Vaccination of pigs with formaldehyde inactivated aluminium hydroxide foot-and-mouth disease vaccines, potentiated with diethylaminoethyldextran (DEAE-D)

Effects of germanium biotite supplement on immune responses of vaccinated mini-pigs to foot-and-mouth disease virus challenge

Since the outbreaks of foot-and-mouth disease (FMD) in South Korea in 2010-2011, a trivalent vaccine has been used as a routine vaccination. Despite the high efficacy of the trivalent vaccine, low antibody formation was reported in the pig industry and there is considerable concern about the ability of the vaccine to protect against the Andong strain responsible for recent outbreaks in South Korea. To overcome these problems, immunostimulators have been widely used to improve vaccine efficacy in South Korea, although without any scientific evidence. Based on the current situation, the aim of this study was to investigate the effects of germanium biotite, a feed supplement used to enhance the immune system, on the immune responses to FMD vaccination through the Andong strain challenge experiment in trivalent vaccinated pigs. Following the challenge, the germanium biotite-fed pigs showed high levels of IL-8 in serum, and increased cellular immune responses to stimulation with the Andong strain antigen compared to nonsupplemented pigs. In addition, higher FMD virus (FMDV) neutralizing antibody titers were detected in the germanium biotite-fed group than in the nonsupplemented group before the challenge. The findings of this study indicate that germanium biotite supplement might enhance immune responses to the FMD vaccine in pigs.

A meta-analysis quantifying transmission parameters of FMDV strain O Taiwan among non-vaccinated and vaccinated pigs

Our aim was to provide additional estimates of main parameters for the transmission of foot-and-mouth disease virus (FMDV) strain O Taiwan (3/97). We used the data of previous experiments in non-vaccinated and vaccinated pigs and combined the data of experiments with the same treatment(s). First, we quantified the reproduction ratio R for the various groups using a final-size method. Our final-size results predicted that vaccination with a four-fold vaccine dose (but not with a single dose) at 1 week before inoculation (-7 dpi) would reduce R compared to the non-vaccinated group. Secondly, we used the daily results of virus excretion to quantify the transmission rate beta (by using generalized linear modelling), and the infectious period T (by using survival analysis). We used the estimates of beta and T to estimate R more precisely as compared to the final-size method and also for the groups for which a finite estimate could not be obtained using a final-size method. Our modelling results predicted that beta for non-vaccinated, for single-dose and four-fold-dose groups would be 6.1 (3.7, 10)day(-1), 2.0 (1.0, 4.0)day(-1) and 0.4 (0.1, 1.4)day(-1), T at 6.5 (5.7, 7.3), 5.3 (4.7, 6.0) and 2.3 (0.9, 5.7) days and R at 40 (21, 74), 11 (4.9, 24) and 1.0 (0.1, 7.8), respectively. These results predicted that both vaccination with a four-fold vaccine dose and with a single dose at -7 dpi would reduce beta, T and R significantly as compared to the non-vaccinated pigs, thereby showing that vaccination will reduce transmission of FMDV significantly already 1 week post vaccination.

Foot and mouth disease virus transmission among vaccinated pigs after exposure to virus shedding pigs

