Wildlife surveillance systems : chronic wasting disease

Increased demand for animal disease surveillance information has led to the development and refinement of methodologies for qualitative and quantitative surveillance system evaluations to maximize efficiency and efficaciousness. The impetus for this surveillance evaluation project was chronic wasting disease (CWD) and the objectives were to apply both qualitative and quantitative methodologies to examine the components of CWD surveillance in Saskatchewan. A retrospective review of deer pathology and hunter-harvest submissions in Saskatchewan was conducted through the Canadian Cooperative Wildlife Health Centre. Qualitative evaluation methods outlined by Klauke et al (1988) were used and included key stakeholder interviews. A quantitative evaluation, with specific focus on disease detection, was conducted to examine system sensitivity, confidence of disease freedom and to compare system components using methods described by Martin et al (2007). The analysis was conducted using a scenario tree and Monte Carlo simulation. Sampling rates of dead and clinically ill deer were low with a high degree of variability by season, year, location and nature of submissions. Ultimately, variability of submission patterns likely affected when and where diseases were detected. Poor data quality reduced the amount of available data for analysis but quality dramatically improved over time. The surveillance evaluation demonstrated that the current surveillance system places more emphasis on monitoring trends in CWD-positive areas, at the expense of early detection. This is explained mostly by the coupling of disease control efforts and surveillance, in that harvests are heavily focused in CWD-positive areas. The system is not sufficient to detect disease in new areas where the disease prevalence is low, primarily due to low submission rates. The quantitative evaluation found that overall sensitivity of the surveillance system and confidence of disease freedom was highly dependent on detection prevalence and the ongoing risk of disease introduction. Surveillance in the eastern part of Saskatchewan was not adequate from 1997-2006 to detect CWD at 0.5-1% prevalence. However, if risk of CWD introduction over this time period was assumed to be low, it can be concluded that the prevalence in this region was not 5% or higher. A detection goal of 0.5-1% prevalence is an ambitious surveillance goal, especially in areas where the risk of disease introduction is high. The use of more targeted surveillance strategies should be further explored to help better meet surveillance these surveillance objectives