Emergency foot-and-mouth disease vaccines a Malaysia 97 and A₂₂ Iraq 64 offer good protection against heterologous challenge with a variant serotype a ASIA/G-IX/SEA-97 lineage virus

The continuous emergence of foot-and-mouth disease virus (FMDV) serotype A variants in South East Asia is of concern for international FMDV antigen banks, especially when in vitro tests predict a low antigenic match. A vaccination-challenge study was performed by using two emergency FMDV vaccines with A22 Iraq 64 (A22 IRQ) and A Malaysia 97 (A MAY 97) strains, against challenge with a variant strain of FMDV A/Asia/G-IX/SEA-97 lineage at 7- and 21-day post-vaccination (dpv). At 7 dpv, three of five female calves vaccinated with A MAY 97 and four of five vaccinated with A22 IRQ did not show lesions on the feet and were considered protected, while at 21 dpv all five calves were protected with each vaccine, indicating equal efficacy of both vaccine strains. Calves were protected despite relatively low heterologous neutralizing antibody titers to the challenge virus at the time of challenge. All the calves developed antibodies to the non-structural proteins, most likely due to the direct intradermolingual (IDL) inoculation. Only one calf from the A MAY 97-7 group had infectious virus in the serum 1–3-day post-challenge (dpc), while no virus could be isolated from the serum of cattle challenged on 21 dpv. The virus could be isolated from the oral swabs of all calves, 1–7 dpc with viral RNA detected 1–10 dpc. Nasal swabs were positive for virus 1–6 dpc in a small number of calves. The time between vaccination and infection did not have an impact on the number of animals with persistent infection, with almost all the animals showing viral RNA in their oro-pharyngeal fluid (probang) samples up to 35 dpc. Despite the poor in vitro matching data and field reports of vaccine failures, this study suggests that these vaccine strains should be effective against this new A/Asia/G/SEA-97 variant, provided they are formulated with a high antigen dose.</p

Application of the Nagoya Protocol to veterinary pathogens: concerns for the control of foot-and-mouth disease

The Nagoya Protocol is an international agreement adopted in 2010 (and entered into force in 2014) which governs access to genetic resources and the fair and equitable sharing of benefits from their utilisation. The agreement aims to prevent misappropriation of genetic resources and, through benefit sharing, create incentives for the conservation and sustainable use of biological diversity. While the equitable sharing of the benefits arising from the utilisation of genetic resources is a widely accepted concept, the way in which the provisions of the Nagoya Protocol are currently being implemented through national access and benefit-sharing legislation places significant logistical challenges on the control of transboundary livestock diseases such as foot-and-mouth disease (FMD). Delays to access FMD virus isolates from the field disrupt the production of new FMD vaccines and other tailored tools for research, surveillance and outbreak control. These concerns were raised within the FMD Reference Laboratory Network and were explored at a recent multistakeholder meeting hosted by the European Commission for the Control of FMD. The aim of this paper is to promote wider awareness of the Nagoya Protocol, and to highlight its impacts on the regular exchange and utilisation of biological materials collected from clinical cases which underpin FMD research activities, and work to develop new epidemiologically relevant vaccines and other diagnostic tools to control the disease

