Thursday, August 12, 2010

SEAC August 2010 Drayton Farm report update and more

2010 10 August 2010 -A report of SEAC’s 17 June discussion about a risk assessment on Drayton farm, Warwickshire is available.

Spongiform Encephalopathy Advisory Committee


Horizon scanning

The Committee Chairs identified the main issues they would be dealing with as follows:

ACDP TSE Working Group

• Infection control guidance is under constant review.

• Much progress has been made in making endoscopy safer through development of less invasive approaches and techniques to reduce risk of potential contamination, but more remains to be done.

• Work is beginning with surgeons on risk reduction in relation to other invasive procedures where instruments are difficult to decontaminate. Advisory Committee on Decontamination Science & Technology

• Quality assurance for decontamination procedures.

• Ways of keeping used surgical instruments wet/damp to maximise removal of protein.

• Introduction of anti-prion agents into validated decontamination cycles. Manufacturers need to know what is required and Trusts need to recognise vCJD transmission risks from conventionally decontaminated surgical instruments.

• Ways of minimising the number of discarded endoscopes and other instruments. Advisory Committee on the Safety of Blood Tissues and Organs

• Risk assessment and risk management of a wide spectrum of issues from blood to liver transplantation.

• Achieving a more consistent approach to consent for blood transfusion across the UK following the recent public consultation. Spongiform Encephalopathy Advisory Committee

• Obtaining more data on vCJD prevalence.

• Preventing new TSE epidemics.

• Ensuring that cost saving measures do not result in prevention of TSE transmission being compromised. CJD Incidents Panel

• Applying new prevalence data when available.

• Engagement of people who need to change practice on the ground.

• Coping with changes caused by cost pressures.


It was agreed that the presentations/discussions had achieved an interesting and useful day for participants. Whilst the purpose of the meeting was not necessarily to reach conclusions or provide advice for Government, there was consensus on the following:

• The TSE committees work well together.

• Advice should continue to be based on the available scientific evidence.

• Infection control and decontamination practice had improved widely as a result of the work on prevention of TSE

10 August 2010 - A report of the 17th June 2010 Joint Meeting of the UK Committees (the Advisory Committee on Dangerous Pathogens TSE Working Group, the Advisory Committee on Decontamination Science and Technology, the Advisory Committee on the Safety of Blood Tissues and Organs, the CJD Incidents Panel and SEAC) that advise Government on TSEs is available.



Drayton farm (in Warwickshire) has been a site of research projects involving experimentally infected TSE animals. Due to the long incubation periods and on site farm bio-security, the animals were kept such that they had access to pasture for most of the year. Infected animals were allowed to graze on pasture and pasture contamination from infected grazing animals contributes to the potential TSE risk of infection for the farm.

The experiments at Drayton have now ended and Defra asked the Veterinary Laboratories Agency to perform a quantitative risk assessment on the residual risks associated with the land where infected animals grazed, or were subject to composted manure or the release of wastewater. This work is of wider interest than just Drayton farm as there are several farms in the UK where such experimentally infected animals were kept.

Defra and the Devolved Administrations asked the advice of SEAC on the risk assessment.

SEAC considered this on 17 June 2010 in London.

Further background material on this subject can be found at:

Spongiform Encephalopathy Advisory Committee

17 JUNE 2010.

Drayton Farm Risk Assessment

The Committee was presented with a Risk Assessment prepared by the Veterinary Laboratories Agency, which assesses the residual TSE risk at Drayton Farm due to the presence of experimental animals and field cases on the site, and the land spreading of composted manure and wastewater. SEAC last considered this issue at its 53rd Meeting on 21-22 September 1998.

Several Members commented that the methodology of the Risk Assessment was sound. However, concerns were raised that some of the specific input values to the risk assessment are problematic because of the large number of assumptions on which these are based.

