Developments in foot-and-mouth disease vaccines.

The current status of foot-and-mouth disease (FMD) vaccine production is reviewed. The production of antigen in bovine tongue epithelium (Frenkel culture) is described and improvements in monolayer and suspension cultures of cell lines are outlined. Inactivation of viral antigen and safety tests are discussed. A 'minimum safety level' is recommended: at the end of the inactivation process, antigen batches of any size should contain less than one virus particle. After inactivation the antigen can be formulated into a vaccine or purified and concentrated for storage at ultra-low temperatures in a vaccine bank. Vaccines prepared with the adjuvants Al(OH)3 and saponin are compared with (double) oil emulsion vaccines. Because oil vaccines can protect both cattle and pigs and induce long-term protection, they are most suitable for use in ring vaccinations. A new generation of vaccines, based on constructed modified-live viruses or (bio-) synthetic peptides, is briefly reviewed.     

Optimisation of the immune response to foot-and-mouth disease vaccines

Considering the many variables influencing the immune response of the host to vaccination against foot-and-mouth disease (FMD), the properties and characteristics of the vaccine and recommendations concerning its mode of application offer the best opportunity for the manufacturer to provide safe, effective protection of livestock. There are a number of critical elements in the production of FMD vaccines, such as the selection of appropriate strain(s), which have a direct bearing on the quality of the immune response. Equally, development of effective immunity depends on proper and timely application of good quality vaccine. In contrast, several of the potential variables in vaccination against FMD such as the use of oil adjuvants for cattle are probably less critical than is sometimes perceived. This presentation considers some of the many variables involved in the production and use of FMD vaccines.     

Evaluation of three 'ready to formulate' oil adjuvants for foot-and-mouth disease vaccine production

Foot-and-mouth disease virus (FMDV) type OR(2)/75, grown on BHK 21 clone 13 cell monolayers, was inactivated with formalin. The virus was clarified and was either concentrated with 8% polyethylene glycol 6000 (PEG) or used in its untreated form for the preparation of oil adjuvant vaccines. The oil adjuvants used in this study were Montanide ISA 206 (which renders a water-in-oil-in-water (w/o/w) type of emulsion), Montanide ISA 57 and Montanide ISA 50V (both of which render water-in-oil (w/o) type of emulsions). The vaccines were tested on guinea pigs and calves. The results indicated that vaccines emulsified using Montanide ISA 57 elicited the best protective immune response in the animals, followed by those emulsified with Montanide ISA 50V and Montanide ISA 206. It was also found that vaccines formulated with virus concentrated using 8% polyethylene glycol (PEG) were more immunogenic than the vaccines formulated with the untreated harvest virus.     

Response and persistence of antibodies to PRP-T and DTwP vaccines with concomitant administration of conjugate vaccines

We first studied the immunogenicity of PRP-T and DTwP vaccines in Filipino infants given at 6, 10 and 14 weeks concomitantly with either an aluminum adjuvanted eleven-valent pneumococcal conjugate vaccine (11PncTD) or a meningococcal diphtheria-conjugated vaccine as compared to a control group that received only DTwP/PRP-T. The GMCs and proportions of infants achieving protective antibody concentrations to DTwP and PRP-T vaccine antigens were similar among the groups. In the second phase, the control group received 11PncTD at 18 weeks and the antibody concentrations were measured at 9 months in all children; 11PncTD induced a booster response to diphtheria in the control group. There was no negative interference from concomitant administration of new conjugate vaccines. In contrast, 11PncTD can boost the antibody response to the carrier proteins.     

Safety and efficacy of foot-and-mouth disease vaccines containing endonuclease-inactivated virions

Inactivation of foot-and-mouth disease virus (FMDV) by means of virion-associated endonuclease was found to be suited to the production of safe and potent vaccines, which proved to be equal or better than those containing formaldehyde or ethyleneimine in guinea-pig potency tests. First order inactivation kinetics were regularly shown, with half life values which varied according to the different temperatures used. Inactivation brought about extensive degradation of FMDV RNA, while it did not adversely influence the integrity of critical viral epitopes on FMDV VP1.     

Strategies for induction of protective immunity to bovine herpesvirus-1 in newborn calves with maternal antibodies

The objective of this study was to evaluate Th1 promoting strategies for vaccination of neonates against bovine herpesvirus-1 (BHV-1). A plasmid encoding a secreted truncated version of glycoprotein D (tgD) and tgD protein formulated with CpG oligodeoxynucleotide (ODN) effectively primed the immune system of newborn lambs, whereas without CpG ODN the tgD protein was less effective. Furthermore, a heterologous DNA prime-protein/CpG boost induced stronger and more balanced immune responses than either the DNA vaccine or a protein/CpG prime-DNA boost. Three of these strategies were compared as an approach to induce protective immunity in newborn calves with BHV-1-specific maternal antibodies. Whereas the DNA vaccine induced minimal protection, the DNA prime-protein boost resulted in reduced temperature response, weight loss and virus shedding in comparison to the placebo group. Close to complete protection against BHV-1 challenge was elicited in the calves immunized with the protein/CpG formulation, as these animals lost very little weight, had only slightly elevated temperatures and shed almost no virus.     

