Characterization of a type O foot-and-mouth disease virus re-emerging in the year 2011 in free areas of the Southern Cone of South America and cross-protection studies with the vaccine strain in use in the region

An IgG1 single-dilution avidity ELISA predicts cross-protection against heterologous foot-and-mouth disease virus challenge after vaccination

This study aims to analyze if the results from different serological assays, used alone or combined, could match the outcome of challenge infection with foot-and-mouth disease virus (FMDV) after vaccination in cattle. Day-of-challenge sera from animals that had been vaccinated 21 days before with monovalent formulations containing inactivated A Iran 96 or A Iran 99 virus strains were used. Challenge and serology were performed with A22 Iraq strain. IgG1 titers and total-IgG avidity indexes were significantly higher in protected animals (p < 0.01) while IgG2-titers were not related to protection (p > 0.05). An IgG1 avidity ELISA was developed to analyze in one step, IgG1 levels and avidity. This assay estimated protection with 96 % accuracy. A strong agreement with challenge results was achieved (K = 0.85), suggesting a role of high-affinity IgG1 in protection against FMDV. These results support the assessment of the single dilution IgG1-Avidity ELISA to predict cross-protection in FMDV-vaccinated cattle.

Foot-and-mouth disease virus strains isolated in Vietnam during 2010-2019: genetic characterization and antigenic relatedness to the Euro SA vaccine

Foot-and-mouth disease is a highly contagious disease that affects cloven-hoofed animals. It has an important socio-economic impact on the livestock industry because it produces a drastic decrease of productivity. The disease has been successfully eradicated from some regions, including North America and Western Europe, but it is still endemic in developing countries. Agriculture plays an important role in the national economy of Vietnam, to which animal production contributes a great proportion. The concurrent circulation of foot-and-mouth disease virus (FMDV) serotypes O, A, and Asia 1 has been detected in recent years, but serotype O remains the most prevalent and is responsible for the highest numbers of outbreaks. Appropriate vaccine strain selection is an important element in the control of FMD and is necessary for the application of vaccination programs in FMD-affected regions. Here, we present updated information about the genetic and antigenic characteristics of circulating strains, collected from endemic outbreaks involving types O and A, between 2010 and 2019. Neutralizing assays showed a good in vitro match between type O strains and the monovalent O1 Campos vaccine strain. High r1 values were obtained (above 0.7) when testing a swine serum pool collected 21 days after vaccination, but the O/VTN/2/2019 strain was an exception. An EPP estimation resulted in a median neutralizing titre of about 1.65 log10, indicating that good protection could be achieved. For type A Asia SEA 97 lineage strains, acceptable individual neutralizing titres were obtained with estimated EPP values over 80% for different combinations of vaccine strains. Taking into account that the r1 value is one tool of a battery of tests that should be considered for estimating the cross-protection of a field strain against a vaccine strain, an in vivo challenge experiment was also performed, yielding a PD50 value of 8.0. The results indicate that South American strains could be potentially used for controlling outbreaks involving these lineages. This study demonstrates the importance of considering strain characteristics when choosing vaccine strains and controls.

Kinetics of foot-and-mouth disease vaccine-induced antibody responses in buffaloes (Bubalus bubalis): avidity ELISA as an alternative to the virus neutralization test

The role of water buffaloes in foot-and-mouth disease (FMD) epidemiology as one of the major hosts of the virus that can develop persistent asymptomatic infection highlights the importance of sustaining surveillance on the antibody response elicited by vaccination in these animals. There is gap in the knowledge on how serological assays that measure antibodies against capsid proteins perform with buffalo samples and which would be the most reliable test to substitute the virus neutralization test (VNT) a cumbersome and low-throughput tool for field surveillance. Alternatively, the liquid-phase blocking sandwich ELISA (LPBE) is commonly used. Previous data from our laboratory demonstrated that the vaccine-induced antibodies assessed by the LPBE yielded low specificity with buffaloes' samples. In contrast, a single-dilution avidity ELISA (AE) aimed to detect high-avidity antibodies against exposed epitopes, combined with an indirect ELISA (IE) to assess IgG levels, produced more reliable results. Here we analyzed for the first time the kinetics of the antibodies induced by vaccination in two different buffalo herds (n = 91) over 120 days using AE, IE, LPBE, and the VNT. Kinetics were similar in the different assays, with an increase of antibodies between 0- and 14-days post-vaccination (dpv) which were maintained thereafter. VNT and AE results were concordant (Kappa value = 0.76), and both assays revealed a decay in the antibody response in calves with maternal antibodies at 90 and 120 dpv, which was not evidenced by the LPBE. These results show that kinetics of antibody responses to FMD vaccination are similar in buffalo and cattle, and support the use of indirect ELISA assays, in particular Avidity ELISA, as alternatives to the VNT for vaccine-immunity monitoring irrespectively of the animal's passive or active immune status.

