Dissociation of foot-and-mouth disease virus into its nucleic acid and protein components.
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The 2001 foot and mouth disease epidemic in the United Kingdom: animal welfare perspectives.
The management of the foot and mouth disease (FMD) epidemic which occurred in the United Kingdom (UK) in 2001 resulted in widespread animal welfare problems. These problems arose firstly because of the large numbers of animals slaughtered to bring the epidemic under control, which meant that the conditions under which animals were slaughtered and the manner in which this was carried out often breached regulations concerning welfare at slaughter. Secondly, the restrictions imposed on movements, especially animal movements, resulted in what appeared to be readily avoidable difficulties with livestock dying from, for example, food shortages and pregnant animals giving birth under unsuitable conditions. This brief review is based on the personal experiences of the authors as well as relevant observations and reports from a variety of sources.
Animal Welfare↗
Bayesian analysis of experimental epidemics of foot-and-mouth disease.
We investigate the transmission dynamics of a certain type of foot-and-mouth disease (FMD) virus under experimental conditions. Previous analyses of experimental data from FMD outbreaks in non-homogeneously mixing populations of sheep have suggested a decline in viraemic level through serial passage of the virus, but these do not take into account possible variation in the length of the chain of viral transmission for each animal, which is implicit in the non-observed transmission process. We consider a susceptible-exposed-infectious-removed non-Markovian compartmental model for partially observed epidemic processes, and we employ powerful methodology (Markov chain Monte Carlo) for statistical inference, to address epidemiological issues under a Bayesian framework that accounts for all available information and associated uncertainty in a coherent approach. The analysis allows us to investigate the posterior distribution of the hidden transmission history of the epidemic, and thus to determine the effect of the length of the infection chain on the recorded viraemic levels, based on the posterior distribution of a p-value. Parameter estimates of the epidemiological characteristics of the disease are also obtained. The results reveal a possible decline in viraemia in one of the two experimental outbreaks. Our model also suggests that individual infectivity is related to the level of viraemia.
Animals↗
Evaluation of the portable Cepheid SmartCycler real-time PCR machine for the rapid diagnosis of foot-and-mouth disease.
The ability of the portable Cepheid SmartCycler real-time PCR machine to detect foot-and-mouth disease (FMD) virus sensitively and accurately was evaluated by comparing the results of the analyses of nasal swab and serum samples from experimentally infected animals with those obtained from the real-time PCR assay currently in use in the laboratory. The results indicated that the ability of the machine to detect viral RNA is greatly affected by the PCR reagents used for the assay. When it was used with PCR beads it was unable to detect weakly positive samples, but when TaqMan core reagents were used for the assay, its sensitivity was significantly increased. The machine could be used for the laboratory-based detection of FMD; however, as with all assays, significant optimisation of assay conditions as well as solid validation of the technique is required.
Animals↗
Molecular phylogeny of leader proteinase gene of type A of Foot-and-mouth disease virus from India.
We previously demonstrated the presence of three genotypes (IV, VI and VII) of type A (subtype A22) of Foot-and-mouth disease virus (FMDV) in India based on 1D gene sequence analysis. In the present study, the leader proteinase (L(pro)) gene sequences of 35 type A FMDV field isolates sampled over a period of 24 years (1977-2000) have been analyzed. Maximum-likelihood (ML) phylogenetic analysis revealed four distinct genetic lineages (A-D), indicating high divergence in L gene of type A FMDV. Lineages A and D correspond to the earlier genotypes IV, and VII, respectively. The genotype VI isolates were divided into two separate lineages (B and C) in the tree with high confidence values (96-99%). One isolate (IND 21/90) showed incongruous grouping between the (1D and L) gene-based analyses, which could be due to intergenotypic recombination. The ML molecular clock hypothesis was easily rejected on the data set studied indicating the absence of clock-like evolution in the L gene. ML codon-substitution models identified positive selection in the amino acid site 194 of C-terminal extension of the Lb(pro) with high posterior probability (>99%). The catalytic triad of the L(pro) at C-51, H-148 and D-163 were conserved across all the Indian isolates studied. Finally, amino acid differences between the lineages have been discussed briefly.
