Published: 15 May 2024
Classical BSE dismissed as the cause of CWD in Norwegian red deer despite strain similarities between both prion agents
Abstract
The first case of CWD in a Norwegian red deer was detected by a routine ELISA test and confirmed by western blotting and immunohistochemistry in the brain stem of the animal. Two different western blotting tests were conducted independently in two different laboratories, showing that the red deer glycoprofile was different from the Norwegian CWD reindeer and CWD moose and from North American CWD. The isolate showed nevertheless features similar to the classical BSE (BSE-C) strain. Furthermore, BSE-C could not be excluded based on the PrPScimmunohistochemistry staining in the brainstem and the absence of detectable PrPSc in the lymphoid tissues. Because of the known ability of BSE-C to cross species barriers as well as its zoonotic potential, the CWD red deer isolate was submitted to the EURL Strain Typing Expert Group (STEG) as a BSE-C suspect for further investigation. In addition, different strain typing in vivo and in vitro strategies aiming at identifying the BSE-C strain in the red deer isolate were performed independently in three research groups and BSE-C was not found in it. These results suggest that the Norwegian CWD red deer case was infected with a previously unknown CWD type and further investigation is needed to determine the characteristics of this potential new CWD strain.
Snip…
Discussion
Some of the original red deer CWD isolate features (WB PrPres pattern, type of PrPSc deposition by IHC), as well as its transmission properties in TgBov suggested the presence of BSE-C prions in the red deer. To fully investigate the possible origin of this case, in vivo and in vitro strain typing approaches were applied to red deer CWD prions. The study of prion transmission properties in a collection of rodent models expressing the prion protein from different species is the best method for definitive strain typing. In vitro approaches such as PMCA allow faster results than the bioassay and usually provide a faithful mimic of the bioassay. In this work, thanks to the collaboration of different laboratories, we combined these approaches to compile the deepest possible investigation of the strain properties of red deer CWD prions in comparison to BSE-C prions. The results allow concluding solidly and reliably that the first red deer case of CWD detected in Norway was not caused by infection with the BSE-C prion agent. The obtained results suggest that the similarities, even after transmission in TgBov, were due to a phenotypic convergence phenomenon rather than strain identity. Phenotypic convergence can be described as the independent evolution of similar phenotypes [46]. This phenomenon is not unusual in the prion field, especially for experimental transmissions. For instance, when transmitted in TgOv-VRQ, both BSE-C and atypical BSE-L can phenotypically converge [36]. Indeed, the red deer CWD case is the first phenotypic mimic of BSE-C ever detected in nature. Previous suspects of natural BSE-C mimics, vCJD and BSE-C cases in goats, were eventually identified as true BSE-C prions by strain typing [24, 47, 48]. Another natural prion disease of small ruminants, CH1641, was initially found to have PrPres properties reminding C-BSE [49] and was later discriminated from BSE on both, molecular and biological grounds [50,51,52]. This red deer case represents a similar situation, as PrPres resemblance with C-BSE did not imply strain similarity and was indeed accompanied by obvious differences in the biological properties.
Even if they are not BSE-C, red deer CWD prions proved to be easily transmissible in vivo in TgBov, like cattle BSE-C isolates. This is of great concern because the TgBov mice models are efficiently used to predict cattle susceptibility to prion agents. Therefore, these results might suggest rather easy transmissibility of red deer CWD prions to cattle. Such a possibility will be of special importance for areas in which free-ranging cervids may be in contact with farmed species like cattle, sheep, goats or pigs [53]. Interestingly, in vitro amplification in bovine PrP context (cattle brain as substrate) was not successful. Similar results were observed in another work assessing European CWD potential to cross several species barriers [54]. This interesting discrepancy between in vitro PMCA and in vivo bioassays suggests that some in vivo cofactor key for crossing this species barrier is lacking in the in vitro system. Other possible explanation could be that the cattle brain may not have a high enough PrP expression level to support the propagation of the red deer CWD prion strain (successful in TgBov mice due to their high bovine PrP expression levels), that is probably less efficient in propagating than BSE-C prions. The in vivo bioassay in human PrP transgenic mice shows that there is a high transmission barrier for red deer CWD prions in humans, this work being the first assessment of red deer CWD zoonotic potential. At least red deer CWD prions transmit less efficiently than BSE-C prions to both TgMet129 and TgVal129 mice, suggesting that they have a lower zoonotic potential than BSE-C prions. Similar results have been obtained for other European CWD isolates (reindeer and moose) by performing bioassay in Met129 Tg35 and Val129 Tg152 human PrP transgenic mouse lines [55]. However, second passages might be needed to fully clarify European CWD zoonotic potential including isolates from all involved cervid species. In addition, the ability to cross species barriers can be modified after adaptation to a new species. This is of significant importance in the case of the human species barrier and prion zoonotic potential. For instance, BSE-C prions increase their virulence towards human PrP transgenic mice when primarily transmitted in sheep, goats and transgenic mice expressing sheep or goat PrP [44]. In addition, atypical BSE prions change their zoonotic abilities once adapted to transgenic mice expressing sheep PrP, producing prion agents that resemble sporadic CJD [36]. Thus, the possible adaptation of red deer CWD prions to other species, cattle being the most probable one as suggested by our results, should be monitored in order to be detected and abrogated as soon as possible.
