Shedding, retention and spreading of chronic wasting disease prions in the environment

ABSTRACT Chronic Wasting Disease (CWD) is a prion disease affecting natural and captive cervid populations. This disease is progressively spreading across the United States and new foci of infectivity are constantly being reported. Despite decades of research, there are still several unanswered questions concerning CWD. Compelling evidence suggest that CWD prions enter the environment through carcasses from diseased animals or by the progressive accumulation of prions shed in excreta. Unfortunately, the role that plants, parasites, predators, and scavengers play in CWD spreading has been poorly studied. During the past funding cycle, our group made important technical and conceptual contributions in this field. Data from our group and others (in collaboration) demonstrate that plants can bind prions into their surfaces as well as transport them from soils to leaves. This is relevant, considering that prions are shown to progressively accumulate in soils and strongly suggests plants as potential vectors for CWD transmission. Unfortunately, the previously mentioned evidence has been collected using proof-of-concept conditions, including the exposure of high titers of rodent (laboratory generated) adapted prions, and grass plants only. We have generated preliminary data showing that carrots grown in CWD infected soil carry prions in their roots and leaves as evaluated by bioassays. In contrast, tomato plants do not share these features. The significance of these findings cannot be ignored considering the interaction of CWD prions with a human and animal edible vegetable. Considering the use of carrots roots and leaves in human and animal nutrition, and the still unknown zoonotic potential of CWD, future research involving edible plants is urgently needed. Another relevant (published) finding from our laboratory involves the high CWD infectivity titers found in nasal bots, a common cervid parasite that develops in the nasal cavity (a hotspot of prion infectivity). These parasites are found in large quantities in CWD pre- clinical and clinical deer, and may importantly contribute to environmental CWD transmission. Our research also identified CWD prions in naturally exposed flies, ticks, and dermestid beetles. However, the prion infectivity titers in these parasites have not been evaluated. Finally, animals other than cervids, including hunters and scavengers, are expected to be exposed to CWD prions. Interestingly, we identified CWD prions and de novo generated porcine prions in tissues from wild pigs living in areas with variable CWD epidemiology. We plan to further investigate all these events and their relevance in natural prion transmission using a complementary set of techniques, including in vitro and in vivo systems. Emphasis will be made in analyzing the strain properties and zoonotic potentials of the prion agents under investigation. For this purpose, we gathered a unique group of collaborators able to supply us with the samples and expertise required to execute this project. Outcomes from this research are expected to deliver new insights on this animal prionopathy and provide regulatory agencies with useful information to control its continuous spread.