[show abstract][hide abstract] ABSTRACT: Great Britain has been rabies-free since 1922, which is often considered to be in part due to the strict laws requiring that imported cats and dogs be vaccinated and quarantined for 6 months immediately on entry into the country. Except for two isolated incidents, this quarantine policy has contributed to ensuring that Great Britain has remained free of rabies. In 2000, amendments to the UK quarantine laws were made and the Pet Travel Scheme (PETS) was launched for companion animals traveling from European Union countries and rabies-free islands. Since its introduction, it has been proposed that other countries including North America should be included within the UK scheme. A quantitative risk assessment was developed to assist in the policy decision to amend the long-standing quarantine laws for dogs and cats from North America. It was determined that the risk of rabies entry is very low and is dependent on the level of compliance (i.e., legally conforming to all of the required regulations) with PETS and the number of pets imported. Assuming 100% compliance with PETS and the current level of importation of cats and dogs from North America, the annual probability of importing rabies is lower for animals traveling via PETS (7.22 x 10(-6), 95th percentile) than quarantine (1.01 x 10(-5), 95th percentile). These results, and other scientific evidence, directly informed the decision to expand the PETS scheme to North America as of December 2002.
[show abstract][hide abstract] ABSTRACT: The use of antibiotics for animal growth promotion has been controversial because of the potential transfer of antibiotic resistance from animals to humans. Such transfer could have severe public health implications in that treatment failures could result. We have followed a risk assessment approach to evaluate policy options for the streptogramin-class of antibiotics: virginiamycin, an animal growth promoter, and quinupristin/dalfopristin, a antibiotic used in humans. Under the assumption that resistance transfer is possible, models project a wide range of outcomes depending mainly on the basic reproductive number (R(0)) that determines the potential for person-to-person transmission. Counter-intuitively, the benefits of a ban on virginiamycin were highest for intermediate values of R(0), and lower for extremely high or low values of R(0).
International Journal of Antimicrobial Agents 10/2004; 24(3):205-12. · 4.42 Impact Factor
[show abstract][hide abstract] ABSTRACT: The emergence of antimicrobial-resistant microorganisms in both humans and food animals is a growing concern. Debate has centred on links between antimicrobial use in the production of food animals and the emergence of resistant organisms in the human population. Consequently, microbial risk assessment (MRA) is being used to facilitate scientific investigations of the risks related to the food chain, including quantification of uncertainty and prioritization of control strategies. MRA is a scientific tool that can be used to evaluate the level of exposure and the subsequent risk to human health relating to a specific organism or particular type of resistance. This paper reviews the recent applications of MRA in the area of antimicrobial resistance, and in particular, it focuses on the methods, assumptions and data limitations. Since MRA outputs are dependent on the quality of data inputs used in their development, we aim to promote the generation of good quality data by describing the properties that data should ideally possess for MRA and by highlighting the benefit of data generation specifically for inclusion in MRAs.
Journal of Antimicrobial Chemotherapy 07/2004; 53(6):906-17. · 5.34 Impact Factor
[show abstract][hide abstract] ABSTRACT: Great Britain (GB) has been "Officially Brucellosis Free" (OBF) since 1991; because this disease has both public-health and international-trade implications, it is in the country's interest to maintain this freedom. A quantitative risk-assessment model was developed to determine the annual risk of importing brucellosis-infected breeding cattle into GB from Northern Ireland and the Republic of Ireland. (These countries exported the largest number of cattle into GB and were not brucellosis free during the development of the assessment in 2000.) We predicted that we can expect to import brucellosis from Northern Ireland every 2.63 years (1.89, 4.17) and from the Republic of Ireland, every 3.23 years (2.13, 5.88). The estimates of risk are sensitive to the assumed proportion of animals missed during routine surveillance that originate from OBF herds and the uncertainty associated with the surveillance test sensitivities. As a result of the assessment, the Department for Environment, Food and Rural Affairs (Defra) introduced post-calving testing for all cattle imported into British herds.
Preventive Veterinary Medicine 05/2004; 63(1-2):51-61. · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: Brucellosis is a widespread, economically devastating and highly infectious zoonosis. In cattle, infection predominantly is caused by Brucella abortus, and is usually detected in pregnant females through abortions. Great Britain (GB) has been declared free from brucellosis (officially brucellosis free (OBF)) since 1993 and as such is required by European Union (EU) regulations to test > or =20% of both beef and dairy cattle >24 months old routinely. Currently, however, GB serologically tests more cattle than required and the issue of reducing the level of testing has come under consideration. We developed a simulation model to determine the rate of spread of brucellosis under a variety of testing regimes. For dairy herds, we found that reducing the level of testing would have a major effect on the rate of spread of infection, should it be imported. For beef herds, reducing the level of testing would have much less effect. We also found that abortion notification is a very-important additional means of surveillance. As a result of our predictions, policy-makers decided not to reduce the level of testing and actively to promote abortion notification.
