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What’s New With Bse?

BSE went from obscurity to crisis because humans from all walks of life refused to believe something bad was happening

Six years have elapsed since that fateful day in May 2003 when a downer cow at a small abattoir in Northern Alberta started a chain of events that eventually tipped the North American beef industry on its ear.

Skeptics dismiss it as an insignificant animal health event, yet remain baffled how affairs surrounding BSE spun so badly out of control. Those who watched events unfold on the Midlands of Great Britain — unchecked for two decades — gave voice and dismissed it as inevitable. The alarmists extol plagues of unprecedented proportions that never materialized.

Perhaps BSE was a disease so misunderstood that the scientific community, agriculture and politicians were powerless to halt its emergence. Perhaps the assumption that economic survival in the beef business depended on feeding meat and bone meal was so deeply rooted that BSE was destined to happen. Undeniably, BSE went from obscurity to crisis because humans from all walks of life refused to believe something bad was happening, brushed it aside and then responded using uncommon logic after it was too late.

It started as early as 1970 in Great Britain. Some think it was the result of prions being recycled from sheep to cattle. The claim that agents other than prions are involved has never been totally debunked. There is no doubt the disease was amplified through the practice of feeding meat and bone meal of ruminant origin on both sides of the ocean. How North America first inherited BSE may never be known with certainty. Its arrival on our shores was probably linked to European cattle imports through the 1960s and ’70s, parts of which eventually ended up in the North American rendering chain and were disseminated from there. The international trade of meat and bone meal, legal and otherwise, was almost certainly a factor in BSE becoming established. Whatever the cause, when BSE was eventually tagged as “homegrown” it invoked destructive trade sanctions and strife within an industry that still lingers — six years later.

The prions have revealed few secrets since their Nobel prize-winning discovery by Stanley Prusiner in 1982. BSE, because of parallels drawn between it and other prion-induced fatal encephalopathies in humans, has single-handedly stimulated the spending of billions on prion research within the agriculture and medical research communities. The pursuit of answers to how rogue proteins

cause disease in animals and humans created millions of dollars of investment in institutes dedicated to prion research, endowed research chairs in Canada and the U.S. and high security laboratories. Never before has so much research money been dedicated to the study of chronic, degenerative brain diseases in humans and animals. Despite the massive investment in research internationally, few revelations have yet to jump from the lab bench into everyday life that help dispel the cloud of myth and worry about BSE and the family of prion diseases it pilots.

Progress slow at best

1. A live test for BSE

Canada tested nearly 270,000 head since 2004, the U.S. about twice that number. The gold standard for tissue that can be tested for BSE in cattle remains an almond-sized piece of brain stem, the obex, collected from dead animals.

In September of 2008, scientists at the Public Health Agency of Canada’s National Microbiology Laboratory (NML) working with scientists from the Canadian Food Inspection Agency’s BSE Reference Laboratories, the Federal Research Institute for Animal Health in Germany, and the University of Manitoba made a discovery that could lead to accurate diagnostic tests on live animals. The researchers found that a protein in cattle urine indicates the presence of BSE with 100 per cent accuracy. It was also determined that the amount of protein corresponded to the stage of disease.

Dr. Stefanie Czub, manager, Virology Section and Quality Assurance, of the Canadian Food Inspection Agency and research team member said, “This is an important discovery and we are hopeful that it will eventually lead to a useful diagnostic test that will simplify surveillance and reduce costs.”

Although a commercial blood test for BSE remains a way down the road, there are several encouraging breakthroughs by different research groups. Research has shown that abnormal prions and products they generate in infected animals and humans can be detected in blood. For instance, the Amorphics Institute, Vancouver have developed special antibodies that attach to specific sites on circulating prion protein that may lead to a useful test in vCJD patients and scrapie infected sheep and goats.

Because circulating prions are not a characteristic of BSE, practical application of this technology in cattle is not expected, but would certainly strengthen diagnostic capability in other species. Researchers at the University of Calgary have identified specific gene sequences in circulating nucleic acids (DNA fragments) in elk experimentally infected with chronic wasting disease (CWD) and cattle infected with BSE that could be detected three to four months prior to development of clinical signs in infected animals. The research team lead by Dr. Cristoph Sensen is hopeful the finding will lead to an economical blood test providing short turnaround times that would be a boon to the cattle industry.

