Dermal prions: enough to make your skin crawl
90 cases of nvCJD predicted at end of 1998
Blood Safety and Screening Conference 21 Feb 99
Draft Factual Accounts
Risk of prion disease transmission from ocular donor tissue transplantation.
Microglial signal transduction of amyloidogenic fragments
Prophylactic potential of pentosan polysulphate in TSEs
Most Parkinson's cases sporadic
Protease-resistant prion protein produced in vitro lacks detectable infectivity.
Similarities between BSE and an experimental isolate of natural scrapie, CH1641.
02 Feb 99 webmaster commentThis November 98 paper int he Am J Path has some very disturbing observations:
Basically, Pammer et al. found that keratinocytes, while normally expressing some prion protein, express very high levels in common skin inflammations such as eczema, psoriasis, contact dermatitus, and near broken skin. Further, these dermal cells are regularly infiltrated by dermal mononuclear cells [T lymphocytes and macrophages] also expressing normal prion.
Worse, TGF-alpha and IFN-gamma strongly up-regulate prion production; these cytokines are strongly expressed in psoriatic dermatitis and at skin inflammatory sites. These lympocytes could carry the infection back to lymph tissues (or vice versa). Mucosal tissues, including reproductive epithelial, show similar properties.
They note that skin grafts [for burns, surgery, and chronic ulcers] are grown in fetal bovine serum plus bovine pituitary extracts.
This has possible implications for horizontal transmission of scrapie [pruritus, common scratching post], for periferal transmission of kuru, for assignation of sporadic CJD, for conjugal and care-giver CJD (recall also cat+owner case in Italy), for transmission of CWD [cramped pens, nose rubbing, fenceline contact], occupational exposure of pathologists, morticians, and beef industry personnel, gelatin and leather safety, and so on.
Puritus can occur in CJD: see Shabtai et al. Neurology. 1996 Apr;46(4):940-1: "We report three patients with Creutzfeldt-Jakob disease, whose first symptom was severe pruritus, similar to that observed in scrapie. The pruritus was resistant to therapy. The underlying mechanisms are unclear, but we speculate that the pruritus may result from brainstem involvement."
In regards to shedding of agent, they note the epidermis is constantly self-renewing, shedding terminally differentiated cells off the body surface. This mechanism would not give time for rogue prion damage in situ because affected cells were being rapidly shed to the environment.
Am J Pathol 1998 Nov;153(5):1353-8 [offline] Pammer J, Weninger W, Tschachler EPrion diseases are transmissible spongiform encephalopathies of humans and animals characterized by the accumulation of a proteinase-resistant isoform of the cellular prion-related protein (PrPc) within the central nervous system. In the present report we demonstrate for the first time the presence of PrPc on squamous epithelia of normal and diseased human skin and show that inflammatory cytokines regulate PrPc expression in cultured human keratinocytes (KCs). By immunohistochemistry, only little expression of PrPc, which was mainly confined to KCs, was detected in normal skin. In contrast, in inflammatory skin diseases including psoriasis and contact dermatitis, PrPc was strongly present on both KCs and infiltrating mononuclear cells. Strong PrPc expression was also observed in squamous cell carcinomas and viral warts whereas basal cell carcinomas were mostly negative. In mucous membranes of the upper digestive tract and the genital region, distinct PrPc expression by basal squamous epithelial cells was a constant feature. In tissue culture, primary KCs constitutively expressed PrPc mRNA and protein. Exposure of these cells to transforming growth factor (TGF)-alpha or interferon (IFN)-gamma led to an increase of PrPc protein expression. The presence of PrPc on epithelial cells of skin and mucous membranes suggests that these cells represent possible first targets for peripheral infection with prions.
J Gen Virol 1996 Jul;77 ( Pt 7):1595-9 Taylor DM, McConnell I, Fraser HScarification of the skin is a possible route of entry for scrapie infectivity in sheep, and for Creutzfeldt-Jakob disease agent in humans within the context of occupational exposure to infected brain in the autopsy room or laboratory. The effectiveness of skin scarification routes as portals of entry for infectivity had not previously been tested experimentally but this study has shown that these are efficient routes for establishing infection in mice using the 139A and ME7 strains of scrapie agent. Scarification had much the same efficiency as inoculation by the intraperitoneal, intravenous or perivenous routes but was not effective in immunocompromised (SCID) mice. It was concluded that replication of infectivity within the lymphoreticular system, which is precluded in SCID mice, is a necessary prerequisite for the development of infection in the central nervous system following inoculation via scarification.
