Canadian and U.S. BSE Risk Steven Anderson, Ph.D, MPP Office of Biostatistics & Epidemiology Center for Biologics Evaluation & Research U.S. Food & Drug Administration TSE Advisory Committee February 12, 2004
Policy questions for BSE in North America • What is the BSE risk for the U.S. and Canada? • Part I - Estimating BSE risk: Potential exposure pathways in U.S. and Canada • What is the risk for the general U.S. population? What are the implications for the blood supply? • Part II – Estimating BSE exposure and risks in the U.S.
Part I – Estimating BSE risk:Potential exposure pathways in U.S. and Canada • Imports from BSE countries of: • A. Live animals • B. Mammalian-derived feed ingredients • Meat and bone meal, meals, etc. • C. U.S. and Canada – bilateral imports / exports • Has implications for movement of potentially infected cattle and contaminated products • Focus on imports from: • U.K. - since 1980 • BSE countries - since 1986
Potential Exposure Pathways – Live AnimalsA. Cattle Imports from United Kingdom
Potential Exposure Pathways – Live AnimalsA. Cattle Imports from BSE countries
Potential Exposure Pathways – FeedB. Feed ingredients from BSE countries U.S. • feed meal imports from UK since 1980 – total 81 tons • 12 tons in 1981 • 10 tons in 1984 • 2 tons in 1985 • 20 tons in 1989 (Disputed by U.S. authorities) • 37 tons in 1997 • U.S.A. imported ~10,500 metric tons of inedible meat byproducts from 1980-2000 from BSE countries Canada • reported no MBM imports from UK since 1980. • Canada imported ~8,523 metric tons of mammalian flours, meals, meat pellets from 1993-2000 from Denmark, Germany, Japan & France.
Cattle and beef trade in North America • Considerable movement of animals, feed ingredients, and beef products • Trade and production practices similar for each country • Import/export could introduce or spread infected animals or contaminated products
C. Cattle trade in North AmericaU.S. Cattle imports and exports 1992 to 2002
Conclusions Part I: Estimating BSE risk U.S. and Canada • Difficult to estimate absolute risk for U.S. and Canada • Most potential for introduction of BSE agent would have occurred prior to 1990 • Potential amount of BSE agent introduced unknown • Numerous chance events would be involved over last 10 to 15 years • Rendering • Fed to other cattle, dead on farm, etc. • Imports of live animals and feed materials from BSE countries occurred since 1980 but was small • Qualitative estimate of risk predicted to be low but difficult to estimate with certainty
Part II – Estimating BSE exposure and risks for the US population Many potential routes for human exposure to beef and bovine products • Primary source of potential BSE exposure • Food • High risk tissues – brain, spinal cord, eyes, dorsal root ganglia, small intestine Other sources • Dietary supplements • Medical products – devices, biologics, drugs
II. BSE exposure pathways for US population via beef • A. Consumption of large amounts high risk tissue (very low probability event) • Bovine brain or spinal cord • B. Consumption of small amounts high risk tissues in processed foods • Advanced meat recovery beef product • Ground beef products, beef sausages, hot dogs, processed meat sauces, etc.
II. BSE exposure pathways for US population via beef U.S. risk Probability of exposure to infected cow in 2003 • 1 positive identified – 35 million slaughtered 1 in 35 million (3.5 x 10-7 ) • Worst case – Based on statistical analysis USDA surveillance (~20,000 tests) ~1 in 1 million (1 x 10-6)
A.Consumption of large amounts high risk tissue: bovine brain • Probability of exposure: brain rarely consumed by Americans (100,000 – 180,000 servings) • Many servings from low risk cattle – calf brains, etc. • Probability infected brain in 2003 3.5 x 10-7 to 10-6 • Quantity of exposure: assume brain late stage BSE-infected cow 5,000 to 6,500 cattle oral ID50 • Conclusions: There is risk of exposure via this route Risk to the U.S. general population is low
B. Consumption of small amounts high risk tissue: advanced meat recovery • Advanced Meat Recovery (AMR): • Removes remaining meat from carcass, vertebral column and bone by machinery • Spinal cord usually removed before process • Dorsal root ganglia on vertebral column • > 70% of carcasses processed with AMR • Process would mix and dilute residual BSE agent present
B. Consumption of small amounts high risk tissue: advanced meat recovery • Machines can process 4,500 to 7,000 lbs bones per hour • Represents material from 20 to >35 animals • 5 – 10 lbs meat recovered per carcass • Estimated as much as 250 million lbs AMR meat produced annually
B. Consumption of small amounts high risk tissue: advanced meat recovery • Probability of exposure: advanced meat recovery (AMR) product consumed frequently • Dilution of BSE infectivity throughout a batch of AMR product • Probability infected cow in 2003 • 3.5 x 10-7 to 10-6 annually • Amount BSE infectivity present – estimated to be low because of dilution via AMR • Estimate ~ < 2 x 10-2(<4 x 10-3 to 2 x 10-2) cattle oral ID50 per average serving • Greater than a hundred of servings from each batch of AMR product
B. Consumption of small amounts high risk tissue: advanced meat recovery • Assuming BSE infected animal(s) enter AMR and residual infectivity present in vertebral column: • Probability exposure via AMR is low • 1 x10-7 to 2 x10-5 per serving beef AMR product per year • Probability ofinfection even lower • Assuming a species barrier of 1,000 • Reduction by oral route of >90% • Assume ~40% population sensitive - methionine homozygous at codon 129 of PrP • Probability of infection would be estimated to be less than < 3 x10-9 (2 x10-10 to 3 x10-9)annually in the U.S.
B. Consumption of small amounts high risk tissue: advanced meat recovery • Conclusions • Our preliminary estimates suggest that there is a low risk of human exposure to BSE agent via beef AMR product • Probability of human infection even lower • There is uncertainty in the estimates and some assumptions were made to estimate the risk • Risk to general population and blood supply is low
Recent BSE risk-reduction measures for food supply & feed • Should dramatically reduce small BSE risk for U.S.A. • Recent USDA measures Dec 30, 2003 prohibit: • Use of “downers” for human food • High risk tissue in AMR • Use of animals >30 months in AMR • January 2003 FDA feed ban prohibits: • Ruminant blood protein in feed • Plate waste, poultry litter • Requires dedicated feed processing lines for non-prohibited and prohibited feeds
Acknowledgements • Dr. Sonja Sandberg (OBE) • Rene Suarez-Soto (OBE) • Dr. David Asher (OBRR) • Dr. Rolf Taffs (OBRR) • Dr. Pedro Piccardo (OBRR) • Others at CBER
Factors considered in estimation • Total cattle slaughtered annually • 70% - 80% processed via AMMR • # animals/batch • 5-9lbs AMR per Animal • Percentage lost to imports, waste, non-use • Conversion lbs to servings • Total est AMR meat servings /yr • Servings AMR meat contaminated/Total AMR servings per yr • And / or • Dilution of ID50s from 1 cow in a batch of AMR