Amino Acid Sequence↗
A preliminary study of the pathogenesis of foot-and-mouth disease virus using in situ hybridization.
Five adult guinea pigs were inoculated intraepithelially in the right hindfoot pad with foot-and-mouth disease virus. Animals were euthanatized with carbon dioxide at 4, 10, 24, 48, and 72 hours post-inoculation. Generalized disease developed in the guinea pigs, as evidenced by depression and inappetance by 24 hours post-inoculation and by the formation of vesicles in the noninoculated hindfoot pad by 48 hours post-inoculation. By in situ hybridization, using a 500 base pair biotinylated RNA probe, viral nucleic acid was detected in the noninoculated fore- and hindfoot pads as early as 10 hours post-inoculation, well before any pathologic changes associated with foot-and-mouth disease virus infection were detected. These tissues remained consistently positive for the presence of viral nucleic acid up to the end of the experiment. At this time, in the forefoot pad, even though virus had first been detected with certainty in that tissue 62 hours previously, there was still no microscopic evidence of foot-and-mouth disease virus-induced damage in the histologic section. Similarly, tongue tissue was positive by in situ hybridization at 4, 48, and 72 hours post-inoculation, yet there was never any microscopic evidence of degeneration or vesicle formation. From this preliminary study, it appears that, in the guinea pig, the virus is widely disseminated to foot pads and tongue, with epidermal lesions resulting only in selected areas.
Animals↗
Foot and mouth disease: lessons to be learned from the experience of France.
The appearance of foot and mouth disease (FMD) in the United Kingdom in late February 2001 took European veterinary services by surprise. Differences in the types of measures taken by European countries, and in the speed with which they were implemented, partly explain the different animal health situations observed. France, as a major importer of British sheep, is an interesting country to study. The measures taken there are described in detail, as is the history of the two cases registered on 13 and 23 March 2001. The crisis management procedure is also detailed. The majority of the decisions taken and protocols followed are part of the national intervention plan for FMD. However, experience has shown that it is also important to remain pragmatic and to be able to adapt to new developments during the implementation of the plan. While pre-emptive killing may indeed have reduced the number of outbreaks in France, the social impact of such measures also needs to be taken into account in the development of animal health policy.
Animals↗
Determinants of early foot-and-mouth disease virus dynamics in pigs.
This paper provides a quantitative description of the early infectious process in pigs experimentally infected with foot-and-mouth disease virus (FMDV), obtained by dose-dependent, time course studies of viral load in serum. Pigs were inoculated by the intravenous or intradermal/subcutaneous route with FMDV and housed together in groups or individually. The effects of dose, inoculation route and exposure intensity on the replication of FMDV in vivo and the development of disease were studied. It was shown that the higher the dose, the shorter was the time to the start of active viraemia and to the onset of clinical signs. Exposure intensity and housing conditions influenced the viral dynamics of FMDV. Increasing the exposure intensity, by increasing the number of infected pigs housed together, had the effect of synchronizing the infection and reducing the variance in the start of active viraemia. Increasing the number of pigs housed together also increased the interaction between the pigs and the activity of individual pigs, which had the effect of shortening the time to the onset of clinical signs such as vesicle formation. Intradermal inoculation was more effective than intravenous inoculation for transmitting FMDV to pigs, resulting in shorter times to the start of active viraemia and in higher clinical scores.
Animals↗
Constitutive expression of alpha interferon by skin dendritic cells confers resistance to infection by foot-and-mouth disease virus.
