Price of TSE Prion Poker goes up Drastically!
Infectious prions in brains and muscles of domestic pigs experimentally challenged with the BSE, scrapie, and CWD agents
Authors: Francisca Bravo-Risi, Fraser Brydon, Angela Chong, Kane Spicker, Justin J. Greenlee https://orcid.org/0000-0003-2202-3054, Glenn Telling, Claudio Soto https://orcid.org/0000-0002-3412-0524, Sandra Pritzkow, Marcelo A. Barria, Rodrigo Morales https://orcid.org/0000-0001-7766-5770 [email protected]
ABSTRACT
Experimental studies suggest that animal species not previously described as naturally infected by prions are susceptible to prion diseases affecting sheep, cattle, and deer. These interspecies transmissions may generate prions with unknown host ranges. Pigs are susceptible to prions from different origins, including deer chronic wasting disease (CWD), sheep scrapie, and bovine spongiform encephalopathy (BSE). Here, we studied prions in brains and muscles from pigs previously infected with these different prion sources. Specifically, we measured the total prion protein (PrP) and PK-resistant PrP by western blot. Seeding activity in these tissues was evaluated using the protein misfolding cyclic amplification (PMCA) technique. We found that BSE-infected pigs contained substantially more seeding competent prions compared with those infected with CWD and scrapie. Moreover, the zoonotic potential of porcine-BSE prions seems to be relevant, as both brains and muscles from BSE-infected pigs induced the misfolding of the human prion protein in vitro. This study helps to understand the potential fate of naturally existing prion strains in a relevant host and calls for caution considering the co-existence between feral swine and other prion-susceptible animal species.
IMPORTANCE
Prions (PrPSc) are proteinaceous, infectious pathogens responsible for prion diseases. Some livestock are highly susceptible to prion diseases. These include cattle (bovine spongiform encephalopathy, BSE), sheep and goat (scrapie), and cervids (chronic wasting disease, CWD). Unfortunately, BSE has been reported to be naturally transmitted to humans and other animal species. Domestic pigs, a relevant livestock animal, have not been reported to be naturally affected by prions; however, they are susceptible to the experimental exposure to BSE, scrapie, and CWD prions. Given the widespread consumption of porcine food products by humans, we aimed to evaluate the levels of pig-derived BSE, scrapie, and CWD prions from experimentally challenged domestic pigs in brain and meat cuts (leg, cheek meat, skirt meat, and tenderloin). We detected pig-adapted prions in the brains and some muscles of these animals. Additionally, we evaluated the in vitro compatibility between pig prions and the human prion protein (as a surrogate of zoonosis). Our results show that only pig-derived BSE prions were able to induce the misfolding of the cellular human prion protein. This data highlights the consequences of prion spillovers to other animal species and their potential availability to humans.
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DISCUSSION
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Importantly, our studies evaluating zoonotic potentials showed that pig-adapted BSE prions were able to induce the misfolding of the human prion protein in vitro. These results were confirmed in two different laboratories, a fact that provides rigor to this study. Importantly, these analyses also show that muscles from these BSE-infected pigs may present a concern if introduced in the human food chain. Importantly, the zoonotic risk of these materials seems to be restricted to the 129M polymorphic version of the human prion protein, in line with the higher susceptibility of BSE to the population carrying this specific protein. Previous reports have shown that mice expressing the 129M human PrPC variant (HuPrP-tg 650 and 340) exhibited a species barrier to BSE prions that was overcome in a first transmission passage (81). Similar outcomes were observed when pig-adapted BSE prions were inoculated in HuPrP-tg340 mice, although with incomplete attack rates (50%) in a first passage. Serial transmissions of this infectious material in the same mice resulted in complete attack rates and reduction in the incubation periods, suggesting that the infectious material successfully adapted in the new host (60). On the contrary, extensive evidence demonstrates that the species barrier between scrapie and CWD prions and humans is strong, if not absolute (39, 42, 82). However, the existence of different prion strains associated with these animal prionopathies urges for a systematic analysis including the whole pathogenic spectrum associated with them. In our study, scrapie- and CWD-adapted prions were not able to induce the misfolding of the human prion protein. However, considering the data from the porcine-BSE prions, we cannot conclude whether the lower load of prions in the CWD- and scrapie-porcine tissues was responsible for these results.
Some of the limitations of the current study have been already discussed. One of the issues involves the unknown prion infectivity titers of the BSE-, scrapie-, and CWD-bearing tissues used to infect pigs. This importantly limits comparisons between the groups. Prion infectivity titers can affect tissue tropisms, especially in subclinical transmissions (as prions may need additional time to reach target tissues). This could be considered an additional source of variability for the dissimilar presence of prions in muscles for the different animal groups included in this study. Another limitation involves the uneven testing of muscle tissues across the three groups and the lack of analysis of other muscles representing different anatomical distributions within the body. The latter may be relevant for understanding the tropism of prions induced by each injectate. Finally, the scrapie and CWD groups were treated with specific prion strains from many that have been described. This is relevant considering that different strains may adapt with different efficiencies into new hosts and result in infectious particles with unique host ranges. Future studies should focus on the above-mentioned limitations. However, we believe that the current study provides a solid background to justify these analyses.