The aim of this study was to design a transmission experiment that enabled quantification of the effectiveness of vaccination against foot and mouth disease (FMD) virus in groups of pigs. Previous experiments showed that intradermal injection of pigs with FMD virus 14 days after vaccination was not suitable to start an infection chain, as inoculated vaccinated pigs resisted challenge. Therefore, we carried out two experiments in which we used direct contact to a non-vaccinated pig as route of infection. In the first experiment only the vaccine effect on susceptibility was quantified by exposing pigs, either vaccinated 14 days before or not vaccinated, each to a non-vaccinated seeder pig inoculated with FMD virus O/NET/2001. Since no significant differences were observed between contact infections in vaccinated or non-vaccinated pigs, we performed a second experiment in which both susceptibility and infectivity were subject to vaccination. We quantified virus transmission in homogenous groups of vaccinated or non-vaccinated pigs in which the infection chain was started by exposure to a third group of non-vaccinated infected pigs. Transmission occurred to all contact-exposed pigs in the non-vaccinated groups and to 9 out of 10 contact-exposed pigs in the vaccinated groups. The rate of transmission (beta) was significantly reduced in the vaccine group. Yet, the estimated reproduction ratio in both groups was still above 1. In conclusion, by adjusting our transmission study design and challenge method, we were able to quantify transmission of FMDV among vaccinated pigs. According to this study a single vaccination was not sufficient to stop pig to pig virus transmission. With these results major outbreaks may still be expected, even in groups of vaccinated pigs.

Passive immunization of guinea pigs with llama single-domain antibody fragments against foot-and-mouth disease

Foot-and-mouth disease (FMD) is a highly contagious disease that occasionally causes outbreaks in Europe. There is a need for therapies that provide rapid protection against FMD in outbreak situations. We aim to provide such rapid protection by passive immunization with llama single-domain antibody fragments (VHHs). Twenty-four VHHs binding serotype O FMDV in vitro were isolated from immunized llamas by phage display and expressed in bakers yeast for further characterization. They recognized four functionally independent antigenic sites. Six strongly FMDV neutralizing VHHs bound to a peptide representing the GH-loop of viral protein 1 known to be involved in binding to the cellular receptor of FMDV. Clone M8, recognizing this antigenic site, and clone M23, recognizing another antigenic site, showed synergistic in vitro virus neutralization. Three FMDV specific VHHs were PEGylated in order to decrease their rapid blood clearance and thus enable in vivo guinea pig protection experiments. Passive immunization with individual VHHs showed no protection, but a mixture of M8 and M23 showed partial transient protection. The protection afforded by these VHHs was however low as compared to the complete protection afforded by convalescent guinea pig serum. In contrast, these VHHs showed far more efficient in vitro FMDV neutralization than convalescent guinea pig serum. This lack of correlation between in vitro neutralization and in vivo protection lends further credence to the notion that opsonophagocytosis of FMDV is important for protection in vivo.

Serological and mucosal immune responses after vaccination and infection with FMDV in pigs

The aim of this study was to determine a possible correlation between humoral immune responses shortly after vaccination and protection against foot-and-mouth disease virus (FMDV) infection and to study the serological and mucosal antibody responses after vaccination and infection. We used three groups of ten pigs, one non-vaccinated group, one group vaccinated with a single dose vaccine and one group vaccinated with a four-fold dose vaccine. At 7 days post vaccination, five pigs per group were challenged intra-dermally with FMDV O TAW 3/97 and the remaining pigs of each group were contact-exposed to the inoculated pigs. In each group, virus excretion and number of contact infections were quantified. The serological and mucosal antibody responses were evaluated until 116 days post infection. Vaccination resulted in a significant decrease of virus excretion. Stepwise linear regression analysis of variables from individual vaccinated pigs revealed the virus excretion after challenge to be correlated with neutralising antibody titres at the day of challenge (p<0.01). In serum and OPF samples comparable isotype-specific antibody responses (IgM, IgG and IgA), could be detected after vaccination as well as after infection. Remarkably, the pigs with the highest IgA responses after vaccination were protected against contact exposure. After infection, a long lasting (up to 116dpi) IgA response was seen in the non-vaccinated and to a lesser extent in the single dose vaccinated pigs. The induction of NSP antibodies in the vaccinated pigs after infection was lower and of shorter duration as compared to the non-vaccinated infected pigs. This experiment shows that vaccination can reduce virus excretion in pigs, which will contribute to reduced transmission of FMDV in the field, even if the pigs are not fully protected. Moreover, vaccines that induce local IgA responses may be more effective, which merits further investigation.