The role of dendritic cells (DC) in the initiation of immune responses against foot-and-mouth disease virus (FMDV) is poorly understood. We analyzed the innate response of freshly isolated swine skin DC to the virus and show a rapid induction of beta interferon (IFN-beta) mRNA but not IFN-alpha mRNA. However, these DC secreted both IFN-alpha and IFN-beta proteins in response to live virus but not killed virus. Furthermore, the surface expression of swine major histocompatibility complex class II (SLA II) or CD80/CD86 molecules and antigen processing functions were not affected by FMDV exposure. Given the demonstrated sensitivity of FMDV to IFN-alpha/beta, there was no productive or nonproductive infection of these cells. Finally, freshly isolated skin DC constitutively expressed intracellular IFN-alpha protein in the absence of stimulation, with no detectable secretion of the cytokine until virus exposure. In situ analysis of these DC showed that these cells express and store IFN-alpha in uninfected animals. This is the first demonstration of the constitutive expression of IFN-alpha in resident, tissue-derived DC and indicates that skin DC can play an important role in the innate immune response of swine to viral infections.
Cells, Cultured↗
Serological and biochemical analysis of some recent type A foot-and-mouth disease virus isolates from the Middle East.
In 1986 and 1987 foot-and-mouth disease virus (FMDV) serotype A was isolated from outbreaks of disease in Saudi Arabia and Iran. Selected virus isolates were antigenically distinct from the prototype A22 virus strain (A22/Iraq/64), but were serologically related to each other. However, polyacrylamide gel electrophoresis showed that whilst the respective Saudi Arabian structural polypeptides were homogeneous, those from an Iran isolate were distinct. Direct sequencing of part of the P-1D (VP1) gene demonstrated considerable difference in nucleotide homology between the two groups of viruses; the Saudi Arabian viruses were closely related to each other but only distantly related to both the A22 prototype virus strain and the Iranian virus isolate. The latter viruses were only slightly more closely related to each other. Thus there appeared to be at least two distinct FMDV type A variants co-circulating in the Middle East, both of which differed considerably from the classical A22 subtype.
Animals↗
Immunogenicity and T cell recognition in swine of foot-and-mouth disease virus polymerase 3D.
Immunization of domestic pigs with a vaccinia virus (VV) recombinant expressing foot-and-mouth disease virus (FMDV) 3D protein conferred partial protection against challenge with infectious virus. The severity reduction of the clinical symptoms developed by the challenged animals occurred in the absence of significant levels of anti-3D circulating antibodies. This observation suggested that the partial protection observed was mediated by the induction of a 3D-specific cellular immune response. To gain information on the T cell recognition of FMDV 3D protein, we conducted in vitro proliferative assays using lymphocytes from outbred pigs experimentally infected with FMDV and 90 overlapping peptides spanning the complete 3D sequence. The use of pools of two to three peptides allowed the identification of T cell epitopes that were efficiently recognized by lymphocytes from at least four of the five animals analyzed. This recognition was heterotypic because anti-peptide responses increased upon reinfection of animals with a FMDV isolate from a different serotype. The results obtained with individual peptides confirmed the antigenicity observed with peptide pools. Detection of cytokine mRNAs by RT-PCR in lymphocytes stimulated in vitro by individual 3D peptides revealed that IFN-gamma mRNA was the most consistently induced, suggesting that the activated T cells belong to the Th 1 subset. These results indicate that 3D protein contains epitopes that can be efficiently recognized by porcine T lymphocytes from different infected animals, both upon primary and secondary (heterotypic) FMDV infection. These epitopes can extend the repertoire of viral T cell epitopes to be included in subunit and synthetic FMD vaccines.
Amino Acid Sequence↗
Foot-and-Mouth disease 'vaccination-to-live': possibilities and constraints.
Major constraints to the adoption of a 'vaccination to live' policy during an outbreak of foot-and-mouth disease (FMD) in a previously FMD-free country are the dual problems in the development of persistent infection (>28 days) in some vaccinated ruminants exposed to virulent virus and reliably detecting these persistently infected animals. Rapid advances in immunology, virology, molecular biology and information management present significant opportunities for improving the management of FMD outbreaks using a variety of scientifically advanced tools without the need for slaughtering large numbers of animals. A more rapid return to FMD-free status should be capable of being achieved without massive slaughter of animals through: (i) improvements in vaccine efficacy, onset of immunity, and marker specificity; (ii) development of anti-viral compounds as an aid in the control of outbreaks with or without vaccination; (iii) improvement of rapid diagnostic tests to detect early infection and persistent infection accurately and (iv) the capture, validation and management of data on animal identification, vaccination and infection status, and movement. The most effective improvements will occur if all these strategies are used in combination.
