Foot-and-mouth Disease Virus Transmission Research Articles

Effective Foot‐and‐Mouth Disease Virus Control Using Silver Nanoparticles

AbstractThis study investigates the antiviral efficacy of chitosan‐stabilized silver nanoparticles (AgNPs) against the Foot‐and‐Mouth Disease virus (FMDV), a highly contagious pathogen affecting cloven‐hoofed animals. In vitro experiments demonstrated that AgNPs effectively inhibited FMDV replication in a dose‐dependent manner. At a concentration of 1.56 μg/ml, AgNPs exhibited no cytotoxicity to baby hamster kidney 21 (BHK21) cells while achieving complete deactivation of FMDV at a titer of 103 TCID50 and inhibiting viral growth at a titer of 104 TCID50. These findings suggest the potential of silver nanoparticles as a novel disinfectant for controlling FMDV transmission and preventing disease outbreaks.

Phylodynamic analysis of foot-and-mouth disease virus evolution in Mar Chiquita, Argentina.

Foot-and-mouth disease is a highly contagious disease affecting cloven-hoofed animals, resulting in considerable economic losses. Its causal agent is foot-and-mouth disease virus (FMDV), a picornavirus. Due to its error-prone replication and rapid evolution, the transmission and evolutionary dynamics of FMDV can be studied using genomic epidemiological approaches. To analyze FMDV evolution and identify possible transmission routes in an Argentinean region, field samples that tested positive for FMDV by PCR were obtained from 21 farms located in the Mar Chiquita district. Whole FMDV genome sequences were obtained by PCR amplification in seven fragments and sequencing using the Sanger technique. The genome sequences obtained from these samples were then analyzed using phylogenetic, phylogeographic, and evolutionary approaches. Three local transmission clusters were detected among the sampled viruses. The dataset was analyzed using Bayesian phylodynamic methods with appropriate coalescent and relaxed molecular clock models. The estimated mean viral evolutionary rate was 1.17 × 10- 2 substitutions/site/year. No significant differences in the rate of viral evolution were observed between farms with vaccinated animals and those with unvaccinated animals. The most recent common ancestor of the sampled sequences was dated to approximately one month before the first reported case in the outbreak. Virus transmission started in the south of the district and later dispersed to the west, and finally arrived in the east. Different transmission routes among the studied herds, such as non-replicating vectors and close contact contagion (i.e., aerosols), may be responsible for viral spread.

Foot and Mouth Disease (FMD): Etiology, Pathogenesis, Prevention and Control in Even or Split Hoofed Livestock

Foot and Mouth Disease (FMD) was first reported in 1987 in Malang, East Java, caused by imported dairy cattle from the Netherlands. After 36 years of FMD freedom, the disease was re-introduced on 5 May 2022 in East Java. The disease is caused by a virus of the genus Aphthovirus of the Picornaviridae family, which affects even-toed or split-hoofed livestock, both wild and domesticated. Transmission of FMD virus from sick animals to other susceptible animals can occur directly and indirectly. FMD virus can be transmitted rapidly, entering the animal's body directly through the mouth or nose and replicating in epithelial cells in the nasopharyngeal area, then entering the blood (viremia), then multiplying in lymphoglandular glands and epithelial cells in the mouth and footpads resulting in vesicle lesions and blisters. Animals or livestock infected with FMD will show clinical symptoms such as fever up to 41oC, the formation of vesicles or blisters on the mouth, gums, tongue, nipples, and skin around the hooves, hypersalivation, weight loss, and livestock production. Handling and controlling FMD in livestock or animals can be done by isolating and quarantining sick animals, vaccination programs, biosecurity measures in animal husbandry, monitoring livestock traffic, and conducting surveillance.