Thu, 21 Jan 1999 Conference announcement See also compiled Medline abstracts of scientists expressing concern about CJD and blood safety
BIOLOGY AND TRANSMISSIBILITY Role of Leukocytes in TSE nvCJD Blood-Borne TSE Infectivity SCREENING AND REGULATION Immunodiagnosis Assessing the Risk from nvCJD Infectivity in Blood FDA Policy Update and Changes Impact of Policy on Manufacturers and Bankers TSE VALIDATIONS Inactivation and Removal Purification of Factor VIII Partitioning during Plasma Fractionation
Dr. Robert G. Rohwer, Director, Laboratory of Molecular Neurovirology Research Service, Veterans Affairs Medical CenterThe blood of TSE infected rodents contains low levels of TSE infectivity. A significant portion of this infectivity remains with platelet poor plasma after component separations. During plasma fractionation most of the infectivity that was recovered was found in cryoprecipitate and the first alcohol precipitate of the Cohn fractionation. However, 99% of the brain-derived infectivity spikes and PrP fibrils indicated high levels of removal of both infectivity and fibrils during the refinement of final products from cryo-poor supernatant and crude Cohn fractions.
Dr. Moira E. Bruce, Head of Pathology and Pathogenesis Section, Institute for Animal HealthIn order to investigate which cells of the immune system are important in TSE pathogenesis, we have produced chimeric mice in which there is a mismatch in PrP expression between follicular dendritic cells and lymphocytes by grafting bone marrow from PrP knockout mice into immunodeficient PrP-expressing recipients and vice versa. The results of scrapie challenge experiments using these chimeric mice have provided strong evidence that the replication of the ME7 strain of scrapie in spleen depends on PrP-expressing follicular dendritic cells and not directly on lymphocytes or other bone marrow derived cells. These observations contrast in several respects with those obtained elsewhere using the RML scrapie isolate, which indicated, firstly, that bone marrow derived cells can support replication in spleen and, secondly, that B cells play a crucial role in neuroinvasion. This inconsistency raises the possibility that different strains of TSE agent may target different cell populations of the immune system.
Dr. Robert G. Will, Consultant Neurologist, National Creutzfeldt-Jakob Disease Surveillance Unit, Western General HospitalThe balance of evidence does not indicate that classical CJD is transmissible through blood or blood products. New variant CJD is a new disease, and there is a possibility that the risks of onward transmissions through blood or blood products may be greater than in classical CJD. Measures to minimize the risks of iatrogenic transmission of new variant CJD have been introduced in the United Kingdom.
Dr. Richard J. Kascsak, Head, Laboratory of Immunological Neurovirology, New York State Institute for BasicResearch Immunological approaches have been of vital importance in the diagnosis and study of prion diseases. Polyclonal and monoclonal antibodies to PrP, the host coded component of prions, have revealed the role of linear (pepscan analysis) and nonlinear epitopes in determining species and site specificity. These antibody-based assays continue to play a key role in the detection and analysis of prions and their component PrP.
Dr. Philip J. Comer, Director of Client Services, Det Norske VeritasWe still do not know how many people may have been infected with nvCJD in the United Kingdom, and so any attempt to assess the actual risk from possible infectivity in blood is fraught with difficulty. In this risk assessment study, which was requested by the UK government, the overall exposure of some characteristic patient groups to infectivity in both blood transfusions and plasma products has been estimated, so that the relative risk to the different patient groups can be assessed, and the sensitivity of the results to the various assumptions evaluated. The model has also been used to assess the effectiveness of alternative risk reduction strategies-e.g., leucodepletion and elimination of UK-sourced plasma.
