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Mad Cow Disease

Bovine spongiform encephalopathy (BSE), also known as mad cow disease, has surfaced in more than 20 countries including the United States.1 Health authorities consider it to be the most likely cause of a variant of Creutzfeldt-Jakob disease (vCJD), a fatal brain disease that has affected 217 people worldwide since the disease was first reported in 1996.1

After four discovered occurrences of BSE in U.S. cattle, Americans are now more aware that BSE presents a locally derived health threat. There is growing concern about BSE and vCJD and the need for corrective action to protect the health of humans and animals in the United States:

  • The conditions that led to the emergence of BSE in Britain have also been present in the United States.
  • The agent that causes BSE has already spread to at least four cows and some other species of animals in the United States. The extent to which BSE and other encephalopathies have entered the human food supply is unknown.

In 2008 alone, more than 350 Americans died of Creutzfeldt-Jakob disease, and the possibility that BSE played a role in some of those deaths cannot be ruled out. vCJD can only be confirmed upon biopsy of brain tissue or at autopsy.1

Brain Disease in Cows

Bovine spongiform encephalopathy is a fatal central nervous system disease first identified in the United Kingdom in 1986.

Affected cows show increased apprehension, poor coordination, difficulty walking, and weight loss. The infections that cause BSE apparently existed for several years before the disease was recognized in England.2-4

BSE is not limited to Britain. It has been found in native cattle in over a dozen countries. The first case in the United States was reported in December 2003.

Related Brain Disease in Humans

vCJD, like other transmissible encephalopathies, robs an affected individual of mental faculties and muscle coordination, eventually leading to coma and death. This category of illnesses is caused by prions, proteins that are normal in their molecular makeup but abnormal in their shape, like springs that have been bent out of configuration. It is believed that vCJD results from contact with prions in tissues of cattle with BSE, or “mad cow disease,” which, in turn, distort normal proteins in human brain and nerve cells. Only minuscule amounts of prion-tainted tissues are required in order to transmit the disease.5 Prions concentrate in the brain and spinal cord, but also have been found in blood and muscle tissue. Prions are very difficult to destroy, even by the chemical or heat disinfectant methods used in hospitals. Heating to 134 degrees Celsius (273 degrees Fahrenheit) does not reduce their infectivity.6

Similar Diseases in Other Species

Transmissible encephalopathies have long been documented in animals in the United States, indicating the need to protect human populations. Scrapie, the encephalopathy analogous to BSE occurring in sheep and which may have been the origin of BSE, was first reported in the United States in 1947, and infected sheep flocks have been identified in virtually all parts of the United States where sheep are raised.7,8

Similar diseases have been found in other species, including chronic wasting disease in deer and elk, and transmissible mink encephalopathy.6 While scrapie is not known to cause human disease, passage of the prions that cause scrapie through other animals may potentially alter their infectivity and disease presentation.

Indirect evidence from mink on fur farms who were routinely fed cattle-derived remains suggests that BSE may have been present as early as 1985 in at least some U.S. cattle. In at least five separate outbreaks, mink fed in this way have developed a disease called transmissible mink encephalopathy (TME) which is remarkably like BSE.3,9 After a 1985 TME outbreak in Stetsonville, Wis., experimenters injected brain tissue from diseased mink into Holstein cattle, finding that the cattle developed spongiform encephalopathy. They then fed remains of these cattle to healthy mink, who soon developed TME.10 Reviewing evidence that the mink disease came from cattle-based feeds, University of Wisconsin researchers concluded, “If this is true, there must exist an unrecognized bovine spongiform encephalopathy (BSE)-like infection in American cattle.”10 In other words, U.S. cattle have been sporadically infected with BSE, which has shown its pathological effects when passed on to other species.

The Failure of U.S. Government Policies

The fact is that U.S. Department of Agriculture (USDA) officials have not been seriously looking for BSE cases. Data from the National Veterinary Sciences Laboratories BSE Surveillance program from 1990 to 2000 show that, of approximately 900 million cattle slaughtered, only 11,954 brains (approximately 1 in 75,000) were examined for BSE. Starting in 2006, the USDA released a new surveillance program in which it annually tests approximately 40,000 cattle for BSE. In 2011 alone, the U.S. slaughtered 35.55 million cattle.11 However, the symptoms of BSE do not commonly manifest in cattle until about 5 years of age, which is after the usual age of slaughter. For example, most U.S. dairy cows are slaughtered before 4 years of age, when even a prion-infected cow is likely to appear healthy. Despite all this, the first official U.S. case was identified in a cow raised in Washington State in 2003, and there have been three more cases since then.