Foot and mouth disease viruses are recurrently introduced to Israel and spread by extensively reared sheep and cattle: Insights from a whole-genome sequence analysis

Despite routine vaccination, Israel experiences recurrent outbreaks of foot and mouth disease (FMD). We analyzed VP1 coding sequences of viruses isolated during FMD outbreaks from 2001 to 2011 in Israel and neighboring nations. The Israeli strains were aligned with strains from neighboring countries in corresponding years, implying repeated FMD virus incursions. In 2007 a large FMD epidemic, caused by a serotype O virus, occurred in Israel. Bayesian analysis of whole-genome sequences of viruses isolated during this epidemic revealed predominant transmission among extensively farmed beef-cattle and small ruminants. Small ruminants were key in spreading to beef-cattle, which then transmitted the virus to feedlot-cattle. Wild gazelles had a minor role in transmission. The results may suggest probable transmission of FMD virus from the Palestinian Authority to Israel. Targeting extensive farms via enhanced surveillance and vaccination could improve FMDV control. Given cross-border transmission, a collaborative FMD mitigation strategy across the Middle-East is crucial.

Animal Movements and FMDV Transmission during the High-Risk Period of the 2001 FMD Epidemic in Uruguay

During the 2001 foot-and-mouth disease (FMD) epidemic in Uruguay, many farms were already infected and foot-and-mouth disease virus (FMDV) had spread throughout the country by the time the first outbreak was detected and a ban on animal movements was implemented. Before this ban, movements of infected animals between livestock premises were probably one of the main factors contributing to the spread of the disease. Understanding and quantifying this contribution allow identifying risk premises or risk areas to help policymakers to implement effective interventions and enhance targeted surveillance. The aim of this study was to describe, visualize, and analyze the network of livestock movements between livestock premises during the initial phase of the 2001 FMD epidemic in Uruguay and gain insight into the risk of transmission by estimating the between herd basic reproduction number (RH) before a ban on animal movements was implemented. Here, we derived RH from the average number of outcontacts of infected premises and the average probability that a contact leads to infection. Additionally, we analyzed the current (2022) network of livestock movements in Uruguay, for the same period as in 2001, and estimated RH assuming the same probability of infection as in 2001. We found that the movements of infected animals during the high-risk period of this epidemic—i.e., the period between FMDV introduction and the detection of the index case—had an important contribution to the virus spread among premises (RH = 1.48). Livestock markets and highly connected farms were responsible for the early long-distance spread of FMDV. The analysis of the 2022 network shows that this network is similar to that of 2001 and highlights the importance of targeting highly connected premises, particularly livestock markets, for surveillance, target early detection, and implement interventions during epidemics.

Assessing the effectiveness of environmental sampling for surveillance of foot-and-mouth disease virus in a cattle herd.

The survival of foot-and-mouth disease virus (FMDV) in the environment provides an opportunity for indirect transmission, both within and between farms. However it also presents the possibility of surveillance and detection via environmental sampling. This study assesses the effectiveness of environmental sampling strategies in the event of an outbreak, using a previous model for transmission of FMDV in a cattle herd that had been parameterized using data from transmission experiments and outbreaks. We show that environmental sampling can be an effective means of detecting FMDV in a herd, but it requires multiple samples to be taken on multiple occasions. In addition, environmental sampling can potentially detect FMDV in a herd more quickly than clinical inspection. For example, taking 10 samples every 3 days results in a mean time to detection of 6 days, which is lower than the mean time to detection estimated for the 2001 UK epidemic (8 days). We also show how environmental sampling could be used in a herd considered to be at risk as an alternative to pre-emptive culling. However, because of the time taken for virus to accumulate at the start of an outbreak, a reasonable level of confidence (> 99%) that an at-risk herd is indeed free from infection is unlikely to be achieved in less than 1 week.

Estimating the transmission parameters of foot-and-mouth disease in Vietnam: A spatial-dynamic kernel-based model with outbreak and host data

