Foot-and-mouth disease in swine. I. The immune response of swine of chemically-treated and non-treated foot-and-mouth disease virus

Laboratory animal models to study foot-and-mouth disease: a review with emphasis on natural and vaccine-induced immunity

Laboratory animal models have provided valuable insight into foot-and-mouth disease virus (FMDV) pathogenesis in epidemiologically important target species. While not perfect, these models have delivered an accelerated time frame to characterize the immune responses in natural hosts and a platform to evaluate therapeutics and vaccine candidates at a reduced cost. Further expansion of these models in mice has allowed access to genetic mutations not available for target species, providing a powerful and versatile experimental system to interrogate the immune response to FMDV and to target more expensive studies in natural hosts. The purpose of this review is to describe commonly used FMDV infection models in laboratory animals and to cite examples of when these models have failed or successfully provided insight relevant for target species, with an emphasis on natural and vaccine-induced immunity.

Natural and vaccine induced immunity to FMD

A brief overview of the foot-and-mouth disease (FMD) literature over the last 100 years will give the impression that a great deal is known about the immune response of livestock to infection and vaccination. At the practical level, this is indeed the case and our knowledge is more than adequate in relation to the production and supply of potent vaccines for the control of the disease. The deficiencies in our understanding of the immune response are at the fundamental level and, arguably, stand in the way of its rational manipulation to achieve goals such as life-long immunity conferred by vaccination. Most of the research activity to date has focused on T cell dependency of the immune response of livestock and important B (and probably T) cell epitopes and has been used by researchers to design highly sophisticated novel vaccines and delivery systems. None of these, to the author's knowledge, exceeds the potency obtained with a good commercial vaccine. Although it is not yet possible to see a clear direction for the development of improved formulations, it is important to reflect on our current knowledge of natural and vaccine-induced immunity and some of the issues surrounding modern inactivated FMD vaccines. This process will perhaps help to discriminate the fact from the fiction and serve to focus on precisely what is needed or desirable for improved products.

Longevity of antibody and cytokine responses following vaccination with high potency emergency FMD vaccines

The ability of high potency emergency foot-and-mouth disease (FMD) vaccines to promote sustainable immune responses in sheep and pigs following a single application was examined. All vaccine formulations induced a rapid seroconversion in both species, as expected, which was maintained at near peak titres for up to 6 months in sheep and 7 months in pigs. The Montanide ISA 206 formulation gave the best results in sheep. Vaccinated pigs challenged with homologous FMDV were protected from disease at 7 months post vaccination. Systemic levels of cytokines IL-6, IL-8, and in some pigs IL-12, increased following vaccination and were often maintained at an increased level for the duration of the trials. These initial results suggest that high potency vaccines may promote longer lasting immunity than the conventional lower potency vaccines in ruminants and a comparable response in pigs. Results indicate that in an outbreak situation, should emergency vaccination be done with these high potency vaccines, protection should be conferred for a long enough period for the outbreak to be brought under control without the need to revaccinate. Given the increased interval for re-vaccination the use of high potency vaccines for routine prophylactic campaigns could provide a more cost-effective and efficient means of maintaining herd immunity and is an area thus worthy of further examination.

Foot-and-mouth disease. A review for the practitioner

Foot-and-mouth disease (FMD) is perhaps the most infectious disease known to human and veterinary medicine. This article is written with the practitioner in mind, concentrating on early recognition, epidemiology, occurrence around the world, and sampling and diagnostic methods. The article stresses that there are numerous FMD viruses, and not all behave in a similar fashion. The practitioner must be acute in his or her herd inspection of animals in which vesicular disease is suspected and knowledgeable as to differential diagnosis.

Emergency vaccination of pigs against foot-and-mouth disease: protection against disease and reduction in contact transmission

The protective ability of two novel oil-based FMD vaccines in pigs was examined. Both vaccine formulations were shown to protect pigs against airborne challenge with homologous FMDV within four days of vaccination, but not at two and three days post-vaccination. Protection was associated with the induction of variable and low titre serum antibody responses. A transmission study showed that protective immunisation resulted in reduced virus excretion. Vaccination at seven days, but not at four days, prior to challenge prevented contact transmission of FMD. The two formulations tested in this study have the favourable characteristics of low viscosity, low reactivity and high potency emergency FMD vaccines for use in strategic vaccination campaigns to assist the control of outbreaks of FMD.

International bank for foot-and-mouth disease vaccine: assessment of Montanide ISA 25 and ISA 206, two commercially available oil adjuvants

The International Vaccine Bank at Pirbright has recently installed large-scale vaccine formulation equipment for the preparation of oil-adjuvanted vaccines. Such vaccines are claimed to offer a number of advantages over Al(OH)3, particularly their ability to raise better immunity in pigs. This paper reports on the potency in pigs, cattle and guinea-pigs of foot-and-mouth disease vaccines prepared with two novel oil adjuvants, Montanide ISA 25 and 206 (Seppic, Paris). The results indicate that vaccines adjuvanted with these oils retain potency for a longer period than our conventional aqueous formulation, following storage at +4 degrees C, and elicit good antibody responses in both pigs and cattle regardless of injection route. In addition they gave no evidence of toxicity or prolonged pyrexia following their administration. Local reactions at the site of inoculation were not observed in cattle vaccinated intramuscularly, even following a booster dose. Pigs vaccinated intramuscularly only showed local reactions if the volume administered exceeded the 2.0 ml dose or the animals received a second vaccination. These observations on the efficacy of such oil formulated vaccines suggest that they have potential as an alternative to the current aqueous formulation.

