Source: http://efsaopinionbseanimalprotein.blogspot.com/2014/07/efsa-scrapie-reduction-unlikely-without.html
Timestamp: 2017-12-16 16:38:06
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EFSA opinion on the BSE related public health risk: EFSA Scrapie reduction unlikely without effective breeding programme
EFSA Scrapie reduction unlikely without effective ...
EFSA Scrapie reduction unlikely without effective breeding programme
Over the last ten years Classical scrapie in sheep has decreased in countries where breeding programmes for resistance were effectively implemented, say EFSA experts.
EFSA has assessed the state of scrapie in the EU since the introduction ten years ago of a series of measures to monitor and control the disease. Scrapie is a fatal disease that affects sheep and goats. It belongs to the same family of diseases as bovine spongiform encephalopathy (BSE) which is found in cattle and is commonly known as mad cow disease. There is no evidence that scrapie has ever been transmitted to humans. The infectious agent is thought to be an abnormal form of a protein, also called a prion.
Experts of EFSA’s Panel on Biological Hazards have concluded that an eradication policy that relies only on the detection and culling of infected flocks and does not include breeding programmes for resistance is unlikely to succeed. This is both because of the characteristics of this disease and because the classical scrapie agent can persist in the environment for years.
“Sheep with a particular genetic makeup are resistant to Classical scrapie and breeding choices allow an increase in the flock’s resistance to the disease” explains Giuseppe Ru, Chair of EFSA’s Working Group on scrapie situation in the EU.
EFSA experts concluded that Classical scrapie in sheep may die out if the percentage of resistant sheep is above a certain threshold.
Occurrence of Classical scrapie varies greatly across the EU and its evolution over time should be considered country-by-country. Overall, it has been reported in 17 Member States; in some of them cases have decreased over time, while in others no clear trend was observed.
EFSA experts recommend strengthening surveillance activities to detect infected flocks and control the disease, increasing the implementation of breeding programmes for resistance in sheep and starting their use in goats too.
Scientific Opinion on the scrapie situation in the EU after 10 years of monitoring and control in sheep and goats
Scrapie comes in two variants. Classical scrapie is transmitted through exposure to scrapie-infected animals (e.g. via milk or placentae) and their environment. Scientific evidence suggests that Atypical scrapie, the second variant, is spontaneous and non-contagious. In this opinion EFSA experts have considered both variants, with a particular focus on Classical scrapie. For media enquiries please contact: EFSA Media Relations Office Tel. +39 0521 036 149 E-mail: Press@efsa.europa.eu
http://www.efsa.europa.eu/en/press/news/140730.htm
RSSS started April 1, 2003. It is a targeted slaughter surveillance program which is designed to identify infected flocks. Samples have been collected from 430,085 animals since April 1, 2003. There have been 473 NVSL confirmed positive animals* (465 classical cases and 8 Nor98-like cases) since the beginning of RSSS. As of June 30, 2014, 32,173 samples have been collected in FY 2014, 26,408 from sheep and 5,765 from goats. As of June 30, 2014, 2 white-faced and 2 black-faced sheep have tested positive for scrapie in FY 2014. The percentage of samples that have tested positive for each face color from FY 2003 through FY 2014 is depicted in Chart 3. In November 2013, administrative units within APHIS Veterinary Services reorganized from 2 Regions to 6 Districts (Figure 1). The distribution of sheep and goat populations by District is depicted in Chart 4a. The number of animals collected for FY 2014 by District where collected is shown in Chart 4b. A monthly comparison of RSSS collections by fiscal year is displayed in Chart 5. Chart 6 is a retrospective 6-month rolling average of the percent positive, black-faced sheep sampled at RSSS collection sites.
*RSSS positives are reported based on collection date and may have been confirmed after June 30, 2014.
INTRODUCTION - Surveillance (Part 2) On-Farm Surveillance Testing sheep and goats in the field is an essential part of scrapie surveillance, and it includes both regulatory testing and on-farm surveillance. As the National Scrapie Eradication Program moves closer towards meeting the goal of identifying the last remaining cases of classical scrapie, finding and testing all sheep and goats meeting targeted sampling criteria is even more important. As of June 30, 2014, 1,174 sheep and 440 goats have been tested on-farm for FY 2014. As of June 30, 15 sheep and 9 goats have tested positive. The number of animals tested on-farm by month and by species for FY 2014 is shown in Chart 7. Total Animals Sampled for Scrapie Testing As of June 30, 2014, 33,787 animals have been sampled for scrapie testing:
•32,173 RSSS samples and 1,614 on-farm samples [includes regulatory testing (necropsy and live-animal) and on-farm surveillance] (Chart 8);
•Of which 27,582 were sheep and 6,205 were goats. Distribution of sampling by type (RSSS or on-farm) and by species is shown in Chart 9. http://www.aphis.usda.gov/animal_health/animal_diseases/scrapie/downloads/monthly_scrapie_report.pdf
Overall, all Nor98 isolates contained highly PK resistant PrPres aggregates, with the main PrPres being a non-glycosylated internal fragment, cleaved at both the N and C termini, which represent the distinctive biochemical feature of Nor98. This biochemical signature, unique among animal TSEs, is reminiscent of PrPres observed in human prion disorders such as GSS and VPSPr.
At present the only epidemiological link between animal and human TSEs has been demonstrated for classical BSE and variant CJD [16], [78], showing for the first time the zoonotic potential of TSEs. Since then, the implementation of active surveillance in livestock has led to the identification of Nor98 and other previously unrecognised animal prion strains, mainly with a sporadic occurrence, whose origin and zoonotic potential are still poorly understood [79]. It has been previously shown that peripheral tissues of sheep with Nor98 might harbour detectable levels of infectivity [49], [50], indicating that infectious material might enter the food chain. On the other hand, the well known genetic aetiology of GSS suggests that the similar PrPSc conformations found in Nor98 and GSS P102L are unlikely to indicate a common infectious source, but might derive from a similar molecular mechanisms involved in PrPC-to-PrPSc conversion.
Citation: Pirisinu L, Nonno R, Esposito E, Benestad SL, Gambetti P, et al. (2013) Small Ruminant Nor98 Prions Share Biochemical Features with Human Gerstmann-Sträussler-Scheinker Disease and Variably Protease-Sensitive Prionopathy. PLoS ONE 8(6): e66405. doi:10.1371/journal.pone.0066405
Received: January 24, 2013; Accepted: May 6, 2013; Published: June 24, 2013
Copyright: © 2013 Pirisinu et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was supported by grants from the Italian Ministry of Health (RF-2009-1474624); the European Union (Neuroprion Network of Excellence CT-2004–506579); the National Institutes of Health (NIH) NS062787, NIH AG-08012, AG-14359; Alliance BioSecure, as well as the Center for Disease Control and Prevention Contract UR8/CCU515004. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066405
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