Foot-and-mouth disease (FMD) affects cloven-hoofed livestock and causes devastating damages to the world’s economies. Being endemic in developing countries, FMD has imposed a significant threat to the FMD-freedom status in developed countries. The globally-concerted effort to eradicate FMD at its source has faced a substantial challenge of having little knowledge about how FMD spreads in developing countries. So far, FMD virus transmission parameters have been estimated based on only a dozen actual outbreak data, mostly in Europe. Meanwhile, the fundamental north-south differences in livestock production, trading, and quarantine systems have questioned the applicability of these estimates to developing countries. In this light, we aim to narrow the knowledge gap by estimating the FMD virus transmission parameters in an endemic country, Vietnam, the world’s fifth- largest pork producer. We use the spatial-dynamic kernel-based approach combined with daily FMD incursion data and FMD-host census data. The estimation also considers livestock composition and livestock quantity by species, which can influence FMD transmission. In line with existing literature, we find that cattle and buffaloes have a larger influence on disease spread than pigs, and FMD transmission depends on the herd size and the distance between susceptible and infected premises. However, our findings show FMD virus can spread over a much more ample space in our case compared with those in existing literature (25 km and 50 km versus 10 km), and the kernels have much fatter tails. This difference is likely due to the weakness in biosecurity systems, poor implementation of surveillance and quarantine measures, and bad husbandry practices such as swill feeding, which are prevalent in developing countries. Thus, our estimated kernels will be helpful for Vietnam in developing suitable biosecurity measures to contain and eradicate the FMD virus. They are also highly relevant for other countries with livestock farming practices and climate conditions similar to those in Vietnam.

BacMam Expressing Highly Glycosylated Porcine Interferon Alpha Induces Robust Antiviral and Adjuvant Effects against Foot-and-Mouth Disease Virus in Pigs.

Foot-and-mouth disease (FMD) is an acute contagious disease that affects cloven-hoofed animals and has severe global economic consequences. FMD is most commonly controlled by vaccination. Currently available commercial FMD vaccines contain chemically inactivated whole viruses, which are thought to be slow acting as they are effective only 4 to 7 days following vaccination. Hence, the development of a novel rapid vaccine or alternative measures, such as antiviral agents or the combination of vaccines and antiviral agents for prompt FMD virus (FMDV) outbreak containment, is desirable. Here, we constructed a recombinant baculovirus (BacMam) expressing consensus porcine interferon alpha (IFN-α) that has three additional N-glycosylation sites driven by a cytomegalovirus immediate early (CMV-IE) promoter (Bac-Con3N IFN-α) for protein expression in mammalian cells. Bac-Con3N IFN-α expressing highly glycosylated porcine IFN-α protein increased the duration of antiviral effects. We evaluated the antiviral effects of Bac-Con3N IFN-α in swine cells and mice and observed sustained antiviral effects in pig serum; additionally, Bac-Con3N IFN-α exhibited sustained antiviral effects in vivo as well as adjuvant effects in combination with an inactivated FMD vaccine. Pigs injected with a combination of Bac-Con3N IFN-α and the inactivated FMD vaccine were protected against FMDV at 1, 3, and 7 days postvaccination. Furthermore, we observed that in combination with the inactivated FMD vaccine, Bac-Con3N IFN-α increased neutralizing antibody levels in mice and pigs. Therefore, we suggest that Bac-Con3N IFN-α is a strong potential antiviral and adjuvant candidate for use in combination with inactivated FMD vaccines to protect pigs against FMDV. IMPORTANCE Early inhibition of foot-and-mouth disease (FMD) virus (FMDV) replication in pigs is highly desirable as FMDV transmission and shedding rates are higher in pigs than in cattle. However, commercial FMD vaccines require at least 4 to 7 days postvaccination (dpv) for protection, and animals are vulnerable to heterologous viruses before acquiring high antibody levels after the second vaccination. Therefore, the development of antiviral agents for use in combination with FMD vaccines is essential. We developed a novel antiviral and immunostimulant, Bac-Con3N IFN-α, which is a modified porcine IFN-α-expressing recombinant baculovirus, to improve IFN stability and allow its direct delivery to animals. We present a promising candidate for use in combination with inactivated FMD vaccines as pigs applied to the strategy had early protection against FMDV at 1 to 7 dpv, and their neutralizing antibody levels were higher than those in pigs administered the vaccine only.

Fibroblast growth factor 11 inhibits foot-and-mouth disease virus gene expression and replication in vitro.

