Study advances CWD prion testing in preserved lymph nodes

A newly published study suggests chronic wasting disease testing may become more practical when only preserved lymph node samples are available. In the Journal of Veterinary Diagnostic Investigation, University of Pennsylvania researchers described an optimized RT-QuIC protocol for detecting CWD prions in preserved retropharyngeal lymph nodes from white-tailed deer, rather than relying only on fresh or frozen tissue. Their reported performance was strong: up to 96% sensitivity and 100% specificity for formalin-fixed samples, and up to 98% sensitivity and 99% specificity for formalin-fixed paraffin-embedded samples. (journals.sagepub.com)

That matters because current routine CWD diagnostics have a built-in specimen mismatch. ELISA generally requires fresh or frozen medial retropharyngeal lymph node tissue, while immunohistochemistry relies on formalin-fixed, paraffin-embedded tissue reviewed microscopically. In practice, that means separate storage pathways, added logistics, and fewer options when samples are archived, mishandled, or collected in field conditions where cold storage is limited. APHIS notes that lymph nodes are important surveillance tissues because they can harbor infectious prions early in disease. (journals.sagepub.com)

The Penn team evaluated 201 retropharyngeal lymph nodes with known CWD status, split almost evenly between positive and negative samples, from free-ranging white-tailed deer in Pennsylvania. According to both the paper and an APHIS project summary, the samples had already been characterized by ELISA and immunohistochemistry, then tested by RT-QuIC across fresh/frozen, formalin-fixed, and formalin-fixed paraffin-embedded conditions. The researchers also looked at PRNP genotypes and reported no meaningful effect of genotype on assay performance. The protocol is also notable for avoiding xylene or other harsh solvent steps often associated with paraffin processing. (journals.sagepub.com)

This study fits into a broader push to move RT-QuIC from promising research tool toward more routine CWD diagnostics. Earlier Pennsylvania work published in 2021 found RT-QuIC showed 100% sensitivity and specificity in a smaller set of 50 deer retropharyngeal lymph nodes tested in a diagnostic laboratory setting. More recently, a multi-institution comparison published in 2024 reported that six U.S. laboratories consistently identified true disease status across archived white-tailed deer lymph node samples and across codon 96 genotypes, reinforcing the assay’s reproducibility across sites. (journals.sagepub.com)

Industry and agency reaction, while not framed as direct commentary on this paper, has been moving in the same direction. APHIS included the University of Pennsylvania project in its 2024 CWD cooperative agreement summaries and said the findings support RT-QuIC use when fresh tissue collection is impractical, retrospective testing is needed, or fixed tissues are not suitable for definitive interpretation by standard slide-based methods. Separately, CWD research planning groups have highlighted standardized RT-QuIC validation for postmortem lymph nodes and antemortem biopsies as a major collaborative objective, underscoring the method’s growing importance in surveillance strategy. (aphis.usda.gov)

Why it matters: For veterinary professionals, especially diagnosticians, pathologists, and wildlife disease teams, the practical value is less about replacing every existing test tomorrow and more about expanding the usable sample pool. Preserved-tissue RT-QuIC could reduce lost opportunities when only archived formalin-fixed material exists, help resolve discordant ELISA and IHC findings, and support surveillance in regions where field collection and transport make frozen storage hard to maintain. It may also improve continuity between wildlife surveillance and diagnostic follow-up by allowing more testing from the same preserved specimen stream. Still, the assay’s role in official surveillance will depend on continued validation, standardization, and regulatory acceptance. (journals.sagepub.com)

There are still limits to keep in view. This was a white-tailed deer study based in Pennsylvania, and performance in other cervid species, field settings, and lower-burden or earlier-stage infections will matter for broader adoption. Even so, the reported specificity is especially encouraging for surveillance contexts, where false positives carry major management consequences for agencies, producers, and pet parents who interact with cervid facilities or affected landscapes through companion animal exposure concerns, public health messaging, and regional disease response. That last point is an inference from the surveillance context rather than a direct claim of the paper itself. (journals.sagepub.com)

What to watch: The next step is whether preserved-sample RT-QuIC moves from strong published performance into larger validation studies, inter-laboratory standardization, and eventual incorporation into agency testing frameworks for CWD surveillance and case resolution. (aphis.usda.gov)