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

Elucidating the Onset of Cross-Protective Immunity after Intranasal Vaccination with the Attenuated African Swine Fever Vaccine Candidate BA71ΔCD2

African swine fever (ASF) is a deadly disease of swine currently causing a worldwide pandemic, leading to severe economic consequences for the porcine industry. The control of disease spread is hampered by the limitation of available effective vaccines. Live attenuated vaccines (LAVs) are currently the most advanced vaccine prototypes, providing strong protection against ASF. However, the significant advances achieved using LAVs must be complemented with further studies to analyze vaccine-induced immunity. Here, we characterized the onset of cross-protective immunity triggered by the LAV candidate BA71ΔCD2. Intranasally vaccinated pigs were challenged with the virulent Georgia 2007/1 strain at days 3, 7 and 12 postvaccination. Only the animals vaccinated 12 days before the challenge had effectively controlled infection progression, showing low virus loads, minor clinical signs and a lack of the unbalanced inflammatory response characteristic of severe disease. Contrarily, the animals vaccinated 3 or 7 days before the challenge just showed a minor delay in disease progression. An analysis of the humoral response and whole blood transcriptome signatures demonstrated that the control of infection was associated with the presence of virus-specific IgG and a cytotoxic response before the challenge. These results contribute to our understanding of protective immunity induced by LAV-based vaccines, encouraging their use in emergency responses in ASF-affected areas.

An Alternative Serological Measure for Assessing Foot-and-Mouth Disease Vaccine Efficacy against Homologous and Heterologous Viral Challenges in Pigs

To analyze the relationship between homologous and heterologous serological titers of immunized pigs and their protection statuses against FMD virus challenges, in the present study, the correlation between the virus neutralization titers at 21 and 28 dpv and the protection statuses at 28 dpv against challenge with FMD virus was analyzed using data sets comprising five different combinations of homologous or heterologous challenge experiments in pigs vaccinated with type O (n = 96), A (n = 69), and Asia 1 (n = 74). As a result, the experiments were divided into three groups (21D-1, 21D-2, and 21D-3) in the 21-dpv model and two groups (28D-1 and 28D-2) in the 28-dpv model. Each response curve of groups 21D-1 and 21D-2 in the 21-dpv model was very similar to each curve of groups 28D-1 and 28D-2 in the 28-dpv model, respectively, even though there was an exceptional extra group (21D-3) in the 21-dpv model. The average titers estimating 0.75 probability of protection ranged from 1.06 to 1.62 log10 in the 21-dpv model and from 1.26 to 1.64 log10 in the 28-dpv model. In summary, we demonstrated that the serological method is useful for predicting the homologous and heterologous protection statuses of vaccinated pigs.

Effect of a Mismatched Vaccine against the Outbreak of a Novel FMD Strain in a Pig Population

In December 2014, a novel foot and mouth disease (FMD) virus was introduced to a pig farm in South Korea, despite the animals being vaccinated. A marginal antigenic matching between the novel and vaccine strains potentially led to the infection of the vaccinated animals. To understand the impact of using an FMD vaccine on the transmission dynamics of an unmatched field strain, simulation models were employed using daily reported data on clinical cases from the farm. The results of this study indicated that immunisation with the FMD vaccine reduced the shedding of the novel FMD virus in pigs. However, there was no evidence to suggest that the immunisation had a significant effect in reducing the development of clinical signs. These findings highlight that the use of an unmatched FMD vaccine can confound the outbreak by altering the disease dynamics of the novel virus. Based on this study, we emphasise the importance of continuous testing to ensure antigenic matching between the circulating strains and the vaccine pool.

A cost-benefit analysis of foot and mouth disease control program for smallholder cattle farmers in Cambodia

The Cambodian government is attempting to mobilise government, donor and private sector funding to implement a coordinated FMD vaccination program (FMDVP). A necessary first step is to convince the farmers of the benefits of participating in and potentially financially supporting this program. Information was collected from 300 farmers in order to estimate the on-farm benefits and costs of their participation in an FMDVP. Implementing a successful vaccination program is difficult, and farmers understand from previous experience that there may be institutional, social, technical and financial constraints which limit its success. A benefit-cost analysis needs to take into account that outbreaks do not occur every year, not all cattle will be successfully vaccinated, not all sick animals successfully treated and sometimes sick animals simply sold. This study sensitises these variables in order to give a realistic estimation of the farmer participation benefits in an FMDVP. A general result is that it is worthwhile for farmers to participate in the FMDVP if there are average annual outbreaks, or at least two major outbreaks, in the ensuing 5 years. However, the results are influenced by the interaction of vaccination success and treatment success and coverage. Ineffective coverage and poor treatment of sick animals reduce the benefits of an FMDVP. It is also important that farmers do not sell sick stock and, if they do, that they are able to breed replacements rather than purchase replacements. There are many factors in the smallholder cattle farming system that will influence the success of an FMDVP; farmers will only choose to participate if they can be convinced of the short and long-term economic benefits.

Mathematical Quantification of Transmission in Experiments: FMDV Transmission in Pigs Can Be Blocked by Vaccination and Separation

Quantitative understanding of transmission with and without control measures is important for the control of infectious diseases because it helps to determine which of these measures (or combinations thereof) will be effective to reduce transmission. In this paper, the statistical methods used to estimate transmission parameters are explained. To show how these methods can be used we reviewed literature for papers describing foot-and-mouth disease virus (FMDV) transmission in pigs and we used the data to estimate transmission parameters. The analysis showed that FMDV transmits very well when pigs have direct contact. Transmission, however, is reduced when a physical barrier separates infected and susceptible non-vaccinated pigs. Vaccination of pigs can prevent infection when virus is administered by a single intradermal virus injection in the bulb of the heel, but it cannot prevent infection when pigs are directly exposed to either non-vaccinated or vaccinated FMDV infected pigs. Physical separation combined with vaccination is observed to block transmission. Vaccination and separation can make a significant difference in the estimated number of new infections per day. Experimental transmission studies show that the combined effect of vaccination and physical separation can significantly reduce transmission (R < 1), which is a very relevant result for the control of between-farm transmission.