Foot-and-mouth disease virus (FMDV) causes highly contagious disease of cloven-hoofed animals such as cattle, swine, and sheep. Although FMD vaccine is the traditional way to protect against the disease, the use of FMD vaccines to protect early infection is limited. The alternative strategy of applying antiviral agents is required to control the spread of FMDV in outbreak situations. Fibroblast growth factor 11 (FGF11) is a member of the intracellular FGF. Here, we identified the inhibitory effect of FGF11 on FMDV gene expression through the transcriptional and translational regulation. For the quantitative analysis of FMDV transcription/translation level, we firstly constructed a plasmid reporter system (FMDV five prime untranslated region (5′ UTR) -luci) conjugating luciferase encoding gene with FMDV 5′ UTR region, which is a non-coding region to control FMDV transcription/translation and includes cis-acting replication element (CRE) and internal ribosome entry site (IRES). FGF11 decreased the gene expression of FMDV 5′ UTR-luci reporter in a dose-dependent manner. We further confirmed the inhibitory function of FGF11 on FMDV gene expression a replication in the FMDV-infected pig cells. FGF11 expression inhibited RNA production of FMDV RNA polymerase 3D gene in the FMDV-infected cells. In addition, while FMDV cell infection induced cytopathic effect (CPE) within 24 hr, FGF11 expression dramatically repressed CPE at the basal level. These results indicate that FGF11 inhibits FMDV gene expression and replication in vitro, implicating to provide intervention strategy for FMDV pathogenesis and transmission.

Subdistrict-Level Reproductive Number for Foot and Mouth Disease in Cattle in Northern Thailand.

Foot and mouth disease (FMD) is an important contagious transboundary disease that causes a significant economic loss for several countries. The FMD virus (FMDV) can spread very rapidly by direct and indirect transmission among susceptible animals. The complexity and magnitude of FMDV transmission at the initial stages of the epidemic can be expressed by the basic reproductive number (R0), and furthermore, control strategies can be assessed by the estimation of the effective reproductive number. In this study, we aimed to describe FMD outbreaks among smallholder cattle farms by subdistricts in the northern Thailand and compute the effective reproductive number for outbreaks caused by FMDV serotype O and overall serotypes, including serotype O, serotype A, and unidentified serotype, at the subdistrict level (Rsd) using an epidemic doubling time method. Field data of FMD outbreaks during 2015–2017 that affected 94 subdistricts in northern Thailand were assessed to estimate the Rsd. Results showed that 63.38% (90/142) of the FMD outbreak episodes in cattle were caused by FMDV serotype O. The average doubling time and the Rsd estimated of the outbreaks caused by FMDV serotype O and overall serotype were 2.80 and 4.67 months, and 1.06 and 1.04, respectively. Our results indicated that transmission of FMD in cattle at the subdistrict level in northern Thailand was not controlled (Rsd > 1), which indicates the endemicity of the disease in the region. Although control measures are in place, the results from this study highlighted the need for enhancing FMD monitoring and control strategies in northern Thailand.

Self-Reporting of Risk Pathways and Parameter Values for Foot-and-Mouth Disease in Slaughter Cattle from Alternative Production Systems by Kenyan and Ugandan Veterinarians.

Countries in which foot-and-mouth disease (FMD) is endemic may face bans on the export of FMD-susceptible livestock and products because of the associated risk for transmission of FMD virus. Risk assessment is an essential tool for demonstrating the fitness of one’s goods for the international marketplace and for improving animal health. However, it is difficult to obtain the necessary data for such risk assessments in many countries where FMD is present. This study bridged the gaps of traditional participatory and expert elicitation approaches by partnering with veterinarians from the National Veterinary Services of Kenya (n = 13) and Uganda (n = 10) enrolled in an extended capacity-building program to systematically collect rich, local knowledge in a format appropriate for formal quantitative analysis. Participants mapped risk pathways and quantified variables that determine the risk of infection among cattle at slaughter originating from each of four beef production systems in each country. Findings highlighted that risk processes differ between management systems, that disease and sale are not always independent events, and that events on the risk pathway are influenced by the actions and motivations of value chain actors. The results provide necessary information for evaluating the risk of FMD among cattle pre-harvest in Kenya and Uganda and provide a framework for similar evaluation in other endemic settings.

