The epidemiology of the acquired forms is arguably more interesting, tractable, and pertinent to their elimination. Kuru for example, is virtually extinct now, despite its very long incubation periods.[17] It had a circumscribed geographical and temporal epidemiology, restricted to ethnic groups in a prescribed region of Papua New Guinea beginning early in the 20th century, presumably originating from a case of sCJD.[17, 18] Cases of iatrogenic CJD (iCJD), as transmitted by dura mater grafting and human pituitary-derived growth hormone are similarly in sharp click here decline, exposures
by these routes having ceased. iCJD in dura mater and growth hormone recipients can probably be viewed as problems that occurred in, and were resolved during, the 20th century.[19] It might appear that vCJD similarly belongs to the past. The epidemic of bovine spongiform encephalopathy (BSE) in cattle that occurred in the UK peaked in 1986 and the peak of resultant zoonosis (vCJD) occurred in 2000, with 28 patients dying of the disease, and five or fewer patients dying of the diseases
per annum in 2005 onwards. There have been no cases of vCJD reported in 2012 in the UK at the time of writing (late 2012).[20] Cases of BSE in cattle have occurred outside the UK, but on a very limited scale by comparison to the UK. The total number of vCJD cases in the UK is 176. The total number of cases in France is 27 selleck screening library and the other 10 affected countries have had five cases or fewer in total.[21] It is important to note that the scale of exposure to BSE in the UK is probably of a different order of magnitude than any previous exposure of a human population to prion infectivity. It is estimated that greater than 400 000 infected cattle entered the human food chain in the UK during the BSE epidemic. A number of
post-hoc explanations for the apparent discrepancy in likely exposure and resultant cases have been advanced, including a substantial species barrier between cows and humans, effects of dose, genetic susceptibility related to variations in both PRNP and non-PRNP genes, age-related susceptibility, and the possible necessity for co-factors, such as inflammation. A role for the codon 129 polymorphisms is plausible, but methionine homozygotes constitute 37% of the oxyclozanide normal population, so this can only be part of the answer. All definite clinical cases of vCJD that have been tested are MM at codon 129 of the prion protein gene, although a single case of possible vCJD has been reported in a PRNP codon 129 heterozygous patient.[22] However, a retrospective prevalence study carried out in the UK, based on the immunohistochemical detection of abnormal prion protein in appendix and tonsil tissue, indicated a prevalence of infection much higher than the numbers of clinical cases would suggest.