In summary, our data shows the dynamic of animal prions when exposed to infectious pigs, as well as their distributions and zoonotic potentials. The data presented here may be relevant to understanding the fate of naturally existing prions in a sympatric animal species relevant for human consumption. This acquires importance considering a recent report describing the interaction between CWD and wild pigs in natural settings.
https://journals.asm.org/doi/10.1128/mbio.01800-25
terry
Infectious prions in brains and muscles of domestic pigs experimentally challenged with the BSE, scrapie, and CWD agents
Authors: Francisca Bravo-Risi, Fraser Brydon, Angela Chong, Kane Spicker, Justin J. Greenlee https://orcid.org/0000-0003-2202-3054, Glenn Telling, Claudio Soto https://orcid.org/0000-0002-3412-0524, Sandra Pritzkow, Marcelo A. Barria, Rodrigo Morales https://orcid.org/0000-0001-7766-5770 [email protected]
ABSTRACT
Experimental studies suggest that animal species not previously described as naturally infected by prions are susceptible to prion diseases affecting sheep, cattle, and deer. These interspecies transmissions may generate prions with unknown host ranges. Pigs are susceptible to prions from different origins, including deer chronic wasting disease (CWD), sheep scrapie, and bovine spongiform encephalopathy (BSE). Here, we studied prions in brains and muscles from pigs previously infected with these different prion sources. Specifically, we measured the total prion protein (PrP) and PK-resistant PrP by western blot. Seeding activity in these tissues was evaluated using the protein misfolding cyclic amplification (PMCA) technique. We found that BSE-infected pigs contained substantially more seeding competent prions compared with those infected with CWD and scrapie. Moreover, the zoonotic potential of porcine-BSE prions seems to be relevant, as both brains and muscles from BSE-infected pigs induced the misfolding of the human prion protein in vitro. This study helps to understand the potential fate of naturally existing prion strains in a relevant host and calls for caution considering the co-existence between feral swine and other prion-susceptible animal species.
IMPORTANCE
Prions (PrPSc) are proteinaceous, infectious pathogens responsible for prion diseases. Some livestock are highly susceptible to prion diseases. These include cattle (bovine spongiform encephalopathy, BSE), sheep and goat (scrapie), and cervids (chronic wasting disease, CWD). Unfortunately, BSE has been reported to be naturally transmitted to humans and other animal species. Domestic pigs, a relevant livestock animal, have not been reported to be naturally affected by prions; however, they are susceptible to the experimental exposure to BSE, scrapie, and CWD prions. Given the widespread consumption of porcine food products by humans, we aimed to evaluate the levels of pig-derived BSE, scrapie, and CWD prions from experimentally challenged domestic pigs in brain and meat cuts (leg, cheek meat, skirt meat, and tenderloin). We detected pig-adapted prions in the brains and some muscles of these animals. Additionally, we evaluated the in vitro compatibility between pig prions and the human prion protein (as a surrogate of zoonosis). Our results show that only pig-derived BSE prions were able to induce the misfolding of the cellular human prion protein. This data highlights the consequences of prion spillovers to other animal species and their potential availability to humans.
Snip…
DISCUSSION
Snip…
Importantly, our studies evaluating zoonotic potentials showed that pig-adapted BSE prions were able to induce the misfolding of the human prion protein in vitro. These results were confirmed in two different laboratories, a fact that provides rigor to this study. Importantly, these analyses also show that muscles from these BSE-infected pigs may present a concern if introduced in the human food chain. Importantly, the zoonotic risk of these materials seems to be restricted to the 129M polymorphic version of the human prion protein, in line with the higher susceptibility of BSE to the population carrying this specific protein. Previous reports have shown that mice expressing the 129M human PrPC variant (HuPrP-tg 650 and 340) exhibited a species barrier to BSE prions that was overcome in a first transmission passage (81). Similar outcomes were observed when pig-adapted BSE prions were inoculated in HuPrP-tg340 mice, although with incomplete attack rates (50%) in a first passage. Serial transmissions of this infectious material in the same mice resulted in complete attack rates and reduction in the incubation periods, suggesting that the infectious material successfully adapted in the new host (60). On the contrary, extensive evidence demonstrates that the species barrier between scrapie and CWD prions and humans is strong, if not absolute (39, 42, 82). However, the existence of different prion strains associated with these animal prionopathies urges for a systematic analysis including the whole pathogenic spectrum associated with them. In our study, scrapie- and CWD-adapted prions were not able to induce the misfolding of the human prion protein. However, considering the data from the porcine-BSE prions, we cannot conclude whether the lower load of prions in the CWD- and scrapie-porcine tissues was responsible for these results.
Some of the limitations of the current study have been already discussed. One of the issues involves the unknown prion infectivity titers of the BSE-, scrapie-, and CWD-bearing tissues used to infect pigs. This importantly limits comparisons between the groups. Prion infectivity titers can affect tissue tropisms, especially in subclinical transmissions (as prions may need additional time to reach target tissues). This could be considered an additional source of variability for the dissimilar presence of prions in muscles for the different animal groups included in this study. Another limitation involves the uneven testing of muscle tissues across the three groups and the lack of analysis of other muscles representing different anatomical distributions within the body. The latter may be relevant for understanding the tropism of prions induced by each injectate. Finally, the scrapie and CWD groups were treated with specific prion strains from many that have been described. This is relevant considering that different strains may adapt with different efficiencies into new hosts and result in infectious particles with unique host ranges. Future studies should focus on the above-mentioned limitations. However, we believe that the current study provides a solid background to justify these analyses.
In summary, our data shows the dynamic of animal prions when exposed to infectious pigs, as well as their distributions and zoonotic potentials. The data presented here may be relevant to understanding the fate of naturally existing prions in a sympatric animal species relevant for human consumption. This acquires importance considering a recent report describing the interaction between CWD and wild pigs in natural settings.
https://journals.asm.org/doi/10.1128/mbio.01800-25
terry