veterinaryresearch.biomedcentral.com
terry
Classical BSE dismissed as the cause of CWD in Norwegian red deer despite strain similarities between both prion agents
Abstract
The first case of CWD in a Norwegian red deer was detected by a routine ELISA test and confirmed by western blotting and immunohistochemistry in the brain stem of the animal. Two different western blotting tests were conducted independently in two different laboratories, showing that the red deer glycoprofile was different from the Norwegian CWD reindeer and CWD moose and from North American CWD. The isolate showed nevertheless features similar to the classical BSE (BSE-C) strain. Furthermore, BSE-C could not be excluded based on the PrPScimmunohistochemistry staining in the brainstem and the absence of detectable PrPSc in the lymphoid tissues. Because of the known ability of BSE-C to cross species barriers as well as its zoonotic potential, the CWD red deer isolate was submitted to the EURL Strain Typing Expert Group (STEG) as a BSE-C suspect for further investigation. In addition, different strain typing in vivo and in vitro strategies aiming at identifying the BSE-C strain in the red deer isolate were performed independently in three research groups and BSE-C was not found in it. These results suggest that the Norwegian CWD red deer case was infected with a previously unknown CWD type and further investigation is needed to determine the characteristics of this potential new CWD strain.
Snip…
Discussion
Some of the original red deer CWD isolate features (WB PrPres pattern, type of PrPSc deposition by IHC), as well as its transmission properties in TgBov suggested the presence of BSE-C prions in the red deer. To fully investigate the possible origin of this case, in vivo and in vitro strain typing approaches were applied to red deer CWD prions. The study of prion transmission properties in a collection of rodent models expressing the prion protein from different species is the best method for definitive strain typing. In vitro approaches such as PMCA allow faster results than the bioassay and usually provide a faithful mimic of the bioassay. In this work, thanks to the collaboration of different laboratories, we combined these approaches to compile the deepest possible investigation of the strain properties of red deer CWD prions in comparison to BSE-C prions. The results allow concluding solidly and reliably that the first red deer case of CWD detected in Norway was not caused by infection with the BSE-C prion agent. The obtained results suggest that the similarities, even after transmission in TgBov, were due to a phenotypic convergence phenomenon rather than strain identity. Phenotypic convergence can be described as the independent evolution of similar phenotypes [46]. This phenomenon is not unusual in the prion field, especially for experimental transmissions. For instance, when transmitted in TgOv-VRQ, both BSE-C and atypical BSE-L can phenotypically converge [36]. Indeed, the red deer CWD case is the first phenotypic mimic of BSE-C ever detected in nature. Previous suspects of natural BSE-C mimics, vCJD and BSE-C cases in goats, were eventually identified as true BSE-C prions by strain typing [24, 47, 48]. Another natural prion disease of small ruminants, CH1641, was initially found to have PrPres properties reminding C-BSE [49] and was later discriminated from BSE on both, molecular and biological grounds [50,51,52]. This red deer case represents a similar situation, as PrPres resemblance with C-BSE did not imply strain similarity and was indeed accompanied by obvious differences in the biological properties.
Even if they are not BSE-C, red deer CWD prions proved to be easily transmissible in vivo in TgBov, like cattle BSE-C isolates. This is of great concern because the TgBov mice models are efficiently used to predict cattle susceptibility to prion agents. Therefore, these results might suggest rather easy transmissibility of red deer CWD prions to cattle. Such a possibility will be of special importance for areas in which free-ranging cervids may be in contact with farmed species like cattle, sheep, goats or pigs [53]. Interestingly, in vitro amplification in bovine PrP context (cattle brain as substrate) was not successful. Similar results were observed in another work assessing European CWD potential to cross several species barriers [54]. This interesting discrepancy between in vitro PMCA and in vivo bioassays suggests that some in vivo cofactor key for crossing this species barrier is lacking in the in vitro system. Other possible explanation could be that the cattle brain may not have a high enough PrP expression level to support the propagation of the red deer CWD prion strain (successful in TgBov mice due to their high bovine PrP expression levels), that is probably less efficient in propagating than BSE-C prions. The in vivo bioassay in human PrP transgenic mice shows that there is a high transmission barrier for red deer CWD prions in humans, this work being the first assessment of red deer CWD zoonotic potential. At least red deer CWD prions transmit less efficiently than BSE-C prions to both TgMet129 and TgVal129 mice, suggesting that they have a lower zoonotic potential than BSE-C prions. Similar results have been obtained for other European CWD isolates (reindeer and moose) by performing bioassay in Met129 Tg35 and Val129 Tg152 human PrP transgenic mouse lines [55]. However, second passages might be needed to fully clarify European CWD zoonotic potential including isolates from all involved cervid species. In addition, the ability to cross species barriers can be modified after adaptation to a new species. This is of significant importance in the case of the human species barrier and prion zoonotic potential. For instance, BSE-C prions increase their virulence towards human PrP transgenic mice when primarily transmitted in sheep, goats and transgenic mice expressing sheep or goat PrP [44]. In addition, atypical BSE prions change their zoonotic abilities once adapted to transgenic mice expressing sheep PrP, producing prion agents that resemble sporadic CJD [36]. Thus, the possible adaptation of red deer CWD prions to other species, cattle being the most probable one as suggested by our results, should be monitored in order to be detected and abrogated as soon as possible.
Classical BSE dismissed as the cause of CWD in Norwegian red deer despite strain similarities between both prion agents - Veterinary Research
The first case of CWD in a Norwegian red deer was detected by a routine ELISA test and confirmed by western blotting and immunohistochemistry in the brain stem of the animal. Two different western blotting tests were conducted independently in two different laboratories, showing that the red...
veterinaryresearch.biomedcentral.com
terry