Foot and mouth disease virus: A review

As seen by prior tragic outbreaks in many places throughout the world, the foot and mouth disease virus, or "FMDV," is one of the most critical challenges in animal health. In this review, the major features of FMDV, as well as aspects of its interactions with cells and hosts, were discussed. On the other hand, present and upcoming FMD treatment approaches. The first vertebrate virus found was the foot-and-mouth disease virus (FMDV). A capsid protein and the viral genome (+ve sense single strand RNA) make up FMDV. The icosahedral symmetry of the viral structure is made up of structural proteins (VP1, VP2, VP3, and VP4) as well as non-structural proteins (L, 1A, 1B, 1C, 1D, 2A, 2B, 2C, 3A, 3B, 3C, and 3D). The viral replication takes place in the cytoplasm of the cell. Because FMDV has a short incubation period, it spreads quickly. Direct contact is the most often used method of FMDV transmission. The occurrence of direct contact via aerosol and mechanical transmission (fomites, feed, and water). The immunological response is stimulated by the infection with FMD. However, due to virus antigenic diversity, the immune response does not always protect against FMD (antigenic shift). FMDV is divided into seven serotypes based on antigenic variation. O, A, C, SAT-1, SAT-2, SAT-3, and Asia-1 are the serotypes in question. O is the most frequent serotype.

Development and Validation of a Mucosal Antibody (IgA) Test to Identify Persistent Infection with Foot-and-Mouth Disease Virus.

It is well known that approximately 50% of cattle infected with foot-and-mouth disease (FMD) virus (FMDV) may become asymptomatic carrier (persistently infected) animals. Although transmission of FMDV from carrier cattle to naïve cattle has not been demonstrated experimentally, circumstantial evidence from field studies has linked FMDV-carrier cattle to cause subsequent outbreaks. Therefore, the asymptomatic carrier state complicates the control and eradication of FMD. Current serological diagnosis using tests for antibodies to the viral non-structural proteins (NSP-ELISA) are not sensitive enough to detect all carrier animals, if persistently infected after vaccination and do not distinguish between carriers and non-carriers. The specificity of the NSP ELISA may also be reduced after vaccination, in particular after multiple vaccination. FMDV-specific mucosal antibodies (IgA) are not produced in vaccinated cattle but are elevated transiently during the acute phase of infection and can be detected at a high level in cattle persistently infected with FMDV, irrespective of their vaccination status. Therefore, detection of IgA by ELISA may be considered a diagnostic alternative to RT-PCR for assessing FMDV persistent infection in ruminants in both vaccinated and unvaccinated infected populations. This study reports on the development and validation of a new mucosal IgA ELISA for the detection of carrier animals using nasal, saliva, and oro-pharyngeal fluid (OPF) samples. The diagnostic performance of the IgA ELISA using nasal samples from experimentally vaccinated and infected cattle demonstrated a high level of specificity (99%) and an improved level of sensitivity (76.5%). Furthermore, the detection of carrier animals reached 96.9% when parallel testing of samples was carried out using both the IgA-ELISA and NSP-ELISA.

Modeling Intervention Scenarios During Potential Foot-and-Mouth Disease Outbreaks Within U.S. Beef Feedlots.

Foot-and-mouth disease (FMD) is a highly contagious disease of livestock and has severely affected livestock industries during the past two decades in previously FMD-free countries. The disease was eliminated in North America in 1953 but remains a threat for re-introduction. Approximately 44% of the on-feed beef cattle in the U.S. are concentrated in feedlots <32,000 heads, but little information is available on dynamics of FMD in large feedlots. Therefore, there is a need to explore possible management and intervention strategies that might be implemented during potential FMD outbreaks on feedlots. We used a within home-pen stochastic susceptible-latent-infectious-recovered (SLIR) FMD dynamics model nested in a meta-population model of home-pens in a feedlot. The combinatory model was previously developed to simulate foot-and-mouth disease virus (FMDv) transmission within U.S. beef feedlots. We evaluated three intervention strategies initiated on the day of FMD detection: stopping movements of cattle between home-pens and hospital-pen(s) (NH), barrier depopulation combined with NH (NH-BD), and targeted depopulation of at-risk home-pens combined with NH (NH-TD). Depopulation rates investigated ranged from 500 to 4,000 cattle per day. We evaluated the projected effectiveness of interventions by comparing them with the no-intervention FMD dynamics in the feedlot. We modeled a small-size (4,000 cattle), medium-size (12,000 cattle), and large-size (24,000 cattle) feedlots. Implementation of NH delayed the outbreak progression, but it did not prevent infection of the entire feedlot. Implementation of NH-BD resulted in depopulation of 50% of cattle in small- and medium-size feedlots, and 25% in large-size feedlots, but the intervention prevented infection of the entire feedlot in 40% of simulated outbreaks in medium-size feedlots, and in 8% in large-size feedlots. Implementation of NH-TD resulted in depopulation of up to 50% of cattle in small-size feedlots, 75% in medium-size feedlots, and 25% in large-size feedlots, but rarely prevented infection of the entire feedlot. Number of hospital-pens in the feedlot was shown to weakly impact the success of NH-TD. Overall, the results suggest that stopping cattle movements between the home-pens and hospital-pens, without or with barrier or targeted cattle depopulation, would not be highly effective to interrupt FMDv transmission within a feedlot.