Reduction of foot-and-mouth disease virus transmission in cattle vaccinated one or two weeks before challenge using a commercial polyvalent vaccine

Immediate vaccination of the most susceptible and epidemiological relevant animals is a crucial part of control measures that facilitate virus elimination in case of entry of foot-and-mouth disease (FMD). The objective of this study was to evaluate the effect of cattle vaccination 7 and 14 days prior challenge using a vaccine commonly applied in systematic vaccination campaigns against transmission of FMD virus (FMDV). Transmission of FMDV was investigated in three groups of ten cattle each: one non-vaccinated group and two groups that were either vaccinated 7 days (−7/vaccinated group) or 14 days (−14/vaccinated group) before intranasal (IN) inoculation. Five cattle heads from each group were inoculated using the IN-route with the A/Argentina/2001 FMDV strain, while the remaining five cattle heads of each group were contact-exposed to inoculated cattle. Clinical signs were recorded; virus isolation and genome detection by RT-PCR were carried out on oesophageal–pharyngeal fluid (OPF) and blood. Neutralizing antibody titers and antibodies against non-structural proteins (NSP) of FMDV were also determined. Results suggest that the experimental design, virus challenge dose, and virus infectivity were appropriate and that the virus had been transmitted to naïve calves. Under the outlined experimental conditions, vaccination 7 and 14 days prior to challenge induced full clinical protection against virus inoculation. Moreover, −7/ or −14/vaccinated calves that had been contact-exposed to −7/ or −14/vaccinated IN-challenged calves, did not become infected. Consequently, no virus transmission occurred from vaccinated and subsequently infected calves to cohabitating vaccinated calves (R = 0). According to our results, early vaccination during an outbreak is effective as virus transmission can be significantly reduced using a vaccine commercially available, routinely applied in systematic vaccination campaigns.

Efficacy of a foot-and-mouth disease vaccine against a heterologous SAT1 virus challenge in goats

Goats are susceptible to infection with foot-and-mouth disease virus (FMDV), but their role in the epidemiology of the disease and response to vaccination is poorly understood. In southern Africa, FMDV serotypes Southern African Territories (SAT) 1, 2 and 3 are known to be endemic. In this study, we evaluated the efficacy of a pentavalent FMD vaccine in goats against heterologous challenge with a pool of field SAT1 FMDV. Forty FMD sero-negative goats (6-12 months of age) of mixed sexes were randomly allocated to one of five treatment groups: full cattle dose (2 ml), 1/3rd (0.67 ml), 1/6th (0.33 ml), 1/12th (0.16 ml) or unvaccinated placebo control. Goats were vaccinated with an inactivated pentavalent FMD vaccine containing serotypes SAT1, SAT2 and SAT3 on day 0 and revaccinated at day 20 post vaccination. Thereafter, thirty-four goats were challenged by tongue inoculation at day 41 post-vaccination using 10^4.57 50% tissue culture infective dose (TCID₅₀) FMDV SAT1 pool. Animals were examined daily and clinical signs were scored. Rectal temperatures were measured daily, with temperatures ≥40 °C defined as fever. Clinical specimens (nasal, oral and rectal swabs) were collected on days 0, 2, 4 and 6 post challenge. Viral shedding was determined using reverse-transcriptase real-time PCR. None of the goats vaccinated with the full cattle dose developed secondary lesions. All vaccinated groups had lower temperatures compared to the unvaccinated controls (P < 0.001). Based on RT-PCR results, goats in the unvaccinated control group shed more virus compared to all groups except for 1/12th (P < 0.05), while goats in the full dose group shed less virus than goats in the 1/12th and the unvaccinated control group (P < 0.05). The results suggest that the 1/3rd (0.67 ml) dose of the vaccine is sufficient to reduce viral shedding after heterologous challenge with a FMDV SAT1 pool.

Cross-protective efficacy of the O1 Manisa + O 3039 bivalent vaccine and the O 3039 monovalent vaccine against heterologous challenge with FMDV O/Jincheon/SKR/2014 in pig

After massive foot-and-mouth disease (FMD) outbreaks originated from Jincheon County from Dec. 2014 to Apr. 2015, the effectiveness of the previous FMD vaccine containing only the O1 Manisa as the O antigen, O1 Manisa + A Malaysia 97 + Asia 1 Sharmir trivalent vaccine, was questioned in South Korea, and a change in the O antigen in FMD vaccines was demanded to control the FMD caused by FMDV O/Jincheon/SKR/2014, the O Jincheon strain. Therefore, the efficacies of O1 Manisa + O 3039 bivalent vaccine and O 3039 monovalent vaccine were studied for cross-protection against heterologous challenge with the O Jincheon strain. In this study, the efficacy of the O1 Manisa + O 3039 bivalent vaccine was better than that of the O 3039 monovalent vaccine, even though the serological relationship (r₁ value) between O Jincheon and O 3039 was matched according to the OIE Terrestrial Manual. According to serological test results from vaccinated specific pathogen free pigs, virus neutralization test titers against Jincheon were good estimates for predicting protection against challenge. A field trial of the O1 Manisa + O 3039 bivalent vaccine was performed to estimate the possibility of field application in conventional pig farms, especially due to concerns about the effect of maternally derived antibodies (MDA) in field application of the FMD vaccine. According to the result of the field trial, the O1 Manisa + O 3039 bivalent vaccine was considered to overcome MDA. The results of the efficacy and field trials indicated that the O1 Manisa + O3039 vaccine could be suitable to replace previous FMD vaccines to control the FMD field situation caused by O Jincheon FMDV.

Effect of vaccine storage temperatures and dose rate on antibody responses to foot and mouth disease vaccination in Cambodia

A field study investigated the effects of foot and mouth disease vaccine storage temperature for 7 days (frozen, refrigerated or held at ambient temperature) and dose (half or full dose) on the serological response to vaccination. It utilised a complete factorial design replicated on 18 smallholder cattle farms in three villages in Pursat province, Cambodia. Antibody responses from the 108 cattle involved were assessed by serological examination of blood samples collected at primary vaccination (day 0), at booster vaccination (day 30) and finally at 60 days post primary vaccination. Vaccination responses to the inactivated vaccine were assessed by testing for antibodies directed against FMD structural proteins in a liquid-phase blocking ELISA (LPBE test) and differentiated from responses to natural infection by examining antibody titres against non-structural viral proteins (NSPE test). LPBE results indicated that the mean log10 LPBE antibody titres of all experimental cattle increased from below protective levels at day 0 to protective levels at 30 days post primary vaccination, and increased further at 60 days post primary vaccination. Storage at ambient temperature for 1 week had no effect on antibody response to vaccination. However, freezing the vaccine for a week or use of a half dose resulted in significant reduction in titres at day 60 (P = 0.04 and P = 0.02, respectively). The results of this study reinforce the need to store FMD vaccines within the range recommended by the manufacturers and to adhere to the specified dosage instructions.