Dr. Malcolm R. Macnaughton, Division Head, Laboratory Sciences, Inveresk ResearchInveresk has performed up to 50 TSE validation studies over the past seven years and has extensive experience with a range of products including several plasma derivatives. This experience extends to the execution of numerous expert reports for risk analysis associated with such products. The presentation will focus on the design, reproducibility, and relevance of such studies that will incorporate an analysis of all types of processing stages. A discussion will be included concerning current guidelines in this area and the relevance for these validations in contributing to the assurance of product safety.
Dr. Dorothy Scott, Center for Biologics Evaluation and Research, Food and Drug AdministrationConsiderable changes in FDA policy concerning CJD issues and blood products have occurred since 1995. The rationale for recent changes is based upon accumulating epidemiologic and laboratory-based evidence suggesting low likelihood of CJD transmission by blood, blood products, and derivatives. Until more is known about how nvCJD is transmitted, strict withdrawal recommendations remain in effect if a donor with this condition is identified.
Dr. Maura Ricketts, Medical Specialist, Blood-Borne Pathogens Division, Bureau of Infectious Diseases, Laboratory Center for Disease Control-CanadaScience, consumers, risk management professionals, ethicists, the law and public policy developers are in turmoil over prion diseases. Data from manufacturers regarding the impact of public policy will be examined to explore risks and benefits to the blood system of recent policy changes.
Dr. William N. DrohanThe American Red Cross and Baxter Healthcare process for purification of coagulation factor VIII from human plasma utilizes cryoprecipitation, solvent and detergent treatment, immunoaffinity adsorption/elution, and ion exchange steps to achieve a highly purified factor VIII product. In order to assess the ability of this process to clear the agent of spongiform encephalopathies, a 10% homogenate of scrapie-infected hamster brain was spiked into the clarified cryoprecipitate starting material. Using intracerebral inoculation into hamsters, the titer of scrapie infectivity was measured in the spiked starting material and that remaining at each stage of the purification process. The results showed clearance of over 10 log10 infectious units of scrapie infectivity throughout the process. The implications for the safety of this coagulation product will be discussed.
Dr. Stephen R. Petteway, Jr.Bayer Biological Products is pursuing a program to assess the potential risk of transmission of human TSE by blood or plasma products. The program involves the development of in vitro assays for the detection of the pathogenic isoform of the prion protein (PrPSC/RES), the application of these assays to assess partitioning and/or removal of TSE/PrPSC/RES by plasma and biotechnology processes, and the correlation of PrPSC/RES and TSE infectivity partitioning. Data demonstrating partitioning/removal of PrPSC/RES/TSE infectivity as a result of plasma and biotechnology manufacturing processes will be presented.
BSE InquiryOn the BSE Web site there are now six more Draft Factual Accounts (DFAs), all published on 22 January and inviting comment by 15 February. The previously published DFAs were 1) The Establishment and Proceedings of the Southwood Working Party on Bovine Spongiform Encephalopathy (111 Pages) 2) The Tyrrell Consultative Committee on Research into Spongiform Encephalopathies (52 Pages) 3) The Spongiform Encephalopathy Advisory Committee (66 Pages) In addition to 3a) supplementary tables re SEAC, the new DFAs are 4) Central Veterinary Laboratory (Part 1) 5) The Early Days 6) Slaughter and Compensation 7) The Ruminant Feed Ban (part1) 8) The Introduction to the SBO Ban 9) Government and Southwood All are accessible by links on the Draft Factual Accounts link on the BSE Inquiry Web Site As a reminder, it is stated there that the BSE Inquiry is publishing a number of draft factual accounts for consultation. The accounts cover the work of the main scientific advisory committees, key events such as the ruminant feed ban and the specified bovine offal ban, slaughter and compensation policy, CJD surveillance and care, risk assessment, bovine by-products, statistics, scientific research and several other areas. The documents are designed to be full accounts of the factual evidence on certain topics which the Inquiry has gathered in the last twelve months and to help the Inquiry in the rest of its work. The summaries are not intended to cover all the areas of the evidence, to make any judgements about the implications of the facts or to point to any conclusions. These will be for the Committee"s report to Ministers on 30 June 1999. The Draft Factual Accounts (DFAs) are intended to help the Committee of Inquiry in their further work. You are invited to point out any errors or material omissions. If you have any comments which do not involve amendments to the factual account please put them in a separate document.