Characterization of monoclonal antibodies against a type SAT 2 foot-and-mouth disease virus.

This paper is the first to describe characterization of monoclonal antibodies (MAbs) against a South African Territories 2 (SAT 2) foot-and-mouth disease virus (isolate Rho 1/48). Twelve MAbs which neutralized homologous virus were characterized in indirect and sandwich ELISA using purified Rho 1/48 virus particles, subunits, trypsin-treated, and chemically denatured virus. All the MAbs inhibited haemagglutination by parental virus. Binding of the MAbs to 73 SAT 2 field isolates was measured in a sandwich ELISA and defined four distinct antigenic regions. Preliminary characterization of escape mutants selected with some of the MAbs using virus neutralization tests, ELISA, and amino acid sequencing is included. MAbs 2, 25, 40, 48 and 64, reacted with a linear epitope on the VP1 loop region. An amino acid change at position 149 (valine to glutamic acid) was detected in mutants selected by MAb 2 and 40 and this eliminated binding and neutralization by all the other MAb. This epitope was conformation-dependent and was conserved in all 73 isolates of SAT 2 examined. Escape mutants isolated with MAb 41 and 44, had changes at positions 156 (glycine to aspartic acid), or 158 (serine to leucine) respectively. These MAbs bound with Rho 1/48 only out of 73 field strain viruses studies and the reactions of MAbs from the other groups was unaltered. MAb 27, 28 and 37 reacted with a conformation-dependent epitope on VP1 which was not conserved in field isolates. All mutants selected by these MAbs had a single amino acid substitution at position 149 (valine to alanine). The same change was always found in field isolates which did not bind MAbs from this group. MAb 11 reacted with a linear epitope associated with amino acids 147 or 148 on VP1 and showed similar binding characteristics to a conformation dependent MAb 7, no amino acid residue changes were found within VP1 for monoclonal antibody 7 mutants.     

Mouse protection test as a predictor of the protective capacity of synthetic foot-and-mouth disease vaccines.

A passive immunity test (MPT) in suckling mice for the quantification of protective anti-foot-and-mouth disease virus (FMDV) antibodies in serum is described. Comparisons with titres obtained using conventional serum neutralization tests show that for cattle given synthetic peptide vaccines this in vivo assay is a better indicator of protection, while for convalescent animals and virus-vaccinates both tests are equally valid predictors of immune status. Cleavage of Fc fragments from anti-virus or anti-peptide IgG results in a marked decrease in MPT titres although binding to virus in ELISA is unaffected, indicating that intact antibodies are required for in vivo clearance of FMDV. Cross-protection studies demonstrate that anti-peptide sera, while less potent than anti-viral sera in conferring passive immunity against FMDV challenge, have a wider protective range than anti-viral sera within the O serotype and also between O and A serotypes. Possible qualitative differences between anti-viral and anti-peptide sera are discussed in the light of these findings.     

Identification of foot-and-mouth disease virus replication in vaccinated cattle by antibodies to non-structural virus proteins

Antibodies raised in cattle against foot-and-mouth disease virus by vaccination or by experimental infection were distinguished. Vaccination elicited only antibodies to virus capsid proteins and the polymerase 3D. Virus replication in cattle elicited additional antibodies directed against the non-structural proteins 2B, 2C, 3AB1, and/or 3C irrespective of prior vaccination or whether the cattle exhibited symptoms of disease. Non-permissive mice inoculated with virus responded in the same way, indicating that antibodies raised due to the transient presence of antigen are safely recognized by the method applied which was radioimmunoprecipitation. All kinds of infections were thus detected and it was possible to differentiate between cattle exposed or not exposed to challenge in the field, and further between protected animals and possible virus carriers.     

Considerations for design and implementation of vaccine field trials for novel foot-and-mouth disease vaccines

Vaccines are commonly used to control Foot-and-Mouth Disease (FMD) in endemic regions and form an important part of contingency plans for FMD-free countries. Conventional FMD vaccines have numerous limitations, and the U.S. government supports the development of next-generation vaccines. In the U.S., vaccine efficacy is typically demonstrated through experimental vaccination and challenge of animals using the World Organization for Animal Health (OIE) standards. Although conventional challenge and immunogenicity studies provide useful information, they have limitations and results do not always accurately predict field performance. Consequently, there is a need to test next-generation vaccines under field conditions to gain a better understanding of field performance to inform policy decisions and support their viability as a commercial product.In June 2017, an expert consultation was organised to discuss and define an optimal field study design for novel FMD vaccines. Cattle were the primary species considered, although parallel strategies for swine and small ruminants were also discussed. Many methodological and logistical considerations in the study design were identified, including: (1) study site selection and the importance of baseline studies to understand exposure risk, (2) ethics of using a placebo and assessing equivalence with conventional vaccines, (3) merits of using individual randomised versus cluster randomised trials, (4) preventive versus reactive vaccination, and (5) methods of randomisation and blinding.The proposed optimal study design was a multicentre (i.e. farm), three-arm, double-blind randomised controlled trial comparing groups receiving the novel vaccine to a conventional vaccine group and a placebo group. Large farms in areas of high exposure risk were identified as ideal study sites, and the primary study outcome was susceptibility to disease or infection, during a six-month observation period, following a single dose of vaccine. This report provides a summary of the important issues to consider when designing a field efficacy study in livestock and proposes a study design that could be utilised for novel FMD vaccines.     