Efficacy of emergency vaccination against foot-and-mouth disease in pigs

Since the foot-and-mouth disease epidemics in Europe in 2001 the use of emergency vaccination, if an outbreak occurs, has become more prominent in EU legislation. Since pigs infected with foot-and-mouth disease virus (FMDV) excrete huge amounts of virus they are considered as amplifiers of the disease and therefore the effect of vaccination on pigs is of great interest, especially in areas with high pig density. The aim of this thesis was to establish if and how soon (herd-) immunity in pigs is induced by vaccination and, furthermore, to study the correlation between immune responses after vaccination and protection against challenge. Transmission of FMDV and the effect of vaccination were studied in animal experiments in which half of the pigs were challenged with FMDV and transmission to contact pigs was studied. The outcome of the experiments was quantified using mathematical models. It was shown that, in the used model, pigs were protected against challenge at two weeks after homologous (vaccine virus same as field virus) as well as after heterologous (vaccine virus other than field virus, but within same serotype) vaccination. After challenge at one week after vaccination, transmission to all contact pigs was observed. However, vaccination did lead to a significant reduction of virus excretion after challenge, which will lead to reduction of virus in the environment which will reduce the risk of transmission to other herds. Vaccination with a 4-fold vaccine dose reduced the number of contact infections after challenge at one week after vaccination. Moreover, virus excretion of vaccinated-infected pigs was reduced even more. For decision making regarding control of the disease, it is important that transmission in non-vaccinated and vaccinated pigs is quantified. Quantified transmission parameters can be used in quantitative modelling, which is regarded as an essential tool for developing strategies in preparation of an outbreak and for predicting and evaluating the effectiveness of control policies during an outbreak. In this thesis, estimates for the transmission rate ß, the infectious period T and the reproduction ratio R for both non-vaccinated and vaccinated pigs were quantified with the results of our studies. It was shown that contact structure influenced the transmission rate and that the between-pen transmission-rate was significantly smaller than the within-pen transmission-rate in non-vaccinated pigs. Vaccination reduced ß, T and R of FMDV in pigs as soon as one week post vaccination and for the group vaccinated with a 4-fold vaccine dose R was estimated to be 1, which will probably be sufficient to reduce between-herd transmission sufficiently. Furthermore, it was shown that in individual pigs, the (reduced) virus excretion after infection was correlated with the neutralising antibody-titre at the moment of infection. After vaccination, IgA responses could be demonstrated and an indication that these responses play a possible role in protection against infection was found. After infection, a prolonged IgA response was demonstrated which was previously only described for carrier cattle and therefore needs further investigation. Also, it was demonstrated that after vaccination and infection systemic and mucosal isotype specific immune responses (IgG, IgM and IgA) were comparable. It was concluded that the currently used vaccines are effective in reducing virus transmission as soon as two weeks after vaccination. More research on optimal vaccine composition and dose is recommended. The correlates of protection that were found might be useful in future vaccine-research

Efficacy of emergency vaccination against foot-and-mouth disease in pigs

Since the foot-and-mouth disease epidemics in Europe in 2001 the use of emergency vaccination, if an outbreak occurs, has become more prominent in EU legislation. Since pigs infected with foot-and-mouth disease virus (FMDV) excrete huge amounts of virus they are considered as amplifiers of the disease and therefore the effect of vaccination on pigs is of great interest, especially in areas with high pig density. The aim of this thesis was to establish if and how soon (herd-) immunity in pigs is induced by vaccination and, furthermore, to study the correlation between immune responses after vaccination and protection against challenge. Transmission of FMDV and the effect of vaccination were studied in animal experiments in which half of the pigs were challenged with FMDV and transmission to contact pigs was studied. The outcome of the experiments was quantified using mathematical models. It was shown that, in the used model, pigs were protected against challenge at two weeks after homologous (vaccine virus same as field virus) as well as after heterologous (vaccine virus other than field virus, but within same serotype) vaccination. After challenge at one week after vaccination, transmission to all contact pigs was observed. However, vaccination did lead to a significant reduction of virus excretion after challenge, which will lead to reduction of virus in the environment which will reduce the risk of transmission to other herds. Vaccination with a 4-fold vaccine dose reduced the number of contact infections after challenge at one week after vaccination. Moreover, virus excretion of vaccinated-infected pigs was reduced even more. For decision making regarding control of the disease, it is important that transmission in non-vaccinated and vaccinated pigs is quantified. Quantified transmission parameters can be used in quantitative modelling, which is regarded as an essential tool for developing strategies in preparation of an outbreak and for predicting and evaluating the effectiveness of control policies during an outbreak. In this thesis, estimates for the transmission rate ß, the infectious period T and the reproduction ratio R for both non-vaccinated and vaccinated pigs were quantified with the results of our studies. It was shown that contact structure influenced the transmission rate and that the between-pen transmission-rate was significantly smaller than the within-pen transmission-rate in non-vaccinated pigs. Vaccination reduced ß, T and R of FMDV in pigs as soon as one week post vaccination and for the group vaccinated with a 4-fold vaccine dose R was estimated to be 1, which will probably be sufficient to reduce between-herd transmission sufficiently. Furthermore, it was shown that in individual pigs, the (reduced) virus excretion after infection was correlated with the neutralising antibody-titre at the moment of infection. After vaccination, IgA responses could be demonstrated and an indication that these responses play a possible role in protection against infection was found. After infection, a prolonged IgA response was demonstrated which was previously only described for carrier cattle and therefore needs further investigation. Also, it was demonstrated that after vaccination and infection systemic and mucosal isotype specific immune responses (IgG, IgM and IgA) were comparable. It was concluded that the currently used vaccines are effective in reducing virus transmission as soon as two weeks after vaccination. More research on optimal vaccine composition and dose is recommended. The correlates of protection that were found might be useful in future vaccine-research

