Application of subjective methods to the determination of the likelihood and consequences of the entry of foot-and-mouth disease into New Zealand

New Zealand has a history of continuous freedom from foot-and-mouth disease and relies on a two-tier system of surveillance to maintain this status. The first involves border control procedures and stringent importation standards, and the second is an exotic disease and pest response programme. As part of an economic evaluation comparing the exotic disease and pest response programme against a hypothetical lower grade “measured response programme” subjective judgements of the risks involved were required. Twenty-eight selected animal health professionals, predominantly veterinarians, were posted a questionnaire that used three techniques (single point estimates, three point estimates and elicitation methods) to determine the risk components in a foot-and-mouth disease outbreak. The two key variables were the probability of an outbreak in New Zealand, and the number of secondary properties to which the disease spread during the epidemic. A Delphi conference of ten selected participants then focused mainly on the two key variables, with a second round postal extension to this group for the first variable. The individual data sets were then analysed and combined using a stochastic simulation technique. The final mean probability of an outbreak was about once in 50 years (0.0199). The mean numbers of farms to which disease would spread during an epidemic under the existing exotic disease and pest response programme, a measured response programme which allowed vaccination and a measured response programme which excluded vaccination were estimated to be 61, 478 and 2230 respectively. The policy implications arising from the quantification of these two key variables are that more expenditure on preparedness is justifiable and current resource planning is barely adequate.     

The epidemiology of foot-and-mouth disease: implications for New Zealand

Foot-and-mouth disease is an acute, highly communicable disease affecting cloven-hoofed animals, both domesticated and wild. It may well be the most contagious disease known in the animal kingdom. The key features that contribute to this include its ability to gain entry and initiate infection through a variety of sites, the small infective dose, the short incubation period, the release of virus before the onset of clinical signs, the massive quantities of virus excreted from infected animals, its ability to spread large distances due to airborne dispersal, and the persistence of the virus in the environment. These features, plus the ability of the virus to be disseminated through the movements of animals, animal products, people, and plant and equipment makes the disease very difficult to control. New Zealand has never experienced a foot-and-mouth disease epidemic, and the economic consequences of an outbreak would be disastrous, due to the eradication costs, the loss of productivity and the impact on the export of animals and animal products. The smuggling of meat products, embryos or semen into the country are perceived as the most likely ways in which the disease could be introduced. The New Zealand Ministry of Agriculture and Fisheries therefore operates a two-tier system of defense against foot-and-mouth disease. The first tier involves border protection through stringent import controls to prevent the entry of infectious material. If this barrier is breached, an emergency response programme is activated, involving a stamping-out eradication strategy. This paper attempts to draw on overseas historical outbreak experiences and research findings to gain insights into the epidemiology of foot-and-mouth disease as it would relate to New Zealand.     

Assessment of the likelihood of the introduction of foot-and-mouth disease through importation of live animals into the Malaysia-Thailand-Myanmar peninsula

OBJECTIVE: To assess the likelihood of an introduction of foot-and-mouth disease (FMD) into the Malaysia-Thailand-Myanmar (MTM) peninsula through terrestrial movement of livestock. ANIMALS: 89,294 cattle and buffalo legally moved into the MTM peninsula. PROCEDURES: A quantitative risk assessment was conducted by use of a stochastic simulation. Patterns of livestock movement were ascertained through review of relevant governmental records and regulations and by interviewing farmers, traders, and local officers when the records did not exist. Parameters identified in the process were the probabilities of livestock having FMD and of FMD infection going undetected during import processes. The probability of an animal accepted for import having FMD was also assessed. Sensitivity analysis was performed to determine the effects that each parameter had on the model. RESULTS: The simulation yielded an average consignment prevalence of 10.95%. Typically, each animal in a quarantine facility had a 2.7% chance of having an inapparent form of FMD infection; hence, it was likely an animal would not be identified as infected. Findings revealed that the mean probability of an animal accepted for import having FMD was 2.9%, and the risk was as high as 11%. CONCLUSIONS AND CLINICAL RELEVANCE: Results of the model allowed for the evaluation of movement regulations currently imposed in the MTM peninsula. Evidence from the study suggested that current practices in animal movement were far from efficient in preventing introduction of FMD-infected animals into the MTM region, and additional measures will be necessary.     

