Immune response and viral persistence in Indian buffaloes (Bubalus bubalis) infected with foot-and-mouth disease virus serotype Asia 1

Kinetics of foot-and-mouth disease vaccine-induced antibody responses in buffaloes (Bubalus bubalis): avidity ELISA as an alternative to the virus neutralization test

The role of water buffaloes in foot-and-mouth disease (FMD) epidemiology as one of the major hosts of the virus that can develop persistent asymptomatic infection highlights the importance of sustaining surveillance on the antibody response elicited by vaccination in these animals. There is gap in the knowledge on how serological assays that measure antibodies against capsid proteins perform with buffalo samples and which would be the most reliable test to substitute the virus neutralization test (VNT) a cumbersome and low-throughput tool for field surveillance. Alternatively, the liquid-phase blocking sandwich ELISA (LPBE) is commonly used. Previous data from our laboratory demonstrated that the vaccine-induced antibodies assessed by the LPBE yielded low specificity with buffaloes' samples. In contrast, a single-dilution avidity ELISA (AE) aimed to detect high-avidity antibodies against exposed epitopes, combined with an indirect ELISA (IE) to assess IgG levels, produced more reliable results. Here we analyzed for the first time the kinetics of the antibodies induced by vaccination in two different buffalo herds (n = 91) over 120 days using AE, IE, LPBE, and the VNT. Kinetics were similar in the different assays, with an increase of antibodies between 0- and 14-days post-vaccination (dpv) which were maintained thereafter. VNT and AE results were concordant (Kappa value = 0.76), and both assays revealed a decay in the antibody response in calves with maternal antibodies at 90 and 120 dpv, which was not evidenced by the LPBE. These results show that kinetics of antibody responses to FMD vaccination are similar in buffalo and cattle, and support the use of indirect ELISA assays, in particular Avidity ELISA, as alternatives to the VNT for vaccine-immunity monitoring irrespectively of the animal's passive or active immune status.

Viral dynamics and immune responses to foot-and-mouth disease virus in African buffalo (Syncerus caffer)

Foot-and-mouth disease (FMD) is one of the most important livestock diseases restricting international trade. While African buffalo (Syncerus caffer) act as the main wildlife reservoir, viral and immune response dynamics during FMD virus acute infection have not been described before in this species. We used experimental needle inoculation and contact infections with three Southern African Territories serotypes to assess clinical, virological and immunological dynamics for thirty days post infection. Clinical FMD in the needle inoculated buffalo was mild and characterised by pyrexia. Despite the absence of generalised vesicles, all contact animals were readily infected with their respective serotypes within the first two to nine days after being mixed with needle challenged buffalo. Irrespective of the route of infection or serotype, there were positive associations between the viral loads in blood and the induction of host innate pro-inflammatory cytokines and acute phase proteins. Viral loads in blood and tonsil swabs were tightly correlated during the acute phase of the infection, however, viraemia significantly declined after a peak at four days post-infection (dpi), which correlated with the presence of detectable neutralising antibodies. In contrast, infectious virus was isolated in the tonsil swabs until the last sampling point (30 dpi) in most animals. The pattern of virus detection in serum and tonsil swabs was similar for all three serotypes in the direct challenged and contact challenged animals. We have demonstrated for the first time that African buffalo are indeed systemically affected by FMD virus and clinical FMD in buffalo is characterized by a transient pyrexia. Despite the lack of FMD lesions, infection of African buffalo was characterised by high viral loads in blood and oropharynx, rapid and strong host innate and adaptive immune responses and high transmissibility.

High seroprevalence of Foot and Mouth Disease in Laos: Call for nationwide vaccination campaigns and disease surveillance

Foot and mouth disease (FMD) virus remains enzootic in Lao People's Democratic Republic (Lao PDR) due to insufficient control measures, including low vaccination coverage. We assessed virus epidemiology and evaluated knowledge, attitude and practice of Lao farmers and animal health stakeholders towards FMD to support politics in devising evidence-based control measures. Sera were collected from 972 domestic ruminants in three provinces of Lao PDR: Vientiane Capital, Vientiane and Xiengkhouang provinces. Seroprevalence of antibodies directed against non-structural proteins of FMD virus was assessed using a commercial ELISA. Positive sera were further characterized by detecting antibodies directed against the structural proteins of FMD serotypes O, A and Asia 1. Information about farm management, biosecurity practices, livestock trade, and past FMD outbreaks was obtained. Overall 35% (340/972) of the ruminants had antibodies against FMD virus with a similar seroprevalence in each province. Seroprevalence depended significantly on the ruminant species (p < .001): 61% of buffaloes, but only 41% of cattle and 15% of goats were seropositive. While antibodies against FMD serotype Asia 1 were absent, 87% (297/340) of the seropositive animals had antibodies against FMD serotype O and 32% (110/340) against FMD serotype A. Many seropositive animals (31%) had antibodies against both serotypes O and A. The majority of the farmers could name the symptoms of FMD and the susceptible animal species. Although many had likely observed FMD outbreaks in their herd and were aware of FMD vaccines, only few vaccinated their animals. This study confirms that FMD remains enzootic in at least three provinces of Lao PDR where vaccination coverage is low. It also shows the relevance of nationwide active and passive disease surveillance, as well as of vaccination campaigns using bivalent FMD vaccines and targeting all susceptible animal species.