Detection of economically important viruses in boar semen by quantitative RealTime PCR technology

The objective of this study was to develop quantitative real-time polymerase chain reaction (ReTi-PCR) tests for the detection of five economically important viruses in swine semen namely, pseudorabies virus (PRV), classical swine fever virus (CSFV), foot-and-mouth disease virus (FMDV), swine vesicular disease virus (SVDV), and porcine reproductive and respiratory syndrome virus (PRRSV). Each ReTi-PCR test was validated for specificity, analytical sensitivity (detection limits), and experimental infection studies were performed to compare the conventional virus isolation methods with the newly developed ReTi-PCR tests.

All five developed ReTi-PCR tests are very rapid compared to virus isolation, highly specific, and even more sensitive (lower detection limits) than conventional virus isolation methods for the detection of mentioned viruses in semen. In semen of experimentally infected boars, viruses were detected much earlier after infection and more frequently by ReTi-PCR tests than by virus isolations. The high throughput of these rapid ReTi-PCR tests makes it possible to screen large number of semen samples for the presence of viruses prior to insemination. This is a substantial advantage, in particular for boar semen the quality of which deteriorates quickly after storage.

In general, the newly developed ReTi-PCR tests are valuable tools for the early, reliable and rapid detection of five economically important viruses, namely PRV, CSFV, FMDV, SVDV, and PRRSV in boar semen. These ReTi-PCR tests will improve the control of viral diseases transmitted via semen.

No foot-and-mouth disease virus transmission between individually housed calves

The foot-and-mouth disease outbreak in The Netherlands in 2001 most likely started on a mixed veal-calf/dairy-goat farm. The outbreak among the 74 calves on this farm appeared to be limited to four animals, and no clinical signs of FMD were reported. Also on a second veal-calf farm minor clinical signs and limited virus transmission were observed. Since FMD is known to be a very contagious disease, and can cause severe lesions, these observations were disputed. Therefore, we carried out two experiments to determine whether the Dutch FMD virus isolate from 2001 does spread among individually housed calves with limited contacts, either indirect (experiment 1) or direct (experiment 2). In experiment 1, four pairs of calves were housed in an individual box at 1m distance from each other. In experiment 2, two groups of three calves were housed in individual boxes, directly bordering each other. We infected one animal per pair in experiment 1, and the calf in the middle in experiment 2. We recorded clinical signs, virus shedding in saliva and the development of antibodies. In addition, we determined whether the virus was transmitted from the inoculated calves to the neighbour(s). All inoculated calves showed mild signs of FMD--fever, and some vesicles on hooves and/or in the mouth--but only one calf showed signs that were visible without physical examination. All inoculated calves shed virus in the saliva and developed neutralising antibodies. None of the contact animals seroconverted, indicating that virus transmission did not occur. These experiments showed that no virus transmission among individual housed calves can occur. This finding supports the hypothesis of the route of virus introduction to The Netherlands in 2001 and show that the observations on the two veal-calf farms were not impossible.

Vaccination of pigs two weeks before infection significantly reduces transmission of foot-and-mouth disease virus

The objective of this study was to investigate whether and at what time interval could vaccination reduce transmission of foot-and-mouth disease virus (FMDV) among pigs. Reduction of virus transmission by vaccination was determined experimentally. Transmission of FMDV was studied in three groups of ten pigs: one non-vaccinated group and two groups that were vaccinated 7 days (-7 dpi) and 14 days before inoculation (-14 dpi), respectively. Five randomly selected pigs from each group were inoculated with FMDV type O Taiwan, while the other five pigs left in the groups were exposed to the inoculated pigs by direct contact. Clinical signs were recorded, virus isolation and RT-PCR were carried out on oropharyngeal fluid (OPF), and the neutralizing antibody titres and the antibody response against non-structural (NS) proteins of FMDV were determined. No virus transmission was observed in the -14 dpi group, whereas virus transmission was observed in all contact pigs affecting both the non-vaccinated and the -7 dpi group. The reproduction ratio R in the -14 dpi vaccinated group was significantly lower than that of the non-vaccinated group. This study confirms the potential of vaccination as an important tool to reduce transmission of FMDV.