Researchers in New York are

reporting development of a nano-sized sensor that detects record low levels of prion proteins. The sensor resembles a molecular-sized tuning fork that changes its rate of vibration when prions attach. A special sensor measures the subtle change in vibration. In experimental trials, the sensor detected prions at concentrations as low as two nanograms per millilitre, the smallest levels measured to date. Researchers are confident the technology will lead to a reliable blood test for prion diseases in both animals and humans.

2. New insights into the origin of BSE

The study of transmissible spongiform encephalopathies (TSE) shows prions and prion diseases are more complex than originally thought. Although several strains of scrapie have long been known, it was generally thought that only one strain of BSE existed. Findings since 2007 now challenge that point of view.

Investigators first described an atypical form of BSE, referred to as “bovine amyloidotic spongiform encephalopathy” (BASE) in two older cattle from Italy. A similar strain was also detected in a cow in Japan. Both the Italian and Japanese strains were detected by routine sampling of animals without symptoms. Pathological changes that result from experimental infection with the BASE strains differ from typical BSE cases. BASE infected cattle appear to be older and show only weight loss and reduced alertness. A BASE strain has converted into a classical BSE following serial transmission in inbred mouse lines. Even though BASE and BSE appear to be distinct diseases caused by different prion strains, there is speculation that BASE may have evolved into BSE following changes in UK rendering practices through the 1980s.

Studies from work conducted in Canada and the U.S. (published 2008) describe atypical forms of the BSE prion as “H” and “L” subtypes and suggest that a rare, genetic abnormality in cattle may be linked to the emergence of atypical BSE strains. The scientific community, for the first time, grabbled with the probability that all three etiologic forms of TSEs (spontaneous, hereditary, and infectious) were present in non-human species.

3. The variant Creutzfeldt-Jakob Disease (vCJD) epidemic that alarmists predicted never materialized.

As of September, 2009 the number of deaths due to definite or probable vCJD cases remained at 164. A total of four definite/probable patients remain alive, bringing the total number of definite or probable vCJD cases to 168. No cases of vCJE have been recorded during the first seven months of 2009. This situation is consistent with the view that the vCJD outbreak in the UK is in decline. The first cases were observed in 1995, and the peak number of deaths was 28 in the year 2000, followed by 20 in 2001, 17 in 2002, 18 in 2003, nine in 2004, five in 2005, five in 2006, five in 2007, only one in 2008, and none to September in 2009.

Surveillance

Determining the risk status of cattle in countries with BSE was standardized by a risk-assessment mechanism established by OIE (World Organization for Animal Health). Chapter 2 of the Terrestrial Code describes internationally accepted criteria and provides surveillance guidelines that set conditions in categorizing countries as a negligible BSE risk, a controlled BSE risk or an undetermined BSE risk. Risk assessment provided the ability to compare “apples to apples” with regard to BSE risk. It was the ability to use scientific tools like risk assessment combined with a strong BSE surveillance program that opened doors for resumption of trade in beef and helped Canada defend itself when under attack by groups like R-Calf.

SRM

The BSE prion concentrates in tissues known as specified risk materials (SRM). Specified risk material include the skull, brain, trigeminal ganglia (nerves attached to the brain), eyes, tonsils, spinal cord, and dorsal root ganglia (nerves attached to the spinal cord) of cattle aged 30 months or older, and the distal ileum (portion of the small intestine) of cattle of all ages. Prions in SRM from infected cattle are very difficult to neutralize. Feed containing SRM consumed by young animals is generally accepted as the primary way BSE is perpetuated in cattle.

To prevent the spread of BSE among cattle, Canada banned protein of bovine origin from cattle feed in 1997. However, meat and bone meal of bovine origin continued to be used in feed for other livestock and inadvertently found its way back into cattle rations through cross-contamination and mixing errors. On July 12, 2007 enhanced federal regulations finally banned SRM of bovine origin from all other animal feeds, pet foods and fertilizers. The move greatly reduced potential contamination of cattle feed during production, distribution and storage. Millions were invested to help accelerate compliance with the enhanced feed ban, help offset adaptation costs by

the industry and for research into new and innovative technologies that effectively extract value from SRM. The federal government and Alberta alone invested nearly $40 million; nationwide, the federal government invested $80 million.

Fear of prions in blood averted

There have been four cases of variant-CJD infection associated with blood transfusion. All four cases had received transfusions of whole blood between 1996 and 1999. The association of prion-induced disease in blood temporarily threatened the international supply of human blood products and the life saving practice of blood transfusion. In North America and Europe, the pre-surgical assessment process has been carefully revised to take full account of the latest knowledge of vCJD and stringent risk assessment for patients with uncertain or incomplete transfusion histories.