Bayesian inference of epidemiological parameters from transmission experiments

Epidemiological parameters for livestock diseases are often inferred from transmission experiments. However, there are several limitations inherent to the design of such experiments that limits the precision of parameter estimates. In particular, infection times and latent periods cannot be directly observed and infectious periods may also be censored. We present a Bayesian framework accounting for these features directly and employ Markov chain Monte Carlo techniques to provide robust inferences and quantify the uncertainty in our estimates. We describe the transmission dynamics using a susceptible-exposed-infectious-removed compartmental model, with gamma-distributed transition times. We then fit the model to published data from transmission experiments for foot-and-mouth disease virus (FMDV) and African swine fever virus (ASFV). Where the previous analyses of these data made various assumptions on the unobserved processes in order to draw inferences, our Bayesian approach includes the unobserved infection times and latent periods and quantifies them along with all other model parameters. Drawing inferences about infection times helps identify who infected whom and can also provide insights into transmission mechanisms. Furthermore, we are able to use our models to measure the difference between the latent periods of inoculated and contact-challenged animals and to quantify the effect vaccination has on transmission.

Sampling guidelines for oral fluid-based surveys of group-housed animals

Formulas and software for calculating sample size for surveys based on individual animal samples are readily available. However, sample size formulas are not available for oral fluids and other aggregate samples that are increasingly used in production settings. Therefore, the objective of this study was to develop sampling guidelines for oral fluid-based porcine reproductive and respiratory syndrome virus (PRRSV) surveys in commercial swine farms. Oral fluid samples were collected in 9 weekly samplings from all pens in 3 barns on one production site beginning shortly after placement of weaned pigs. Samples (n=972) were tested by real-time reverse-transcription PCR (RT-rtPCR) and the binary results analyzed using a piecewise exponential survival model for interval-censored, time-to-event data with misclassification. Thereafter, simulation studies were used to study the barn-level probability of PRRSV detection as a function of sample size, sample allocation (simple random sampling vs fixed spatial sampling), assay diagnostic sensitivity and specificity, and pen-level prevalence. These studies provided estimates of the probability of detection by sample size and within-barn prevalence. Detection using fixed spatial sampling was as good as, or better than, simple random sampling. Sampling multiple barns on a site increased the probability of detection with the number of barns sampled. These results are relevant to PRRSV control or elimination projects at the herd, regional, or national levels, but the results are also broadly applicable to contagious pathogens of swine for which oral fluid tests of equivalent performance are available.

Challenges of Generating and Maintaining Protective Vaccine-Induced Immune Responses for Foot-and-Mouth Disease Virus in Pigs

Vaccination can play a central role in the control of outbreaks of foot-and-mouth disease (FMD) by reducing both the impact of clinical disease and the extent of virus transmission between susceptible animals. Recent incursions of exotic FMD virus lineages into several East Asian countries have highlighted the difficulties of generating and maintaining an adequate immune response in vaccinated pigs. Factors that impact vaccine performance include (i) the potency, antigenic payload, and formulation of a vaccine; (ii) the antigenic match between the vaccine and the heterologous circulating field strain; and (iii) the regime (timing, frequency, and herd-level coverage) used to administer the vaccine. This review collates data from studies that have evaluated the performance of foot-and-mouth disease virus vaccines at the individual and population level in pigs and identifies research priorities that could provide new insights to improve vaccination in the future.

Experimental infections using the foot-and-mouth disease virus O/JPN/2010 in animals administered a vaccine preserved for emergency use in Japan

The effectiveness of a vaccine preserved for emergency use in Japan was analyzed under experimental conditions using cows and pigs in order to retrospectively evaluate the effectiveness of the emergency vaccination performed in the 2010 epidemic in Japan. Cows and pigs were administered a vaccine preserved for emergency use in Japan at 3 or 30 days before virus infection (dbv) and were subsequently infected with the foot-and-mouth disease virus (FMDV) O/JPN/2010, which was isolated in the 2010 epidemic in Japan. All animals vaccinated at 30 dbv and one of three pigs vaccinated at 3 dbv showed no vesicular lesions during the experimental period. The virus titers and viral RNA loads obtained from clinical samples were lower in the vaccinated cows than in the non-vaccinated cows. The viral excretion periods were shorter in the vaccinated cows than in the non-vaccinated cows. In contrast, in the vaccinated pigs, the virus titers and viral RNA loads obtained from the samples, except for those obtained from sera, were not decreased significantly, and the viral excretion periods were not sufficiently shortened. These results suggest that the vaccine can protect against clinical signs of infection by the FMDV O/JPN/2010 in animals; however, it should be noted that in vaccinated and infected animals, especially pigs, clinical samples, such as saliva and nasal swabs, may contain excreted viruses, even if no clinical signs were exhibited.

Infection Dynamics of Foot-and-Mouth Disease Virus in Cattle Following Intranasopharyngeal Inoculation or Contact Exposure

For the purpose of developing an improved experimental model for studies of foot-and-mouth disease virus (FMDV) infection in cattle, three different experimental systems based on natural or simulated natural virus exposure were compared under standardized experimental conditions. Ante-mortem infection dynamics were characterized in cattle exposed to FMDV through a novel, simulated natural intranasopharyngeal (INP) inoculation system or through standardized and controlled systems of within- or between-species direct contact exposure (cattle-to-cattle or pig-to-cattle). All three systems were efficient in causing synchronous, generalized foot-and-mouth disease in cattle exposed to one of three different strains of FMDV representing serotypes O, A and Asia1. There was more within-group variation in the timing of clinical infection following natural and simulated natural virus exposure systems when compared with the conventionally used system of needle inoculation (intraepithelial lingual inoculation). However, the three optimized exposure systems described herein have the advantage of closely simulating field conditions by utilizing natural routes of primary infection, thereby facilitating engagement of mucosal host defence mechanisms. Overall, it is concluded that INP inoculation and standardized systems of direct contact exposure provide effective alternatives to conventional (needle) inoculation systems for studies in which it is desirable to simulate the natural biology of FMDV infection.

