Evidence from epidemiological studies allow a conclusion that scrapie transmits prenatally and that semen and embryos are presumptive hazards for the transmission of scrapie. The three lines of evidence derive from epidemiological, field and clinical studies, experimentation, and causal reasoning, where inferences are made from the body of scientific knowledge and an understanding of animal structure and function. It leads to the second question, which concerns the sanitary safety of artificial breeding technologies, and is whether scrapie transmits in sheep and goats by means of semen and washed or unwashed in vivo derived embryos. The first question is whether scrapie transmits prenatally in sheep and goats. The present venture lays a foundation for a possible systematic review and applies three lines of evidence and reasoning to two questions. Systematic reviews have clearly formulated questions, can identify relevant studies and appraise their quality and can summarise evidence and reasoning with an explicit methodology. The remedy may be analysis according to a systematic review, allowing comprehensive and accessible treatment of evidence and reasoning, clarifying the issue and specifying the uncertainties. Unsettled knowledge as to whether scrapie transmits prenatally in sheep and goats and transmits by semen and preimplantation embryos has a potential to compromise measures for controlling, preventing and eliminating the disease. Despite stable appearances, prion disease nonetheless impairs adult survival and likely resilience in this deer herd, limiting its potential for growth despite refuge from hunter harvest and favorable habitat and winter conditions. Predation by mountain lions ( Puma concolor ) may be helping keep CWD in check.
High apparent prevalence (~30%) since at least 2005 likely drove observed changes in the proportion and age distribution of wild-type native prion protein ( PRNP ) gene homozygotes among deer sampled. Here we describe unexpected stability in prevalence and abundance in a mule deer herd where CWD has been left unmanaged. Understanding population responses over time is key to forecasting long-term impacts.
Prion infection shortens a deer’s lifespan, and when prevalence (proportion of adults infected) becomes sufficiently high CWD can affect herd dynamics. Unchecked epidemics raise ecological, socioeconomic, and public health concerns. The contagious prion disease “chronic wasting disease” (CWD) infects mule deer ( Odocoileus hemionus ) and related species.
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