A history of FMD research and control programmes in Southeast Asia: lessons from the past informing the future

Foot and mouth disease (FMD) is a major animal health problem within Southeast Asia (SEA). Although Indonesia and more recently the Philippines have achieved freedom from FMD, the disease remains endemic on continental SEA. Control of FMD within SEA would increase access to markets in more developed economies and reduce lost productivity in smallholder and emerging commercial farmer settings. However, despite many years of vaccination by individual countries, numerous factors have prevented the successful control of FMD within the region, including unregulated ‘informal’ transboundary movement of livestock and their products, difficulties implementing vaccination programmes, emergence of new virus topotypes and lineages, low-level technical capacity and biosecurity at national levels, limited farmer knowledge on FMD disease recognition, failure of timely outbreak reporting and response, and limitations in national and international FMD control programmes. This paper examines the published research of FMD in the SEA region, reviewing the history, virology, epidemiology and control programmes and identifies future opportunities for FMD research aimed at the eventual eradication of FMD from the region.

The Carrier Conundrum; A Review of Recent Advances and Persistent Gaps Regarding the Carrier State of Foot-and-Mouth Disease Virus

The existence of a prolonged, subclinical phase of foot-and-mouth disease virus (FMDV) infection in cattle was first recognized in the 1950s. Since then, the FMDV carrier state has been a subject of controversy amongst scientists and policymakers. A fundamental conundrum remains in the discordance between the detection of infectious FMDV in carriers and the apparent lack of contagiousness to in-contact animals. Although substantial progress has been made in elucidating the causal mechanisms of persistent FMDV infection, there are still critical knowledge gaps that need to be addressed in order to elucidate, predict, prevent, and model the risks associated with the carrier state. This is further complicated by the occurrence of a distinct form of neoteric subclinical infection, which is indistinguishable from the carrier state in field scenarios, but may have substantially different epidemiological properties. This review summarizes the current state of knowledge of the FMDV carrier state and identifies specific areas of research in need of further attention. Findings from experimental investigations of FMDV pathogenesis are discussed in relation to experience gained from field studies of foot-and-mouth disease.

Model of persistent foot-and-mouth disease virus infection in multilayered cells derived from bovine dorsal soft palate

Foot‐and‐mouth disease virus (FMDV) causes a highly contagious vesicular disease in livestock, with serious consequences for international trade. The virus persists in the nasopharynx of cattle and this slows down the process to obtain an FMDV‐free status after an outbreak. To study biological mechanisms, or to identify molecules that can be targeted to diagnose or interfere with persistence, we developed a model of persistent FMDV infection in bovine dorsal soft palate (DSP). Primary DSP cells were isolated after commercial slaughter and were cultured in multilayers at the air‐liquid interface. After 5 weeks of culture without further passage, the cells were infected with FMDV strain O/FRA/1/2001. Approximately, 20% of cells still had a polygonal morphology and displayed tight junctions as in stratified squamous epithelia. Subsets of cells expressed cytokeratin and most or all cells expressed vimentin. In contrast to monolayers in medium, multilayers in air demonstrated only a limited cytopathic effect. Integrin α_Vβ₆ expression was observed in mono‐ but not in multilayers. FMDV antigen, FMDV RNA and live virus were detected from day 1 to 28, with peaks at day 1 and 2. The proportion of infected cells was highest at 24 hr (3% and 36% of cells at an MOI of 0.01 and 1, respectively). At day 28 after infection, at a time when animals that still harbour FMDV are considered carriers, FMDV antigen was detected in 0.2%–2.1% of cells, in all layers, and live virus was isolated from supernatants of 6/8 cultures. On the consensus level, the viral genome did not change within the first 24 hr after infection. Only a few minor single nucleotide variants were detected, giving no indication of the presence of a viral quasispecies. The air‐liquid interface model of DSP brings new possibilities to investigate FMDV persistence in a controlled manner.

Establishment of persistent foot-and-mouth disease virus (FMDV) infection in MDBK cells

In addition to acute infection and disease, foot-and-mouth disease virus (FMDV) can cause persistent infection in ruminants. Such "carrier" animals represent a potential risk for FMDV transmission to susceptible animals. However, the mechanisms and the factors that determine FMDV persistence remain unknown. We describe here the establishment of FMDV type O persistent infection in a bovine epithelial cell line (Madin-Darby bovine kidney; MDBK). Preliminary experiments to assess the permissivity of MDBK cells to FMDV O infection revealed an unusual pattern of infection: after the initial phase of acute cell lysis, new monolayers formed within 48-72 h post-infection. We found that some cells survived cytolytic infection and subsequently regrew, thereby demonstrating that this bovine cell line can be persistently infected with FMDV type O. Further evidence that MDBK cells were persistently infected with FMDV includes: (i) detection of viral RNA in cells as well as in cell culture supernatants, (ii) detection of viral antigens in the cells by immunofluorescence analysis, and (iii) production of infectious viral particles for up to 36 cell passages. Furthermore, preliminary sequence analysis of persistent virus revealed a single nucleotide substitution within the VP1 coding region, resulting in the V50A amino acid substitution. This bovine model of FMDV persistence holds promise for the investigation of the viral and cellular molecular determinants that promote FMDV persistence.

