Location: Virus and Prion Research2013 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 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 inoculated sheep are being co-housed with pregnant ewes.
1. Partial effectiveness of a common cleaning product to disinfect prions. Diseases such as mad cow disease, scrapie, and chronic wasting disease of animals and Creutzfeldt-Jakob disease in humans are collectively known as transmissible spongiform encephalopathies. They are caused by an infectious protein, rather than a virus or bacterium, which is notoriously difficult to inactivate. Decontaminating surfaces or instruments is essential to prevent potential spread of these diseases. ARS researchers in Ames, IA tested whether sodium percarbonate, a chemical similar to hydrogen peroxide and contained in such products as OxiClean, in combination with a detergent (sodium dodecyl sulfate) could effectively disinfect surfaces contaminated with prions. The treatment rendered the prions sensitive to degradation with protein-destroying enzymes, but only limited reduction in infectivity was observed. Thus, this treatment alone is not sufficient to inactivate prions, but could be used in combination with other treatments to decontaminate prion contaminated areas.
2. Determined the likelihood of transmission of chronic wasting disease (CWD) to cattle. CWD is a prion disease, similar to mad cow disease in cattle, which naturally occurs in cervid animals, such as deer and elk, in the United States. Prion diseases are caused by an infectious protein, rather than a virus or bacterium. The prion that causes CWD is contagious through animal contact and through the environment, so cattle could be exposed to the agent of CWD through contact with infected farmed or free-ranging cervids, or exposure to contaminated premises. The purpose of this study by ARS researchers in Ames, IA, was to determine whether cattle could become infected with CWD if it was inoculated directly into the brain, a much more rigorous route of infection. Only 2 of the 14 cattle inoculated this way developed disease. Additional studies are required to assess the potential for cattle to develop CWD through a more natural route of exposure, but a low rate of transmission following inoculation into the brain suggests a low risk of transmission through contact with infected animals or a contaminated environment. However, if this ever occurred it was also determined that currently used diagnostic techniques would detect and differentiate CWD from other prion diseases in cattle, such as mad cow disease.
3. Produced a genetically unique calf for studies of inherited bovine spongiform encephalopathy (BSE). Diseases such as BSE in cattle, more commonly known as mad cow disease, and Creutzfeldt-Jakob disease (CJD) in humans are caused by an infectious protein called a prion, rather than a virus or bacterium. A usually non-harmful form of this prion protein is normally produced in animals and humans, however, animals and humans born with a certain genetic form of this protein are more susceptible to developing an inherited form of these diseases. Proteins are made up of subunits called amino acids, and these amino acids are encoded by the DNA that makes up genes. In humans, when the amino acid lysine is encoded by the DNA in a certain position of the prion gene, instead of the commonly occurring amino acid glutamate, a genetic form of CJD can occur. Recently, occurrence of this same amino acid in a cow was associated with a case of BSE. Before this case of BSE, the lysine for glutamate amino acid substitution had not been identified in cattle. Researchers at ARS, National Animal Disease Center, Ames, Iowa, in collaboration with Iowa State University were able to produce a calf with this lysine for glutamate amino acid substitution. This animal and its progeny will be used to determine if a genetic form of BSE occurs and for further study of BSE in cattle. It is important to distinguish whether cases of BSE that arise in the United States are due to an infectious or genetic cause.
Greenlee, J.J., Nicholson, E.M., Smith, J.D., Kunkle, R.A., Hamir, A.N. 2012. Susceptibility of cattle to the agent of chronic wasting disease from elk after intracranial inoculation. Journal of Veterinary Diagnostic Investigation. 24(6):1087-1093.