Clinical variation in foot and mouth disease: sheep and goats

Association of the time that elapsed from last vaccination with protective effectiveness against foot-and-mouth disease in small ruminants

Routine and emergency vaccination of small ruminants against foot-and-mouth disease (FMD) is mandatory in many endemic countries, yet data on the field effectiveness of the vaccines used is scarce. We conducted an investigation of a serotype O FMD outbreak that took place in a sheep and goat pen, and estimated the effectiveness of various routine vaccination statuses. We also evaluated the protection provided by colostrum administration and emergency vaccination. Animals which were routinely vaccinated twice were not clinically affected while disease incidence was observed among animals routinely vaccinated only once (p = 0.004 according to a two-sided Fisher's exact test). In groups vaccinated only once, there was a significant association between the average time that elapsed since last vaccination and the disease incidence (n = 5; Spearman correlation coefficient: r_s = 1.0, p < 0.01). In addition, non-vaccinated lambs fed colostrum from dams vaccinated more than 2 months before parturition had a mortality rate of 33%. Administration of emergency vaccination 2 days after the occurrence of the index case was the probable reason for the rapid blocking of the FMD spread within 6 days from its onset in the pen.

Estimation of the transmission of foot-and-mouth disease virus from infected sheep to cattle

The quantitative role of sheep in the transmission of foot-and-mouth disease virus (FMDV) is not well known. To estimate the role of sheep in the transmission of FMDV, a direct contact transmission experiment with 10 groups of animals each consisting of 2 infected lambs and 1 contact calf was performed. Secretions and excretions (oral swabs, blood, urine, faeces and probang samples) from all animals were tested for the presence of FMDV by virus isolation (VI) and/or RT-PCR. Serum was tested for the presence of antibodies against FMDV. To estimate FMDV transmission, the VI, RT-PCR and serology results were used. The partial reproduction ratio R₀^p i.e. the average number of new infections caused by one infected sheep introduced into a population of susceptible cattle, was estimated using either data of the whole infection chain of the experimental epidemics (the transient state method) or the final sizes of the experimental epidemics (the final size method). Using the transient state method, R₀^p was estimated as 1.0 (95% CI 0.2 - 6.0) using virus isolation results and 1.4 (95% CI 0.3 - 8.0) using RT-PCR results. Using the final size method, R₀^p was estimated as 0.9 (95% CI 0.2 - 3.0). Finally, R₀^p was compared to the R₀’s obtained in previous transmission studies with sheep or cattle only. This comparison showed that the infectivity of sheep is lower than that of cattle and that sheep and cattle are similarly susceptible to FMD. These results indicate that in a mixed population of sheep and cattle, sheep play a more limited role in the transmission of FMDV than cattle.

Foot-and-mouth disease: technical and political challenges to eradication

Foot-and-mouth disease (FMD) is a highly-contagious livestock disease with global socioeconomic ramifications. The disease negatively impacts both individual farmers through reduced herd viability and nations through trade restrictions of animals and animal derivatives. Vaccines for FMD prevention have existed for over 70 years, yet the disease remains enzootic in a large percentage of the globe. FMD persistence is due in part to technical limitations of historic and current vaccine technologies. There also exist many socioeconomic and political barriers to global FMD eradication. Here we highlight the barriers to eradication and discuss potential avenues toward FMD eradication.

Prediction of province-level outbreaks of foot-and-mouth disease in Iran using a zero-inflated negative binomial model