Foot and mouth disease: a look from the wild side

We review the literature and discuss control options regarding foot and mouth disease (FMD) in wildlife around the world. There are more than 100 species of wild, feral, laboratory, or domesticated animals that have been infected naturally or experimentally with FMD virus. Apart from the African buffalo (Syncerus caffer) in sub-Saharan Africa, wildlife has not been demonstrated to play a significant role in the maintenance of FMD. More often, wildlife are passively infected when outbreaks of FMD occur in domestic livestock, and, in some wild ungulates, infection results in severe disease. Efforts to control FMD in wildlife may not be successful when the disease is endemic in livestock and may cause more harm to wildlife, human livelihoods, and domestic animals. Currently in sub-Saharan Africa, the complete eradication of FMD on a subcontinental scale in the near term is not possible, given the presence of FMD-infected African buffalo and the existence of weak veterinary infrastructures in some FMD-endemic countries. Therefore efforts to control the disease should be aimed at improved vaccines and improved use of vaccines, improved livestock management practices, and utilization of programs that can help in disease control such as the FMD Progressive Control Program and regulatory frameworks that facilitate trade such zonation, compartmentalization, and commodity-based trade. Though not meeting the definition of wildlife used in this review, feral domestic animals warrant a special concern with regard to FMD control.

Montanide ISA™ 201 adjuvanted FMD vaccine induces improved immune responses and protection in cattle

Despite significant advancements in modern vaccinology, inactivated whole virus vaccines for foot-and-mouth disease (FMD) remain the mainstay for prophylactic and emergency uses. Many efforts are currently devoted to improve the immune responses and protective efficacy of these vaccines. Adjuvants, which are often used to potentiate immune responses, provide an excellent mean to improve the efficacy of FMD vaccines. This study aimed to evaluate three oil adjuvants namely: Montanide ISA-201, ISA-206 (SEPPIC, France) and GAHOL (an in-house developed oil-adjuvant) for adjuvant potential in inactivated FMD vaccine. Groups of cattle (n=6) were immunized once intramuscularly with monovalent FMDV 'O' vaccine formulated in these adjuvants, and humoral (serum neutralizing antibody, IgG1 and IgG2) and cellular (lymphoproliferation) responses were measured. Montanide ISA-201 adjuvanted vaccine induced earlier and higher neutralizing antibody responses as compared to the two other adjuvants. All the adjuvants induced mainly serum IgG1 isotype antibody responses against FMDV. However, Montanide ISA-201 induced relatively higher IgG2 responses than the other two adjuvants. Lymphoproliferative responses to recall FMDV antigen were relatively higher with Montanide ISA-201, although not always statistically significant. On homologous FMDV challenge at 30 days post-vaccination, 100% (6/6) of the cattle immunized with Montanide-201 adjuvanted vaccine were protected, which was superior to those immunized with ISA-206 (66.6%, 4/6) or GAHOL adjuvanted vaccine (50%, 3/6). Virus replication following challenge infection, as determined by presence of the viral genome in oropharynx and non-structural protein serology, was lowest with Montanide ISA-201 adjuvant. Collectively, these results indicate that the Montanide ISA-201 adjuvanted FMD vaccine induces enhanced immune responses and protective efficacy in cattle.

Difference in the level of interferon gamma mRNA transcripts on stimulation of cattle and buffalo mononuclear cells with foot and mouth disease virus-antigen: a possible role of sequence variation in promoter region

In an attempt to resolve the claim that buffaloes differ from cattle in disease progression, this study was undertaken to compare the mitogen (conA) or antigen (foot and mouth disease virus) induced expression levels of interferon gamma (IFN-γ mRNA in peripheral blood mononuclear cells (PBMCs) by real-time quantitative PCR. In general, the levels of IFN-γ mRNA were lower in buffaloes than in crossbred cattle. Significantly higher levels of IFN-γ mRNA were also observed in crossbred cattle when induced with FMD virus (1 μg). Analysis of the partial promoter sequences of the IFN-γ gene from the respective species revealed a conserved 4 base (GTCT) deletion in all the buffalo promoter sequences. In-silico analysis indicated the binding of glucocorticoid receptor (GR) and erythroid nuclear factor (NF-E) to this region in cattle. GR has been shown to be a transcription factor by itself and also regulates other major transcription factors like NF-κB and AP-1. The differential expression levels of IFN-γ mRNA between these species could be due to this deletion in the promoter region of buffalo. Further studies involving mobility shift and promoter assays would throw more light on the differential expression levels.