Animal Identification Systems↗
Molecular epidemiology of the foot-and-mouth disease virus outbreak in the United Kingdom in 2001.
The objective of this study was to quantify the extent to which the genetic diversity of foot-and-mouth disease virus (FMDV) arising over the course of infection of an individual animal becomes fixed, is transmitted to other animals, and thereby accumulates over the course of an outbreak. Complete consensus sequences of 23 genomes (each of 8,200 nucleotides) of FMDV were recovered directly from epithelium tissue acquired from 21 farms infected over a nearly 7-month period during the 2001 FMDV outbreak in the United Kingdom. An analysis of these consensus sequences revealed very few apparently ambiguous sites but clear evidence of 197 nucleotide substitutions at 191 different sites. We estimated the rate of nucleotide substitution to be 2.26 x 10(-5) per site per day (95% confidence interval [CI], 1.75 x 10(-5) to 2.80 x 10(-5)) and nucleotide substitutions to accrue in the consensus sequence at an average rate of 1.5 substitutions per farm infection. This is a sufficiently high rate showing that detailed histories of the transmission pathways can be reliably reconstructed. Coalescent methods indicated that the date at which FMDV first infected livestock in the United Kingdom was 7 February 2001 (95% CI, 20 January to 19 February 2001), which was identical to estimates obtained on the basis of purely clinical evidence. Nucleotide changes appeared to have occurred evenly across the genome, and within the open reading frame, the ratio of nonsynonymous-to-synonymous change was 0.09. The ability to recover particular transmission pathways of acutely acting RNA pathogens from genetic data will help resolve uncertainties about how virus is spread and could help in the control of future epidemics.
Animals↗
The foot-and-mouth disease epidemic in Dumfries and Galloway, 2001. 1: Characteristics and control.
The foot-and-mouth disease epidemic in Dumfries and Galloway in south-west Scotland comprised 177 infected premises (IPS) in 24 geographical clusters, and ran from March 1 until May 23, 2001. Initial seeding of infection was by livestock (predominantly sheep) that had passed through Longtown Market in adjacent Cumbria. Thereafter, spread within existing, and to new, clusters was associated with the movement of personnel and vehicles, with further transmission by Longtown Market contacts and across common boundaries. Sheep and cattle premises were equally affected. After the peak of the epidemic at the beginning of the third week of March, the upper possible limit of attack rates for premises contiguous to IPS, and premises within 3 km, remained around 10 per cent, with new clusters emerging more distantly. Control procedures included traditional methods of slaughter of all animals on IPS and, elsewhere, of animals considered by veterinary assessment to be Dangerous Contacts; movement restrictions; enhanced biosecurity; tracing of potential sources and spread of virus; and surveillance of premises subsequently considered at risk. These methods were supplemented by the novel pre-emptive slaughter, without veterinary assessment, of all susceptible livestock on all premises contiguous to IPS, and of small ruminants and pigs within a 3 km radius (known as the Protection Zone) around IPS. In total, approximately 80,000 cattle, 564,000 sheep, 2600 pigs and 500 goats were slaughtered, the novel methods accounting for 29 per cent of all cattle and 75 per cent of all sheep killed. Limitations of existing national databases necessitated the development of local databases to administer control procedures.
Animals↗
Inhibition of host cell ribosomal ribonucleic acid methylation by foot-and-mouth disease virus.