Humoral response of pregnant sows to foot and mouth disease vaccination

Four groups of sows were inoculated, either once or twice, with O1BFS 1860 foot and mouth disease oil-emulsion vaccine during pregnancy and samples of serum, for analysis, were collected at intervals for greater than 300 days. The pregnant sows responded well to vaccination regardless of their state of gestation. Single vaccination produced protective levels of antibody (greater than 1.53 log10SN50) in 3 out of 4 sows while double vaccination produced protective levels in all 6 sows tested. Anti-FMD IgM antibodies could be detected for 40-60 days after vaccination or revaccination. Anti-FMD IgG antibodies appeared within 10 days of vaccination and persisted, in each sow, for the duration of the study. The anti-FMD IgA response observed was less easy to characterize due to significant animal to animal variation. Although there was no evidence of a fall in the neutralizing antibody titres over one year post vaccination the anti-FMD IgG antibody population did show signs of a change in its heterogeneity and avidity.

Foot-and-mouth disease virus: immunogenicity and structure of fragments derived from capsid protein VP and of virus containing cleaved VP

Peptide fragments were obtained from the immunogenic capsid protein VP3, ca. 24 kilodaltons (kd), of foot-and-mouth disease virus type A12 119ab by three procedures: (1) spontaneous proteolysis of in virion VP3 in tissue cultures to produce a 15 kd peptide, designated S fragment; (2) trypsin treatment of purified virus to produce a 16 kg peptide, designated T fragment; and (3) cyanogen bromide cleavage of purified VP3 to produce a 13 kd fragment. Following isolation and purification by gel electrophoresis, VP3 and each of the three fragments were immunogenic for livestock. Lyophilization appeared to impair the immunogenicity of VP3. In addition, viruses containing VP3 fragments produced either by the spontaneous- or trypsin-induced proteolysis were as immunogenic as virus with its VP3 intact. Amino acid sequencing of N-terminal regions revealed that the S fragment was homologous with the N-terminus of VP3, whereas the 13 kd fragment possessed a unique N-terminus. Thus, putative common immunogenic amino acid sequences would appear to reside within an overlap region of the 15 kd S and 13 kd fragments. Sequencing of cDNA prepared to viral genome RNA provided three kinds of information: it (1) placed the above overlap region in the second and third quarters of VP3; (2) demonstrated that the codons for the C-terminus of VP1 and N-terminus of VP3 are contiguous; and (3) supported earlier evidence that these same codons program a chain reversal where VP1 and VP3 are joined in the precursor polyprotein.

Cloned viral protein vaccine for foot-and-mouth disease: responses in cattle and swine

A DNA sequence coding for the immunogenic capsid protein VP3 of foot-and-mouth disease virus A12, prepared from the virion RNA, was ligated to a plasmid designed to express a chimeric protein from the Escherichia coli tryptophan promoter-operator system. When Escherichia coli transformed with this plasmid was grown in tryptophan-depleted media, approximately 17 percent of the total cellular protein was found to be an insoluble and stable chimeric protein. The purified chimeric protein competed equally on a molar basis with VP3 for specific antibodies to foot-and-mouth disease virus. When inoculated into six cattle and two swine, this protein elicited high levels of neutralizing antibody and protection against challenge with foot-and-mouth disease virus.

Potentiation of FMD vaccines with polycationic-nucleic acid complexes

The effect of various polycations on the immune response potentiated with poly I:C was studied. It was found that low molecular weight polycations had no potentiating effect. Polylysine was ineffective whereas protamine was superior to lysozyme, poly-arginine, poly-histidine, DEAE-Dextran and histone. A foot-and-mouth disease trivalent vaccine composed of strains A24 Cruzeiro, O1 Caseros and C2 Resende elicited no immune response in swine when adjuvanted with aluminium hydroxide but was effective when emulsified in oil. In general, the immune response was potentiated ten-fold when the emulsion contained poly I:C. The antibody production was in most cases further potentiated by a factor of ten when the nucleic acid double-strand was complexed with 1 : 10 (w/w) DEAE-Dextran. Protamine was as effective, or perhaps even more, than DEAE-Dextran to this effect. Guinea pigs vaccinated with a water-in-oil emulsion type monovalent C3 vaccine showed an increase in antibody production when the vaccine contained poly I:C or poly I:C complexed with 1 : 10 (w/w) protamine.

Quantitation of the antigenicity and immunogenicity of purified foot-and-mouth disease virus vaccine for swine and steers

The antigenicity and immunogenicity of a purified preparation of foot-and-mouth disease virus [type A(12), strain 119 (FMDV A-119)] inactivated with 6.0 mmN-acetylethylenimine at 37 C were compared in swine and steers. Three antigen doses were tested, 640, 160, and 40 ng. In accordance with findings for guinea pigs, as previously determined by dose-response curves, as little as fourfold changes in antigen in the region of the minimum effective dose produced marked differences in the serological and immune responses of swine. The minimum effective dose of antigen for antibody formation in swine and guinea pigs, as determined by mouse median protective dose (PD(50)) values, was 160 ng. The minimum immunogenic dose for swine was also 160 ng. The vaccinated swine were challenged with either FMDV A-119 or with heterologous subtype A(24) strain Cruzeiro or type A strain A-CANEFA-1. Those immunized with 640 ng of antigen were about equally immune to the three challenge viruses; most swine having a mouse PD(50) value of 2.0 or greater were immune regardless of which strain was used for challenge. In steers, the smallest dose tested, 40 ng, was satisfactory in eliciting circulating antibodies and immunity. Physical and biological tests indicated that the antigen used in the vaccine is stable for at least 9 months at 4 C.