Comments on Draft Factual Account should be sent to: The Secretary The BSE Inquiry 6th Floor Hercules House Hercules Road London SE1 7DU
Cornea 1999 Jan;18(1):2-11 Hogan RN, Brown P, Heck E, Cavanagh HDRecent new reports of possible iatrogenic transmission of Creutzfeldt-Jakob disease (CJD) in Europe have prompted renewed scrutiny of current Eye Bank Association of America criteria for evaluation of potential corneal donors in this country. A prior study evaluated the risk of CJD occurring in U.S. corneal donors by using data to 1994. This report updates these data, analyses the risk by using data to 1997, and predicts potential risk into the next decade.
EBAA data inclusive through 1997 were reviewed and correlated with incidence figures for CJD in the United States as provided by the Communicable Disease Center in Atlanta.
The annual incidence of CJD has remained stable at 1 case per million population. Thus approximately 270 new cases of CJD would be expected to occur each year in the United States. From this, the calculated risk of a prion-infected corneal donor appearing in the donor pool is 0.045 cases per year. If the data are corrected for age (90% of CJD patients are older than 60 years) and for possible infected but asymptomatic CJD patients (prevalence, 70 cases per million), at worst, 2.12 cases per year would appear for potential corneal donation (0.005% of all donors). [These figures could easily be too low by a factor of ten. --webmaster]
Whereas donors completely without any neurologic symptoms cannot be screened by using any currently available laboratory method, those with a characteristic quadrate clinical prodrome including cognitive changes, speech abnormalities, cerebellar findings, and myoclonus could all be potentially excluded by using tightened medical record and historical screening criteria.
Although no cases of bovine spongiform encephalopathy (mad-cow disease) or new variant CJD have been reported in the United States, if such should occur, only 4.2 cases of CJD would be expected in potential donors each year (0.009% of all donors). [This calculation makes no sense. Surely it would depend on the (undetermined) level of nvCJD. Did the authors simply use UK nvCJD death statistics to date? This would be terribly naive. -- webmaster] Tightening of exclusionary queries would significantly reduce the risk of even this number of patients appearing for corneal donation.
Historical queries of potential corneal donors should be tightened to assure exclusion of donors with early neurologic alterations. Any patient undergoing autopsy for evaluation of possible central nervous system (CNS) disease should be absolutely excluded. With this approach, the risk of inclusion of CJD-infected transplant tissues derived from ocular sources is very small, and all previously reported cases would have been prospectively excluded from surgical use. Clearly, the benefits of corneal transplantation in the overall population continue significantly to outweigh the risks of transmission of prion disease.
[If recipients of corneas are an elderly population on average, iatrogenic CJD might never show up before they died of other causes. Ignoring this and assuming efficient transmission, 2-20 cases of sporadic CJD a year might be attributable to cornea transplants, that is 1-8% of all CJD in the US. --webmaster]
J Neurosci 1999 Feb 1;19(3):928-939 Combs CK, Johnson DE, Cannady SB, Lehman TM, Landreth GEMicroglial interaction with amyloid fibrils in the brains of Alzheimer's and prion disease patients results in the inflammatory activation of these cells. We observed that primary microglial cultures and the THP-1 monocytic cell line are stimulated by fibrillar beta-amyloid and prion peptides to activate identical tyrosine kinase-dependent inflammatory signal transduction cascades. The tyrosine kinases Lyn and Syk are activated by the fibrillar peptides and initiate a signaling cascade resulting in a transient release of intracellular calcium that results in the activation of classical PKC and the recently described calcium-sensitive tyrosine kinase PYK2. Activation of the MAP kinases ERK1 and ERK2 follows as a subsequent downstream signaling event. We demonstrate that PYK2 is positioned downstream of Lyn, Syk, and PKC. PKC is a necessary intermediate required for ERK activation. Importantly, the signaling response elicited by beta-amyloid and prion fibrils leads to the production of neurotoxic products. We have demonstrated in a tissue culture model that conditioned media from beta-amyloid- and prion-stimulated microglia or from THP-1 monocytes are neurotoxic to mouse cortical neurons. This toxicity can be ameliorated by treating THP-1 cells with specific enzyme inhibitors that target various components of the signal transduction pathway linked to the inflammatory responses.