A study of protein and ribonucleic acid (RNA) synthesis in cells infected by foot-and-mouth disease virus has indicated possible mechanisms of viral control over host cell metabolism. Foot-and-mouth disease virus infection of baby hamster kidney cells resulted in 50% inhibition of host cell protein synthesis at 180 min postinfection. A viral-induced interference with host cell RNA methylation was observed to be more rapidly inhibited than protein synthesis. To determine the nature of methylation inhibition, the kinetics of several host cell methylated RNA species were examined subsequent to virus infection. Data from sucrose zonal centrifugation and methylated albumin kieselguhr chromatography showed that methylation of nuclear RNA was inhibited 50% at 60 min postinfection. Inhibition of nuclear ribosomal RNA precursors and formation of nascent ribosomes correlated with inhibition kinetics of nuclear RNA methylation. It is suggested that the viral interference with the host nuclear RNA methylation is directly responsible for the observed loss of nascent ribosome formation. Moreover, early in the infectious cycle, methylation inhibition of host cell RNA could, in part, account for the cessation of host protein synthesis.
Animals↗
Detection of carriers of foot-and-mouth disease virus among vaccinated cattle.
To investigate and optimise detection of carriers, we vaccinated 15 calves with an inactivated vaccine based on foot-and-mouth disease virus (FMDV) A Turkey strain and challenged them and two further non-vaccinated calves with the homologous virus four weeks later. To determine transmission to a sensitive animal, we put a sentinel calf among the infected cattle from 60 days post-infection until the end of the experiment at 609 days post-infection. Samples were tested for the presence of FMDV, viral genome, specific IgA antibodies, antibodies against FMDV non-structural (NS) proteins or neutralising antibodies. Virus and viral genome was intermittently isolated from probang samples and the number of isolations decreased over time. During the first 100 days significantly more samples were positive by RT-PCR than by virus isolation (VI), whereas, late after infection more samples were positive by virus isolation. All the inoculated cattle developed high titres of neutralising antibodies that remained high during the entire experiment. An IgA antibody response was intermittently detected in the oropharyngeal fluid of 14 of the 17 calves, while all of them developed detectable levels of antibodies to NS proteins of FMDV in serum, which declined slowly beyond 34 days post-infection. Nevertheless, at 609 days after inoculation, 10 cattle (60%) were still positive by NS ELISA. Of the 17 cattle in our experiment, 16 became carriers. Despite frequent reallocation between a different pair of infected cattle no transmission to the sentinel calf occurred. It remained negative in all assays during the entire experiment. The results of this experiment show that the NS ELISA is currently the most sensitive method to detect carriers in a vaccinated cattle population.
Animals↗
Effect of heat on foot-and-mouth disease virus (FMDV) in the components of milk from FMDV-infected cows.
Foot-and-mouth disease virus (FMDV) survived in skim milk, cream and the pelleted cellular debris components of milk obtained from FMDV-infected cows after pasteurization at 72 degrees C for 0-25 min. Virus was recovered from whole milk of infected cows after that milk was heated at 72 degrees C. for 5 min. and from the skim milk component after it was heated at the same temperature for 2 min. Evaporation of the whole milk samples after they were heated at 72 degrees C. for 3 min. did not inactivate the virus, but evaporation of infected skim milk samples after they were heated at 72 degrees C. for 0-5 min. did inactivate the virus. FMDV survived in the cream component after it was heated at 93 degrees C. for 0-25 min.
Animals↗
A comparative study on the immune response of sheep to foot and mouth disease virus vaccine type Asia-1 prepared with different inactivants and adjuvants.
Foot and mouth disease virus type Asia-1 was inactivated either with formaldehyde or binaryethylenimine (BEI). Inactivated vaccines were prepared incorporating aluminium hydroxide gel or mineral oil as an adjuvant. The antibody response to the adult sheep was studied by ELISA and SN test for a period of 6 months. There was no difference in the antibody response between vaccines inactivated with formaldehyde or BEI. Whereas significant difference in the antibody response was observed between gel and oil vaccines. The high titres of antibody stimulated by oil vaccines persisted longer than those of gel vaccines within the period of study.
Animals↗