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.

Emergence of a novel genetic lineage 'A/ASIA/G-18/2019' of foot and mouth disease virus serotype A in India: A challenge to reckon with

Foot and mouth disease (FMD) has engendered large scale socioeconomic crises on numerous occasions owing to its extreme contagiousness, transboundary nature, complicated epidemiology, negative impact on productivity, trade embargo, and need for intensive surveillance and expensive control measures. Emerging FMD virus variants have been predicted to have originated and spread from endemic Pool 2, native to South Asia, to other parts of the globe. In this study, 26 Indian serotype A isolates sampled between the year 2015 and 2022 were sequenced for the VP1 region. BLAST and maximum likelihood phylogeny suggest emergence of a novel genetic group within genotype 18, named here as 'A/ASIA/G-18/2019' lineage, that is restricted so far only to India and its eastern neighbour, Bangladesh. The lineage subsequent to its first appearance in 2019 seems to have displaced all other prevalent strains, in support of the phenomenon of 'genotype/lineage turnover'. It has diversified into two distinct sub-clusters, reflecting a phase of active evolution. The rate of evolution of the VP1 region for the Indian serotype A dataset was estimated to be 6.747 × 10-3 substitutions/site/year. India is implementing a vaccination centric FMD control programme. The novel lineage showed good antigenic match with the proposed vaccine candidate A IND 27/2011 when tested in virus neutralization test, while the existing vaccine strain A IND 40/2000 showed homology with only 31% of the isolates. Therefore, in order to combat this challenge of antigenic divergence, A IND 27/2011 could be the preferred strain in the Indian vaccine formulations.

Advances in the eradication of foot-and-mouth disease in South America: 2011-2020

For more than 70 years, the countries of South America have been attempting to eliminate foot-and-mouth disease (FMD), but a regional strategy had not been established by all the affected countries until 1988. The Action Plan 1988-2009 of the Hemispheric Program for the Eradication of Foot-and-Mouth Disease (PHEFA 1988-2009) resulted in an FMD-free status in 88.4% of the bovine population of South America. However, countries of the Andean sub-region maintained an FMD endemic. In addition, sporadic outbreaks in vaccinated cattle populations have been reported in countries of the Southern Cone, endangering the disease-free status in these countries. Within this context, the PHEFA 2011-2020 was approved to eliminate FMD from the subcontinent, and this review describes the most important milestones during its execution. FMD in Ecuador and sporadic outbreaks in the Southern Cone sub-region were effectively eliminated. The outbreaks that occurred in Colombia in 2017 and 2018 were successfully controlled. The type C virus was removed from the vaccines in use in most countries, based on a risk assessment. This review also describes the progress made by the countries advancing toward official recognition as FMD-free in all their territories, with Bolivia, Brazil, and Peru leading the progressive suspension of vaccination to achieve FMD-free status without vaccination. Consequently, at the end of PHEFA 2011-2020, Venezuela was, and still is, the only country in the region whose control program has suffered setbacks, and no evidence has suggested that the transmission and infection of the bovine population have been eliminated. At the end of 2020, a new PHEFA Action Plan 2021-2025 was approved with a five-year horizon, to complete the eradication of the disease in the Americas.