The Pathogenesis of Foot-and-Mouth Disease in Pigs

The greatest proportion of foot-and-mouth disease (FMD) clinical research has been dedicated to elucidating pathogenesis and enhancing vaccine protection in cattle with less efforts invested in studies specific to pigs. However, accumulated evidence from FMD outbreaks and experimental investigations suggest that critical components of FMD pathogenesis, immunology, and vaccinology cannot be extrapolated from investigations performed in cattle to explain or to predict outcomes of infection or vaccination in pigs. Furthermore, it has been shown that failure to account for these differences may have substantial consequences when FMD outbreaks occur in areas with dense pig populations. Recent experimental studies have confirmed some aspects of conventional wisdom by demonstrating that pigs are more susceptible to FMD virus (FMDV) infection via exposure of the upper gastrointestinal tract (oropharynx) than through inhalation of virus. The infection spreads rapidly within groups of pigs that are housed together, although efficiency of transmission may vary depending on virus strain and exposure intensity. Multiple investigations have demonstrated that physical separation of pigs is sufficient to prevent virus transmission under experimental conditions. Detailed pathogenesis studies have recently demonstrated that specialized epithelium within porcine oropharyngeal tonsils constitute the primary infection sites following simulated natural virus exposure. Furthermore, epithelium of the tonsil of the soft palate supports substantial virus replication during the clinical phase of infection, thus providing large amounts of virus that can be shed into the environment. Due to massive amplification and shedding of virus, acutely infected pigs constitute a considerable source of contagion. FMDV infection results in modulation of several components of the host immune response. The infection is ultimately cleared in association with a strong humoral response and, in contrast to ruminants, there is no subclinical persistence of FMDV in pigs. The aim of this review is to provide an overview of knowledge gained from experimental investigations of FMD pathogenesis, transmission, and host response in pigs. Details of the temporo-anatomic progression of infection are discussed in relation to specific pathogenesis events and the likelihood of transmission. Additionally, relevant aspects of the host immune response are discussed within contexts of conventional and novel intervention strategies of vaccination and immunomodulation.

Potential impact of species and livestock density on the epidemic size and effectiveness of control measures for foot-and-mouth disease in Japan

The characteristics of a livestock area, including farm density and animal species, influence the spread of foot-and-mouth disease (FMD). In this study, the impact of livestock area on FMD epidemics was examined using an FMD transmission model. For this simulation, three major livestock areas were selected: the 2010 FMD epidemic area in Japan as the baseline area (BS), a cattle and pig mixed production area (CP) and a cattle production area (C). Simulation results demonstrated that under the 24-hr culling policy, only 12% of epidemics among 1,000 simulations were abated within 100 days in the CP area, whereas 90% of the epidemics ceased in the BS area. In the C area, all epidemics were successfully contained within 100 days. Evaluation of additional control measures in the CP area showed that the 0.5-km pre-emptive culling, even when only targeting pig farms, raised the potential for successful containment to 94%. A 10-km vaccination on day 7 or 14 after initial detection was also effective in halting the epidemics (80%), but accompanied a large number of culled or vaccinated farms. The combined strategy of 10-km vaccination and 0.5-km pre-emptive culling targeting pig farms succeeded in containing all epidemics within 100 days. The present study suggests the importance of preparedness for the 24-hr culling policy and additional control measures when an FMD outbreak occurs in a densely populated area. Considering the characteristics of the livestock area is important in planning FMD control strategies.

A Malaysia 97 monovalent foot-and-mouth disease vaccine (>6PD50/dose) protects pigs against challenge with a variant FMDV A SEA-97 lineage virus, 4 and 7 days post vaccination

Pigs play a significant role during outbreaks of foot-and-mouth disease (FMD) due to their ability to amplify the virus. It is therefore essential to determine what role vaccination could play to prevent clinical disease and lower virus excretion into the environment. In this study we investigated the efficacy of the double oil emulsion A Malaysia 97 vaccine (>6PD50/dose) against heterologous challenge with an isolate belonging to the A SEA-97 lineage at 4 and 7 days post vaccination (dpv). In addition, we determined whether physical separation of pigs in the same room could prevent virus transmission. Statistically there was no difference in the level of protection offered by 4 and 7 dpv. However, no clinical disease or viral RNA was detected in the blood of pigs challenged 4 dpv, although three of the pigs had antibodies to the non-structural proteins (NSPs), indicating viral replication. Viral RNA was also detected in nasal and saliva swabs, but on very few occasions. Two of the pigs vaccinated seven days prior to challenge had vesicles distal from the injection site, but on the inoculated foot, and two pigs had viral RNA detected in the blood. One pig sero-converted to the NSPs. In contrast, all unvaccinated and inoculated pigs had evidence of infection. No infection occurred in any of the susceptible pigs in the same room, but separated from the infected pigs, indicating that strict biosecurity measures were sufficient under these experimental conditions to prevent virus transmission. However, viral RNA was detected in the nasal swabs of one group of pigs, but apparently not at sufficient levels to cause clinical disease. Vaccination led to a significant decrease in viral RNA in vaccinated pigs compared to unvaccinated and infected pigs, even with this heterologous challenge, and could therefore be considered as a control option during outbreaks.

Efficacy of a high potency O1 Manisa monovalent vaccine against heterologous challenge with a FMDV O Mya98 lineage virus in pigs 4 and 7 days post vaccination

Early protection with a high potency (>6PD50) foot-and-mouth disease (FMD) O1 Manisa (Middle-East South Asia lineage) vaccine against challenge with O/VIT/2010 (O Mya98 lineage) was tested in pigs. Only two pigs that were vaccinated seven days prior to challenge had any demonstrable antibodies as a result of vaccination at the time of challenge. However, 80% and 60% of pigs that were vaccinated seven and four days prior to coronary band challenge were protected. Vaccination significantly reduced the amount of virus excreted in nasal swabs, saliva and faeces compared to unvaccinated and infected controls. Virus and viral RNA could be detected in some pigs until termination of the experiment 14 days after challenge. Antibodies to the non-structural proteins (NSP) were detected in only one pig that was challenged four days post vaccination (dpv) and transiently in two pigs that were challenged sevendpv at only one time point. For each vaccine and control group, a group of unvaccinated pigs were kept in the same room but with no direct contact with the infected pigs to determine whether vaccination prevented transmission. Despite the presence of live virus and viral RNA in these indirect contact pigs, the groups in contact with the vaccinated and infected pigs did not develop clinical signs nor did they sero-convert. Contact pigs in the same room as unvaccinated challenged controls did show signs of disease and virus infection that resulted in sero-conversion to the NSP. A breach of the wall that separated the two groups at nine days post challenge might have contributed to this finding. This study showed that high potency vaccine can provide protection to pigs soon after vaccination and that aerosol transmission within rooms is a rare event.