Preventive Veterinary Medicine 04/2004; 63(1-2):63-73. · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: The risk of dispersing foot-and-mouth disease virus into the atmosphere, and spreading it to susceptible holdings as a result of burning large numbers of carcases together on open pyres, has been estimated for six selected pyres burned during the 2001 outbreak in the UK. The probability of an animal or holding becoming infected was dependent on the estimated level of exposure to the virus predicted from the concentrations of virus calculated by the Met Office, Bracknell. In general, the probability of infection per animal and per holding decreased as their distance from the pyre increased. In the case of two of the pyres, a holding under the pyre plumes became infected on a date consistent with when the pyre was lit. However, by calculating their estimated probability of infection from the pyres it was concluded that it was unlikely that in either case the pyre was the source of infection.
The Veterinary record 03/2004; 154(6):161-5. · 1.80 Impact Factor
[show abstract][hide abstract] ABSTRACT: European directives require that all veterinary medicines be assessed to determine the harmful effects that their use may have on the environment. Fundamental to this assessment is the calculation of the predicted environmental concentration (PEC), which is dependent on the type of drug, its associated treatment characteristics, and the route by which residues enter the environment. Deterministic models for the calculation of the PEC have previously been presented. In this article, the inclusion of variability and uncertainty within such models is introduced. In particular, models for the calculation of the PEC for residues excreted directly onto pasture by grazing animals are considered and comparison of deterministic and stochastic results suggest that uncertainty and variability cannot be ignored.
[show abstract][hide abstract] ABSTRACT: European directives require that all veterinary medicines be assessed to determine the harmful effects that their use may have on the environment. Fundamental to this assessment is the calculation of the predicted environmental concentration (PEC).
[show abstract][hide abstract] ABSTRACT: 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.
The Veterinary record 07/2002; 150(25):769-72. · 1.80 Impact Factor
[show abstract][hide abstract] ABSTRACT: The relationships between the inhaled dose of foot and mouth disease virus and the outcomes of infection and disease were examined by fitting dose-response models to experimental data. The parameters for both the exponential and beta-poisson models were estimated using maximum likelihood and Bayesian methods. The median probability of infection given a single inhaled TCID50 was estimated to be 0.031 with 95% Bayesian credibility intervals (CI) of 0.018-0.052 for cattle, and 0.045 (CI = 0.024-0.080) for sheep. These estimates were used to construct dose-response curves and uncertainty distributions for use in quantitative risk assessments.
Epidemiology and Infection 05/2002; 128(2):325-32. · 2.87 Impact Factor
[show abstract][hide abstract] ABSTRACT: Quantitative risk assessments estimate the probability of unwanted events occurring and stochastic modelling can incorporate real-life uncertainty and variability into these estimates. There is now a focus on whether these techniques can be applied successfully to the risks associated with food-borne microbiological hazards. With microbiological food-risk assessments, in order to assess the risk to human health, it is not only necessary to estimate the probability of the organisms being present at each stage of the food production pathway, but also to estimate the burden of organisms present at each stage. We are currently undertaking a risk assessment of the risks to human health consequent upon the presence of campylobacters in on-farm poultry. This paper will examine the initial model framework and the methodological issues arising from the complexity of the risk assessment pathway.
International Biodeterioration & Biodegradation. 01/2002;
[show abstract][hide abstract] ABSTRACT: A quantitative risk assessment model investigating the risk of human infection with campylobacter from the consumption of chicken meat/products is currently being formulated. Here such an approach is used to evaluate the probability that a random bird, selected at slaughter from Great Britain's national poultry flock, will be campylobacter-positive. This is determined from the probability that a flock chosen at random contains at least one colonized bird and the within-flock prevalence of such a flock at slaughter. The model indicates that the probability bird chosen at random being campylobacter-positive at slaughter is 0.53. This probability value has associated uncertainty, the 5th percentile being 0.51 and the 95th percentile 0.55. The model predicts that delaying the age at first exposure to campylobacter can have a significant impact on reducing the probability of a bird being campylobacter-positive at slaughter. However, implementation of current biosecurity methods makes this difficult to achieve.
Epidemiology and Infection 11/2001; 127(2):195-206. · 2.87 Impact Factor
[show abstract][hide abstract] ABSTRACT: A computer simulation model which describes the spatial and temporal variation in the extent of listerial contamination within a damaged silage bale is presented. The silage bale is assumed to be split into a number of distinct sites and these sites are represented by a two dimensional lattice structure. Each site is classified in relation to its listerial composition. This classification results in three states which are dormant, active and unpopulated. Sites change state as a result of the movement of oxygen through the bale. This movement is initiated when a hole is punched in the plastic covering of the bale. The model is stochastic in nature and at any time following damage, the proportion of the bale which is contaminated is calculated. Furthermore, the spatial distribution of contaminated sites is predicted. The models are a first attempt at introducing structure into the selection process for feeding silage. We highlight areas of future research which will be invaluable for validation and practical use of the model.
[show abstract][hide abstract] ABSTRACT: We consider the problem of fitting mathematical models for bacterial growth and decline to experimental data. Using models which represent the phases of the growth and decline cycle in a piecewise manner, we describe how least-squares fitting can lead to potentially misleading parameter estimates. We show how these difficulties can be overcome by extending a data set to include hypothetical observations (dummy data points) which reflect biological beliefs, and the resulting stabilization of parameter estimates is analysed mathematically. The techniques are illustrated using real and simulated data sets.
IMA journal of mathematics applied in medicine and biology 07/1999; 16(2):155-70.