A survey to investigate movements off sheep and cattle farms in New Zealand, with reference to the potential transmission of foot-and-mouth disease

AIM: To quantify the numbers and extent of movements off sheep and cattle farms in New Zealand, in order to construct more realistic simulation models to investigate how infectious diseases such as foot-and-mouth disease (FMD) might spread. METHODS: Farmers from 500 randomly selected farms, comprising 100 from each of the following sectors, viz beef, dairy, grazing/dairy heifer rearing, sheep, and mixed sheep and beef, were asked to fill in diaries in which they recorded the movements of all animals, products, people, vehicles and equipment coming on to or leaving their farms during two separate 3-week periods, representing relatively 'busy' and 'quiet' times of the year with respect to livestock movements. Where possible, the destination of each movement was identified and geo-coded, to allow the distance travelled to be calculated. Each movement was then classified according to the risk of transfer of FMD virus (FMDV), should the disease have been present on the study farm at the time of the movement. The data were then analysed to establish movement frequencies and distributions of distances travelled, by the different pastoral livestock sectors. RESULTS: Two hundred and seventeen farmers returned one or more diaries. One hundred and ninety-three farmers completed a Busy-period diary, recording a total of 12,052 movements off their farms, a crude average of 62.4 per 3-week period, or 2.97 per day. Of these, 4.0% involved the transport of livestock, equating to 0.12 livestock consignments per day. In contrast, 186 Quiet-period diaries were returned, recording a total of 10,885 movements off, representing a crude average of 58.5 during the 3-week period, or 2.78 per day. Of these, 2.1% involved livestock, equating to 0.06 livestock consignments per day. The mean and median distances travelled during the Busy periods were 30.9 km and 13.1 km, respectively (range 0-1,167 km). In comparison, the mean and median distances travelled during Quiet periods were 41.3 and 14 km, respectively (range 0.4-1,203 km). CONCLUSIONS: People, vehicles, livestock and other items can travel off pastoral livestock farms in New Zealand to other farms either directly or via saleyards over extensive distances. This has implications for the potential spread of infectious diseases such as FMD. Movement parameters intended for use in the InterSpread Plus inter-farm simulation model of FMD were established, which will facilitate the prediction of likely spread and efficacy of controls in the unlikely event of a real-life outbreak.     

A survey to investigate movements off sheep and cattle farms in New Zealand,with reference to the potential transmission of foot-and-mouth disease

AIM: To quantify the numbers and extent of movements off sheep and cattle farms in New Zealand, in order to construct more realistic simulation models to investigate how infectious diseases such as foot-and-mouth disease (FMD) might spread.

METHODS: Farmers from 500 randomly selected farms, comprising 100 from each of the following sectors, viz beef, dairy, grazing/dairy heifer rearing, sheep, and mixed sheep and beef, were asked to fill in diaries in which they recorded the movements of all animals, products, people, vehicles and equipment coming on to or leaving their farms during two separate 3-week periods, representing relatively ‘busy’ and ‘quiet’ times of the year with respect to livestock movements. Where possible, the destination of each movement was identified and geo-coded, to allow the distance travelled to be calculated. Each movement was then classified according to the risk of transfer of FMD virus (FMDV), should the disease have been present on the study farm at the time of the movement. The data were then analysed to establish movement frequencies and distributions of distances travelled, by the different pastoral livestock sectors.

RESULTS: Two hundred and seventeen farmers returned one or more diaries. One hundred and ninety-three farmers completed a Busy-period diary, recording a total of 12,052 movements off their farms, a crude average of 62.4 per 3-week period, or 2.97 per day. Of these, 4.0% involved the transport of livestock, equating to 0.12 livestock consignments per day. In contrast, 186 Quiet-period diaries were returned, recording a total of 10,885 movements off, representing a crude average of 58.5 during the 3-week period, or 2.78 per day. Of these, 2.1% involved livestock, equating to 0.06 livestock consignments per day. The mean and median distances travelled during the Busy periods were 30.9 km and 13.1 km, respectively (range 0–1,167 km). In comparison, the mean and median distances travelled during Quiet periods were 41.3 and 14 km, respectively (range 0.4–1,203 km).

CONCLUSIONS: People, vehicles, livestock and other items can travel off pastoral livestock farms in New Zealand to other farms either directly or via saleyards over extensive distances. This has implications for the potential spread of infectious diseases such as FMD. Movement parameters intended for use in the InterSpread Plus inter-farm simulation model of FMD were established, which will facilitate the prediction of likely spread and efficacy of controls in the unlikely event of a real-life outbreak.     

Estimating the risk of importation of foot-and-mouth disease into Europe

The opinions of a number of recognised world experts on foot-and-mouth disease (FMD) were sought in order to answer key questions relating to the importation of the disease into European countries from countries outside Europe. In addition, their opinions were sought on where in Europe a primary outbreak of FMD was most likely to occur and the number of outbreaks likely to occur within European countries in the next five years. The Balkans group of countries was considered to be the most likely group within Europe to have a primary outbreak of FMD and also most likely to have the highest number of primary outbreaks. Turkey was considered to be the country outside Europe which was most likely to be the source of an outbreak within Europe as a whole, and the illegal importation of livestock was considered to be the most likely route of introduction of FMD into Europe. Results specific to the Islands group of countries, which included the UK and Ireland, suggested that this group was likely to have a mean of one primary outbreak of FMD in the five years from September 2000, and that the importation of foodstuffs by people entering those countries from Turkey was the most likely source of an outbreak.     

