CWD Management in Illinois: Improving Turnaround Time

In an effort to protect the health of the Illinois white-tailed deer herd from chronic wasting disease (CWD), the Illinois Department of Natural Resources (IDNR) is constantly evaluating and improving the CWD surveillance and the adaptive management program to decrease the spread and impact of CWD. In Illinois, CWD surveillance uses three sources of data, hunter harvest, suspect deer, and special permit CWD surveillance, to help identify occurrence and introduction of CWD to new areas¹. Furthermore, CWD surveillance informs the adaptive management to focus localized efforts and remove CWD-infected animals via sharpshooting—within a 2-section buffer zone around a known CWD-positive section (1 section = ~1 mile²).¹ For almost 20 years, IDNR used Immunohistochemistry (IHC) as the diagnostic test for CWD. However, since July 1^st, 2020, IDNR began using both IHC and ELISA (with a confirmatory IHC test) in their CWD diagnostic tools. The main goal was to improve the turnaround time of diagnostic results for hunters, meat processors, and State wildlife managers.

What is CWD, and how is managed in Illinois?

CWD is a highly transmissible spongiform encephalopathy (TSE) that affects deer, moose, and elk. CWD has been expanding through the United States since first recognized in farmed mule deer (Odocoileus hemionus hemionus) and black-tailed deer (Odocoileus hemionus columbianus) in Colorado and Wyoming in 1967.² As of September 2021, CWD has been identified in 26 states in the United States. Illinois identified the first CWD case in wild white-tailed deer (Odocoileus virginianus) in 2002.³ As of October 1, 2021, there were 19 Illinois counties infected with CWD.

Since 2002, the CWD management program has used a localized management program conducted between January and March, following the hunter harvest seasons. During the localized management program, deer are removed in the target areas only with the permission of the landowner. The samples obtained during hunter-harvest and sharpshooting seasons (localized focus culling) provide data for researchers and managers to better understand CWD transmission and implement strategies to slow down CWD propagation, preventing further geographical spread.

CWD infectious agent: prions

CWD is a prion disease with no cure or treatment and causes a chronic and slow-wasting process that always leads to death. The infectious protein that causes CWD (PrP^CWD) is resistant to degradation and is a misfolded form of the normal cellular protein PrP^C. After infection, animals develop characteristic neurodegenerative changes at all central nervous system (CNS) levels, especially in the brain. Although, with time, peripheral accumulation of the infective prion protein can be found in other tissues. Gold-standard tissues for postmortem identification of CWD-affected animals include the obex (part of the medulla oblongata where the brain joins with the spinal cord) and the retropharyngeal lymph nodes (RLN).⁴

CWD diagnostic tests used in Illinois: IHC and ELISA

There are multiple diagnostic strategies to detect CWD— these include antibody-antigen interaction methods like Immunohistochemical (IHC), enzyme-linked immunosorbent assay (ELISA), and western blotting. However, more recent diagnostic techniques, such as the protein misfolding cyclic amplification (PMCA)⁵ and real-time quaking induced conversion (RT-QuIC)⁶ have been used to explore antemortem prion protein detection⁷ and to further CWD research under laboratory experimental conditions.

IHC and ELISA of brainstem and RLN are considered the gold-standard postmortem methods for CWD diagnosis and are the only two diagnostic tools approved by the USDA for CWD surveillance testing.⁸ Since the fall of 2002, in Illinois, wild white-tailed deer samples were evaluated using IHC staining (Figure 1). At the time, CWD testing was conducted by the Illinois Department of Agriculture’s Animal Disease Laboratories at Galesburg or Centralia. After both Animal Disease Laboratories closed in June 2016, the Veterinary Diagnostic Laboratory at the University of Illinois Urbana-Champaign (VDL) continued with the IHC CWD diagnostic work starting on July 1^st, 2016 (FY 2017).

During FY 2021 (from July 1st, 2020, to June 30th, 2021), in partnership with Wisconsin Veterinary Diagnostic Laboratory (WVDL) and the University of Missouri Veterinary Medical Diagnostic Laboratory (VMDL), the IDNR surveillance management program improved the turnaround time of results of CWD by using a combination of ELISA (Figure 2) for large scale hunter harvest surveillance and IHC for special permit surveillance (Special permit from IDNR)¹ and suspect deer surveillance.

Since IHC serves as the gold standard diagnostic test, all ELISA positive test results must be confirmed by IHC. Therefore, samples from animals that tested positive from ELISA are fixed in formalin and then analyzed using IHC. Using both diagnostic tools provide IDNR with a faster turnaround test result for all negative samples, allowing the laboratories to spend more time confirming suspect positive ELISA test results with IHC (Table 1 and Table 2)

Example 1, within one week of the kill date (a 7-day period), 29.5% of test results were sent to IDNR during FY 2021 (Table 1). This percent is greater compared with the previous 6 FY (2015 to 2020). Example 2, during FY 2021, only 4.3% of test results were sent to IDNR on week 6 of the kill date (from the remaining samples to be tested). This is also a lower percentage compared to previous FYs. Furthermore, the cumulative percent of CWD-test results (Table 2) indicate that by week 6 of the kill date, 93.1% of samples had CWD-test results. Moreover, by week 12 of the kill date, 99.6% of samples had CWD-test results compared to the previous five FYs. During FY 2021, most of the samples received were processed within the first 2 weeks after the kill date (Figure 3). Therefore, for 2021 there are fewer test results received in the last weeks (Table 1), but a higher percentage of all the samples with completed test results by weeks 10 to 12 (Table 2).