2 Feb 99 webmaster listserve commentaryThe graphic below treats the epidemic as a superpositioning of various sub-epidemics by genotype. The graphic is for conceptual illustrative purposes only and is not intended to predict the extent of the epidemic. Published predictions to date have failed to specifiy which epidemic they are seeking to predict. The main point is that little has been released on the prion genotype and karyotype of individuals affected so far. Much more useful data may come in soon from the appendix and tonsil survey.
The DoH page has 134 referrals for 1996, 160 for 1997, and 150 for 1998 which are compatible with the story. The table does not relate deaths to the referal column of that year but to several years earlier (plus they include outside referrals to St. Marys). The implication is that the referal column has been a fairly reliable leading indicator when divided by 5. There have been 910 total referrals since 1990 so 182 cases of nvCJD would emerge from waiting out the present set of referrals according to this interpretation. On 150 total referrals [1998 only], 1/5 gives 30 cases of total CJD whereas 56 are reported of which 12 [21%] were nvCJD. How many referrals are backlogged [not allocated] -- no one is saying.
The DoH columns are called deaths (surely a strongly lagging indicator) in"probable and definite" referrals. At the bottom however, there are "definite nvCJD cases still alive." Does the death column also include living but definites? The DoH page is simply a pass-through facility for the Surveillance Unit, they evaluate nothing themselves. If DoH wants to wait until death, then this could simply be put down to panic management or beef export boosterism. Some of the cases are still alive 18 months after reliable scientific confirmation as nvCJD -- ie, a case like this today would show up in July 2000. How long did the Vicky Rimer case go on?
The Lancet article establishes that a positive tonsil in a referral is a definite nvCJD. Note that 9/20 or 45% were nvCJD in this series. Applying this rate to 200 referrals gives 90 cases of nvCJD for 1999. Collinge's cases may or may not show up in the DoH referral column which does not break out referrals to the Unit and referrals to St. Mary's. The DoH stats page deferred all of Collinge's cases to 1999. The next table will be published on Monday 1 March 1999.
Both the tonsil or appendix test are likely applicable pre-clinically to pre-referral individuals. While not every positive may go on to die of nvCJD, these numbers could form an upper bound to the scope of the epidemic (though other classes of patients may show up later). My gut feeling is that the UK is not going to put any serious money into CJD research if there are just going to be a few tens of thousands of deaths, any more than the US worries about listeria in the meat with 1500 deaths a year.
This puts an impossible burden on the scientists should they later be left with a very brief window in which to develop a therapy for much larger numbers. What constitutes an appropriate research effort.? A further year or two spent in denial now could look very, very stupid later. I looked through 20 pages of post-doc ads in the most recent Nature: lots of positions for plant taxonomists etc but not a single one for nvCJD. So spend 7 billion on bailouts but never mind 30k x 200 postdocs for an adequate research program.
Another bizarre press report: "Dr Ironside said ... that [the victim] acquired the BSE agent from a dietary source. This was likely to have been random and only one occasion would have been sufficient, he said."
This reminds me of the old tales of a cow getting the odd random lump of bad rendered protein, no reason to slaughter the rest of the herd just because one unlucky cow drew a short straw.
How could anyone get a rare random hit given the colossal amount of meat from both subclinical and clincial cows that went into the human food chain? We are talking about billions of pounds of meat (with its innervation and lymphoreticular components) here. The debate now is over whether there is such a thing as a saturation of dose, whether anyone had less than that. Ironside's statement could have to do with panic managment, make it sound like a church getting hit by lightning. The average person knows this happens but goes on singing from the hymnal.
Anderson's group fights off surveys in every paper. As usual, they are campaigning against actual data collection. I am quite confident that this paper did not predict nor are its scenarios particularly consistent with the latest burst of cases to 43. Meaningful results are unlikely because biological parameters are not simply not known. There has never been a discussion of genetic issues in any of their papers. They could not possibly "show that the minimum length of the incubation period is approximately nine years' given the meagre data. Maybe according to assumptions in their unvalidated model.