Quantification of transmission of foot-and-mouth disease virus caused by an environment contaminated with secretions and excretions from infected calves

Foot-and-mouth disease virus (FMDV) infected animals can contaminate the environment with their secretions and excretions. To quantify the contribution of a contaminated environment to the transmission of FMDV, this study used calves that were not vaccinated and calves that were vaccinated 1 week prior to inoculation with the virus in direct and indirect contact experiments. In direct contact experiments, contact calves were exposed to inoculated calves in the same room. In indirect contact experiments, contact calves were housed in rooms that previously had held inoculated calves for three days (either from 0 to 3 or from 3 to 6 days post inoculation). Secretions and excretions from all calves were tested for the presence of FMDV by virus isolation; the results were used to quantify FMDV transmission. This was done using a generalized linear model based on a 2 route (2R, i.e. direct contact and environment) SIR model that included information on FMDV survival in the environment. The study shows that roughly 44% of transmission occurs via the environment, as indicated by the reproduction ratio R0(2R)environment that equalled 2.0, whereas the sum of R0(2R)contact and R0(2R)environment equalled 4.6. Because vaccination 1 week prior to inoculation of the calves conferred protective immunity against FMDV infection, no transmission rate parameters could be estimated from the experiments with vaccinated calves. We conclude that a contaminated environment contributes considerably to the transmission of FMDV therefore that hygiene measures can play a crucial role in FMD control.

Vaccination of cattle only is sufficient to stop FMDV transmission in mixed populations of sheep and cattle

We quantified the transmission of foot-and-mouth disease virus in mixed cattle-sheep populations and the effect of different vaccination strategies. The (partial) reproduction ratios (R) in groups of non-vaccinated and vaccinated cattle and/or sheep were estimated from (published) transmission experiments. A 4 × 4 next-generation matrix (NGM) was constructed using these estimates. The dominant eigenvalue of the NGM, the R for a mixed population, was determined for populations with different proportions of cattle and sheep and for three different vaccination strategies. The higher the proportion of cattle in a mixed cattle-sheep population, the higher the R for the mixed population. Therefore the impact of vaccination of the cattle is higher. After vaccination of all animals R = 0·1 independent of population composition. In mixed cattle-sheep populations with at least 14% of cattle, vaccination of cattle only is sufficient to reduce R to < 1.

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.

Effect of handling and storage conditions and stabilizing agent on the recovery of viral RNA from oral fluid of pigs

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Inactivation of salivary enzymes by heating oral fluid for 15 min at 60 °C was detrimental to hepatitis E virus (HEV) RNA.

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HEV, F-RNA coliphage and murine norovirus RNA are not degraded in oral fluid stored at 4 °C for ≤24 h.

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Recovery of HEV RNA from oral fluid after 30 days at −20 °C was higher in the absence of RNA stabilizer.

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RNeasy Protect Saliva Mini kit does not work well for viral RNA.

There is an increasing interest in using oral fluid to determine herd health and documenting the circulation of viruses in commercial swine populations but little is known about the stability of viruses in oral fluid. Hepatitis E virus (HEV) is a zoonotic virus which is widespread in swine herds. Information on optimal handling methods such as heat treatments, freezing and RNA stabilization agents is needed to prevent or minimize degradation of viral RNA by degradative enzymes. The objectives of the study were to determine optimum handling conditions of the oral fluid before RNA extraction and to compare the performance of the RNeasy Protect Saliva Mini kit, which contains a stabilizing agent, with that of the QIAamp Viral RNA Mini kit, which does not contain a stabilizing agent. Preliminary studies with oral fluid inoculated with HEV indicated that a heat treatment of 60 °C for 15 min was detrimental to HEV RNA. HEV was recovered from 25/25 and 24/25 samples of oral fluid when samples were incubated for ≤24 h at 4 °C and 30 days at −20 °C, respectively, without a stabilizing agent and extracted with the QiaAMP kit. In contrast, HEV RNA was detected in 16/25 and 11/25 samples when samples were incubated with a stabilizing agent for 24 h at 37 °C and 30 days at −20 °C, respectively, and extracted with the RNeasy Protect Saliva kit. Moreover, the mean number of genome copies/ml of HEV recovered from oral fluid stored at −20 °C without the stabilizing agent was 2.9 log units higher than oral fluid stored at −20 °C in the presence of the stabilizing agent. The recovery of RNA from HEV, F-RNA coliphage MS2 and murine norovirus (MNV), which are surrogates for norovirus, was significantly greater when oral fluid was incubated for 24 h at 4 °C than when oral fluid was stabilized with RNAprotect Saliva Reagent for 24 h at 37 °C, where the relative differences between the two processes were 1.4, 1.8, and 2.7 log genome copies/ml for MS2, MNV, and HEV, respectively. The findings suggest that it is unnecessary to stabilize oral fluid from swine for the detection of viral RNA, provided the samples are stored at 4 °C or frozen at −20 °C, and that the RNeasy Protect Saliva Mini kit did not perform well for the detection of viral RNA.

Identification of factors associated with increased excretion of foot-and-mouth disease virus

We investigated which variables possibly influence the amount of foot-and-mouth disease virus (FMDV) shed in secretions and excretions by FMDV infected animals, as it is likely that the amount of FMDV shed is related to transmission risk. First, in a separate analysis of laboratory data, we showed that the total amount of FMDV in secretions and excretions from infected animals is highly correlated with maximum titres of FMDV. Next, we collected data from 32 published scientific articles in which FMDV infection experiments were described. The maximum titres of FMDV reported in different secretions and excretions (the response variable) and the experimental conditions in which they occurred (the explanatory variables), were recorded in a database and analyzed using multivariate regression models with and without random effects. In both types of models, maximum titres of FMDV were significantly (p<0.05) associated with types of secretions and excretions, animal species, stage of the disease and days post infection. These results can be used to prioritize biosecurity measures in contingency plans.

