Detection of prions in wild pigs (Sus scrofa) from areas with reported chronic wasting disease cases, United States

Authors: SOTO, PAULINA - University Of Texas Health Science Center; BRAVO-RISI, FRANSCISCA - University Of Texas Health Science Center; BENAVENTE, REBECA - University Of Texas Health Science Center; STIMMING, TUCKER - University Of Texas Health Science Center; BODENCHUK, MICHAEL - Colorado Department Of Agriculture; WHITLEY, PATRICK - Colorado Department Of Agriculture; TURNAGE, CLINT - Colorado Department Of Agriculture; SPRAKER, TERRY - Colorado State University; Greenlee, Justin; TELLING, GLENN - Colorado State University; MALMBERG, JENNIFER - Colorado Department Of Agriculture; GIDLEWSKI, THOMAS - Colorado Department Of Agriculture; NICHOLS, TRACY - Colorado Department Of Agriculture; BROWN, VIENNA - Colorado Department Of Agriculture; MORALAS, RODRIGO - University Of Texas Health Science Center

Submitted to: Emerging Infectious Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2024
Publication Date: 12/17/2024
Citation: Soto, P., Bravo-Risi, F., Benavente, R., Stimming, T., Bodenchuk, M.J., Whitley, P., Turnage, C., Spraker, T.R., Greenlee, J.J., Telling, G., Malmberg, J., Gidlewski, T., Nichols, T., Brown, V.R., Moralas, R. 2024. Detection of prions in wild pigs (Sus scrofa) from areas with reported chronic wasting disease cases, United States. Emerging Infectious Diseases. 31(1):168-173. https://doi.org/10.3201/eid3101.240401.
DOI: https://doi.org/10.3201/eid3101.240401

Interpretive Summary: Prion diseases are a neurodegenerative disease that can spread between animals. They are caused when the normal cellular prion protein misfolds and accumulates in the host’s central nervous system. This change is irreversible and invariably causes neurological disease and death of the host. The prion disease that affects sheep, scrapie, has been recognized for hundreds of years. However, chronic wasting disease, a similar disease found in deer and elk, has only been recognized since the 1960s. Since the original identification of chronic wasting disease in Colorado, it has spread to 32 US states and five Canadian provinces. This manuscript addresses the role that wild pigs may play in transmission of chronic wasting disease. In vitro assays that are able to identify prions from deer or porcine sources were used to analyze brain and lymph nodes from a large number of wild pigs. Transgenic mice expressing the prion protein of either deer or pigs were used to further test some of the tissues for infectivity. The results suggest that wild pigs living in areas with deer infected with chronic wasting disease are exposed to prions, but the levels of infectivity are low. When inoculated with tissues from wild pigs, mice expressing deer prions are sub-clinically infected and no transmission is detected in mice expressing the prion protein of pigs. This work supports that pigs are unlikely to become infected with chronic wasting disease prions, but pigs could play a role in disease spread by distributing prions across the landscape. This information will be of interest to regulatory officials and officials tasked with protecting animal health such as state Departments of Agriculture, Natural Resources, or Parks and Wildlife.

Technical Abstract: Chronic wasting disease (CWD) is the prion disease with the greatest potential for spreading, affecting at least seven cervid species. An essential feature of prions lies in their ability to infect some species and not others. This phenomenon seems to be largely dictated by the similarities between the donor (infectious) and recipient prion protein (PrP) sequences. Considering this, it has been postulated that some carnivores may be susceptible to CWD prion infection; while predators or scavengers may not get infected but spread prions after they cross their digestive tracts. This project aims to identify the presence of infectious prions (PrPSc) in wild pigs living in areas with varying CWD epidemiology. To this end, brains and retropharyngeal lymph nodes from wild pigs were tested for their presence of infectious prions using the PMCA technique. The PMCA analyses were performed using homologous pig PrP substrate or heterologous deer PrP substrate. We further injected selected wild pig tissues into mice expressing the porcine and cervid versions of the prion protein to assess for their potential to transmit disease. Our results show positive in vitro PrPSc detection using porcine and cervid substrates. The considerably higher detection using cervid substrate suggests that although swine are exposed to CWD prions, disease transmission is inefficient. Bioassays confirmed these results and demonstrated that the PrPSc titers carried by wild pigs are not enough to induce disease. These results suggest that wild pigs are exposed to CWD prions on the landscape and may play a role in CWD epidemiology.