A Member suggested that the outputs of the Risk Assessment needed to be checked against the available data to ascertain whether these were consistent. For example, there are data from Iceland and the Ripley flock which clearly show that there is a risk from re-introducing livestock onto land which has previously held a scrapie infected flock. This should have raised questions in the minds of the authors about why the model comes out with a very low risk.

Additionally, a Member suggested that more consideration should be given to whether the theoretical assumptions based on regulations, actually correlate with the real life activity on the farm.

A Member noted that the Risk Assessment adds little to SEAC’s previous advice on this issue provided in 1998, and the Chair stated that because there are no additional data available, it is difficult for SEAC to update its previous advice on this issue.

The Committee agreed that:

• The methodology of the Risk Assessment is sound; however:

• there are serious problems with the input assumption to the model, given the lack of data;

• The outputs of the model are therefore uncertain; and

• There is no need to revise SEAC’s advice of 21-22 September 1998. Extract from Minutes of SEAC 53, 21/22 September 1998.

Item 9 - Disposal of excreta from cattle experimentally infected with BSE (paper SEAC 53/6)

42. The Committee had previously considered options for disposal of waste from cattle exposed to BSE in January 1998. Members had before them paper SEAC 53/6 providing details of possible disposal options for excreta from two long term experiments which were starting at Drayton Experimental Husbandry Farm. Alternative measures to incineration had been examined due to the practical and cost problems of pursuing this option for such a long period. Further information about the farm and methods of disposal which would comply with Good Agricultural Practice were provided. The key change was the proposal to utilise crops from the farm and the Committee were asked to note the concerns of a neighbouring farmer with a watercourse on his property which ran through the experimental farm about possible run off.

43. The Committee noted that the animals were being held in brand new buildings and that there were arrangements for separation of solid and liquid waste. The housing arrangements and husbandry procedures would ensure rigorous separation of the different groups of animals. It was reported that the Committee’s views would be applied to disposal arrangements for excreta from the sheep experimentally exposed to BSE at the Institute for Animal Health.

44. The Committee confirmed their previous advice that the waste from challenged animals should be incinerated for the first 28 days (which represented an extended “safe” clearance time from cattle intestines) and that, thereafter, the excreta should be composted for one year. They agreed that there was no scientific basis why composted material should not be spread on land as fertiliser prior to planting crops which could then be used for human consumption or animal feed, although coppicing may present the most desirable option from the point of view of public perception. However, the Committee felt it would be prudent not to spread the material on pasture which would be grazed by cattle, and that the experimental animals which were part of the cattle bioassay experiment should not be given the food from the farm. This was in order to prevent any future challenge of a positive result that contaminated food may have been a route of exposure which might lead to a consequent claim that the tissue being assayed was not really positive.

Detection of protease-resistant cervid prion protein in water from a CWD-endemic area

T.A. Nichols,1,2 Bruce Pulford,1 A. Christy Wyckoff,1,2 Crystal Meyerett,1 Brady Michel,1 Kevin Gertig,3 Edward A. Hoover,1 Jean E. Jewell,4 Glenn C. Telling5 and Mark D. Zabel1,*

1Department of Microbiology, Immunology and Pathology; College of Veterinary Medicine and Biomedical Sciences; Colorado State University; Fort Collins, CO USA; 2National Wildlife Research Center; Wildlife Services; United States Department of Agriculture; Fort Collins, CO USA; 3Fort Collins Utilities; Fort Collins; CO USA; 4Department of Veterinary Sciences; Wyoming State Veterinary Laboratory; University of Wyoming; Laramie, WY USA; 5Department of Microbiology, Immunology, Molecular Genetics and Neurology; Sanders Brown Center on Aging; University of Kentucky; Lexington, KY USA Key words: prions, chronic wasting disease, water, environment, serial protein misfolding cyclic amplification Abbreviations: CWD, chronic wasting disease; sPMCA, serial protein misfolding cyclic amplification; PrPC, cellular prion protein; PrPSc, disease-related, misfolded murine PrP; PrPCWD, disease-related, misfolded cervid PrP; PrPRES, protease-resistant PrP; FCWTF, Fort Collins water treatment facility

