Location: Virus and Prion Research2014 Annual Report
1a. Objectives (from AD-416):
1. Investigate the pathobiology of atypical transmissible spongiform encephalopathies (TSEs) in natural hosts. A. Investigate the pathobiology of atypical scrapie. B. Investigate the pathobiology of atypical bovine spongiform encephalopathy (BSE). 2. Investigate the horizontal transmission of TSEs. A. Assess the horizontal transmission of sheep scrapie in the absence of lambing. B. Determine routes of transmission in chronic wasting disease (CWD) infected premises. C. Assess oral transmission of CWD in reindeer. 3. Investigate determinants of CWD persistence. A. Determine CWD host range using natural routes of transmission. B. Investigate the pathobiology of CWD.
1b. Approach (from AD-416):
The studies will focus on three animal transmissible spongiform encephalopathy (TSE) agents found in the United States: bovine spongiform encephalopathy (BSE); scrapie of sheep and goats; and chronic wasting disease (CWD) of deer, elk, and moose. The research will address sites of accumulation, routes of infection, environmental persistence, and ante mortem diagnostics with an emphasis on controlled conditions and natural routes of infection. Techniques used will include clinical exams, histopathology, immunohistochemistry and biochemical analysis of proteins. The enhanced knowledge gained from this work will help mitigate the potential for unrecognized epidemic expansions of these diseases in populations of animals that could either directly or indirectly affect food animals.
3. Progress Report:
Research efforts directed toward meeting objective 1 of our project plan, Investigate the pathobiology of atypical transmissible spongiform encephalopathies (TSEs) in natural hosts, include work in previous years starting with the inoculation of animals for studies designed to address the pathobiology of atypical scrapie, atypical bovine spongiform encephalopathy (BSE), as well as a genetic version of BSE. Animals inoculated with atypical scrapie have not yet developed disease. Atypical BSE animals have developed disease and evaluation of the samples is currently underway. Animals inoculated with a genetic version of BSE have developed disease and the manuscript has been published (2012). In addition, we have investigated the possibility that atypical scrapie was present earlier than previously detected in the national flock by analyzing archived field isolates using methods that were unavailable at the time of original diagnosis. Sample quality was sufficiently degraded that modern methods were not suitable for evaluation. In research pertaining to objective 2, Investigate the horizontal transmission of TSEs, we have initiated a study to determine if cohousing non-lambing scrapie inoculated sheep is sufficient to transmit scrapie to neonatal lambs. At this time, scrapie free ewes have lambed in the presence of scrapie inoculated animals and the lambs are cohoused with these inoculated animals.
1. Evaluated enzyme immunoassay for rapid identification of prion disease in livestock. Scrapie of sheep and bovine spongiform encephalopathy of cattle are diseases that cause damage to the central nervous system including the retina in the eye. The infectious agent is an abnormal protein called a prion that has misfolded from its normal state and is resistant to breakdown by the host cells. Current diagnostic methods require the testing of brain material, which can be difficult to collect and may lead to contamination of the environment and exposure of personnel to the infectious agent. Eyes can be readily collected without opening the skull. ARS researchers at Ames, Iowa demonstrated that the enzyme immunoassay results using eyes of negative controls or samples collected from sheep or cattle with clinical signs were in agreement with approved confirmatory assays (western blot or immunohistochemistry). These results indicate the retina is a useful tissue for rapid diagnosis of prion disease in clinically ill sheep and cattle and could be considered to greatly increase the number of samples submitted for prion disease diagnosis with a minimal investment of time and limited exposure of personnel to prion agents.
2. Evaluated E211K cattle as a model for inherited human prion disease. Prion diseases cause damage to the central nervous system of animals and humans. The infectious agent is an abnormal protein called a prion that has misfolded from its normal state and is resistant to breakdown by the host cells and thus accumulates and damages those cells. Some forms of prion disease are genetic and can be inherited. Current models of genetic prion disease in humans rely on mouse models expressing either the human prion protein (E200K) or a combination of both mouse and human sequences. In addition to being an entirely artificial system these mouse models have a short lifespan making them a less than ideal system to study a naturally occurring genetic disorder with a long incubation time and late onset of disease. Cattle, however, exhibit a number of similarities to humans with regard to prion disease and perhaps most notable is the late onset of genetic prion disease. ARS researchers at Ames, Iowa have produced cattle containing both 1 and 2 chromosome copies of the cattle prion gene (E211K) and evaluated many aspects of this prion protein from cattle including protein stability, protein expression levels and ratios, as well as evidence of oxidative stress. Taken together, these results highlight the differences between mouse models of genetic prion disease and a naturally occurring prion disease system in cattle and suggest that cattle will provide a more relevant understanding of genetic prion disease in humans than do current rodent models.
Smith, J.D., Greenlee, J.J. 2014. Detection of misfolded prion protein in retina samples of sheep and cattle by use of a commercially available enzyme immunoassay. American Journal of Veterinary Research. 75(3):268-272.