Simulated economic consequences of foot-and-mouth disease epidemics and their public control in France

The efficient management of foot-and-mouth disease (FMD) epidemics in France was examined through a simulation model which combines epidemiological and economic modules. From the reactions of the importing countries in terms of the products subject to import bans and the regionalization commitments, the economic module assesses the financial consequences of FMD outbreaks borne not only by the breeding sector but also by the other economic sectors on regional and national levels. Among the control options for FMD, the strategy of stamping out infected herds and dangerous in-contact herds most often contributes to reducing the economic consequences of FMD epidemics. Implementing a campaign of emergency vaccination is socially optimal if the additional export losses associated with the delay of slaughtering the vaccinated animals are offset by the gains of reducing the duration of the FMD epidemic. The importance of reducing as much as possible the total duration of the import bans is stressed by the estimated cost of an extra week of import bans. The optimal control strategy was unaffected by the introduction of stochastic parameters.     

Attitudes of New Zealand farmers to methods used to control wild rabbits

Four years after the release of Rabbit haemorrhagic disease virus (RHDV) in New Zealand, we conducted a mail survey of farmers to ascertain their attitudes and practices about rabbit control. A multistage sampling frame (stratified by rabbit-proneness and farm type) was used to select 828 farms in eight geographical regions. The useable response proportion of the survey was 69.3%, and 21% of respondents considered rabbits to be a problem on their farms. Although practices for rabbit control had changed from 1995 to 2001, shooting (practised by 85% of respondents) remained the predominant method used (albeit less frequently than in 1995). Ten percent of farmers used RHDV baiting; of those, 90% released the virus relatively infrequently. Farmers perceived shooting to be the most-humane and environmentally safe method, while RHDV was perceived to be the most effective. Perception of the level of competition for grazing between rabbits and livestock was the factor most-strongly associated with the use of shooting and RHDV. Most (60%) respondents considered the introduction of RHDV to have been beneficial.     

The potential extent of transmission of foot-and-mouth disease: a study of the movement of animals and materials in Southland, New Zealand

A survey of Southland farms was conducted to assess the potential for foot-and-mouth disease dissemination through normal movement patterns of farm animals and materials over a period similar to what would be expected from the time the virus arrived on a property to the time of diagnosis. Each farmer participating in the survey was required to complete a diary, recording all movements of people, animals and materials on to or off a farm during a 14-day period. The mean number of movements recorded per farm was 50. The distribution of movement distances showed the majority of movements occurred within the immediate neighbourhood of the origin, with 31.5% and 59.5% of all movements occurring within 5 km and 10 km respectively. In order to contain 95% of all movements, an area where movement was controlled would have to have a radius of 100 km. The data was then used to construct a spatial simulation model to study the movements off a hypothetical index farm. When secondary movements off primary destinations were included in the model, the mean number of movements to be traced to contain the disease was 100 (range 77-160) for a 14-day simulation period. The area required to contain 95% of all movements tended to increase slightly, depending on the length of simulation run. The mean number of high risk movements that occurred over the 100 km radius was 3.4.     

Potential impact of an introduction of foot-and-mouth disease into the California State Fair

OBJECTIVE: To estimate the potential spread of foot-and-mouth disease (FMD) if infected livestock had been exhibited at the 2005 California State Fair. DESIGN: Epidemic model. ANIMALS: Dairy cattle, dairy goats, and pygmy goats exhibited between August 24 and August 28 by 195 exhibitors. PROCEDURES: 2 stochastic models were used to simulate epidemics of FMD that might originate from 1, 3, 5, 7, or 10 index cases at the state fair. Data obtained from state fair exhibitors were used to determine the spatial distribution and types of herds to which livestock visiting the state fair returned. RESULTS: Mean estimated numbers of latently infected animals on day 5 were 12.3 and 75.9, respectively, when it was assumed that there were 1 and 10 index cases. Regardless of the number of index cases, mean estimated numbers of subclinically infected and clinically infected animals were low throughout the 5-day study period. Mean estimated duration of the resulting epidemic ranged from 111 to 155 days, mean number of infected premises ranged from 33 to 244, and mean probability that at least 1 animal that became infected with FMD would subsequently leave the state ranged from 28% to 96% as the number of index cases increased from 1 to 10, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that following introduction of FMD at the California State Fair, infection would likely go undetected until after animals left the fair and that the subsequent outbreak would spread rapidly.     