Some advantages of including the ELISA test are that ELISA uses fresh tissue, eliminating exposure to Formaldehyde for those taking and processing the samples. Furthermore, fresh samples can be shipped frozen and stored in less expensive containers (e.g., Whirl-Pak bags). Thus, they require less storage space and, therefore, reduce shipping costs. In addition, ELISA typically has a 4-day turnaround for results depending on the capacity of the diagnostic laboratory. IHC, on the other hand, requires formalin-fixed tissue, shipping and handling of samples may cause exposure to chemicals, sample storage requires more space than frozen samples, and shipping costs are higher than for frozen samples. Furthermore, IHC typically has a 14-day turnaround for results depending on the capacity of the diagnostic laboratory.

References:

1. Illinois Chronic Wasting Disease (CWD): 2019-2020 Surveillance and Management Report. Available online: https://www2.illinois.gov/dnr/programs/CWD/Documents/2019-2020%20CWD%20Annual%20Summary.pdf
2. Rivera, N.A., Brandt, A.L., Novakofski, J.E. and Mateus-Pinilla, N.E., 2019. Chronic wasting disease in cervids: Prevalence, impact and management strategies. Veterinary Medicine: Research and Reports, 10, p.123.
3. Mateus-Pinilla, N., Weng, H.Y., Ruiz, M.O., Shelton, P. and Novakofski, J., 2013. Evaluation of a wild white-tailed deer population management program for controlling chronic wasting disease in Illinois, 2003–2008. Preventive Veterinary Medicine, 110(3-4), pp.541-548.
4. Fox, K.A., Jewell, J.E., Williams, E.S. and Miller, M.W., 2006. Patterns of PrPCWD accumulation during the course of chronic wasting disease infection in orally inoculated mule deer (Odocoileus hemionus). Journal of General Virology, 87(11), pp.3451-3461.
5. Morales, R., Duran-Aniotz, C., Diaz-Espinoza, R., Camacho, M.V. and Soto, C., 2012. Protein misfolding cyclic amplification of infectious prions. Nature protocols, 7(7), pp.1397-1409.
6. Schmitz, M., Cramm, M., Llorens, F., Müller-Cramm, D., Collins, S., Atarashi, R., Satoh, K., Orru, C.D., Groveman, B.R., Zafar, S. and Schulz-Schaeffer, W.J., 2016. The real-time quaking-induced conversion assay for detection of human prion disease and study of other protein misfolding diseases. Nature protocols, 11(11), pp.2233-2242.
7. Kramm, C., Soto, P., Nichols, T.A. and Morales, R., 2020. Chronic wasting disease (CWD) prion detection in blood from pre-symptomatic white-tailed deer harboring PRNP polymorphic variants. Scientific Reports, 10(1), pp.1-8.
8. AFWA Technical Report on Best Management Practices for Prevention, Surveillance, and Management of Chronic Wasting Disease. Available online: https://www.fishwildlife.org/application/files/9615/3729/1513/
   AFWA_Technical_Report_on_CWD_BMPs_FINAL.pdf

Figure 1 and Figure 2: Wildlife Veterinary Epidemiology Laboratory, Illinois Natural History Survey, University of Illinois at Urbana-Champaign. Available online: https://publish.illinois.edu/wildlifevetlab/resources/

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Dr. Nelda Rivera‘s research focuses on the ecology and evolution of new and re-emerging infectious diseases and the epidemiology of infectious diseases, disease surveillance, and reservoir hosts’ determination. She is a member of the Wildlife Veterinary Epidemiology Laboratory and the Novakofski & Mateus Chronic Wasting Disease Collaborative Labs. She earned her M.S. at the University of Illinois at Urbana-Champaign and D.V.M at the University of Panamá, Republic of Panamá.

Dr. Nohra Mateus-Pinilla is a veterinary Epidemiologist working in wildlife diseases, conservation, and zoonoses. She studies Chronic Wasting Disease (CWD) transmission and control strategies to protect the free-ranging deer herd’s health. Dr. Mateus works at the Illinois Natural History Survey- University of Illinois. She earned her M.S. and Ph.D. from the University of Illinois Urbana-Champaign.

William Brown is a Geographic Information Systems (GIS) manager in the Department of Pathobiology at the College of Veterinary Medicine, University of Illinois at Urbana-Champaign. He has more than 25 years of experience in GIS and collaborates with researchers studying vector borne and zoonotic disease and other diseases of wildlife. He also provides GIS and data analysis support to local health departments.