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.

Prevalence of foot-and-mouth disease antibodies in dairy herds in The Netherlands four years after vaccination

A total of 298 serum samples were collected from Dutch cattle born in 1988 or before, and examined in the virus neutralisation test for antibodies against foot-and-mouth disease virus types A10 Holland. O BFS, and C1Detmold. All the cattle had been vaccinated at least twice during the annual vaccination programme, which stopped in 1991. Antibody titres equal to or higher than the titre at which 95 per cent of the cattle would be expected to be protected against challenge, were found in 57 to 73 per cent of the younger age groups, and in 100 per cent of the older animals. Since the animals tested constituted only 10.5 per cent of the total cattle population on the farms tested, it is concluded that should the virus be introduced, foot-and-mouth disease would be detected as easily in the Netherlands as in a country with no history of vaccination.

Outer membrane protein PhoE as a carrier for the exposure of foreign antigenic determinants at the bacterial cell surface

PhoE protein is an abundant outer membrane protein of the Escherichia coli K-12 outer membrane. This protein can be used as an exposure system to produce foregin antigenic determinants and for their transport to the bacterial cell surface. The system is very flexible, since insertions varying in length and nature could be made in different cell surface-exposed regions of PhoE, without interfering with the assembly process of the mutant proteins into the outer membrane. Two antigenic determinants of the structural VP1 protein of foot-and-mouth disease virus were inserted in different combinations in four cell surface-exposed regions of PhoE. The epitopes were exposed at the bacterial cell surface and they keep their antigenic and immunogenic properties in this PhoE-associated conformation. Immunization of guinea pigs with one hybrid protein, containing a combination of the two epitopes inserted in the fourth exposed region, resulted in complete protection against challenge with the virus. A T-cell epitope of the 65 kDa heat shock protein of Mycobacterium tuberculosis was inserted in the fourth exposed region of PhoE and in vitro proliferation of two T-cell specific clones was demonstrated. Thus, the PhoE exposure system has been shown to be suitable for presentation of both B-cell and T-cell determinants to the immune system. Furthermore, good expression of the hybrid protein in attenuated Salmonella strains, which can be used as live oral vaccines, was shown.

Protection of guinea-pigs against foot-and-mouth disease virus by immunization with a PhoE-FMDV hybrid protein

A hybrid protein was constructed containing two antigenic determinants of the structural protein VP1 of foot-and-mouth disease virus, inserted in a cell surface-exposed region of Escherichia coli outer membrane protein PhoE. Immunization of guinea-pigs with partially purified protein resulted in high levels of neutralizing antibodies and complete protection against challenge with the virus.

A complex-trapping-blocking (CTB) ELISA, using monoclonal antibodies and detecting specifically antibodies directed against foot-and-mouth disease types A, O and C. II. Application

The complex-trapping-blocking (CTB) enzyme-linked immunosorbent assay (ELISA) was evaluated to detect antibodies directed against foot-and-mouth disease virus (FMDV) strains A10 Holland, O1 BFS, and C1 Detmold. Log10 serum titres of uninfected, unvaccinated cattle (n = 100) were less than 1.80 in the CTB-ELISA. Sera from cattle vaccinated with either monovalent or trivalent vaccines were tested in both the CTB-ELISA and the serum neutralisation test (SNT); titres in both tests correlated positively (P less than 0.001). Titres of sera from cattle, sheep, and pigs vaccinated twice with FMDV A10 Holland also correlated positively in both tests. In another experiment, cattle vaccinated with FMDV strain C1 Detmold were intradermolingually challenged 3 weeks after primary vaccination; at the same time two controls were challenged. At 8 days after challenge, serum titres of the controls were distinctly higher in the CTB-ELISA than in the SNT, whereas serum titres of the vaccinated cattle were equally high in both tests. In potency tests for monovalent vaccines against FMDV strains A10 Holland, O1 BFS or C1 Detmold, serum titres correlated strongly in both tests with protection against the homologous FMDV strain. We concluded that the CTB-ELISA is not only sensitive, but easier to perform and more rapid and reproducible than the SNT. The CTB-ELISA may be useful in evaluating the immune response in cattle during FMD vaccine potency tests.