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.

A Meta-Population Model of Potential Foot-and-Mouth Disease Transmission, Clinical Manifestation, and Detection Within U.S. Beef Feedlots.

Foot-and-mouth disease (FMD) has not been reported in the U.S. since 1929. Recent outbreaks in previously FMD-free countries raise concerns about potential FMD introductions in the U.S. Mathematical modeling is the only tool for simulating infectious disease outbreaks in non-endemic territories. In the majority of prior studies, FMD virus (FMDv) transmission on-farm was modeled assuming homogenous animal mixing. This assumption is implausible for U.S. beef feedlots which are divided into multiple home-pens without contact between home-pens except fence line with contiguous home-pens and limited mixing in hospital pens. To project FMDv transmission and clinical manifestation in a feedlot, we developed a meta-population stochastic model reflecting the contact structure. Within a home-pen, the dynamics were represented assuming homogenous animal mixing by a modified SLIR (susceptible-latent-infectious-recovered) model with four additional compartments tracing cattle with subclinical or clinical FMD and infectious status. Virus transmission among home-pens occurred via cattle mixing in hospital-pen(s), cowboy pen rider movements between home-pens, airborne, and for contiguous home-pens fence-line and via shared water-troughs. We modeled feedlots with a one-time capacity of 4,000 (small), 12,000 (medium), and 24,000 (large) cattle. Common cattle demographics, feedlot layout, endemic infectious and non-infectious disease occurrence, and production management were reflected. Projected FMD-outbreak duration on a feedlot ranged from 49 to 82 days. Outbreak peak day (with maximum number of FMD clinical cattle) ranged from 24 (small) to 49 (large feedlot). Detection day was 4–12 post-FMD-introduction with projected 28, 9, or 4% of cattle already infected in a small, medium, or large feedlot, respectively. Depletion of susceptible cattle in a feedlot occurred by day 23–51 post-FMD-introduction. Parameter-value sensitivity analyses were performed for model outputs. Detection occurred sooner if there was a higher initial proportion of latent animals in the index home-pen. Shorter outbreaks were associated with a shorter latent period and higher bovine respiratory disease morbidity (impacting the in-hospital-pen cattle mixing occurrence). This first model of potential FMD dynamics on U.S. beef feedlots shows the importance of capturing within-feedlot cattle contact structure for projecting infectious disease dynamics. Our model provides a tool for evaluating FMD outbreak control strategies.

Quantifying the Transmission of Foot-and-Mouth Disease Virus in Cattle via a Contaminated Environment.

Indirect transmission via a contaminated environment can occur for a number of pathogens, even those typically thought of as being directly transmitted, such as influenza virus, norovirus, bovine tuberculosis, or foot-and-mouth disease virus (FMDV). Indirect transmission facilitates spread from multiple sources beyond the infectious host, complicating the epidemiology and control of these diseases. This study carried out a series of transmission experiments to determine the dose-response relationship between environmental contamination and transmission of FMDV in cattle from measurements of viral shedding and rates of environmental contamination and survival. Seven out of ten indirect exposures resulted in successful transmission. The basic reproduction number for environmental transmission of FMDV in this experimental setting was estimated at 1.65, indicating that environmental transmission alone could sustain an outbreak. Importantly, detection of virus in the environment prior to the appearance of clinical signs in infected cattle and successful transmission from these environments highlights there is a risk of environmental transmission even before foot-and-mouth disease (FMD) is clinically apparent in cattle. Estimated viral decay rates suggest that FMDV remained viable in this environment for up to 14 days, emphasizing the requirement for stringent biosecurity procedures following outbreaks of FMD and the design of control measures that reflect the biology of a pathogen.IMPORTANCE Effective control of a disease relies on comprehensive understanding of how transmission occurs, in order to design and apply effective control measures. Foot-and-mouth disease virus (FMDV) is primarily spread by direct contact between infected and naive individuals, although the high levels of virus shed by infected animals mean that virus can also be spread through contact with contaminated environments. Using a series of transmission experiments, we demonstrate that environmental transmission alone would be sufficient to sustain an outbreak. Key observations include that a risk of transmission exists before clinical signs of foot-and-mouth disease (FMD) are apparent in cattle and that survival of virus in the environment extends the transmission risk period. This study highlights the role a contaminated environment can play in the transmission of FMDV and presents approaches that can also be applied to study the transmission of other pathogens that are able to survive in the environment.

