Location: Virus and Prion Research2011 Annual Report
1a. Objectives (from AD-416)
Obj. 1. Assess the cross species transmissibility of transmissible spongiform encephalopathies (TSEs) in livestock and wildlife. Obj. 2. Investigate the pathobiology of TSEs in natural and secondary hosts. Obj. 3. Investigate pathogenesis and ante mortem detection of bovine spongiform encephalopathy (BSE). Obj. 4. Develop a method to detect central nervous system (CNS) tissue contamination on carcasses. Obj. 5. Discover effective methods to inactivate TSE agents in agricultural settings.
1b. Approach (from AD-416)
Studies are focused on the four animal Transmissible Spongiform Encephalopathy (TSE) agents found in the United States: bovine spongiform encephalopathy (BSE); scrapie of sheep and goats; chronic wasting disease (CWD) of deer, elk, and moose; and transmissible mink encephalopathy (TME). These agents will be tested for cross-species transmissibility into various livestock and cervid species using both oral and intracerebral inoculation. Sites of accumulation, routes of infection, methods of isolate differentiation, and in the case of BSE, genetics of susceptibility and ante-mortem diagnostics, will be investigated. Existing technology developed at the National Animal Disease Center and those used in the meat packing industry for the detection of fecal contamination on carcasses will be adapted to detect CNS tissue contamination on carcasses. Methods of TSE inactivation will be evaluated for efficacy in agricultural settings.
3. Progress Report
This is the final report for project 3625-32000-086-00D, terminated in September 2011 and replaced by 3625-32000-103-00D. The project plan involved 5 objectives. In Objective 1, Assess cross-species transmissibility of transmissible spongiform encephalopathies (TSEs) in livestock and wildlife, numerous experiments assessing the susceptibility of various TSEs in different host species were conducted. Most notable is deer inoculated with scrapie, which exhibits similarities to chronic wasting disease (CWD) in deer suggestive of sheep scrapie as an origin of CWD. In Objective 2, Investigate the pathobiology of TSEs in natural and secondary hosts, deer were inoculated with CWD-infected blood. Several animals developed clinical signs, a result consistent with CWD infectivity in blood. Also, biochemical strain typing commonly used for rodent models of TSE was investigated to assess the importance of genetic variability in natural hosts and how to apply these methods to natural hosts. Objective 3, Investigate pathogenesis and antemortem detection of bovine spongiform encephalopathy (BSE), involves several different research areas. Our results in genetic susceptibility of BSE support the now widely accepted conclusion that atypical BSE is a spontaneous TSE in cattle. This has important implications for the ruminant feed ban, food safety, and our understanding of the origins of BSE. Also as part of Obj. 3, we identified the first recognized case of genetic BSE where a natural case of BSE was identified in an animal containing a polymorphism analogous to a human polymorphism that causes a genetic TSE. Bovine spongiform encephalopathy has long been believed to only be a feed-borne disease. Together, our results show for the first time the presence of three different etiologies for BSE as are known to occur in humans. As part of our investigation, classical, and atypical BSE isolates were inoculated into cattle. Upon completion, this work will represent the first thorough comparison of domestic and international BSE isolates, including both classical and atypical BSE. An antemortem diagnostic technique based upon retinal function was developed and is routinely applied to experimental animals on site. This technique detects a TSE before the onset of clinical signs. Work is ongoing to increase the number of animals containing the E211K polymorphism, a potential cause of genetic BSE; this will provide the only means by which to prove the novel allele may cause BSE. The unusual E211K BSE material has also been successfully amplified in one of these animals. Objective 4, Develop a method to detect CNS tissue contamination on carcasses, resulted in a successful method that may be applied through adaptation of existing technology currently used to detect fecal contamination on carcasses. In Objective 5, Determine effective methods to inactivate TSE agents in agricultural settings, compounds applicable to agricultural settings were evaluated; the results are being prepared for publication. As part of this objective, a natural host model for assessing inactivation was developed. Despite experimental success the model is not suitable due to incubation time.
1. Deer inoculated with domestic isolates of sheep scrapie. Scrapie-affected deer exhibit 2 different patterns of disease associated prion protein. In some regions of the brain the pattern is much like that observed for scrapie, while in others it is more like chronic wasting disease (CWD), the transmissible spongiform encephalopathy typically associated with deer. This work conducted by ARS scientists at the National Animal Disease Center, Ames, IA suggests that an interspecies transmission of sheep scrapie to deer may have been the origin of CWD. This is important for husbandry practices with both captive deer, elk and sheep for farmers and ranchers attempting to keep their herds and flocks free of CWD and scrapie.
2. Demonstrated transmissibility of K211 BSE, a rare genetic form of bovine spongiform encephalopathy (BSE), to cattle. Cattle containing the rare K211 PRNP gene have been produced in-house and used in this study conducted by ARS scientists at the National Animal Disease Center, Ames, IA. These animals have been inoculated with both K211 BSE and classical BSE. The K211 BSE is transmissible and progresses far more rapidly in K211 cattle than does classical BSE. Because of their genetic susceptibility to BSE, K211 PRNP cattle have a very rapid incubation time and may be more susceptible to TSEs, which are two characteristics that make them highly desirable for future studies of antemortem diagnostics and residual infectivity or risk materials after decontamination. The possibility remains that K211 BSE transmitted to conventional cattle will result in a disease phenotype similar to classical BSE. If this turns out to be true, then it will be very important in that it suggests a very rare genetic form of BSE could have been the original source of brain material responsible for the U.K. BSE epidemic. Current human and animal feed bans regarding specified risk materials from cattle protect humans and animals from a recurrence of such an epidemic.
Hamir, A.N., Greenlee, J.J., Stanton, T.B., Smith, J.D., Doucette, S., Kunkle, R.A., Stasko, J.A., Richt, J.A., Kehrli, Jr., M.E. 2011. Experimental inoculation of raccoons (Procyon lotor) with Spiroplasma mirum and transmissible mink encephalopathy (TME). Canadian Journal of Veterinary Research. 75(1):18–24.