To identify events that could predict province-level frequency of foot-and-mouth disease (FMD) outbreaks in Iran, 5707 outbreaks reported from April 1995 to March 2002 were studied. A zero-inflated negative binomial model was used to estimate the probability of a 'no-outbreak' status and the number of outbreaks in a province, using the number of previous occurrences of FMD for the same or adjacent provinces and season as covariates. For each province, the probability of observing no outbreak was negatively associated with the number of outbreaks in the same province in the previous month (odds ratio [OR]=0.06, 95% confidence interval [CI]: 0.01, 0.30) and in 'the second previous month' (OR=0.10, 95% CI: 0.02, 0.51), the total number of outbreaks in the second previous month in adjacent provinces (OR=0.57, 95% CI: 0.36, 0.91) and the season (winter [OR=0.18, 95% CI: 0.06, 0.55] and spring [OR=0.27, 95% CI: 0.09, 0.81], compared with summer). The expected number of outbreaks in a province was positively associated with number of outbreaks in the same province in previous month (coefficient [coef]=0.74, 95% CI: 0.66, 0.82) and in the second previous month (coef=0.23, 95% CI: 0.16, 0.31), total number of outbreaks in adjacent provinces in the previous month (coef=0.32, 95% CI: 0.22, 0.41) and season (fall [coef=0.20, 95% CI: 0.07, 0.33] and spring [coef=0.18, 95% CI: 0.05, 0.31], compared to summer); however, number of outbreaks was negatively associated with the total number of outbreaks in adjacent provinces in the second previous month (coef=-0.19, 95% CI: -0.28, -0.09). The findings indicate that the probability of an outbreak (and the expected number of outbreaks if any) may be predicted based on previous province information, which could help decision-makers allocate resources more efficiently for province-level disease control measures. Further, the study illustrates use of zero inflated negative binomial model to study diseases occurrence where disease is infrequently observed.

Globalization and Livestock Biosecurity

Globalization has resulted in enhanced trade in livestock and livestock products leading to increased risk of diseases to livestock and human beings. The emergence of highly contagious viral diseases of livestock and poultry such as foot-and-mouth disease, peste des petits ruminants, African swine fever (ASF), Newcastle disease, avian influenza and zoonotic diseases caused by viruses like Ebola, West Nile, Nipah, Hendra and swine influenza (H1N1) have necessitated the formulation of policies and regulatory frameworks for preventing ingress of exotic diseases and controlling dissemination of endemic diseases within the country. Biosecurity measures are important to maintain and improve animal health and reduce the risks. In this review, the risks of introduction of infections through livestock and livestock products, routes of transmission and general biosecurity measures to reduce these risks have been discussed.

Risk assessment and cost-effectiveness of animal health certification methods for livestock export in Somalia

Livestock export is vital to the Somali economy. To protect Somali livestock exports from costly import bans used to control the international spread of disease, better certification of livestock health status is required. We performed quantitative risk assessment and cost-effectiveness analysis on different health certification protocols for Somali livestock exports for six transboundary diseases.

Examining stock at regional markets alone without port inspection and quarantine was inexpensive but was ineffective for all but contagious bovine pleuropneumonia, contagious caprine pleuropneumonia and peste des petits ruminants. While extended pre-export quarantine improves detection of infections that cause clinical disease, if biosecurity is suboptimal quarantine provides an opportunity for transmission and increased risk. Clinical examination, laboratory screening and vaccination of animals for key diseases before entry to the quarantine station reduced the risk of an exported animal being infected. If vaccination could be reliably performed weeks before arrival at quarantine its effect would be greatly enhanced.

The optimal certification method depends on the disease. Laboratory diagnostic testing was particularly important for detecting infections with limited clinical signs in male animals (only males are exported); for Rift Valley fever (RVF) the probability of detection was 99% or 0% with and without testing.

Based on our findings animal inspection and certification at regional markets combined with quarantine inspection and certification would reduce the risk of exporting infected animals and enhance disease control at the regional level. This is especially so for key priority diseases, that is RVF, foot-and-mouth disease and Brucellosis. Increased data collection and testing should be applied at point of production and export.

Detection and seroprevalence of foot and mouth disease in sheep and goats in Punjab, Pakistan

Foot and mouth disease (FMD) is a highly contagious disease of ruminants that causes huge economic losses around the globe. However, the prevalence of FMDV in small ruminants has been overlooked in Pakistan. A seroepidemiological study was conducted in Chakwal, Faisalabad and Khanewal districts of Punjab, Pakistan to determine the prevalence of FMD in sheep and goats. A total 1200 serum samples were collected from sheep (n = 180) and goats (n = 920) and were subjected to 3ABC non-structural protein enzyme-linked immunosorbent assay for detection of antibodies against non-structural proteins of FMD virus. Samples collected from clinical cases were also confirmed for FMDV using RT-PCR. The overall seroprevalence of FMD in sheep and goats was 21% (n = 252) while 19.44% (n = 35) in sheep and 21.27% (n = 217) prevalence was recorded in goats. Highest seroprevalence (32.5%) was observed in southern Punjab (Khanewal), followed by (25.75%) central Punjab (Faisalabad) and the lowest seroprevalence (4.75%) was detected in northern Punjab (Chakwal). There was no statistically significant difference in seroprevalence between sheep and goats. Among different risk factors tested, age and sex were found to be significantly associated with the prevalence of disease while pregnancy and herd type had no association with the prevalence of the disease. This study illustrate that FMD is highly prevalent in sheep and goats in Punjab. Therefore, a broader study is needed to ascertain the countrywide prevalence of FMD in small ruminants.