Effect of collection material and sample processing on pig oral fluid testing results

The effect of sampling material, sample processing, and collection order on the detection of analytes in pig oral fluid specimens was evaluated. Oral fluid samples were collected from 104 pens of commercial wean-to-finish pigs using ropes made of three different materials. Processed (centrifuged and filtered) and unprocessed oral fluid samples were tested using commercial ELISAs for porcine reproductive and respiratory syndrome virus (PRRSV) antibodies and total IgM, IgA, and IgG. Unprocessed samples were tested for PRRSV nucleic acid and processed samples were assayed for PRRSV neutralizing antibodies. Analysis of the data using repeated measures ANOVA and Tukey-Kramer adjusted t tests found statistically significant, non-uniform, and assay-dependent effects of all three factors. Therefore, when testing oral fluid specimens, swine health specialists, veterinarians, and diagnosticians should be aware of the potential impact of these factors on specific analytes. For monitoring health and welfare parameters, oral fluid samples should be collected using cotton-based materials and undergo minimal post-collection processing.

Transmission rate of African swine fever virus under experimental conditions

African swine fever (ASF) is a highly lethal, viral disease of swine. No vaccine is available, so controlling an ASF outbreak is highly dependent on zoosanitary measures, such as stamping out infected herds and quarantining of affected areas. Information on ASF transmission parameters could allow for more efficient application of outbreak control measures. Three transmission experiments were carried out to estimate the transmission parameters of two ASF virus isolates: Malta'78 (in two doses) and Netherlands'86. Different criteria were used for onset of infectiousness of infected pigs and moment of infection of contact pigs. The transmission rate (β), estimated by a Generalized Linear Model, ranged from 0.45 to 3.63 per day. For the infectious period, a minimum as well as a maximum infectious period was determined, to account for uncertainties regarding infectiousness of persistently infected pigs. While the minimum infectious period ranged from 6 to 7 days, the average maximum infectious period ranged from approximately 20 to nearly 40 days. Estimates of the reproduction ratio (R) for the first generation of transmission ranged from 4.9 to 24.2 for the minimum infectious period and from 9.8 to 66.3 for the maximum infectious period, depending on the isolate. A first approximation of the basic reproduction ratio (R0) resulted in an estimate of 18.0 (6.90-46.9) for the Malta'78 isolate. This is the first R0 estimate of an ASFV isolate under experimental conditions. The estimates of the transmission parameters provide a quantitative insight into ASFV epidemiology and can be used for the design and evaluation of more efficient control measures.

Vaccination against foot-and-mouth disease I: epidemiological consequences

An epidemic of foot-and-mouth disease (FMD) can have devastating effects on animal welfare, economic revenues, the export position and society as a whole, as occurred during the 2001 FMD epidemic in the Netherlands. Following the preemptive culling of 260,000 animals during this outbreak, the Dutch government adopted emergency vaccination as preferred control policy. However, a vaccination-to-live strategy has not been applied before, posing unprecedented challenges for effectively controlling the epidemic, regaining FMD-free status and minimizing economic losses. These three topics are covered in an interdisciplinary model analysis. In this first part we evaluate whether and how emergency vaccination can be effectively applied to control FMD epidemics in the Netherlands. For this purpose we develop a stochastic individual-based model that describes FMD virus transmission between animals and between herds, taking heterogeneity between host species (cattle, sheep and pigs) into account. Our results in a densely populated livestock area with >4 farms/km(2) show that emergency ring vaccination can halt the epidemic as rapidly as preemptive ring culling, while the total number of farms to be culled is reduced by a factor of four. To achieve this reduction a larger control radius around detected farms and a corresponding adequate vaccination capacity is needed. Although sufficient for the majority of simulated epidemics with a 2 km vaccination zone, the vaccination capacity available in the Netherlands can be exhausted by pig farms that are on average ten times larger than cattle herds. Excluding pig farms from vaccination slightly increases the epidemic, but more than halves the number of animals to be vaccinated. Hobby flocks - modelled as small-sized sheep flocks - do not play a significant role in propagating the epidemic, and need not be targeted during the control phase. In a more sparsely populated livestock area in the Netherlands with about 2 farms/km(2) the minimal control strategy of culling only detected farms seems sufficient to control an epidemic.

Direct contact transmission of three different foot-and-mouth disease virus strains in swine demonstrates important strain-specific differences

A novel direct contact transmission model for the study of foot-and-mouth disease virus (FMDV) infection of swine was utilized to investigate transmission characteristics of three FMDV strains belonging to serotypes A, O and Asia1. Each strain demonstrated distinct transmission characteristics and required different exposure times to achieve successful contact transmission. While a 4h exposure was sufficient for strain A24 Cruzeiro (A24Cru), both O1 Manisa and Asia1 Shamir transmission required 18 h or more. Viral excretion levels from donors (for all three strains) and virus present in room air (for A24Cru and O1 Manisa) were evaluated and associated with clinical signs and observed transmission pattern. Although all directly inoculated donor animals showed acute FMD, A24Cru had the highest levels of viral shedding in saliva and nasal swabs followed by O1 Manisa and Asia1 Shamir. Virus levels in room air were higher and were detected longer for A24Cru than for O1 Manisa. These results provide direct evidence for important strain-specific variation in transmission characteristics and emphasize the need for thorough evaluation of different FMDV viral strains using a well defined contact transmission methodology. This information is critical for vaccine and biotherapeutic efficacy testing, pathogenesis and disease modeling of FMDV transmission.

Assess the Effect of the Foot and Mouth Disease Type O Inactivated Vaccine (O/MYA98/BY/2010 Strain) for Pigs

Recently, O-type foot and mouth disease epidemic situation has changed, there has been MYA98 epidemic strains, has caused many Asian countries for many kinds of animal damage. In January 2011, a new matching vaccine developed, namely Foot and mouth disease type O inactivated vaccine (O/MYA98/BY/2010 strain). In order to master this vaccine effectiveness in pig production, all the individual pigs in the ten farms had been immunized.A total of 97786 individuals or times immunized pigs were observed. All pigs were traced surveillance for foot and mouth clinical signs. A total of 295 serum samples were detected for antibody titers.The results show that although there adverse side effects, but other than the vaccine adverse reactions and extent has significantly decreased, pigs immunized were non-occurrence of type O foot and mouth disease, the antibody titer is eligible. So here we show , the vaccine is safe and effective, can be widely used.

