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Oraby, Tamer; Al-Zoughool, Mustafa; Elsaadany, Susie; Krewski, Daniel
doi: 10.1080/15287394.2016.1173988pmid: 27556562
Bovine spongiform encephalopathy (BSE) appeared in the United Kingdom in the mid 1980s, and has been attributed to the use of meat and bone meal (MBM) in cattle feed contaminated with a scrapie-like agent. Import of infectious materials from a country where BSE has occurred is believed to be the major factor underlying the spread of the BSE epidemic to other countries. This study presents a new stochastic model developed to estimate risk of BSE from importation of cattle infected with the BSE agent. The model describes the propagation of the BSE agent through the Canadian cattle herd through rendering and feeding processes, following importation of cattle with infectious prions. This model was used estimate the annual number of newly infected animals each year over the period 1980–2019. Model predictions suggested that the number of BSE infections in Canada might have been approximately 40-fold greater than the actual number of clinically diagnosed cases. Under complete compliance with the 2007 ban on feeding MBM, this model further predicts that BSE is disappearing from the Canadian cattle system. A series of sensitivity analyses was also conducted to test the robustness of model predictions to alternative assumptions about factors affecting the evolution of the Canadian BSE epidemic.
Al-arydah, M.; Croteau, M. C.; Oraby, T.; Smith?, R. J.; Krewski, D.
doi: 10.1080/15287394.2016.1174001pmid: 27556563
The application of a recently developed mathematical model for predicting the spread of chronic wasting disease (CWD) in wild deer was assessed under different scenarios where harvesting is employed in disease management. A process-based mathematical model for CWD transmission in wild deer populations was recently developed and parameterized by Al-arydah et al. (2011) to provide a scientific basis for understanding the factors that affect spread of CWD and evaluate concomitant disease-control strategies. The impact of gender on CWD transmission was shown to have a significant influence on the spread of the disease in the wild. Our model demonstrates a range of harvesting rates in which CWD is controlled and deer populations survive. However, if harvesting rates are too low, the disease remains endemic for decades. Conversely, the Canadian deer population is eradicated if harvesting rates are excessive. Future investigation includes building the model to assess the spread of CWD under different disease-management scenarios.
Al-Zoughool, Mustafa; Oraby, Tamer; Krewski, Daniel
doi: 10.1080/15287394.2016.1174004pmid: 27556564
Seventeen typical cases of bovine spongiform encephalopathy (BSE) were detected in Canada the period of 2003-2011. The clinical incidence of BSE was censored by early slaughter, death, or exportation of infected cattle due to the long incubation period of BSE disease. The aim of this study was to estimate the infection incidence of BSE in birth cohorts during 1996–2004 and project infection frequency through to 2007. An estimate of the number of asymptomatic infected cattle slaughtered for human consumption is also provided. The number of incident, asymptomatic cases was assumed to follow a Poisson process. A Bayesian back-calculation approach was used to project the risk of contracting BSE in those birth cohorts. Model parameters and inputs were taken from scientific literature and governmental data sources. The projected number of infected cattle in birth cohorts spanning the period 1996–2007 was 492, with median 95% credible interval 258–830. If the requirement to remove specified risk material (SRM) from cattle prior to entering the food chain was not in place, the predicted number of slaughtered infected in the human food chain from 1996–2010 was 298, with a 95% credible interval 156–500. The magnitude of the BSE epidemic in Canada for 1996–2007 birth cohorts was estimated to be approximately 28-fold higher than the number of clinical cases detected through to October 2011. Although some of those cattle were slaughtered for human consumption, the requirement of SRM removal may have prevented most of the infectious material from entering the food chain.