Evaluation of the benefit of emergency vaccination in a foot-and-mouth disease free country with low livestock density

Foot-and-mouth disease (FMD) is highly contagious and one of the most economically devastating diseases of cloven-hoofed animals. Scientific-based preparedness about how to best control the disease in a previously FMD-free country is therefore essential for veterinary services. The present study used a spatial, stochastic epidemic simulation model to compare the effectiveness of emergency vaccination with conventional (non-vaccination) control measures in Switzerland, a low-livestock density country. Model results revealed that emergency vaccination with a radius of 3 km or 10 km around infected premises (IP) did not significantly reduce either the cumulative herd incidence or epidemic duration if started in a small epidemic situation where the number of IPs is still low. However, in a situation where the epidemic has become extensive, both the cumulative herd incidence and epidemic duration are reduced significantly if vaccination were implemented with a radius of 10 km around IPs. The effect of different levels of conventional strategy measures was also explored for the non-vaccination strategy. It was found that a lower compliance level of farmers for movement restrictions and delayed culling of IPs significantly increased both the cumulative IP incidence and epidemic duration. Contingency management should therefore focus mainly on improving conventional strategies, by increasing disease awareness and communication with stakeholders and preparedness of culling teams in countries with a livestock structure similar to Switzerland; however, emergency vaccination should be considered if there are reasons to believe that the epidemic may become extensive, such as when disease detection has been delayed and many IPs are discovered at the beginning of the epidemic.

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.

Laboratory capacity for diagnosis of foot-and-mouth disease in Eastern Africa: implications for the progressive control pathway

BACKGROUND

Accurate diagnosis is pertinent to any disease control programme. If Eastern Africa is to work towards control of foot-and-mouth disease (FMD) using the Progressive Control Pathway for FMD (PCP-FMD) as a tool, then the capacity of national reference laboratories (NRLs) mandated to diagnose FMD should match this task. This study assessed the laboratory capacity of 14 NRLs of the Eastern Africa Region Laboratory Network member countries using a semi-structured questionnaire and retrospective data from the World Reference Laboratory for FMD annual reports and Genbank® through National Centre for Biotechnology Information for the period 2006-2010.

RESULTS

The questionnaire response rate was 13/14 (93%). Twelve out of the 13 countries/regions had experienced at least one outbreak in the relevant five year period. Only two countries (Ethiopia and Kenya) had laboratories at biosecurity level 3 and only three (Ethiopia, Kenya and Sudan) had identified FMD virus serotypes for all reported outbreaks. Based on their own country/region assessment, 12/13 of these countries /regions were below stage 3 of the PCP-FMD. Quarantine (77%) and vaccination (54%) were the major FMD control strategies employed. The majority (12/13) of the NRLs used serological techniques to diagnose FMD, seven used antigen ELISA and three of these (25%) also used molecular techniques which were the tests most frequently requested from collaborating laboratories by the majority (69%) of the NRLs. Only 4/13 (31%) participated in proficiency testing for FMD. Four (31%) laboratories had no quality management systems (QMS) in place and where QMS existed it was still deficient, thus, none of the laboratories had achieved accreditation for FMD diagnosis.

CONCLUSIONS

This study indicates that FMD diagnostic capacity in Eastern Africa is still inadequate and largely depends on antigen and antibody ELISAs techniques undertaken by the NRLs. Hence, for the region to progress on the PCP-FMD, there is need to: implement regional control measures, improve the serological diagnostic test performance and laboratory capacity of the NRLs (including training of personnel as well as upgrading of equipment and methods, especially strengthening the molecular diagnostic capacity), and to establish a regional reference laboratory to enforce QMS and characterization of FMD virus containing samples.

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.

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.