Ability to quickly detect nervous tissue in meat products reassures

A test that instantly detects nervous tissue in beef accidentally contaminated during processing offers assurances that SRMs do not make their way into the system. Ensuring the absence of SRM in the food supply chain is a confidence builder for consumers and trading partners. Researchers at Agriculture Research Services (USDA) claim detection of fluorescent pigments unique to nervous tissue using a light-based spectroscopic monitoring technique is rapid, non-invasive and requires no special sample preparation.

Getting downers out of the system

Food safety is a vital issue for meat processors in Canada and the U.S. The handling of downer cattle at the Hallmark/Westland Meat Packing Company, Chino, California in February 2008 and the subsequent recall of 143 million pounds of raw and frozen meat products riveted the world’s attention on how North American packing industry was handling non-ambulatory cattle. In addition to welfare concerns, fears were raised that non-ambulatory cattle forced to slaughter might have bought BSE into the food chain. Industry, especially in the U.S., in an unprecedented move impelled regulatory change that all but eliminated non-ambulatory cattle from being presented for slaughter and laid very clear ground rules how animals were to be handled at destination in the event of accidents during transport.

Unanswered questions

Despite 40 years of research there are still many unanswered questions about prions and diseases like BSE. Questions like: How do prions hitch a ride across the intestinal barrier to cause disease? How does the affinity between prions and soil minerals influence their persistence in nature? What purpose do mineral complexes like ferritin or elemental copper play in the development of prion diseases in animals and people? What secrets about detection and prevention of BSE remain linked to genetics? What threats, if any, do new prion strains pose?

Perhaps the most perplexing of all questions is the one about the true significance of prion diseases. In living the BSE story has the world overlooked more important health issues like cancer, HIV and the fact that kids still go to bed hungry every night? — Dr. Ron Clarke

Ron Clarke is a veterinarian who writes from Stony Plain, Alta.

the industry and for research into new and innovative technologies that effectively extract value from SRM. The federal government and Alberta alone invested nearly $40 million; nationwide, the federal government invested $80 million.

Fear of prions in blood averted

There have been four cases of variant-CJD infection associated with blood transfusion. All four cases had received transfusions of whole blood between 1996 and 1999. The association of prion-induced disease in blood temporarily threatened the international supply of human blood products and the life saving practice of blood transfusion. In North America and Europe, the pre-surgical assessment process has been carefully revised to take full account of the latest knowledge of vCJD and stringent risk assessment for patients with uncertain or incomplete transfusion histories.

Ability to quickly detect nervous tissue in meat products reassures

A test that instantly detects nervous tissue in beef accidentally contaminated during processing offers assurances that SRMs do not make their way into the system. Ensuring the absence of SRM in the food supply chain is a confidence builder for consumers and trading partners. Researchers at Agriculture Research Services (USDA) claim detection of fluorescent pigments unique to nervous tissue using a light-based spectroscopic monitoring technique is rapid, non-invasive and requires no special sample preparation.

Getting downers out of the system

Food safety is a vital issue for meat processors in Canada and the U.S. The handling of downer cattle at the Hallmark/Westland Meat Packing Company, Chino, California in February 2008 and the subsequent recall of 143 million pounds of raw and frozen meat products riveted the world’s attention on how North American packing industry was handling non-ambulatory cattle. In addition to welfare concerns, fears were raised that non-ambulatory cattle forced to slaughter might have bought BSE into the food chain. Industry, especially in the U.S., in an unprecedented move impelled regulatory change that all but eliminated non-ambulatory cattle from being presented for slaughter and laid very clear ground rules how animals were to be handled at destination in the event of accidents during transport.

Unanswered questions

Despite 40 years of research there are still many unanswered questions about prions and diseases like BSE. Questions like: How do prions hitch a ride across the intestinal barrier to cause disease? How does the affinity between prions and soil minerals influence their persistence in nature? What purpose do mineral complexes like ferritin or elemental copper play in the development of prion diseases in animals and people? What secrets about detection and prevention of BSE remain linked to genetics? What threats, if any, do new prion strains pose?

Perhaps the most perplexing of all questions is the one about the true significance of prion diseases. In living the BSE story has the world overlooked more important health issues like cancer, HIV and the fact that kids still go to bed hungry every night? — Dr. Ron Clarke

Ron Clarke is a veterinarian who writes from Stony Plain, Alta.

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