It is time for them to fish or cut bait. I want to see a prediction from this group that is clean enough to be rejectable/verifiable near term -- no one can possibly go wrong spraying out 20 year scenario families or making unrefutable claims about BSE events lost to history. How many nvCJD cases for 1999 or 2000, for example. Their best single number and spare us the explanation of it:
Proc R Soc Lond B Biol Sci 1998 Dec 22;265(1413):2443-52 Ghani AC, Ferguson NM, Donnelly CA, Hagenaars TJ, Anderson RM New research web siteUnderstanding the epidemiology and aetiology of new-variant Creutzfeldt-Jakob (vCJD) disease in humans has become increasingly important given the scientific evidence linking it to bovine spongiform encephalopathy (BSE) in cattle and hence the wide exposure of the population of Great Britain (GB) to potentially infectious tissue. The recent analysis undertaken to determine the risk to the population from dorsal route ganglia illustrated the danger in presenting point estimates rather than ranges of scenarios in the face of uncertainty.
We present a mathematical template that relates the past pattern of the BSE epidemic in cattle to the future course of any vCJD epidemic in humans, and use extensive scenario analysis to explore the wide range of possible outcomes given the uncertainty in epidemiological determinants. We demonstrate that the average number of humans infected by one infectious bovine and the incubation period distribution are the two epidemiological factors that have the greatest impact on epidemic size and duration. Using the time-series of the BSE epidemic and the cases seen to date, we show that the minimum length of the incubation period is approximately nine years, and that at least 20% of the cases diagnosed to date were exposed prior to 1986.
We also demonstrate that the current age distribution of vCJD cases can only arise if younger people were either exposed to a greater extent, more susceptible to infection, or have shorter incubation periods. Extensive scenario analyses show that given the information currently available, the very high degree of uncertainty in the future size of the epidemic will remain for the next 3-5 years. Furthermore, we demonstrate that this uncertainty is unlikely to be reduced by mass screening for late-stage infection.
J Gen Virol 1999 Jan;80 (Pt 1):11-4 Hill AF, Antoniou M, Collinge J[From the full-text, the authors were able to replicate the 1994 conversion results of Kocisko et al. The methods used are reported in commendable detail: while a null result in terms of infectivity bioassay, there is considerable interest in why this should be so. For example, is protease-resistance a poor proxy for the actual conformational shift needed?
They provide no quantitative information on how many femtograms of protein was converted; while it was enough to show up as a gel band, the amount of product injected was never compared to the 5 femtograms thought to be the minimal infectious dose. They did not use over-producing hyper-sensitive mice and collided with the lab mouse lifespan barrier at 550 days. This experiment must have begun in mid to late 1966 as it was submitted in July 1998.
I disagree with their view that recombinant protein is a necessary starting point in proving 'protein-only'; de novo synthesis of a fragment is a very viable alternative. Recombinant protein is convenient but perhaps flawed material in terms of modified arginine, carbohydrate, copper, GPI, and denaturation history. Here they produced MH2M in erythroleukaemia cells, which just about guarantees the wrong carbohydrate moieties. There was no chaperone provided to the in vitro conversion; this could greatly affect efficiency or stablity of product.
I think a positive result at this point would be anti-climactic and no great step forward towards characterizing the participants of in vivo conversion. Continuing negative results also mean little (think about getting RNA polymerase and all its little helpers working correctly). However, this is still some sort of holy grail for the old-timers. -- webmaster]
Abstract: The 'protein-only' hypothesis of prion propagation argues that infectious prions consist of PrP(Sc), a conformational isomer of host-derived prion protein (PrP(C)), which can be distinguished from PrP(C) by its partial resistance to proteases. While protease-resistant PrP has been produced by mixing PrP(Sc) and recombinant-derived PrP(C) in vitro, bioassay of any new infectivity has been precluded by the need to use a large molar excess of same species PrP(Sc). Transgenic mice expressing a chimaeric hamster-mouse PrPC (MH2M PrP(C)) are, unlike conventional mice, highly susceptible to Sc237 hamster scrapie. In addition, they produce MH2M PrP(Sc) and infectivity which is pathogenic for conventional mice. We have therefore attempted to produce MH2M PrP(Sc) in vitro as any infectivity produced could be distinguished from the hamster PrP(Sc) used to promote the conversion by bioassay in conventional mice. Although protease-resistant MH2M PrP was produced, no infectivity was detected on bioassay. These results argue that acquisition of protease resistance by PrP(C) is not sufficient for the propagation of infectivity.