Foot-and-mouth disease in pigs: current epidemiological situation and control methods

Foot-and-mouth disease (FMD) is the paradigm of a transboundary animal disease. Beyond any doubt, it is the most serious challenge for livestock's health. Official Veterinary Services from free countries invest considerable amount of money to prevent its introduction, whereas those from endemic countries invest most of their resources in the control of the disease. A very important volume of scientific production is developed every year in different aspects of FMD, and for that reason, the current knowledge makes the diagnosis of the disease easier to a great extent. However, FMD is still endemic in about two-thirds of the countries, and periodically re-emergent in several countries. This paper is a review of recent publications, focusing mainly on control measures and current world epidemiological situation, emphasizing primarily pigs.

Homologous whole bacterin vaccination is not able to reduce Streptococcus suis serotype 9 strain 7997 transmission among pigs or colonization

Streptococcus suis (S. suis) is an important porcine pathogen worldwide, and antibiotics are often applied to treat or prevent clinical signs. Vaccination could be an alternative measure to reduce the abundant use of antimicrobials. The aim of this study was to determine the effect of vaccination with homologues whole bacterin vaccine containing S. suis serotype 9 strain 7997 on transmission of this serotype among pigs and on mucosal colonization. Caesarean derived, colostrum deprived pigs (N=50) were housed pair wise. Thirteen pairs were vaccinated intramuscularly with 2-3×10(9) colony forming units (CFU) inactivated S. suis serotype 9 per dose and α-tocopherolactetaat as adjuvant at 3 and 5 weeks of age; twelve pairs served as non-vaccinated controls. At 7 weeks of age, one pig of each pair was intranasally inoculated with 1-2×10(9)CFU of the homologues strain, whereas the other pig of each pair was contact-exposed. Tonsil brushings and saliva swabs were collected for 4 weeks, and tested for the presence of S. suis by bacteriological culture. No differences in number of S. suis in the tonsils or saliva samples or in clinical signs were observed between vaccinated and control pigs. In all pairs, transmission between inoculated and contact exposed pigs occurred, and no difference was observed in rate at which this occurred. The estimated transmission rate parameter β between vaccinated pigs was β(v)=5.27/day, and for non-vaccinated pigs β(nv)=2.77/day (P=0.18). It was concluded that vaccination against S. suis serotype 9 did not reduce transmission, nor colonization and that there were no indications that protection against clinical signs was induced.

Efficient surveillance of pig populations using oral fluids

Currently virus surveillance in swine herds is constrained by the cost-effectiveness and efficiency of sampling methods. The objective of this study was to assess the value of using oral fluids collected by barn personnel as a method of surveillance based on PCR testing. Approximately 12,150 pigs in 10 wean-to-finish barns on 10 farms were monitored for the presence of porcine circovirus type 2 (PCV2), porcine reproductive and respiratory syndrome virus (PRRSV), influenza A virus (IAV), and Torque teno virus genogroups 1 (TTV1) and 2 (TTV2) by sampling oral fluid specimens. Oral fluid samples were collected from 6 pens at each site starting at the time of pig placement (∼3 weeks of age) and continuing thereafter at 2-week intervals for a period of 18 weeks. Data were analyzed both on a pen basis and barn basis. Overall, 508 (85%) samples were positive for PCV2, 73 (12%) for PRRSV, 46 (8%) for IAV, 483 (81%) for TTV2, and 155 (26%) for TTV1 during the study period. The estimated arithmetic means of the quantitative PCR-positive oral fluids for PCV2, PRRSV, and IAV were 1×10(4.62), 1×10(4.97), and 1×10(5.49)per ml. With a single exception, all barns were positive for PCV2 and TTV2 at every sampling point in the study. Virus detection varied among barns, particularly for IAV and PRRSV. The pen level, cumulative distribution of agent combinations between all 10 barns were statistically different. The most commonly observed patterns were PCV2+TTV2 (239 pen samples, 40%), PCV2+TTV1+TTV2 (88 pen samples, 15%), and PCV2 alone (66 pen samples, 11%). This "proof-of-concept" project showed that a variety of viruses could be detected either intermittently or continuously in pig populations and demonstrated that barn herd virus status is highly variable, even among barns in the same production system. Oral fluid sampling is a promising approach for increasing the efficiency and cost effectiveness of virus surveillance in swine herds.

Promising multiple-epitope recombinant vaccine against foot-and-mouth disease virus type O in swine

In order to develop a completely safe immunogen to replace the traditional inactivated vaccine, a tandem-repeat multiple-epitope recombinant vaccine against foot-and-mouth disease (FMD) virus (FMDV) type O was developed. It contained three copies each of residues 141 to 160 and 200 to 213 of VP1 of the O/China/99 strain of FMDV coupled with a swine immunoglobulin G heavy-chain constant region (scIgG). The data showed that the multiple-epitope recombinant vaccine elicited high titers of anti-FMDV specific antibodies in swine at 30 days postvaccination (dpv) and conferred complete protection against a challenge with 10³ 50% swine infective doses of the O/China/99 strain. The anti-FMDV specific antibody titers were not significantly different between the multiple-epitope recombinant vaccine and the traditional vaccine (t test, P > 0.05). The number of 50% pig protective doses was 6.47, which is higher than the number recommended by the World Organization for Animal Health. The multiple-epitope recombinant vaccine resulted in a duration of immunity of at least 6 months. We speculate that the multiple-epitope recombinant vaccine is a promising vaccine that may replace the traditional inactivated vaccine for the prevention and control of FMD in swine in the future.

Probability of exporting infected carcasses from vaccinated pigs following a foot-and-mouth disease epidemic

Emergency vaccination is an effective control strategy for foot-and-mouth disease (FMD) epidemics in densely populated livestock areas, but results in a six-month waiting period before exports can be resumed, incurring severe economic consequences for pig exporting countries. In the European Union, a one-month waiting period has been discussed based on negative test results in a final screening. The objective of this study was to analyze the risk of exporting FMD-infected pig carcasses from a vaccinated area: (1) directly after final screening and (2) after a six-month waiting period. A risk model has been developed to estimate the probability that a processed carcass was derived from an FMD-infected pig (P(carc)). Key variables were herd prevalence (P(H)), within-herd prevalence (P(A)), and the probability of detection at slaughter (P(SL)). P(H) and P(A) were estimated using Bayesian inference under the assumption that, despite all negative test results, > or =1 infected pigs were present. Model calculations indicated that P(carc) was on average 2.0 x 10(-5) directly after final screening, and 1.7 x 10(-5) after a six-month waiting period. Therefore, the additional waiting time did not substantially reduce P(carc). The estimated values were worst-case scenarios because only viraemic pigs pose a risk for disease transmission, while seropositive pigs do not. The risk of exporting FMD via pig carcasses from a vaccinated area can further be reduced by heat treatment of pork and/or by excluding high-risk pork products from export.