A survey on the frequency of foot-and-mouth disease virus carriers in cattle in north-east of Iran by RT-PCR: implications for revising disease control strategy

Foot-and-mouth disease (FMD) is endemic in Iran. It is essential to timely evaluate the current disease control programme in Iran. Here, we report the frequency of FMD virus (FMDV) carrier state in cattle slaughtered in Mashhad abattoir, Mashhad, Khorasan Razavi, north-east of Iran, which contains long common borders with Afghanistan and Turkmenistan. Soft palate samples were collected immediately after slaughter for the detection of FMDV by RT-PCR. The results show that 37.7% of cattle (96 of 255) were carriers of the virus. Among positive samples (96), 58 (60.4%) belonged to serotype O. No evidence was detected for the presence of Asia 1 and A serotypes. Nucleotide sequencing and phylogenic dendogram showed close similarity and common lineage between our samples and viruses isolated in Pakistan. With an approximate more than 80% of cattle population vaccination coverage such a high rate of carrier state may show an extensive FMDV exposure. Therefore, limiting control programmes to timely prophylactic vaccination may be insufficient. This is also true when meat market instabilities act as a temptation to import livestock, legally or illegally, through the eastern frontiers. It is recommended to change the current prophylactic vaccination strategy to a well-developed regional control programme, with close monitoring of animal movement through eastern frontiers, supported by government commitment and educational programmes. Timely estimation of the frequency of carrier state both in cattle and small ruminants is also advocated as a gauge to monitor the virus status in the region.

Outbreak investigations and genetic characterization of foot-and-mouth disease virus in Ethiopia in 2008/2009

The study was conducted in three regional states of Ethiopia: Amhara, Oromia, and Addis Ababa from August 2008 to April 2009 with the objectives of identifying the genetic diversity of serotypes and topotypes in Ethiopia, and determining the attack rate and associations of potential risk factors with foot-and-mouth disease (FMD) seropositivity. A total of 496 cattle were clinically and serologically examined for presence of specific lesions and nonstructural protein for FMD, respectively. Of which, 140 (28.2%) manifested clinical signs and lesions suggestive of FMD, and 219 (44.2%) were seropositive. From a total of 7,781 animals observed and recorded on a designed format in six districts, 1,409 (19.6%) were infected, and 15 (0.12%) died during outbreaks of FMD. Epidemiological investigations revealed that the morbidity rate of the disease was 21.1% in Akaki-kality sub-city, but the mortality rate was <2% in all districts. Furthermore, the mortality and case fatality rates were relatively higher, 1.6% and 8.9% in calves than the other age groups, respectively. From a total of 33 bovine epithelial tissue-cultured samples, 19 (57.6%) showed CPE for FMD virus, in which 16 samples had serotype O and EA-3 topotype, while three samples had found serotype A, Africa topotype, and G-VII strain. Various strains of FMD viruses were isolated in Ethiopia in this study, and therefore, further detailed studies on the evaluation of available vaccines and the development of a vaccine which contains cocktails of antigens of FMD virus strains in the country should be encouraged.

Parameterization of the duration of infection stages of serotype O foot-and-mouth disease virus: an analytical review and meta-analysis with application to simulation models

Foot-and-mouth disease (FMD) is considered one of the most important infectious diseases of livestock because of the devastating economic consequences that it inflicts in affected regions. The value of critical parameters, such as the duration of the latency or the duration of the infectious periods, which affect the transmission rate of the FMD virus (FMDV), are believed to be influenced by characteristics of the host and the virus. Disease control and surveillance strategies, as well as FMD simulation models, will benefit from improved parameter estimation. The objective of this study was to quantify the distributions of variables associated with the duration of the latency, subclinical, incubation, and infectiousness periods of FMDV transmission. A double independent, systematic review of 19 retrieved publications reporting results from experimental trials, using 295 animals in four reference laboratories, was performed to extract individual values related to FMDV transmission. Probability density functions were fitted to data and a set of regression models were used to identify factors associated with the assessed parameters. Latent, subclinical, incubation, and infectious periods ranged from 3.1 to 4.8, 2 to 2.3, 5.5 to 6.6, and 3.3 to 5.7 days, respectively. Durations were significantly (p < 0.05) associated independently with route of exposure, type of donor, animal species, strains, characteristics of sampling, and clinical signs. These results will contribute to the improvement of disease control and surveillance strategies and stochastic models used to simulate FMD spread and, ultimately, development of cost-effective plans to prevent and control the potential spread of the disease in FMD-free regions of the world.