J Gen Virol 1999 Jan;80 (Pt 1):1-4 Hope J, Wood SC, Birkett CR, Chong A, Bruce ME, Cairns D, Goldmann W, Hunter N, Bostock CJNew variant Creutzfeldt-Jakob disease (vCJD) and bovine spongiform encephalopathy (BSE) are caused by the same strain of pathogen and, as sheep can develop experimental BSE, this has raised concern that humans may be at risk from eating mutton if BSE has naturally transmitted to sheep. Biochemical typing of abnormal prion proteins (PrPsc) has been suggested to detect BSE in sheep. Although this approach is ingenuous, we can now report biochemical evidence of strain variation in contemporary and archival brain tissue from cases of experimental BSE or experimental and natural scrapie in sheep. Interestingly, we found at least one isolate of natural scrapie (CH 1641) with a very similar, but not identical, PrPsc profile to BSE but which differs from BSE in its transmission characteristics to mice.
Lancet Volume 353, Number 9147 9 January 1999 free fulltext Christine Farquhar, Alan Dickinson, Moira BruceVariant Creutzfeldt-Jakob disease (CJD) probably results from exposure to the bovine spongiform encephalopathy agent. There is no treatment to slow or halt variant CJD, and the diagnosis is usually made when patients are terminally ill. During the long incubation period when there are no symptoms, there is a potential but unknown risk of transfer of infection by blood transfusion, treatment with blood products, transplantation, or reuse of surgical instruments.
Scrapie was the first described transmissible spongiform encephalopathy (TSE). After peripheral infection with scrapie, titre rises in lymph nodes and spleen before transfer to the central nervous system (CNS). A fraction of the host's "prion protein" (PrPC) aggregates into a protease-resistant isoform (PrPSC), and this marker enables tracking of infectious spread throughout the host. From mouse models we know that the timing of these events depends on the infecting TSE strain and host PrP genotype.1 PrP aggregates have been identified in lymphoid tissue removed from a patient long before variant CJD was diagnosed.2
Dextran sulphate 500 (DS500) prolongs scrapie incubation period in mice and reduces disease susceptibility.3 Another polyanion and heparin analogue, pentosan polysulphate (PS syn SP54, Tavan, Elmiron) is less toxic in vivo.4 It is also more effective in lengthening incubation and reducing susceptibility when given at high dose (3x10 mg) weeks before scrapie inoculation. In a model in which infectivity enters the CNS very quickly, however, PS is only effective if given close to scrapie injection.5
We report results of a single administration of low-dose PS given intraperitoneally after a normally 100% lethal intraperitoneal scrapie injection in mice. Two mouse-passaged scrapie strains were inoculated into six different inbred mouse strains. PS (sodium salt, Sigma) was given intraperitoneally or orally after scrapie, as either 250 µg or 1 mg in saline. Controls matched for age and sex were given saline. Individual incubation periods and scrapie diagnosis were by standard methods.
... [table too hard to reproduce] ...
Intraperitoneal PS given 7 h after scrapie prolonged survival significantly in all cases (table). Depending on mouse strain, 250 µg of PS increased the mean incubation period of the ME7 scrapie strain by up to 66%. 1 mg of PS protected VM mice completely from the 22A scrapie strain; animals died from unrelated causes between 500 and 707 days after inoculation whereas controls succumbed to scrapie by 428 days (mean 376); this represents at least a hundredfold reduction in the sensitivity of these mice to infection. After ME7 infection, there were survivors in treated groups. For the CBA mouse strain, 1 mg PS was completely protective. Treated animals dying of unrelated causes up to 526 days after inoculation displayed neither clinical symptoms of scrapie nor pathological changes: untreated CBA mice all died from scrapie by 310 days (mean 283). Oral PS was ineffective in delaying disease.