A complex-trapping-blocking (CTB) ELISA, using monoclonal antibodies and detecting specifically antibodies directed against foot-and-mouth disease types A, O and C. I. Method and characteristics

A complex-trapping-blocking (CTB) enzyme-linked immunosorbent assay (ELISA) was developed for the detection of antibodies directed against foot-and-mouth disease virus (FMDV) strains A10 Holland, O1 BFS, and C1 Detmold. For each strain two monoclonal antibodies directed against different antigenic sites of FMDV were used. The assay used either infectious, not inactivated antigen or inactivated antigen. We concluded that the CTB-ELISA was sensitive, type-specific, and more reproducible (P less than 0.05) than the serum neutralisation test (SNT). In addition, the test was easy to perform and results could be recorded within 3 hours. The cross-reactivity of bovine reference sera raised against the three FMDV strains was comparable in the CTB-ELISA and the SNT.

Comparison of a liquid-phase blocking sandwich ELISA and a serum neutralization test to evaluate immunity in potency tests of foot-and-mouth disease vaccines

Sera from cattle vaccinated against either foot-and-mouth disease virus (FMDV) strains A10 Holland, O1 BFS, or C1 Detmold were tested in a serum neutralization test (SNT) and a liquid-phase blocking sandwich ELISA (LBE), and the titers were compared with the results of intradermolingual challenge tests. The LBE test results were significantly more reproducible (P less than 0.005) than the SNT results. The correlation coefficients between SNT and LBE were 0.91 for FMDV strains A10 Holland and O1 BFS, and 0.82 for FMDV strain C1 Detmold (P less than 0.0005). The regression coefficient for strain A10 Holland was 0.80, for strain O1 BFS the value was 0.87, and for strain C1 Detmold it was 0.64. In probit analysis, titers at which 95% of the cattle were protected against challenge with the homologous strain were determined for the SNT and the LBE. In the SNT the 95% protection levels for strains A10 Holland were greater than or equal to 0.84, for O1 BFS greater than or equal to 1.59, and for C1 Detmold greater than or equal to 0.83. In the LBE they were greater than or equal to 1.28, greater than or equal to 1.71, and greater than or equal to 1.74, respectively. Because the SNT and the LBE are highly significantly correlated, and the LBE is more reproducible, the LBE is likely to predict protection more reliably than the SNT.

Innocuity testing of foot-and-mouth disease vaccines. I. Formaldehyde-inactivated alhydrogel vaccines

Conditions that contribute to efficient innocuity testing of formaldehyde (FA)-inactivated alhydrogel vaccines were investigated. Under our conditions good yields of 146S antigen were obtained if the antigen was eluted by potassium phosphate buffer (pH 7.4) and concentrated by ultrafiltration. Non-inactivated virus added to the vaccine and adsorbed overnight could be recovered if residual FA was removed from the vaccine by washing the gel thoroughly with Frenkel culture medium before the addition of the virus. It was shown that the presence of high concentrations of inactivated virus in the concentrated eluate could prevent the detection of small amounts infectious virus in intradermolingual tests in cattle. This interference phenomenon was not found if (more susceptible) monolayers of foetal calf thyroid cells were used for the detection of virus. Intensive pre-washing of the gel with Frenkel culture medium, elution with potassium phosphate, concentration by ultrafiltration and the use of thyroid cells for the final detection of surviving virus is therefore advised for safety testing.