Geographic and topographic determinants of local FMD transmission applied to the 2001 UK FMD epidemic

Background

Models of Foot and Mouth Disease (FMD) transmission have assumed a homogeneous landscape across which Euclidean distance is a suitable measure of the spatial dependency of transmission. This paper investigated features of the landscape and their impact on transmission during the period of predominantly local spread which followed the implementation of the national movement ban during the 2001 UK FMD epidemic. In this study 113 farms diagnosed with FMD which had a known source of infection within 3 km (cases) were matched to 188 control farms which were either uninfected or infected at a later timepoint. Cases were matched to controls by Euclidean distance to the source of infection and farm size. Intervening geographical features and connectivity between the source of infection and case and controls were compared.

Results

Road distance between holdings, access to holdings, presence of forest, elevation change between holdings and the presence of intervening roads had no impact on the risk of local FMD transmission (p > 0.2). However the presence of linear features in the form of rivers and railways acted as barriers to FMD transmission (odds ratio = 0.507, 95% CIs = 0.297,0.887, p = 0.018).

Conclusion

This paper demonstrated that although FMD spread can generally be modelled using Euclidean distance and numbers of animals on susceptible holdings, the presence of rivers and railways has an additional protective effect reducing the probability of transmission between holdings.

Foot-and-mouth disease virus infection in fetal lambs: tissue tropism and cytokine response

Foot-and-mouth disease virus (FMDV) can cause transplacental infection and death in fetal lambs. This study investigates the pathogenesis of FMDV infection in ovine fetuses using in-situ hybridization (ISH) to detect viral transcripts in tissue and real-time reverse transcriptase polymerase chain reaction (RT-PCR) assays to quantify the fetal cytokine response to infection. FMDV ribonucleic acid (RNA) was localized mainly to the heart and skeletal muscles of fetuses and was only occasionally expressed in the lingual epithelium, demonstrating that FMDV has a different tissue tropism in the fetus compared with that in adult sheep. There was early expression of genes encoding anti-viral cytokines (IFN-alpha and IFN-beta) in fetuses at 2 and 4 days post-infection (dpi), followed by a marked rise in the transcription of pro-inflammatory cytokine genes (IFN-gamma, TNF-alpha and IL-1alpha) from 7 to 18 dpi, particularly in the heart. The degree of cytokine mRNA expression correlated with fetal infection and was likely to be a factor in fetal death. In contrast, cytokine gene expression in infected neonatal lambs was much less and mainly occurred between 2 and 4 dpi. This study identifies two key factors in the pathogenicity of FMDV in fetal lambs: viral tropism for cardiac and skeletal muscles, and a marked cytokine response following infection.

Diagnostic evaluation of multiplexed reverse transcription-PCR microsphere array assay for detection of foot-and-mouth and look-alike disease viruses

A high-throughput multiplexed assay was developed for the differential laboratory detection of foot-and-mouth disease virus (FMDV) from viruses that cause clinically similar diseases of livestock. This assay simultaneously screens for five RNA and two DNA viruses by using multiplexed reverse transcription-PCR (mRT-PCR) amplification coupled with a microsphere hybridization array and flow-cytometric detection. Two of the 17 primer-probe sets included in this multiplex assay were adopted from previously characterized real-time RT-PCR (rRT-PCR) assays for FMDV. The diagnostic accuracy of the mRT-PCR assay was evaluated using 287 field samples, including 247 samples (213 true-positive samples and 35 true-negative samples) from suspected cases of foot-and-mouth disease collected from 65 countries between 1965 and 2006 and 39 true-negative samples collected from healthy animals. The mRT-PCR assay results were compared to those of two singleplex rRT-PCR assays, using virus isolation with antigen enzyme-linked immunosorbent assays as the reference method. The diagnostic sensitivity of the mRT-PCR assay for FMDV was 93.9% (95% confidence interval [CI], 89.8 to 96.4%), and the sensitivity was 98.1% (95% CI, 95.3 to 99.3%) for the two singleplex rRT-PCR assays used in combination. In addition, the assay could reliably differentiate between FMDV and other vesicular viruses, such as swine vesicular disease virus and vesicular exanthema of swine virus. Interestingly, the mRT-PCR detected parapoxvirus (n = 2) and bovine viral diarrhea virus (n = 2) in clinical samples, demonstrating the screening potential of this mRT-PCR assay to identify viruses in FMDV-negative material not previously recognized by using focused single-target rRT-PCR assays.

