CWD and New Developments in Disease Diagnostics

By Deepanker Tewari

In this inaugural blog from our flagship organization journal, the American Association of Veterinary Laboratory Diagnosticians (AAVLD)’s Journal of Veterinary Diagnostic Investigation, I am choosing to highlight chronic wasting disease (CWD), an infectious prion disease affecting cervids that has a big impact on big-game and deer farmers. CWD is the same group of fatal diseases as mad cow disease in cattle and Creutzfeldt-Jakob disease in humans. CWD is limited to cervids and infects deer, elk, reindeer, moose, etc. Disease was noticed first in North America and has now been detected in Europe (Norway) and Asia (South Korea). In the United States, the disease footprint has been expanding steadily both in captive and wild populations.

Even though human infection has not been recorded with CWD, disease management is important to reduce the spread and burden of prions in our environment. The disease was first detected as a fatal wasting syndrome of deer in the 1960s. The late stages of disease involve histopathologic changes in neural tissues as seen with other transmissible spongiform encephalopathy (TSE) diseases along with clinical signs in affected animals. However, what is interesting with CWD is that lymphoid tissue precedes neural tissue in showing accumulation of abnormal prion protein. Official diagnosis in the United States is accomplished at postmortem with immunohistochemistry (IHC) in obex and lymph nodes. Also, an infected animal sheds prion in excreta and urine thus creating the potential for earlier detection with antemortem testing.

Amplification-based detection methods are now beginning to take root in diagnostic labs for CWD detection. We recently interacted with 6 other laboratories in the United States that have also been at the forefront of evaluating these technologies in a diagnostic setting to improve detection of prions. Besides improving detection, antemortem detection is also a focus for improving disease control and management. With such approaches, my lab’s exposure to this new technique started with us evaluating the application of real-time quaking-induced conversion (RT-QuIC) for detection of CWD and collaborating with Drs. Ed Hoover (Colorado State University, CSU) and Davin Henderson (previously at CSU and now at CWD Evolution Inc.). The technique, as depicted in Figure 1, simply relies on amplifying the abnormal prions in the presence of recombinant prion protein with quaking and measuring the amplification at the end.

Working with the wildlife group in Pennsylvania, we had access to tissues, which we had characterized already with IHC and enzyme-linked immunosorbent assay (ELISA). We took these specimens and subjected them to RT-QuIC and, to our surprise, saw 100% sensitivity and specificity using this methodology. With previous work focusing on the influence of genotype on genetic resistance, we investigated whether Pennsylvania (PA) deer were all homozygous in the limited population we were examining; we did notice some diversity for codons that are said to afford some relative resistance against disease, but we also found that these animals did get infected, thus showing us that the genotypes under study would not offer complete resistance to disease. To us, this opens up possibilities of exploring the new method for application for testing antemortem samples (e.g., feces and urine) or even easier-to-obtain tissue specimens like recto-anal mucosal-associated tissues, eyelids and skin, etc., and building some predictive tools for assessing infections on the farm. By working together with others having similar interests, we are hoping this testing modality will find use in routine animal diagnostics soon.

Article details

Detection by real-time quaking-induced conversion (RT-QuIC), ELISA, and IHC of chronic wasting disease prion in lymph nodes from Pennsylvania white-tailed deer with specific PRNP genotypes

Deepanker Tewari, David Steward, Melinda Fasnacht, Julia Livengood

First Published June 2, 2021

DOI: 10.1177/10406387211021411

Journal of Veterinary Diagnostic Investigation

About the author

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Deepanker Tewari, BVSc, PhD is a board-certified veterinarian in the American College of Veterinary Microbiologists (ACVM). He has trained at Cambridge University, Penn State, and Haryana Agricultural University and has worked at the Rockefeller University and National Institutes of Health. He currently serves as the Lab Director at the Pennsylvania Veterinary Laboratory, part of the Pennsylvania Animal Diagnostic Laboratory System, and is an adjunct Professor at Penn State. Dr Tewari is past president of the AAVLD, has also served the ACVM and the National Animal Health Laboratory Network (NAHLN). Dr. Tewari’s main interests are emerging infections, One Health, and enhancing disease preparedness.