Proper Timing of Foot-and-Mouth Disease Vaccination of Piglets with Maternally Derived Antibodies Will Maximize Expected Protection Levels

We investigated to what extent maternally derived antibodies interfere with foot-and-mouth disease (FMD) vaccination in order to determine the factors that influence the correct vaccination for piglets. Groups of piglets with maternally derived antibodies were vaccinated at different time points following birth, and the antibody titers to FMD virus (FMDV) were measured using virus neutralization tests (VNT). We used 50 piglets from 5 sows that had been vaccinated 3 times intramuscularly in the neck during pregnancy with FMD vaccine containing strains of FMDV serotypes O, A, and Asia-1. Four groups of 10 piglets were vaccinated intramuscularly in the neck at 3, 5, 7, or 9 weeks of age using a monovalent Cedivac-FMD vaccine (serotype A TUR/14/98). One group of 10 piglets with maternally derived antibodies was not vaccinated, and another group of 10 piglets without maternally derived antibodies was vaccinated at 3 weeks of age and served as a control group. Sera samples were collected, and antibody titers were determined using VNT. In our study, the antibody responses of piglets with maternally derived antibodies vaccinated at 7 or 9 weeks of age were similar to the responses of piglets without maternally derived antibodies vaccinated at 3 weeks of age. The maternally derived antibody levels in piglets depended very strongly on the antibody titer in the sow, so the optimal time for vaccination of piglets will depend on the vaccination scheme and quality of vaccine used in the sows and should, therefore, be monitored and reviewed on regular basis in countries that use FMD prophylactic vaccination

Quantification of within- and between-pen transmission of Foot-and-Mouth disease virus in pigs

Quantified transmission parameters of Foot-and-Mouth Disease Virus (FMDV) are needed for epidemic models used for control and surveillance. In this study, we quantified the within- and between-pen transmission of FMDV in groups of pigs by estimating the daily transmission rate $\beta$, i.e. the number of secondary infections caused by one infectious pig during one day, using an SIR (susceptible-infectious-removed) model. Within-pen transmission was studied in four groups of ten pigs in which 5 infected and 5 susceptible pigs had direct contact; between-pen transmission was studied in one group of ten pigs in which 5 infected and 5 susceptible pigs had indirect contact. Daily results of virus isolation of oropharyngeal fluid were used to quantify the transmission rate $\beta$, using Generalised Linear Modelling (GLM) and a maximum likelihood method. In addition, we estimated the expected time to infection of the first pig within a pen $T_{w}$ and in the indirect-contact pen $T_{b}$. The between-pen transmission rate $\beta$$_{b}$ was estimated to be 0.59 (0.083–4.18) per day, which was significantly lower than the within-pen transmission rate $\beta$$_{w}$ of 6.14 (3.75–10.06). $T_{w}$ was 1.6 h, and $T_{b}$ was 16 h. Our results show that the transmission rate is influenced by contact structure between pigs

Isolation of single-domain antibody fragments that preferentially detect intact (146s) particles of foot-and-mouth disease virus for use in vaccine quality control

Intact (146S) foot-and-mouth disease virus (FMDVs) can dissociate into specific (12S) viral capsid degradation products. FMD vaccines normally consist of inactivated virions. Vaccine quality is dependent on 146S virus particles rather than 12S particles. We earlier isolated two llama single-domain antibody fragments (VHHs) that specifically recognize 146S particles of FMDV strain O1 Manisa and shown their potential use in quality control of FMD vaccines during manufacturing. These 146S-specific VHHs were specific for particular O serotype strains and did not bind strains from other FMDV serotypes. Here, we describe the isolation of 146S-specific VHHs against FMDV SAT2 and Asia 1 strains by phage display selection from llama immune libraries. VHHs that bind both 12S and 146S particles were readily isolated but VHHs that bind specifically to 146S particles could only be isolated by phage display selection using prior depletion for 12S particles. We obtained one 146S-specific VHH—M332F—that binds to strain Asia 1 Shamir and several VHHs that preferentially bind 146S particles of SAT2 strain SAU/2/00, from which we selected VHH M379F for further characterization. Both M332F and M379F did not bind FMDV strains from other serotypes. In a sandwich enzyme-linked immunosorbent assay (ELISA) employing unlabeled and biotinylated versions of the same VHH M332F showed high specificity for 146S particles but M379F showed lower 146S-specificity with some cross-reaction with 12S particles. These ELISAs could detect 146S particle concentrations as low as 2.3–4.6 µg/l. They can be used for FMD vaccine quality control and research and development, for example, to identify virion stabilizing excipients.</p