Multiple high doses of PS are licensed in the USA for the treatment of interstitial cystitis. Although direct testing of the efficacy of PS in reducing susceptibility to variant CJD is not possible, further animal studies are essential to examine the possible use of PS for risk reduction.
1 Farquhar CF, Dornan J, Somerville RA, et al. Effect of Sinc genotype, agent isolate, and route of infection on the accumulation of protease-resistant PrP in non-central nervous system tissues during the development of murine scrapie. J Gen Virol 1994; 75: 495-504. 2 Hilton DA, Fathers E, Edwards P, et al. Prion immunoreactivity in appendix before clinical onset of variant Creutzfeldt-Jakob disease. Lancet 1998; 352: 703-04. 3 Farquhar CF, Dickinson AG. Prolongation of scrapie incubation period by an injection of dextran sulphate 500 within the month before or after infection. J Gen Virol 1986; 67: 463-73 4 Diringer H, Ehlers B. Chemoprophylaxis of scrapie in mice. J Gen Virol 1991; 72: 457-60. 5 Ladogana A, Casaccia P, Ingrosso L, et al. Sulphate polyanions prolong the incubation period of scrapie-infected hamsters. J Gen Virol 1992; 73: 661-65.
January 26, 1999 By BRENDA C. COLEMANCHICAGO - Most cases of Parkinson's disease are not the result of a genetic defect but are instead caused by factors that are probably environmental, according to a landmark study of more than 17,000 twins.
"For the first time, today we can say that for people with Parkinson's disease diagnosed after age 50, it's most commonly caused by environmental factors," said Dr. Caroline M. Tanner of the Parkinson's Institute in Sunnyvale, Calif., who led the study. It is published in Wednesday's Journal of the American Medical Association.
The environmental factors are unknown but may include chemical exposures, diet and smoking - the last of which paradoxically seems to lessen the risk of developing Parkinson's, she added in a teleconference call Tuesday.
A genetic cause is most common in the approximately 10 percent of people with the disease who are diagnosed before age 50, she said. At least 1 million Americans have Parkinson's, Tanner said, making it second only to Alzheimer's disease in frequency as a degenerative disease of the brain and nerves.
Parkinson causes slow deterioration of the nerves' ability to control the muscles. It usually starts with small tremors, then progresses to a shuffling gait and increasing weakness. There is no cure, and drug therapy tends to lose effectiveness over time. In 1997, researchers identified a long-sought gene defect that can cause a form of Parkinson's, but the proportion of cases arising from the defect was unknown before this study.
In the new study, researchers tracked down more than 17,000 men enrolled in a World War II-era twin registry. The researchers found 161 twin pairs in which at least one brother had Parkinson's disease and data on the pairs was complete.
Among the 161 sets, there were 16 in which Parkinson's had struck before age 50. Of the four sets of identical twins, who have exactly the same genetic material, both brothers had Parkinson's. Among the 12 fraternal pairs, who share only half their genetic material, there were only two in which both brothers had Parkinson's.
Researchers calculated that if one twin developed the disease by age 50, the other was six times more likely to get it if he were an identical twin than if he were a fraternal twin. Tanner said environmental factors most likely to play a role in typical Parkinson's include exposure to chemicals such as pesticides and herbicides, diet and tobacco smoking. The apparent protective effect of smoking was found in the twins and in previous research, Tanner said.
She and J. William Langston, president of the Parkinson's Institute and senior author, said the protection is probably real, perhaps caused by smoking's stimulation of the liver to produce enzymes that neutralize some toxin that would otherwise provoke Parkinson's.
"But there are about 2,000 chemicals in cigarette smoke, so we still have a big job ahead of us in finding what chemicals might actually be protective," Langston said. "And we don't recommend smoking to prevent Parkinson's disease."
An expert not involved in the study said it presents a compelling reason to search for better treatments, since the drugs now available may lessen symptoms but don't really attack the disease or prevent disability.
And surgery is promising but still largely experimental, noted Dr. Jeffrey L. Cummings of the University of California, Los Angeles. In an editorial accompanying the study, he recommended that the new findings should refocus research on environmental triggers for typical Parkinson's disease and genetic influences in early-onset disease.