The role of African buffalo in the epidemiology of foot-and-mouth disease in sympatric cattle and buffalo populations in Kenya.

Quantitative knowledge on the contribution of African buffalo to the epidemiology of foot-and-mouth disease virus (FMDV) in East Africa is lacking, and this information is essential for the design of control programs in the region. The objective of this study was to investigate the epidemiology of FMDV in buffalo, including the role of buffalo in the circulation of FMDV in livestock populations. We collected blood and oropharyngeal fluids from 92 wild buffalo and 98 sympatric cattle in central Kenya and sequenced the virus' VP1 coding region. We show that FMDV has a high seroprevalence in buffalo (~77%) and targeted cattle (~93%). In addition, we recovered 80 FMDV sequences from buffalo, all of which were serotype SAT1 and SAT2, and four serotype O and A sequences from sympatric cattle. Notably, six individual buffalo were co-infected with both SAT1 and SAT2. Amongst sympatric buffalo and cattle, the fact that no SAT1 or 2 sequences were found in cattle suggests that transmission of FMDV from buffalo to sympatric cattle is rare. Similarly, there was no evidence that serotype O and A sequences found in cattle were transmitted to buffalo. However, viruses from FMDV outbreaks in cattle elsewhere in Kenya were closely related to SAT1 and SAT2 viruses found in buffalo in this study, suggesting that FMDV in cattle and buffalo do not constitute independently evolving populations. We also show that fine-scale geographic features, such as rivers, influence the circulation of FMDV in buffalo and that social segregation amongst sympatric herds may limit between-herd transmission. These results significantly advance our understanding of the ecology and molecular epidemiology of FMDV at wildlife-livestock interfaces in East Africa and will help to inform the design of control and surveillance strategies for this disease in the region.

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.

Estimating viral bottleneck sizes for FMDV transmission within and between hosts and implications for the rate of viral evolution.

RNA viruses exist as populations of closely related genomes, characterized by a high diversity of low-frequency variants. As viral genomes from one population disperse to establish new sites of replication, the fate of these low-frequency variants depends to a large extent on the size of the founding population. Focusing on foot-and-mouth disease virus (FMDV) we conjecture that variants are more likely to be transmitted through wide bottlenecks, but more likely to approach fixation in new populations following narrow bottlenecks; therefore, the longer-term rate of accumulation of 'nearly neutral' variants at high frequencies is likely to be inversely related to the bottleneck size. We examine this conjecture in vivo by estimating bottleneck sizes relating 'parent' and 'daughter' populations observed at different scales ranging from within host to between host (within the same herd, and in different herds) using a previously established method. Within hosts, we find bottleneck sizes to range from 5 to 20 viral genomes between populations transmitted from the pharynx to the serum, and from 4 to 54 between serum and lesion populations. Between hosts, we find bottleneck sizes to range from 2 to 39, suggesting inter-host bottlenecks are of a similar size to intra-host bottlenecks. We establish a statistically significant negative relationship between the probability of genomic consensus level change and bottleneck size, and present a simple sampling model that captures this empirical relationship. We also present a novel in vitro experiment to investigate the impact of bottleneck size on the frequency of mutations within FMDV populations, demonstrate that variant frequency in a population increases more rapidly during small population passages, and provide evidence for positive selection during the passage of large populations.