Biosecurity practices and travel history of individuals exhibiting livestock at the 2005 California State Fair

OBJECTIVE

To determine biosecurity practices and travel history of individuals exhibiting livestock at the 2005 California State Fair.

DESIGN

Survey.

STUDY POPULATION

137 individuals exhibiting livestock at the fair.

PROCEDURES

Exhibitors were asked to complete a survey to gather information about the animals they exhibited, the biosecurity practices they used, and the distances they traveled to exhibit their animals.

RESULTS

132 of the 137 (96%) respondents came from California, with respondents representing 40 of California's 58 counties. Median number of livestock exhibitions attended by respondents during the past 12 months was 3 (range, 1 to 7). Respondents indicated that 787 of the 812 (97%) animals they exhibited would be returned home after the fair. Nine (7%) respondents indicated that they did not take any particular biosecurity precautions before arriving at the fair, and 14 (10%) indicated that they did not take any particular biosecurity precautions while at the fair. Only 36 (26%) respondents indicated that they quarantined their animals when returning to their farm of residence after the fair.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that there was extensive movement of livestock among exhibitions in California, posing a potential threat for widespread dispersion of disease throughout the state and beyond, particularly given the low percentages of exhibitors who used various biosecurity measures.

Analysis of foot-and-mouth disease virus replication using strand-specific quantitative RT-PCR

Foot-and-mouth disease virus (FMDV) is a positive-sense, single stranded RNA virus and its replication involves the synthesis of a negative strand intermediate. In the present study, a strand-specific quantitative RT-PCR assay was developed for analysis of FMDV replication. Strand-specific detection of viral positive and negative strand RNA was achieved using a high reverse transcription (RT) temperature (62 degrees C) and a tagged RT primer. In both the positive and negative strand assays, the lowest reliably detectable concentration was 1 x 10(2) copies/microl. The assays developed were successfully used to analyse viral replication in tissues collected from experimentally infected sheep during both acute and persistent infection. The results showed that while replication was observed in all tissues examined during acute infection, active viral replication during persistent infection was only detected in the tonsil. These results are consistent with the current opinion that the tonsil in sheep is the main predilection site for virus persistence. This assay will be used in the future to look further at replication in experimentally infected animals, including the study of individual cell types, and will improve our understanding of FMDV pathogenesis.

Foot-and-mouth disease virus (O/UKG/2001) is poorly transmitted between sheep by the airborne route

Foot-and-mouth disease virus (FMDV) can be spread by the airborne route and therefore atmospheric dispersion models have been developed to predict where the virus might spread during a disease outbreak. Airborne transmission between sheep of the FMDV strain involved in the outbreak in Europe in 2001 (O/UKG/2001) was studied experimentally. Recipient animals were exposed to two donor sheep excreting virus for 2, 4, 6, 8 or 24 h. Although FMDV was detected in air samples collected during challenge, none of the recipient sheep became infected. These data suggest that O/UKG/2001 is not efficiently transmitted by the airborne route between sheep.

Bayesian spatiotemporal analysis of foot-and-mouth disease data from the Republic of Turkey

A flexible hierarchical Bayesian spatiotemporal regression model for foot-and-mouth disease (FMD) was applied to data on the annual number of reported FMD cases in Turkey from 1996 to 2003. The longitudinal component of the model was specified as a latent province-specific stochastic process. This stochastic process can accommodate various types of FMD temporal profiles. The model accounted for differences in FMD occurrence across provinces and for spatial correlation. Province-level covariate information was incorporated into the analysis. Results pointed to a decreasing trend in the number of FMD cases in western Turkey and an increasing trend in eastern Turkey from 1996 to 2003. The model also identified provinces with high and with low propensities for FMD occurrence. The model's use of flexible structures for temporal trend and of generally applicable methods for spatial correlation has broad application to predicting future spatiotemporal distributions of disease in other regions of the world.