The USDA has been slow to take steps against the potential spread of encephalopathies from one animal to another, or from animals to humans. The measures instituted so far by the U.S. government are grossly inadequate, as evidenced by the following examples:

  • U.S. feed producers are blatantly violating restrictions on feed production. Despite a 1997 Food and Drug Administration (FDA) ban on the feeding of most mammalian remains to ruminants, which unfortunately includes significant exceptions impairing the protective intent of the law, a January 2001 FDA report showed that, of 180 renderers, 16 percent lacked warning labels on feeds designed to differentiate those intended for ruminants from those for nonruminants, and 28 percent had no system to prevent the actual mixing of these feeds.
  • The Government Accountability Office issued a follow up report in 2005, noting many program weaknesses in compliance inspections, including FDA’s guidance for inspectors to visually examine facilities and equipment and review invoices and other documents instead of routinely sampling cattle feed to test for potentially prohibited material.
  • Although the World Health Organization called for the riskiest parts of bovine tissues (i.e., brain, eyes, spinal cord, intestines) not to be used in the human food supply or in animal feed to protect from BSE, the United States still allows the feeding of these potentially risky tissues to people, pigs, pets, poultry, and fish.
  • There are few restrictions on the use of animal byproducts, including blood and blood products, gelatin, milk, and milk products, in feeds through which prions may be transmitted.
  • There are no limits on the use of nonruminant, such as pig or horse, remains in feeds, due to an exemption in the 1997 ban. Because prions are so difficult to destroy, if the remains of a BSE-infected cow are fed to a pig or horse and then the pig or horse remains are fed to cows, the cows may subsequently be infected. Similarly, ruminant remains can be fed to poultry and, in turn, poultry feces are routinely used in cattle feed.
  • There are no limits on the “recycling” of beef or other meat products in the form of garbage from restaurants or other institutions for use in animal feeds.

Monitoring for human illness is even more haphazard. Individuals showing signs of dementia due to such a condition may be misdiagnosed as suffering from Alzheimer’s disease or stroke, and most dying with neurological illnesses are never autopsied, so their brains are never examined.

There is simply no way of knowing whether vCJD has begun in the United States or not. Death certificates from 1979 to 2006 show that 6,971 people were identified with CJD in the United States. While the presumption is that they had the “classical” form of the disease, rather than the new variant form which is believed to come from animal tissues, this remains uncertain. While most victims were older (a sign of classical CJD), a small number were surprisingly young.12 The reported cases are probably underestimates due to the problems of misdiagnosis and underreporting.

On a more optimistic note, restrictions on blood products are becoming more stringent, which is appropriate given that they may also be vectors of disease.13 Nonetheless, it is clear that diseases closely related to vCJD exist in the United States, both in animals and humans, that these diseases should be considered highly infectious, that monitoring programs are too spotty to track the extent of these diseases, and that current preventive steps are far too lax.

Recommendations

The following are PCRM’s recommendations to the government for protecting the public against vCJD:

  • Ban the use of animal-derived livestock feeds for any species, given the likelihood that animal byproducts will, in turn, be recycled to ruminants (that is, cows, sheep, and goats).
  • Prohibit animal byproducts in all medications, supplements, or cosmetics.
  • Label all foods containing animal byproducts (such as gelatin or “natural flavorings”), indicating both the presence of animal byproducts and the species of origin.
  • Provide warning labels on all foods that carry a risk of vCJD, using standards similar to those for tobacco and alcohol products.
  • Institute comprehensive monitoring programs to check for diseased animals and humans in the United States. Monitoring programs for BSE and other encephalopathies in animals should include but not be limited to testing all suspect animals rather than a fraction of them. For humans, monitoring programs should be implemented that require all states to report CJD cases and dementia of unknown cause (especially in young individuals) to the Centers for Disease Control and Prevention so that any cases where vCJD is suspected can be confirmed or dismissed by autopsy.

It should be recognized that the consumption of livestock products is clearly linked to a much higher risk of serious and sometimes fatal diseases, apart from the risk of transmissible encephalopathies. These diseases include coronary artery disease, colon and possibly other forms of cancer, diabetes, hypertension, obesity, and infection with salmonella, campylobacter, and E.coli O157:H7, among others. Making meat “safe” is not a realistic or attainable goal. Ironically, while the feeding of animal remains to other animals is now acknowledged as a dangerous practice that is restricted in some countries, the feeding of animal remains to humans is encouraged by government programs and massive industry efforts.

References

1. Centers for Disease Control and Prevention. vCJD (Variant Creutzfeldt-Jakob Disease) Fact Sheet: Variant Creutzfeldt-Jakob Disease. Available at http://www.cdc.gov/ncidod/dvrd/vcjd/factsheet_nvcjd.htm. Accessed May 4, 2012.
2. Walker KD, Hueston WD, Hurd HS, Wilesmith JW. Comparison of bovine spongiform encephalopathy risk factors in the United States and Great Britain. J Am Vet Med Assoc. 1991;199:1554-1561.
3. Marsh RF. Bovine spongiform encephalopathy: a new disease of cattle? Arch Virol. 1993;7(Suppl):255-259.
4. Prusiner SB. The prion diseases. Sci Am. 1995;272:48-51,54-71.
5. Collee JG. A dreadful challenge. Lancet. 1996;347:917-918.
6. Steelman VM. Creutzfeld-Jakob disease: recommendations for infection control. Am J Infect Control. 1994;22:312-318.
7. Bleem AM, Crom RL, Francy B, Hueston WD, Kopral C, Walker K. Risk factors and surveillance for bovine spongiform encephalopathy in the United States. JAVMA. 1994;204:644-651.
8. Miller LD, Davis AJ, Jenny AL. Surveillance for lesions of bovine spon- giform encephalopathy in US cattle. J Vet Diagn Invest. 1992;4:338-339.
9. Robinson MM, Hadlow WJ, Huff TP, et al. Experimental infection of mink with bovine spongiform encephalopathy. J Gen Virol. 1994;75:2151-2155.
10. