Evaluation of the application of veterinary judgement in the pre-emptive cull of contiguous premises during the epidemic of foot-and-mouth disease in Cumbria in 2001

This paper presents a detailed analysis of the application of contiguous culling in Cumbria between May 1 and September 30, during the outbreak of foot-and-mouth disease in 2001. The analysis shows that the application of veterinary risk assessment and judgement identified and removed groups of susceptible stock which were at risk of direct transmission of infection and avoided infected animals being left that might have spread the disease. When compared with an automatic contiguous cull, fewer culls were made and some of these were reduced in scale, providing economies in the use of resources. The data suggest that farms contiguous to an infected premises faced a 5 per cent risk of infection by direct transmission and a 12 per cent risk of infection by indirect transmission.     

Factors associated with the early detection of foot-and-mouth disease during the 2001 epidemic in the United Kingdom

An essential objective of an effective foot-and-mouth disease (FMD) eradication campaign is to shorten the infectious period by rapidly detecting and destroying cases of disease. The purpose of our investigation was to identify factors associated with the early detection of clinical FMD during the 2001 outbreak in the United Kingdom. We performed a logistic regression analysis, using early versus late detection of disease as the outcome of interest.During the 2001 FMD outbreak in the United Kingdom, infected premises were more likely to be detected early under the following circumstances: 1) cattle (particularly dairy) were infected rather than sheep; 2) a recently confirmed infected premises was within 3 km of the new case; and 3) the case was initially reported by the farmer, rather than a Local Disease Control Centre-initiated surveillance activity (patrol, tracing, pre-emptive cull). Our findings suggest that reporting by farmers and initiatives that increase farmer education and awareness should be encouraged.     

Relationship of speed of slaughter on infected premises and intensity of culling of other premises to the rate of spread of the foot-and-mouth disease epidemic in Great Britain, 2001

During the foot-and-mouth disease epidemic in the UK in 2001, two major control policies were the rapid identification of cases and the culling of animals on infected premises and on dangerous contact premises. Dangerous contact premises were divided into two groups, premises contiguous to an infected premises and non-contiguous premises. In England, the largest numbers of geographically clustered infected premises were in Cumbria, the South West (Somerset, Devon and Cornwall) and the Settle/Clitheroe area straddling the Yorkshire-Lancashire border. In each of these clusters, the rate of spread of the disease, the average time from the first lesion to slaughter on infected premises, and the intensity of culling of contiguous premises and non-contiguous premises were calculated for seven-day periods. Linear regression analysis was used to look for relationships between these factors and the rate of spread of the disease. The average time from the first lesion to slaughter had a statistically significant relationship in two of the three clusters and the intensity of culling of non-contiguous premises had a significant relationship in one. The intensity of culling of contiguous premises had no significant relationship in any of the three clusters.     

Experiences of University of Liverpool veterinary students during the 2001 epidemic of foot-and-mouth disease

The 2001 epidemic of foot-and-mouth disease disrupted the teaching of practical farm animal work for much of that year. Many students in their clinical years in the Faculty of Veterinary Science at the University of Liverpool, went to help to control the disease, both in place of some normal term-time activities and as part of their extramural studies out of term time. This paper, which is based on a questionnaire survey of the students, describes their experiences, the types of work they did, the skills they acquired and their views on the effects of the epidemic on their studies. The vast majority of students felt they had benefited from their experiences and had contributed to combating the epidemic.     

Predictive spatial modelling of alternative control strategies for the foot-and-mouth disease epidemic in Great Britain, 2001

A spatial simulation model of foot-and-mouth disease was used in March and early April 2001 to evaluate alternative control policies for the 2001 epidemic in Great Britain. Control policies were those in operation from March 20, 2001, and comprised a ban on all animal movements from February 23, 2001, and a stamping-out policy. Each simulation commenced with the known population of infected farms on April 10, 2001, and ran for 200 days. For the control policy which best approximated that actually implemented from late March, the model predicted an epidemic of approximately 1800 to 1900 affected farms, and estimated that the epidemic would be eradicated between July and October 2001, with a low probability of continuing beyond October 2001. This policy included the slaughter-out of infected farms within 24 hours, slaughter of about 1.3 of the surrounding farms per infected farm within a further 48 hours, and minimal interfarm movements of susceptible animals. Delays in the slaughter of animals on infected farms beyond 24 hours after diagnosis slightly increased the epidemic size, and failure to achieve pre-emptive slaughter on an adequate number of at-risk farms substantially increased the expected size of the epidemic. Vaccination of up to three of the most outbreak-dense areas carried out in conjunction with the adopted control policy reduced the predicted size of the epidemic by less than 100 farms. Vaccination of buffer zones (designed to apply available vaccine and manpower as effectively as possible) carried out in place of the adopted control policy allowed the disease to spread out of control, producing an epidemic involving over 6000 farms by October 2001, with no prospect of immediate eradication.     

The foot-and-mouth disease epidemic of 2001 in the UK: implications for the USA and the "war on terror"

While there is no evidence to suggest that the recent epidemic of foot-and-mouth disease (Fmd) in the Uk and its subsequent spread to continental Europe were caused by bioterrorism, the extent of the epidemic shows that Fmd could be a very powerful weapon for a bioterrorist wishing to cause widespread disease in livestock and economic disruption for the targeted country. This paper describes the epidemic. It then examines the contentious issues that arose through the use of extensive slaughter to control the epidemic and explores how, in turn, the concerns of society are being translated into a radical change in policy within the European Union with respect to the control of Fmd and other foreign animal diseases. The crisis generated by the Fmd epidemic in Europe in 2001 provides many lessons to be learned for the US and highlights the need for creative thinking in research and teaching within colleges of veterinary medicine to more effectively address the threat of epidemic diseases under the "new world order." There is general agreement that the veterinary profession in the US plays a unique role in protecting the nation against epidemic livestock diseases, whether caused naturally or through bioterrorism. The profession also has a significant role in protecting the public's health, since several epidemic diseases of animals, such as rift valley fever, are zoonotic. However, improved financial support at the federal and state levels is urgently needed to support epidemic-diseases research and teaching in colleges of veterinary medicine.     

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.     

A decision-tree to optimise control measures during the early stage of a foot-and-mouth disease epidemic

A decision-tree was developed to support decision making on control measures during the first days after the declaration of an outbreak of foot-and-mouth disease (FMD). The objective of the tree was to minimise direct costs and export losses of FMD epidemics under several scenarios based on livestock and herd density in the outbreak region, the possibility of airborne spread, and the time between first infection and first detection. The starting point of the tree was an epidemiological model based on a deterministic susceptible–infectious–recovered approach. The effect of four control strategies on FMD dynamics was modelled. In addition to the standard control strategy of stamping out and culling of high-risk contact herds, strategies involving ring culling within 1 km of an infected herd, ring-vaccination within 1 km of an infected herd, and ring-vaccination within 3 km of an infected herd were assessed. An economic model converted outbreak and control effects of farming and processing operations into estimates of direct costs and export losses. Ring-vaccination is the economically optimal control strategy for densely populated livestock areas whereas ring culling is the economically optimal control strategy for sparsely populated livestock areas.     

Clinical and laboratory investigations of five outbreaks of foot-and-mouth disease during the 2001 epidemic in the United Kingdom

Clinical and laboratory investigations of five outbreaks of foot-and-mouth disease (FMD) were made during the early stages of the 2001 epidemic in the UK. The first outbreak, confirmed on February 20, was at an abattoir in Essex which specialised in the processing of culled sows and boars. On February 23, the disease was confirmed at a pig farm in Northumberland which held cull sows and boars fed on waste food; the findings indicated that it was the first of the five premises to be infected. The disease had probably been present since early February, and it was the most likely origin of the epidemic. The other premises investigated were a waste food-fed cull sow/boar pig unit in Essex, approximately 30 km from the abattoir, which was probably infected at the same time or before the abattoir, a sheep and cattle farm approximately 6 km from the Northumberland pig farm, which was probably infected by airborne virus from it in the period immediately before February 13, and a sheep and cattle farm in Devon which had clinical disease from February 20 and was probably infected by sheep transported from Northumberland on February 13 which arrived on February 15.     

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.     

Temporal and geographical distribution of cases of foot-and-mouth disease during the early weeks of the 2001 epidemic in Great Britain

Estimates of the likely dates of infection of the early cases of the 2001 foot-and-mouth disease (FMD) epidemic indicate that at least 57 premises in 16 counties in Great Britain were infected before the first case was disclosed. Nationwide animal movement controls were imposed within three days of the first case being confirmed on February 20, when FMD was only known to be in two counties, and these controls limited its geographical spread. After the first few cases were confirmed, new cases were rapidly discovered, and the epidemic curve for the daily number of confirmed cases peaked five weeks later, 11 days later than the peak of the curve based on the estimated dates of infection. In the peak week, both curves showed an average daily number of 43 new cases. The estimated dates of infection are believed to be relatively unbiased for the early cases, for which they were derived from a known contact with infection. However, for the later cases they were estimated mainly from the age of the clinical signs of the disease, and were biased by species and other factors, a bias which would probably have made the estimated dates later than was in fact the case.     

Risk factors for local spread of foot-and-mouth disease, 2010 epidemic in Japan

To provide a basis for effective foot-and-mouth disease (FMD) prevention measures, factors associated with local spread were investigated in this study using data of the 2010 FMD epidemic in Japan. Thirty-eight local clusters within a 500-m radius from source farms were selected. In the clusters with pig source farms, more neighboring farms were infected in a short time compared with the clusters with cattle source farms. The influence of distance and wind upon local spread did not show a significant difference between infected and noninfected neighboring farms. Large-size pig farms posed a greater risk of inducing local spread; the odds ratio with reference to small-size cattle farms was 16.73. Middle-size and large-size cattle farms had a greater risk of infection; odds ratios with reference to small-size cattle farms were 15.65 and 25.52, respectively. The present results are useful for understanding features of local spread and prioritizing farms for control measures.     

Identification of case clusters and counties with high infective connectivity in the 2001 epidemic of foot-and-mouth disease in Uruguay

OBJECTIVE: To evaluate the influence of individual spatial units (ie, counties) on the epidemic spread of foot-and-mouth disease (FMD) virus. SAMPLE POPULATION: 163 counties in Uruguay where there was an outbreak of FMD between April 23 and July 11, 2001. PROCEDURE: A geographically referenced database was created, and the distance between counties (13,203 county pairs), road density of counties (163 counties), and time when cases were reported in those counties (11 weeks of the epidemic) were considered to assess global spatial and spatial-temporal autocorrelation, determine the contribution of links connecting pairs of counties with infected animals, and allow us to hypothesize the influence for spread during the epidemic for counties with greater than the mean infective link contributions. RESULTS: Case clusters were indicated by the Moran Iand Mantel tests during the first 6 weeks of the epidemic. Spatial lags between pairs of counties with infected animals revealed case clustering before and after vaccination was implemented. Temporal lags predicted autocorrelation for up to 3 weeks. Link indices identified counties expected to facilitate epidemic spread. If control measures had been implemented in counties with a high index link (identifiable as early as week 1 of the epidemic), they could have prevented (by week 11 of the epidemic) at least 2.5 times as many cases per square kilometer than the same measures implemented in counties with average link indices. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of spatial autocorrelation and infective link indices may identify network conditions that facilitate (or prevent) disease spread.     

The 2001 epidemic of foot-and-mouth disease in the United Kingdom: epidemiological and meteorological case studies

The possibility of the airborne spread of foot-and-mouth disease during the 2001 epidemic in the uk has been investigated in three epidemiological case studies. On the basis of evidence from field investigations, and a simple meteorological analysis, it is concluded that the spread of disease was consistent with the airborne transport of virus. The distances ranged from less than 1 km to 16 km; six of the farms were over 6 km from the source and involved the passage of virus over the sea combined with meteorological conditions which strongly favoured airborne disease transmission. The results of detailed atmospheric modelling demonstrated that airborne virus could have challenged livestock on all the farms studied. However, with one exception the 24-hour average daily concentrations of the virus were significantly below the experimentally estimated threshold for infection. A detailed model intercomparison established that, under stable atmospheric conditions, peak concentrations of virus up to two orders of magnitude higher might have been experienced for short periods, owing to fluctuations within the plume of virus, and model limitations. This finding would significantly reduce the apparent discrepancy between the experimentally estimated threshold for infection and the modelling results.     

A generic spreadsheet model of a disease epidemic with application to the first 100 days of the 2001 outbreak of foot-and-mouth disease in the UK

A generic, stochastic spreadsheet model was developed to calculate the number of cases within the first 100 days of a propagating epidemic and with the ability to incorporate generic control measures. Foot-and-mouth disease (FMD) epidemics were simulated with a range of assumptions about the number of cases incubating the disease on day 1 and the efficiency of control measures. Particularly severe epidemics resulted from scenarios with low efficiency of control measures and high numbers incubating. Control measures that prevented 0.8 of cases from resulting in new cases were able to reduce substantially the cumulative number of cases. The results of various scenarios using the model were compared to the number of cases of FMD in the first 100 days of the 2001 outbreak in the UK, with specific reference to cases in Cumbria and Anglesey. Potential practical and educational applications of the model are discussed.     

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.     

Results of epidemic simulation modeling to evaluate strategies to control an outbreak of foot-and-mouth disease

OBJECTIVE: To assess estimated effectiveness of control and eradication procedures for foot-and-mouth disease (FMD) in a region of California. SAMPLE POPULATION: 2,238 herds and 5 sale yards in Fresno, Kings, andTulare counties of California. PROCEDURE: A spatial stochastic model was used to simulate hypothetical epidemics of FMD for specified control scenarios that included a baseline eradication strategy mandated by USDA and supplemental control strategies of slaughter or vaccination of all animals within a specified distance of infected herds, slaughter of only high-risk animals identified by use of a model simulation, and expansion of infected and surveillance zones. RESULTS: Median number of herds affected varied from 1 to 385 (17% of all herds), depending on type of index herd and delay in diagnosis of FMD. Percentage of herds infected decreased from that of the baseline eradication strategy by expanding the designated infected area from 10 to 20 km (48%), vaccinating within a 50-km radius of an infected herd (41%), slaughtering the 10 highest-risk herds for each infected herd (39%), and slaughtering all animals within 5 km of an infected herd (24%). CONCLUSIONS AND CLINICAL RELEVANCE: Results for the model provided a means of assessing the relative merits of potential strategies for control and eradication of FMD should it enter the US livestock population. For the study region, preemptive slaughter of highest-risk herds and vaccination of all animals within a specified distance of an infected herd consistently decreased size and duration of an epidemic, compared with the baseline eradication strategy.     

Descriptive epidemiology of the 2001 foot-and-mouth disease epidemic in Great Britain: the first five months.

In February 2001, foot-and-mouth disease (FMD) was confirmed in Great Britain. A major epidemic developed, which peaked around 50 cases a day in late March, declining to under 10 a day by May. By mid-July, 1849 cases had been detected. The main control measures employed were livestock movement restrictions and the rapid slaughter of infected and exposed livestock. The first detected case was in south-east England; infection was traced to a farm in north-east England to which all other cases were linked. The epidemic was large as a result of a combination of events, including a delay in the diagnosis of the index case, the movement of infected sheep to market before FMD was first diagnosed, and the time of year. Virus was introduced at a time when there were many sheep movements around the country and weather conditions supported survival of the virus. The consequence was multiple, effectively primary, introductions of FMD virus into major sheep-keeping areas. Subsequent local spread from these introductions accounted for the majority of cases. The largest local epidemics were in areas with dense sheep populations and livestock dealers who were active during the key period. Most affected farms kept both sheep and cattle. At the time of writing the epidemic was still ongoing; however, this paper provides a basis for scientific discussion of the first five months.     

Serosurveillance of wild deer and wild boar after the epidemic of foot-and-mouth disease in The Netherlands in 2001

Blood samples from 140 wild deer and 208 wild boar shot in the aftermath of the epidemic of foot-and-mouth disease in The Netherlands in 2001 were examined for antibodies to foot-and-mouth disease virus. They were all negative.     

Airborne transmission of foot-and-mouth disease virus from Burnside Farm,Heddon-on-the-Wall,Northumberland, during the 2001 epidemic in the United Kingdom

The results of a detailed assessment of the atmospheric conditions when foot-and-mouth disease (FMD) virus was released from Burnside Farm, Heddon-on-the-Wall, Northumberland at the start of the 2001 epidemic in the UK are consistent with the hypothesis that the disease was spread to seven of the 12 farms in the immediate vicinity of the source by airborne virus, and airborne infection could not be ruled out for three other premises; the remaining two premises were unlikely to have been infected by airborne virus. The distances involved ranged from less than 1 km up to 9 km. One of the farms which was most probably infected by airborne virus from Burnside Farm was Prestwick Hall Farm, which is believed to have been key to the rapid spread of the disease throughout the country. In contrast, the results of detailed atmospheric modelling, based on a combination of clinical evidence from the field and laboratory experiments have shown that by assuming a relationship between the 24-hour average virus concentrations and subsequent infection, threshold infection levels were seldom reached at the farms close to Burnside Farm. However, significant short-term fluctuations in the concentration of virus can occur, and short-lived high concentrations may have increased the probability of infection and explain this discrepancy.