Muringai, Violet; Goddard, Ellen
doi: 10.1080/15287394.2016.1174008pmid: 27556567
In this study, the objective was to examine whether or not changes in bovine spongiform encephalopathy (BSE) concerns exert an effect on people’s risk perceptions and risk attitudes regarding consuming beef in Canada, 8 years after finding the first domestic animal with BSE. Data were collected from two surveys (2071 respondents) conducted with the same respondents in 2008 and 2011 in Canada. Data on meat consumption for the same households were also available from the Nielsen Homescan panel over the period 2002 to 2009. Based on census data, the current sample is generally not representative of the Canadian population, but the sample is unique in that the same individuals responded to two surveys and there is an ability to track their evolving household purchases of beef before the first survey and between the two surveys. In essence, alterations in beef risk perceptions are significantly influenced by changes in concerns regarding (1) feed given to livestock, (2) animal diseases and BSE, (3) trust in manufacturers, the government, and farmers, and (4) demographic characteristics. There were significant differences in beef purchases across households, with alterations to their risk perceptions and risk attitudes. In conclusion, although the first domestic incident of BSE was in 2003, concerns regarding BSE are still contributing to consumers’ risk perceptions but not to their risk attitudes with respect to consumption of beef in 2011.
Chiu, Angie; Goddard, Ellen; Parlee, Brenda
doi: 10.1080/15287394.2016.1174011pmid: 27556568
Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) found in both farmed and wild deer, elk, and moose in the United States and Canada. Surveillance efforts in North America identified the geographical distribution of the disease and mechanisms underlying distribution, although the possibility of transmission to other cervids, including caribou, and noncervids, including humans, is not well understood. Because of the documented importance of caribou (Rangifer tarandus) to human populations in the northern regions of Canada, a risk-management strategy for CWD requires an understanding of the extent of potential dietary exposure to CWD. Secondary 24-h dietary recalls conducted among Inuvialuit and Inuit in 4 communities in the Northwest Territories and Nunavut were employed in this study. Econometric demand systems were estimated to model the impacts of individual- and community-level socioeconomic characteristics on expenditures on caribou and other foods, in order to examine the households’ ability to consume other foods in response to changing levels of caribou consumption. Thirty-five percent of respondents reported consuming caribou in the survey period, and caribou comprised, on average, 26% of daily dietary intake by weight, or approximately 65 g/d, across individuals in the 4 communities. Consuming caribou was also shown to exert positive impacts on dietary quality, as measured by calorie intake and dietary diversity. Communities with less access to employment, income and food stores are predicted to be constrained in their ability to obtain an adequate diet in the event of scarcity of caribou meat.
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ABSTARCTChronic wasting disease (CWD) is a neurodegenerative, protein misfolding disease affecting cervids in North America in epidemic proportions. While the existence of CWD has been known for more than 40 years, risk management efforts to date have not been able to curtail the spread of this condition. An expert elicitation exercise was carried out in May 2011 to obtain the views of international experts on both the etiology of CWD and possible CWD risk management strategies. This study presents the results of the following three components of the elicitation exercise: (1) expert views of the most likely scenarios for the evolution of the CWD among cervid populations in Canada, (2) ranking analyses of the importance of direct and indirect transmission routes, and (3) rating analyses of CWD control measures in farmed and wild cervids. The implications of these findings for the development of CWD risk management strategies are described in a Canadian context.
A high degree of uncertainty exists for chronic wasting disease (CWD) transmission factors in farmed and wild cervids. Evaluating the factors is important as it helps to inform future risk management strategies. Expert opinion is often used to assist decision making in a number of health, science, and technology domains where data may be sparse or missing. Using the “Classical Model” of elicitation, a group of experts was asked to estimate the most likely values for several risk factors affecting CWD transmission. The formalized expert elicitation helped structure the issues and hence provide a rational basis for estimating some transmission risk factors for which evidence is lacking. Considered judgments regarding environmental transmission, latency of CWD transmission, management, and species barrier were provided by the experts. Uncertainties for many items were determined to be large, highlighting areas requiring more research. The elicited values may be used as surrogate values until research evidence becomes available.