Redefining the zoonotic potential of chronic wasting disease

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The rapid expansion of chronic wasting disease (CWD), a prion disease of free-ranging and farmed deer, elk and moose, is a major and ongoing threat in North America. Approximately 1 in 36 Americans hunt deer and elk and eat venison, and it is estimated that 7,000 – 15,000 CWD-infected cervids are consumed annually. This fuels growing concerns about the human health risks imposed by CWD. There are no documented cases of CWD transmission to humans, even though with the long incubation periods of all prion diseases and the unknown presentation of CWD in humans definite conclusions are not possible. The zoonotic potential of prion diseases has been exemplified by bovine spongiform encephalopathy (BSE, mad cow disease) which resulted in a new form of human prion disease (vCJD). BSE was transmissible to Cynomolgus macaques and transgenic mice expressing the human prion protein. Initial results of CWD transmission studies to the same non-human primate and mouse models of human prion disease were not successful, corroborating the conclusion that the zoonotic potential of CWD is low, if not absent. Our groups were part of a consortium that inoculated Cynomolgus macaques via different routes with CWD. Some animals exhibited subtle clinical signs reminiscent of prion disease, and upon euthanasia, weak signs of vacuolation, PrPSc deposition and astrocytosis in the brain were found, while no proteinase K (PK) resistant prion protein (PrP) was detectable. We have now demonstrated for the first time that CWD from macaques can transmit clinical prion disease to transgenic mouse models of CWD and human prion disease, albeit in the absence of detectable PK-resistant PrP. Bona fide PrPSc was only detected upon 3rd passage from mouse to bank vole models. Altogether, this is the first evidence that CWD very likely has zoonotic potential. The goal of the current proposal is to redefine the zoonotic potential of CWD by characterizing the biological properties of CWD prions emerging upon experimental transmission into macaques, for obtaining important information on how CWD could manifest in humans. In Aim 1, we will study whether CWD from macaque (CWDmac) in bank voles represents a new prion strain, by comparing biochemical and biological properties to an array of known prion strains from different species. Aim 2 addresses the question whether CWDmac represents an intermediate prion strain, adaptable to cervids or humans upon passage, and possessing an expanded host range. We will address this by in vivo passage in cervidized or humanized mouse models. In vitro, we will utilize serial PMCA and a newly generated PrP0/0 cell culture model for infection, upon reconstitution with PrP from different species. In Aim 3, we will shed light on the observed dissociation between infectivity and the presence of bona fide PrPSc. We propose to identify atypical PrP fragments associated with CWDmac, and we will elucidate brain cell responses to CWDmac exposure by innovative single cell RNA sequencing. In summary, our studies will uncover the possible manifestation of CWD in humans, which is of critical importance for drawing definite conclusions about the zoonotic potential of CWD.