A Weighted Surveillance Approach for Detecting Chronic Wasting Disease Foci

Abstract

ABSTRACT:A key component of wildlife disease surveillance is determining the spread and geographic extent of pathogens by monitoring for infected individuals in regions where cases have not been previously detected. A practical challenge of such surveillance is developing reliable, yet cost-effective, approaches that remain sustainable when monitoring needs are prolonged or continuous, or when resources to support these efforts are limited. In order to improve the efficiency of chronic wasting disease (CWD) surveillance in Colorado, United States, we developed a weighted surveillance system exploiting observed differences in CWD prevalence across demographic strata within infected mule deer (Odocoileus hemionus) populations. We used field data to estimate sampling weights for individuals from eight demographic strata distinguished by differences in apparent health, sex, and age. In this system, individuals from a sample source with high prevalence and low inclusion probability (e.g., clinical CWD ''suspects'') received $10.3 times more weight than those from a source with low prevalence and high inclusion probability (e.g., apparently healthy, hunter-harvested individuals). We simulated use of this alternative surveillance system for a deer management unit in Colorado and evaluated the potential effects of using biased weights on the probability of failing to detect CWD and on relative surveillance costs. We found that this system should be transparent, cost-effective, and reasonably robust to the inadvertent use of biased weights. By implementing this, or a similar, weighted surveillance system, wildlife agencies should be able to maintain or improve current surveillance standards while, perhaps, collecting and examining fewer samples, thereby increasing the efficiency and costeffectiveness of ongoing CWD surveillance programs.

Surveillance for Highly Pathogenic Avian Influenza in Wild Turkeys (Meleagris gallopavo) of Minnesota, USA during 2015 Outbreaks in Domestic Poultry

“…Additionally, if individuals involved in a morbidity or mortality event have a higher probability of being infected with influenzas of interest, including samples from these events may increase the overall probability of detection of the surveillance program. These types of differential probabilities of infection between apparently healthy and sick individuals have been exploited for other wildlife diseases to maximize the efficiency of detection surveillance efforts [15]. However, passive surveillance is only useful when the goal of a surveillance program is detection of a pathogen.…”

Seeded Amplification of Chronic Wasting Disease Prions in Nasal Brushings and Recto-anal Mucosa-Associated Lymphoid Tissues from Elk by Real-Time Quaking-Induced Conversion

“…CWD was first described nearly 50 years ago as a fatal, wasting, spongiform encephalopathy of cervids in Colorado and Wyoming (4). The disease has since been documented in 23 U.S. states, 2 Canadian provinces, and, via exportation of farmed cervids, the Republic of Korea (5)(6)(7)(8). Four of the 23 states (Texas, Iowa, Pennsylvania, and Ohio) were considered CWD free prior to 2012, with primary cases in three of these states reportedly arising in farmed cervids (9)(10)(11).…”

Surveillance and Monitoring of White-Tailed Deer for Chronic Wasting Disease in the Northeastern United States

“…After years of USDA-funded testing, Colorado documented a 90% reduction in samples submitted for CWD testing in response to a sample fee of US$25 that was imposed on hunters that wanted their deer tested (CDPW 2011). States in the Northeast may alter surveillance efforts with an emphasis on weighted (Walsh and Miller 2010) or targeted surveillance to reduce sample size and cost, and others that are at risk for CWD infection may not continue surveillance without the availability of federal funding.…”

“…Weighted sampling efforts appear to be warranted in areas that are at the greatest risk for CWD infection based on associations of CWD with environmental and landscape covariates (Osnas et al 2009;Walsh and Miller 2010;Walter et al 2011). For example, a 1% increase in clay particle content increased odds of infection by up to 8.9% in mule deer in Colorado, because clay soil binds the infectious prion that causes CWD, making it bioavailable for long durations (Walter et al 2011).…”

“…Alternate methods included use of weighted surveillance in New York (e.g., testing of high-risk deer based on sex and age; Walsh and Miller 2010), testing of roadkilled deer, and targeted surveillance of deer exhibiting signs characteristic of CWD. West Virginia and Pennsylvania were the only states in the Northeast that detected CWD in road-killed deer, totaling three positive cases since 2005.…”