Transmission risks and control of foot-and-mouth disease in The Netherlands: spatial patterns

In 2001 the epidemics of foot-and-mouth disease virus (FMDV) in Great Britain, The Netherlands and France have shown how fast FMDV may spread between farms. The massive socio-economic impact of these epidemics and the intervention measures taken demonstrate the need for quantitative assessments of the efficacy of candidate intervention strategies. Here we use a mathematical model to describe the spatial transmission of FMDV in The Netherlands and use the Dutch 2001 outbreak data to estimate model parameters. We assess the effect of ring culling strategies using a novel and fast approach producing risk maps, and discuss its consequences for ring vaccination. These risk maps identify both the geographical areas of low risk, where a given intervention strategy is likely to achieve epidemic control within only two or three farm-to-farm infection generations, and high-risk areas, where control is likely to take (much) longer. Our results indicate that certain densely populated livestock areas in the Netherlands remain high-risk areas even for strategies that extend EU minimum measures with culling or vaccination within a ring radius of several kilometres. Depending on an economic assessment, area-wide vaccination might be judged appropriate once an FMDV outbreak would have been confirmed in or close to such a high-density area. The modeling approach developed here could be readily applied to outbreak data for other diseases and in other countries.

The development of oral fluid-based diagnostics and applications in veterinary medicine

The purpose of this review was to discuss the history of the development and implementation of oral fluid diagnostics for infectious diseases of humans and domestic animals. The use of oral fluid for the assessment of health and diagnosis of disease in humans and animals has a surprisingly long history. As early as 1909, Pollaci and Ceraulo reported sensitive and specific agglutination of 'Micrococcus melitensis' (Brucella melitensis) by oral fluid from patients diagnosed with Malta Fever. A 1986 report of the detection of antibodies against human immunodeficiency virus (HIV) in oral fluid from patients with acquired immunodeficiency syndrome (AIDS) marked the start of a remarkably rapid series of developments in oral fluid-based assays. Cumulatively, the literature strongly supports implementation of oral fluid-based diagnostics in veterinary diagnostic medicine. Pathogen-specific IgA, IgM and IgG antibodies have all been demonstrated in oral fluid collected from diverse domestic animal species in response to infection. A variety of infectious agents, both local and systemic, are shed in oral fluid, including some of the most economically significant pathogens of production animals (e.g. foot-and-mouth disease virus, classical swine fever virus and porcine reproductive and respiratory syndrome virus) Ultimately, point-of-care rapid assays (i.e. cow-side, sow-side or pen-side tests) and access to real-time infectious disease data will revolutionize our delivery of health management services.

IgA antibody response of swine to foot-and-mouth disease virus infection and vaccination

Foot-and-mouth disease virus (FMDV) continues to be a significant economic problem worldwide. Control of the disease involves the use of killed-virus vaccines, a control measure developed decades ago. After natural infection, the primary site of replication of FMDV is the pharyngeal area, suggesting that a mucosal immune response is the most effective. Humoral immunity to killed-virus vaccination induces antibodies that can prevent the clinical disease but not local infection. Determining whether infection or vaccination stimulates IgA-mediated local immunity depends on the method of analysis. Different assays have been described to analyze the quality of antibody responses of cattle and swine to FMDV, including indirect double-antibody sandwich enzyme-linked immunosorbent assay (IDAS-ELISA) and antibody capture assay-ELISA (ACA-ELISA). We tested these assays on swine and show that vaccinated animals had FMDV-specific IgM and IgG but no IgA in either serum or saliva. After the infection, both assays detected FMDV-specific IgM, IgG, and IgA in serum. Notably, serum IgA was more readily detected using the ACA-ELISA, whereas IgA was not detected in saliva with this assay. FMDV-specific IgA antibodies were detected in saliva samples using the IDAS-ELISA. These data show that parenterally administered, killed-virus vaccine does not induce a mucosal antibody response to FMDV and illuminates limitations and appropriate applications of the two ELISAs used to measure FMDV-specific responses. Further, the presence of the IgA antivirus in serum correlates with the presence of such antibodies in saliva.

Passive immunization with llama single-domain antibody fragments reduces foot-and-mouth disease transmission between pigs

We aim to develop a method that confers rapid protection against foot-and-mouth disease (FMD) by passive immunization with recombinant llama single-domain antibody fragments (VHHs). Previously constructed genetic fusions of two VHHs (VHH2s) that either neutralizes FMDV or binds to porcine immunoglobulin to increase the serum half-life, conferred only limited protection to pigs. We therefore now generated VHH3s containing an additional FMDV binding VHH. Two VHH3s neutralized FMDV more potently than single VHHs and were highly produced by yeast cells. Injection of a mixture of these two VHH3s 24h before FMD challenge infection of pigs reduced and delayed the development of clinical disease, viraemia and viral shedding. Furthermore, it significantly (P=0.023) delayed FMD transmission. Thus, we have shown a proof of concept of passive FMD immunoprophylaxis using VHHs.

Experimental evaluation of foot-and-mouth disease vaccines for emergency use in ruminants and pigs: a review

Changes to foot-and-mouth disease (FMD) control policies since 2001 mean that emergency vaccination must be considered more readily as a control measure in the future. Since field application of vaccine for emergency use has only rarely been applied, the effectiveness of single dose administration, as a control measure in an outbreak situation, is poorly understood. In this review we consider all the available experimental data from studies utilizing either experimental or readily available, commercially produced vaccines, in order to assess their likely effectiveness as an additional means of controlling FMD transmission and spread in an emergency. Overall it is concluded that such vaccines offer an additional and valuable means of FMD control for both ruminants and pigs. They are able to reduce clinical disease, sub-clinical infection and excretion and onward transmission of virus. However, to be most effective, vaccination should be rapidly applied to give maximum opportunity for immunity to develop. We also identify areas for future research and emphasize the importance of vaccine efficacy studies in providing data for models that can help to predict the efficacy of differing FMD control strategies.

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.