuable for assessing viral circulation in immunized populations. The extensive and coordinated application in South America of vaccination together with this serosurvey tool indicated the effectiveness of systematic vaccination to prevent FMD spread and to restrain silent viral circulation intra- and inter- herds, and gave input to an old controversy related to the real epidemiological significance, if any, of carrier animals under the vaccination conditions in South America. The fitness of NCP tests to assess viral circulation in a population supported the incorporation into the OIE code of the "free of FMD with vaccination" category as a step prior to the recognition of the "free of FMD without vaccination" category. Likewise it released the path to allow animals, vaccinated for protective purposes during emergencies, to live for the term of their productive lives.

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. The resulting patterns were correlated to the epidemiological status. On this basis, results of over 100,000 sera derived from cattle populations in regions with various well-documented epidemiological situations were compiled and are exemplified in this paper.Distinct distributions of antibody reactivity patterns reflecting the various epidemiological situations were attained. Whereas non-affected areas presented a rather homogenous negative pattern with very limited test-positive reactions, affected regions revealed quite heterogeneous profiles, including positive and negative categories, with distributions that varied according to the region. The use of graphic prints encompassing I-ELISA 3ABC antibody profile responses constituted an adequate epidemiological indicator of the risk of foot-and-mouth disease viral activity, providing immediate visualization for a rapid inference of the epidemiological situation of a region. Moreover, such profiles allowed for convenient follow-up of infection after a focus as a function of time and geographical spread.

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. The system is based on the detection of antibodies against non-capsid proteins required for viral replication. These proteins, in principle, are removed from the viral suspensions destined for production of BEI inactivated vaccines. Within the validation steps, evaluation of potential induction of antibodies to non-capsid proteins caused by traces of these proteins eventually remaining in the vaccines was a major concern. This report presents a review on the experience gathered through the application of the system to various experimental and field immunization conditions. It was concluded that vaccination is not expected to induce antibody responses to non-capsid proteins that could lead to misinterpretation of serological investigations. Progress on the development of approaches towards vaccine certification to guarantee absence of interference will be discussed.

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. For regularly vaccinated livestock, a clear negative profile was proved in samples from regions without recent history of FMD. In contrast, at 90 and 900 days post-outbreak, coexistence of a positive and a negative population was established. These findings indicated that, irrespective of vaccination, the test allowed a classification of the herd-disease status. A high degree of agreement was observed between I-ELISA-3ABC and EITB results for clearly reactive and non-reactive sera. For samples with reactivity values close to that of the cut-off, the EITB profiles upheld the definition of the infection condition. On this basis, screening by I-ELISA-3ABC, together with confirmation of suspect or positive samples by EITB is proposed as an adequate and accurate approach for large-scale epidemiological surveillance.

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.

SAMPLE POPULATION

A total of 2,194 serum samples were acquired from animals at different farms and were separated according to age: animals < and > 2 years old.

PROCEDURE

Specific antibodies to replicating virus were detected by use of the EITB assay that utilizes a set of 5 bioengineered nonstructural antigens as serologic probes.

RESULTS

EITB-positive reaction was restricted to sera from cattle in areas with the last outbreaks of FMD during 1989-1990, and to animals > 2 years old. All cattle sera from regions that were free of clinical FMD since (or prior to) 1989 were EITB negative. In contrast, use of the VIAA test yielded a rather homogeneous distribution of positive results when regions without FMD during the last 4 years preceding sample collection were compared with those affected during 1989-1990. VIAA test-positive reaction was also found in sera from animals born after the last FMD outbreak.

CONCLUSIONS

The EITB assay proved to be a sensitive, specific, safe, rapid, and economic tool for monitoring the progress of FMD eradication programs, mainly because it eliminated false-positive results form the VIAA test.

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. Postmortem specimens were asceptically removed.

ANIMALS

Three bovids and 3 pigs were studied, as well as 1 control animal for each species.

PROCEDURE

Various tissues were examined for the presence of FMDV-specific sequences by dot-blot hybridization assay, using a molecularly cloned FMDV cDNA corresponding to the polymerase coding region.

RESULTS

The FMDV-specific genomic sequences were only detected in RNA from spleen, lung, larynx, tonsils, pancreas, liver, esophagus, and WBC of bovids.

CONCLUSIONS

It was established that, at late stages of the persistent infection, when virus isolation was not possible, cattle may carry FMDV-specific sequences in different tissues. Retention of viral sequences could not be demonstrated in specimens from experimentally infected swine, 28 days after viral 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. These results, together with the substantial rates of genomic variation observed between some pairs of strains recovered at close time periods, suggested the coexistence of heterogeneous populations in which variants evolve independently from each other, and predominate at irregular time intervals. Furthermore, non-related patterns of variation were observed in the four animals. Similarly, genetic diversity of representative strains from major serotype O outbreaks in endemic disease regions of southeastern Brazil and central eastern Argentina which occurred between 1958 and 1983, suggested that outbreak strains are also likely to represent fluctuations of heterogeneous populations which evolve independently from each other. The possible role of persistent infections in the introduction of variant populations in the field is discussed.