Chronic wasting disease (CWD) is the only known transmissible spongiform encephalopathy affecting free-ranging wildlife. Although the exact mode of natural transmission remains unknown, substantial evidence suggests that prions can persist in the environment, implicating components thereof as potential prion reservoirs and transmission vehicles.1-4 CWD-positive animals may contribute to environmental prion load via decomposing carcasses and biological materials including saliva, blood, urine and feces.5-7 Sensitivity limitations of conventional assays hamper evaluation of environmental prion loads in soil and water. Here we show the ability of serial protein misfolding cyclic amplification (sPMCA) to amplify a 1.3 x 10-7 dilution of CWD-infected brain homogenate spiked into water samples, equivalent to approximately 5 x 107 protease resistant cervid prion protein (PrPCWD) monomers. We also detected PrPCWD in one of two environmental water samples from a CWD endemic area collected at a time of increased water runoff from melting winter snow pack, as well as in water samples obtained concurrently from the flocculation stage of water processing by the municipal water treatment facility. Bioassays indicated that the PrPCWD detected was below infectious levels. These data demonstrate detection of very low levels of PrPCWD in the environment by sPMCA and suggest persistence and accumulation of prions in the environment that may promote CWD transmission.


CWD has been endemic in the area for forty years, and it remains unclear how long prions can persist in the environment. If persistent for at least several years, CWD prions deposited into the environment from thousands of infected carcasses may accumulate on soil and vegetation such that it can be washed into surface water draining the basin during snowmelt or rainstorms. Symptomatic and asymptomatic positive animals can also contribute to environmental CWD load via biological materials such as saliva, blood, urine and feces.5-7,32,36,38 Deer and elk defecate approximately 900,000 kg of feces and urinate approximately 14 million liters of urine in the area immediately surrounding the Cache la Poudre river per year.39-42 Although urine and feces likely contain much lower prion loads than blood or saliva, the sheer amount of excreta may contribute significantly to overall environmental prion contamination. The data presented here demonstrate that sPMCA can detect low levels of PrPCWD in the environment, corroborate previous biological and experimental data suggesting long term persistence of prions in the environment2,3 and imply that PrPCWD accumulation over time may contribute to transmission of CWD in areas where it has been endemic for decades. This work demonstrates the utility of sPMCA to evaluate other environmental water sources for PrPCWD, including smaller bodies of water such as vernal pools and wallows, where large numbers of cervids congregate and into which prions from infected animals may be shed and concentrated to infectious levels.

see full text ;

Wednesday, October 14, 2009

Detection of protease-resistant cervid prion protein in water from a CWD-endemic area

Fifth threat The precise nature of prions remains elusive. Very recent data indicate that abnormal prion protein (PrPTSE) can be generated from the brains of normal animals, and under some conditions (including contaminated waste water) PrPTSE can be destroyed whereas the BSE infectious titre remains almost unchanged, a finding that underlines the possibility of having BSE without any detectable diagnostic marker. These are just two areas of our incomplete knowledge of the fundamental biology of prions which constitute a fifth threat to the European approach to prion diseases.

The L-type BSE prion is much more virulent in primates and in humanized mice than is the classical BSE prion, which suggests the possibility of zoonotic risk associated with the L-type BSE prion. These findings emphasize the critical importance of understanding tissue distribution of L-type BSE prions in cattle because, among the current administrative measures for BSE controls, the specified risk materials removal policy plays a crucial role in consumer protection.

In Japan, atypical BSE was detected in an aged Japanese Black cow (BSE/JP24) (8). We recently reported the successful transmission of BSE/JP24 prions to cattle and showed that the characteristics of these prions closely resemble those of L-type BSE prions found in Italy (9). In this study, we report the peripheral distribution of L-type BSE prions in experimentally challenged cattle.

Thursday, August 12, 2010

Seven main threats for the future linked to prions

Terry S. Singeltary Sr. P.O. Box 42 Bacliff, Texas USA 77518

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