Aerosol exposure of cattle to foot-and-mouth disease virus.

Slight modifications of a small, plastic covered greenhouse provided a chamber for the exposure of cattle of all ages to aerosols of foot-and-mouth disease virus. Particle size distributions of aerosols were 76% less than 3 microns, 17% 3-6 microns, and 7% greater than 6 microns immediately after the deVilbis no. 40 nebulizer used was turned off and 90% less than 3 microns, 8% 3-6 microns, and 2% greater than 6 microns 20-30 min later. Pharyngeal virus growth curves and viremia patterns correlated well with the dose of virus to which test cattle were exposed and were similar to those of cattle inoculated intranasally.     

Evaluation of modified Vaccinia Ankara-based vaccines against foot-and-mouth disease serotype A24 in cattle

To prepare foot-and-mouth disease (FMD) recombinant vaccines in response to newly emerging FMD virus (FMDV) field strains, we evaluated Modified Vaccinia virus Ankara-Bavarian Nordic (MVA-BN®) as an FMD vaccine vector platform. The MVA-BN vector has the capacity to carry and express numerous foreign genes and thereby has the potential to encode antigens from multiple FMDV strains. Moreover, this vector has an extensive safety record in humans. All MVA-BN-FMD constructs expressed the FMDV A24 Cruzeiro P1 capsid polyprotein as antigen and the FMDV 3C protease required for processing of the polyprotein. Because the FMDV wild-type 3C protease is detrimental to mammalian cells, one of four FMDV 3C protease variants were utilized: wild-type, or one of three previously reported mutants intended to dampen protease activity (C142T, C142L) or to increase specificity and thereby reduce adverse effects (L127P). These 3C coding sequences were expressed under the control of different promoters selected to reduce 3C protease expression. Four MVA-BN-FMD constructs were evaluated in vitro for acceptable vector stability, FMDV P1 polyprotein expression, processing, and the potential for vaccine scale-up production. Two MVA-BN FMD constructs met the in vitro selection criteria to qualify for clinical studies: MVA-mBN360B (carrying a C142T mutant 3C protease and an HIV frameshift for reduced expression) and MVA-mBN386B (carrying a L127P mutant 3C protease). Both vaccines were safe in cattle and elicited low to moderate serum neutralization titers to FMDV following multiple dose administrations. Following FMDV homologous challenge, both vaccines conferred 100% protection against clinical FMD and viremia using single dose or prime-boost immunization regimens. The MVA-BN FMD vaccine platform was capable of differentiating infected from vaccinated animals (DIVA). The demonstration of the successful application of MVA-BN as an FMD vaccine vector provides a platform for further FMD vaccine development against more epidemiologically relevant FMDV strains.     

The Northumberland epidemic of foot-and-mouth disease, 1966.

The spread of foot-and-mouth disease during an epidemic in Northumberland in July, August and September 1966 was analysed. Although strong emitters, for example pigs, were not involved, in 18 of the 32 outbreaks spread could be attributed to the airborne route and in another 4, spread by this route was the most likely. Airborne spread was in general between 1 and 8 km but on two occasions as much as 20 km. Other means of spread included movement by animals, people and vehicles and carriage of virus between animals in neighbouring fields. No spread by milk or milk lorries took place. Sheep were involved in 9 farms; on each, lesions older than 48 h were found and it is likely that the sheep were the source of virus for other animals, especially cattle, on the farm and on neighbouring farms. The analysis suggests that control measures such as slaughtering direct contacts, as used in this epidemic, or ring vaccination as well as movement control would be effective in limiting spread.     

Influence of antigenic forms and adjuvants on the IgG subclass antibody response to Aujeszky's disease virus in mice.

The influence of antigenic forms of Aujeszky's disease virus (ADV) and adjuvant types on the production of IgG subclass antibodies in mice was investigated. Particulate antigen, inactivated ADV, alone induced IgG1 and lower IgG2a antibody production, while the antigen adsorbed onto aluminum phosphate gel (alum) enhanced IgG1 antibody production but suppressed IgG2a antibody production as well as solubilized ADV antigen adsorbed onto alum. QS21 saponin purified from Quillaja saponaria promoted the production of IgG1 and IgG2a antibodies in a large extent against the both particulate and soluble antigens, while this saponin has strong hemolytic activity. Lablaboside F saponin isolated from Dolichos lablab without hemolytic activity, also induced the production of large IgG1 and little IgG2a antibody against both antigens. Oil-based adjuvant, ISA70 of water-in-oil type and ISA25 of oil-in-water type, increased IgG1 and IgG2a antibodies against the both soluble and particulate antigens, whereas a combination of ISA25 and soluble antigen reduced IgG2a antibody response. These results indicate that IgG1 antibody production was not suppressed by a combination of antigenic form and adjuvant type, however, IgG2a antibody production was influenced.