A review of chronic wasting disease (CWD) spread, surveillance, and control in the United States captive cervid industry

Figures & data

Figure 1. Percent change in the number of captive cervids, by state, between 2002 and 2007, with states reporting cases of chronic wasting disease (CWD) in 2007 indicated with diagonal lines (adapted from Anderson and Chomphosy, 2014).

Figure 2. Flowchart outlining literature screening process and outcomes.

Table 1. Peer-reviewed primary research articles addressing the spread, surveillance, and control of chronic wasting disease (CWD) in captive cervid facilities in the U.S. published as of November 2023.

Topic	Analysis	Authors (Year) [Citation]
Diagnostic testing	‘ … evolution of diagnostic tests for chronic wasting disease … ’	Haley and Richt (2017) [11]
	‘ … compare ELISA, IHC, and RT-QuIC … ’	Holz et al. (2022) [30]
Fencing	‘ … animal-activated cameras to estimate rates of interaction between wild and farmed deer … ’	Vercauteren et al. (2007) [31]
	‘ … effectiveness of a baited electric fence … for reducing fence-line contact between elk.’	Fischer et al. (2011) [32]
	‘ … secondary electric fence to prevent contacts in white‐tailed deer … ’	Khouri et al. (2022) [33]
Genetics	‘ … infection status and disease stage … correlate our findings with PRNP genotype … ’	Haley et al. (2019) [22]
	‘ … prion genotype was strongly linked to progression of prion accumulation in the obex … ’	Keane et al. (2008) [19]
	‘ … genome-wide association analyses … ’	Seabury et al. (2020) [34]
	‘ … selective breeding program for farmed white-tailed deer … ’	Haley et al. (2021)
	‘ … custom Affymetrix Axiom single-nucleotide polymorphism array … ’	Seabury et al. (2022) [35]
Preventive treatment	‘ … infection rates … receiving pentosan polysulfate, tannic acid, tetracycline HCl, or no treatment … ’	Wolfe et al. (2012) [36]
	‘ … ability of CWD-infected brain material to pass through the gastrointestinal tract of coyotes … ’	Nichols et al. (2015) [20]
	‘ … incidence and disease course … while being maintained on sustained-release Cu boluses or unsupplemented … ’	Wolfe et al. (2020) [37]
Spread and surveillance	‘ … sustained horizontal transmission of CWD most plausibly explained epidemic dynamics … ’	Miller et al. (2004) [18]
	‘ … graph theory in the context of infectious disease epidemics of farmed animals … ’	Rorres et al. (2018) [38]
	‘ … time aggregated network analysis … ’	Makau et al. (2020) [39]
	‘ … qualitative risk assessment for CWD transmission to cervid farms … ’	Kincheloe et al. (2021) [40]
	‘ … risk factors related to multiple pathways of CWD transmission to farmed cervid herds.’	Schultze et al. (2023) [21]
Vaccination	‘ … CWD vaccines consisting of cervid prion peptide sequences … ’	Pilon et al. (2013) [41]
	‘ … orally inoculated with attenuated Salmonella expressing PrP … ’	Goñi et al. (2015) [42]
	‘ … oral immunization of white-tailed deer … ’	Taschuk et al. (2017) [43]
	‘ … novel CWD vaccine in elk … targets a YYR disease-specific epitope to induce antibody responses … ’	Wood et al. (2018) [44]

Figure 3. Overview of chronic wasting disease (CWD) transmission routes to uninfected captive cervid herds.

Table 2. Qualitative risk assessment of chronic wasting disease (CWD) for captive cervid facilities in Minnesota and Wisconsin, USA, between 2002 and 2019 [40].

Transmission Pathway	Risk Type	Risk Level	Uncertainty	Exposure Type	Farms
Introduction of farmed cervids	Direct	High	Low	From farm later found to be CWD-positive	35%
		Moderate	High	From farms with no CWD test positive animals in prior 5 years	50%
		Negligible	Low	No record of introductions from other farms in prior 5 years	15%
Contact with wild cervids from farm location <80 km from detection of a CWD-positive wild cervid		High	Low	Farmed cervid escapes/re-entry or wild cervid entry	24%
		Moderate	High	Single perimeter fencing	41%
		Negligible	Low	Double perimeter fencing or >80 km^2 from wild CWD-positive	35%
Introduction of cervid parts	Indirect	High	Low	From <80 km from CWD-positive wild cervids	6%
		Moderate	High	From other areas	3%
		Negligible	Low	No introductions	91%
Introduction of contaminated fomites or scavenger entrance		High	Low	From CWD-positive farms	?
		Moderate	High	From locations <80 km from CWD-positive wild cervids or farms with no CWD positives
		Negligible	Low	No indirect contacts

Table 3. Risk levels of chronic wasting disease (CWD) experienced by captive cervid farms in Minnesota and Wisconsin, USA, between 2002 and 2019 [40].

State	Risk Level	Farms Experiencing Risk (%)
Minnesota	High	75%
	Moderate	13%
	Negligible	13%
Wisconsin	High	50%
	Moderate	50%
	Negligible	0%

Figure 4. Contact networks between captive cervid farms in Pennsylvania, USA (Panel A), with the largest strongly connected component (139 farms) shown in blue (Panel B), between 2003 and 2011 [38].

Figure 5. Timeline of chronic wasting disease (CWD) in North America and diagnostic test development.

Caption: Immunohistochemistry (IHC), enzyme-linked immunosorbent assay (ELISA), western blot (WB), protein misfolding cyclic amplification (PMCA), and real-time quaking-induced conversion (RT-QuIC). States, provinces, and countries are indicated as follows: United States of America (orange), Canada (blue), and outside North America (yellow). Timeline adapted from Haley and Richt (2017), Hibler et al., 2003, CWD Alliance, and Rivera et al. (2019).

Figure 6. Summary of identified risk factors based on their biological plausibility to spread CWD (adapted from EFSA 2019 [49]).

Figure 7. National-level regulation for chronic wasting disease in the U.S., as of 2023.

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