Analysis of cattle movement networks in Paraguay: Implications for the spread and control of infectious diseases

Beef exports represent a substantial part of Paraguay's agricultural sector. Cattle movements involve a high risk due to the possible spread of bovine diseases that can have a significant impact on the country's economy. We analyzed cattle movements from 2014 to 2018 using the networks analysis methodology at the holding and district levels at different temporal scales. We built two types of networks to identify network characteristics that may contribute to the spread of two diseases with different epidemiological characteristics: i) a network including all cattle movements to consider the transmission of a disease of rapid spread like foot and mouth disease, and ii) a network including only cow movements to account for bovine brucellosis, a disease of slow spread that occurs mainly in adult females. Network indicators did not vary substantially among the cattle and cow only networks. The holdings/districts included in the largest strongly connected components were distributed throughout the country. Percolation analysis performed at the holding level showed that a large number of holdings should be removed to make the largest strongly connected component disappear. Higher values of the centrality indicators were found for markets than for farms, indicating that they may play an important role in the spread of an infectious disease. At the holding level (but not at the district level), the networks exhibited characteristics of small-world networks. This property may facilitate the spread of foot and mouth disease in case of re-emergence, or of bovine brucellosis in the country through cattle movements. They should be taken into account when implementing surveillance or control measures for these diseases.

Assessment on Different Vaccine Formulation Parameters in the Protection against Heterologous Challenge with FMDV in Cattle

Foot-and-mouth disease (FMD) remains one of the major threats to animal health worldwide. Its causative agent, the FMD virus (FMDV), affects cloven-hoofed animals, including farm animals and wildlife species, inflicting severe damage to the international trade and livestock industry. FMDV antigenic variability remains one of the biggest challenges for vaccine-based control strategies. The current study analyzed the host’s adaptive immune responses in cattle immunized with different vaccine protocols and investigated its associations with the clinical outcome after infection with a heterologous strain of FMDV. The results showed that antigenic payload, multivalency, and revaccination may impact on the clinical outcome after heterologous challenge with FMDV. Protection from the experimental infection was related to qualitative traits of the elicited antibodies, such as avidity, IgG isotype composition, and specificity diversity, modulating and reflecting the vaccine-induced maturation of the humoral response. The correlation analyses of the serum avidity obtained per vaccinated individual might suggest that conventional vaccination can induce high-affinity immunoglobulins against conserved epitopes even within different FMDV serotypes. Cross-reaction among strains by these high-affinity antibodies may support further protection against a heterologous infection with FMDV.

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.

Foot and mouth disease vaccine strain selection: current approaches and future perspectives

INTRODUCTION

Lack of cross protection between foot and mouth disease (FMD) virus (FMDV) serotypes as well as incomplete protection between some subtypes of FMDV affect the application of vaccine in the field. Further, the emergence of new variant FMD viruses periodically makes the existing vaccine inefficient. Consequently, periodical vaccine strain selection either by in vivo methods or in vitro methods become an essential requirement to enable utilization of appropriate and efficient vaccines.

AREAS COVERED

Here we describe the cross reactivity of the existing vaccines with the global pool of circulating viruses and the putative selected vaccine strains for targeting protection against the two major circulating serotype O and A FMD viruses for East Africa, the Middle East, South Asia and South East Asia.

EXPERT COMMENTARY

Although in vivo cross protection studies are more appropriate methods for vaccine matching and selection than in vitro neutralization test or ELISA, in the face of an outbreak both in vivo and in vitro methods of vaccine matching are not easy, and time consuming. The FMDV capsid contains all the immunogenic epitopes, and therefore vaccine strain prediction models using both capsid sequence and serology data will likely replace existing tools in the future.

Selection of vaccine strains for serotype O foot-and-mouth disease viruses (2007-2012) circulating in Southeast Asia, East Asia and Far East