Quantification of foot and mouth disease virus excretion and transmission within groups of lambs with and without vaccination

Sheep are well known to be susceptible for foot and mouth disease virus (FMDV), but it is unknown whether the infection can spread and persist in a sheep population. We therefore quantified virus transmission by performing experiments with FMD virus strain O/NET/2001 in groups of lambs. We used six groups of four lambs each, in which half of each group was inoculated and the other half was contact-exposed. To quantify the effectiveness of a single vaccination we also included six groups of four lambs each, vaccinated with O Manisa vaccine, 14 days prior to inoculation. Oropharyngeal fluid was obtained with a swab (OPF-swab), and blood samples were collected daily to determine virus excretion and serological response. We calculated the transmission rate beta (the number of new infections per day per infectious animal), and the reproduction ratio R (the number of secondary infections caused by one infectious individual). The mean daily virus excretion and the number of days the lambs excreted virus in the OPF differed significantly between vaccinated and non-vaccinated lambs. The transmission rate beta in the unvaccinated groups was 0.105 (95% confidence limit 0.044; 0.253) per day. The duration of the infectious period (T) was 21.11 (95% confidence limit 10.6; 42.1) days. With the final size of infection we estimated the reproduction ratio R in the non-vaccinated groups to be 1.14 (0.3; 3.3), and in vaccinated groups 0.22 (0.01; 1.78). Virus transmission as quantified by the final size did not differ statistically between the vaccinated and the non-vaccinated groups of lambs. In conclusion, FMDV seems able to persist in a sheep population, although the reproduction ratio was only slightly larger than one. As a consequence, vaccination might only have a small effect on transmission, in spite of the fact that virus excretion and duration of virus excretion is significantly reduced after vaccination.

The effect of vaccination on foot and mouth disease virus transmission among dairy cows

The aim of this study was to quantify the effect of a single vaccination of dairy cows on foot and mouth disease virus (FMDV) transmission. To estimate if vaccination could significantly reduce virus transmission, we performed two replicates of a transmission experiment with one group of vaccinated and one group of non-vaccinated dairy cows (ten animals per group). Half of both groups were intranasally inoculated, with FMDV field isolate O/NET2001, and housed with the other half of the group (contact-exposed cows) from the next day onwards. Virus transmission was quantified by estimating the reproduction ratio R, which is the average number of secondary cases caused by one infectious animal. In the non-vaccinated groups all cows became infected and Rnv was significantly above 1. In the vaccinated groups infection was demonstrated in three inoculated cows, and no transmission was observed (Rv was 0, not significantly below 1). Transmission was significantly reduced in the groups of vaccinated cows when compared to the groups of unvaccinated cows. Our findings indicate that after a single vaccination cows are protected against infection of FMD and that most likely no virus transmission will occur within a vaccinated herd.

Factors associated with the clinical diagnosis of foot and mouth disease during the 2001 epidemic in the UK

The purpose of this investigation was to identify factors associated with the clinical diagnosis of foot and mouth disease during the 2001 epidemic in the United Kingdom. Using logistic regression, we compared: (1) reports of suspect disease that resulted in the declaration of FMD to reports that did not, and (2) laboratory-positive cases to laboratory-negative cases. From 6,801 reports of suspect disease, 2,026 cases of FMD were identified. Suspect cases were more likely to become clinical cases if: (1) the report originated from the disease control authorities ('active surveillance') rather than the public, usually farmers ('passive surveillance'); (2) cattle were the species suspected of disease, as opposed to sheep; (3) the report was filed during the peak of the epidemic; (4) the reporting premises was within 3 km of an FMD case detected within the previous 2 weeks; or (5) the report originated from certain local disease control centres. There were significant two-way interactions between: type of surveillance and species suspected of disease, type of surveillance and proximity of other infected premises, species suspected and time in the epidemic, and time in the epidemic and proximity of other infected premises. Clinical cases were more likely to be laboratory positive if: (1) they were found by passive versus active surveillance, (2) cattle were suspected of disease (versus sheep), (3) oldest lesions were less than 3 days, (4) the report was filed at any time other than the peak of the epidemic, or (5) the report originated from certain local disease control centres. Significant two-way interactions were found between: type of surveillance and species suspected of disease, and type of surveillance and time in the epidemic.

Predictions for the timing and use of culling or vaccination during a foot-and-mouth disease epidemic

First-fortnight incidence (FFI) is a modelling parameter that can be used to predict both the prevalence and duration of a foot-and-mouth disease (FMD) epidemic at regional and national levels. With an indication of how long an epidemic may last by the end of week two, it becomes possible to estimate whether vaccination would be economically viable from the start of an epidemic. Where FFI indicates that an epidemic is unlikely to last for as long as an export ban on agricultural produce, it may be inappropriate to implement a policy of 'vaccination to live'. Alternatively where FFI indicates that an epidemic will equal or exceed the ban length, then the benefits of vaccination should be considered at an early stage, during or after the first fortnight. Since blanket vaccination of the national or regional herds and flocks would be both costly and heighten the risk of producing carrier animals, targetting vaccination through risk assessment becomes useful.