A survey of the methods used by farmers to castrate calves in New Zealand

AIMS: To identify the methods used to castrate calves and the age at which castration is carried out on farms in New Zealand. METHODS: A survey was carried out by questionnaire sent to the 14,000 recipients of Meat Matters produced by Meat New Zealand. The questionnaires on return were analysed on a national and regional basis. RESULTS: Of the 3,788 respondents, 74% (2,825) castrated calves on their farms. Of these 2,825 respondents 85% (2,403) used a rubber ring, 18% (512) carried out surgical castration and only a few respondents, 25, used a clamp. The ring was used on calves with an average age of 2.2 months and 93% of calves castrated by ring were castrated during the first 3 months of life. Surgical castration was carried out on calves with an average age of 4.3 months, 54% of them were castrated in the first 3 months of life and 39% during the following 3 months. Respondents from the West Coast (40%), Otago (38%) and Southland (50%) were more likely to use surgical castration than respondents from elsewhere (<17%). Local anaesthetic was used by only 3% (94) of respondents and a similar percentage employed a veterinarian to do the castration. CONCLUSIONS: There are marked regional differences in methodology used for castration of calves. The survey gives a sound basis for future research into humane and cost effective methods.     

Application of modelling to determine the absence of foot-and-mouth disease in the face of a suspected incursion

AIM: To use disease modelling to inform a response team about the number of animals per herd/flock to be examined, and the start date and duration of clinical surveillance required to be confident that foot-and-mouth disease (FMD) was not present on an island in New Zealand with a population of approximately 1,600 cattle, 10,000 sheep and a small number of pigs, goats and alpacas. METHODS: Because the probability of detecting clinical disease in (the) primary case(s) in larger herds and flocks was extremely low, deterministic and stochastic mathematical SLIR (susceptible, latent, infectious, recovered) models for the transmission of infection were constructed to estimate the date when clinical lesions in herds and flocks would be detected with 95% confidence. Surveillance targeted the first wave of infections following a suspect index case. RESULTS: If 70 cattle in herds of about 400 cattle were examined it was estimated it would take approximately 13 (90% stochastic range 9-19) days from first exposure before it would be possible to achieve 95% confidence for detecting clinical signs for a low-virulence virus, and 9 (7-14) days for a high-virulence virus. The duration of sufficiently accurate clinical detection was 17 (15-19) days and 13 (12-14) days for low- and high-virulence viruses, respectively. A sample of 70 sheep from flocks of >1,000 would be required to achieve clinical detection at about the same time but with a shorter period of detection than for cattle. The duration of effective detection could be increased by examining a larger sample in most sheep flocks, however the small size of many cattle herds in the study population limited the confidence of detecting group-level disease in cattle, therefore necessitating repeated herd inspections. The model suggested that group-level detection was not feasible if it was based on elevated body temperature alone because of short durations of fever in infected animals. CONCLUSION AND CLINICAL RELEVANCE: Simulation modelling is a useful and powerful tool for informing ongoing surveillance activities in the face of an exotic disease incursion. Results of modelling suggested to start clinical inspection activities at 4 days and to continue regular inspection twice a week for about 35 days after the date of first exposure, to satisfy the required 95% confidence threshold of clinical detection of FMD in cattle herds and sheep flocks.     

Diagnosis and screening of foot-and-mouth disease

Foot-and-mouth disease (FMD) diagnostic methods are reviewed. As the presence of clinical signs alone is inconclusive, laboratory diagnosis should always be carried out. The presence of FMD virus can be demonstrated by cell culture isolation, complement fixation test, ELISA or the more recent polymerase chain reaction (PCR) method. Serological diagnosis is also a valuable tool. The virus neutralization test has been replaced by ELISA and the antibody response to some viral non-structural proteins allows to discriminate between vaccinated and infected animals on a herd basis. More rapid and accurate tests as well as an earlier detection system in preclinical state are still needed.

Résumé

Les différentes méthodes de diagnostic de la FA (fièvre aphteuse) sont exposées. Le recours au laboratoire est indispensable; la seule présence de signes cliniques ne permettant pas d'établir le diagnostic. Le virus peut être mis en évidence par isolement en culture cellulaire, par le test de fixation du complément, l'ELISA ou la technique récente de polymérisation en chaine (PCR). La recherche des anticorps est aussi reconnue comme outil diagnostic. Le test de séroneutralisation a été supplanté par l'ELISA et la réponse anticorps contre certaines des protéines virales non structurales permet la différenciation entre troupeaux vaccinés et troupeaux infectés. Des tests plus rapides et précis, la possibilité de détecter le virus lors de la phase préclinique seraient d'utilité certaine.