Foot-and-mouth disease (FMD) is endemic in Southeast Asia (SEA) and East Asia with circulation of multiple serotypes and multiple genotypes within each serotype of the virus. Although countries like Japan and South Korea in the Far East were free of FMD, in 2010 FMD serotype O (O/Mya-98) outbreaks were recorded and since then South Korea has experienced several FMD outbreaks despite regular vaccination. In this study a total of 85 serotype O FMD viruses (FMDV) isolated from 2007 to 2012 from SEA, East Asia and Far East were characterized by virus neutralisation tests using antisera to four existing (O/HKN/6/83, O/IND/R2/75, O/SKR/2010 and O/PanAsia-2) and one putative (O/MYA/2009) vaccine strains, and by full capsid sequencing. Serological studies revealed broad cross-reactivity with the vaccine strains; O/PanAsia-2 exhibited a good match with 95.3%, O/HKN/6/83 with 91.8%, O/IND/R2/75 with 80%, and the putative strain O/MYA/2009 with 89.4% isolates employed in this study. Similarly O/PanAsia-2 and O/IND/R2/75 vaccines showed a good match with all eight viruses belonging to O-Ind-2001d sublineage whereas the vaccines of O/Mya-98 lineage, O/MYA/2009 and O/SKR/2010 exhibited the lowest match indicating their unsuitability to protect infections from O-Ind-2001d viruses. A Bayesian analysis of the capsid sequence data indicated these circulating viruses (n = 85) to be of either SEA or Middle East-South Asian (ME-SA) topotype. The ME-SA topotype viruses were mainly detected in Lao PDR, Vietnam, Myanmar and Thailand reflecting the trade links with the Indian subcontinent, and also within the SEA countries. Implications of these results in the context of FMD control in SEA and East Asian countries are discussed.

Global Foot-and-Mouth Disease Research Update and Gap Analysis: 3 - Vaccines

This study assessed research knowledge gaps in the field of FMDV (foot-and-mouth disease virus) vaccines. The study took the form of a literature review (2011-15) combined with research updates collected in 2014 from 33 institutes from across the world. Findings were used to identify priority areas for future FMD vaccine research. Vaccines play a vital role in FMD control, used both to limit the spread of the virus during epidemics in FMD-free countries and as the mainstay of disease management in endemic regions, particularly where sanitary controls are difficult to apply. Improvements in the performance or cost-effectiveness of FMD vaccines will allow more widespread and efficient disease control. FMD vaccines have changed little in recent decades, typically produced by inactivation of whole virus, the quantity and stability of the intact viral capsids in the final preparation being key for immunogenicity. However, these are exciting times and several promising novel FMD vaccine candidates have recently been developed. This includes the first FMD vaccine licensed for manufacture and use in the USA; this adenovirus-vectored FMD vaccine causes in vivo expression of viral capsids in vaccinated animals. Another promising vaccine candidate comprises stabilized empty FMDV capsids produced in vitro in a baculovirus expression system. Recombinant technologies are also being developed to improve otherwise conventionally produced inactivated vaccines, for example, by creating a chimeric vaccine virus to increase capsid stability and by inserting sequences into the vaccine virus for desired antigen expression. Other important areas of ongoing research include enhanced adjuvants, vaccine quality control procedures and predicting vaccine protection from immune correlates, thus reducing dependency on animal challenge studies. Globally, the degree of independent vaccine evaluation is highly variable, and this is essential for vaccine quality. Previously neglected, the importance of evaluating vaccination programme effectiveness and impact is increasingly being recognized.

No significant differences in the breadth of the foot-and-mouth disease serotype A vaccine induced antibody responses in cattle, using different adjuvants, mixed antigens and different routes of administration

Inactivated whole virus foot-and-mouth disease (FMD) vaccines are used worldwide for protection against FMD, but not all vaccines induce protection against all genetic variants of the same FMD virus serotype. The aim of this study is to investigate whether the "breadth" of the antibody response against different strains of the same FMD virus serotype in cattle could be improved by using a different adjuvant, a mix of antigens and/or different routes of administration. To this end, six groups of five cattle were vaccinated with different FMD virus serotype A strain vaccines formulated with Montanide ISA 206 VG adjuvant. Antibody responses for homologous and heterologous cross-reactivity against a panel of 10 different FMD virus serotype A strains were tested by a liquid-phase blocking ELISA. Results of cattle vaccinated with ISA 206 VG adjuvanted vaccine were compared with results obtained in a previous study using aluminium hydroxide-saponin adjuvant. No significant effect of adjuvant on the breadth of the antibody response was observed, neither for mixing of antigens nor for the route of administration (subcutaneous vs. intradermal). Comparison of antigen payload, however, increased both homologous and heterologous titres; a 10-fold higher antigen dose resulted in approximately four times higher titres against all tested strains. Our study shows that breadth of the antibody response depends mainly on the vaccine strain; we therefore propose that, for vaccine preparation, only FMD virus strains are selected that, among other important characteristics, will induce a wide antibody response to different field strains.