A review of foot-and-mouth disease with special consideration for the clinical and epidemiological factors relevant to predictive modelling of the disease

Modelling the epidemiology of foot-and-mouth disease (FMD) has been undertaken since the early 1970s. We review here clinical factors and modelling procedures that have been used in the past, differentiating between those that have proved to be more relevant in controlling FMD epidemics, and those that have showed less significance. During the 2001 UK FMD epidemic, many previously developed FMD models were available for consideration and use. Accurate epidemiological models can become useful tools for determining relevant control policies for different scenarios and, conversely, inaccurate models may become an abuse for disease control. Inaccuracy presents two opposing difficulties. Firstly, too much control (in terms of animal slaughter for 2001) would negatively impact the farming community for many subsequent years, whilst too little control would permit an epidemic to persist. Accuracy however, presents the optimal permutation of control measures that could be implemented for a given set of conditions, and is a prerequisite to boosting public confidence in the use of epidemiological models for future epidemics.

Comparison of two 3ABC enzyme-linked immunosorbent assays for diagnosis of multiple-serotype foot-and-mouth disease in a cattle population in an area of endemicity

The development of a serological test for foot-and-mouth disease virus (FMDV) which is quick and easy to use, which can identify all seven serotypes, and which can differentiate vaccinated from convalescing or potential virus carriers would be a major advance in the epidemiological toolkit for FMDV. The nonstructural polyprotein 3ABC has recently been proposed as such an antigen, and a number of diagnostic tests are being developed. This paper evaluates the performance of two FMDV tests for antibodies to nonstructural proteins in an unvaccinated cattle population from a region of Cameroon with endemic multiple-serotype FMD. The CHEKIT-FMD-3ABC bo-ov (CHEKIT) enzyme-linked immunosorbent assay (ELISA) (Bommeli Diagnostics/Intervet) is a commercially available test that was compared with a competitive 3ABC ELISA (C-ELISA) developed in Denmark. The tests were compared with the virus neutralization test as the "gold standard." Diagnostic sensitivity and specificity were examined over a range of test cutoffs by using receiver operating characteristic curves, which allowed comparison of the overall performance of each test. The results indicated that the CHEKIT ELISA kit was 23% sensitive and 98% specific and the Danish C-ELISA was 71% sensitive and 90% specific at the recommended cutoff. These results have important implications if the tests are to be used to screen herds or individual cattle in surveillance programs, at border crossings for import-export clearance, or following emergency vaccination in an outbreak situation.

Foot-and-mouth disease

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. The disease was initially described in the 16th century and was the first animal pathogen identified as a virus. Recent FMD outbreaks in developed countries and their significant economic impact have increased the concern of governments worldwide. This review describes the reemergence of FMD in developed countries that had been disease free for many years and the effect that this has had on disease control strategies. The etiologic agent, FMD virus (FMDV), a member of the Picornaviridae family, is examined in detail at the genetic, structural, and biochemical levels and in terms of its antigenic diversity. The virus replication cycle, including virus-receptor interactions as well as unique aspects of virus translation and shutoff of host macromolecular synthesis, is discussed. This information has been the basis for the development of improved protocols to rapidly identify disease outbreaks, to differentiate vaccinated from infected animals, and to begin to identify and test novel vaccine candidates. Furthermore, this knowledge, coupled with the ability to manipulate FMDV genomes at the molecular level, has provided the framework for examination of disease pathogenesis and the development of a more complete understanding of the virus and host factors involved.

Early dissemination of foot-and-mouth disease virus through sheep marketing in February 2001

The results of epidemiological investigations suggest that livestock on up to 79 premises, spread widely throughout the British Isles, may have been exposed to infection by foot-and-mouth disease (FMD) virus by the movement of infected sheep before the first case of the disease was confirmed at an abattoir in Essex on February 20, 2001. A further 36 premises may have been infected by this route before the national livestock movement ban was imposed on February 23.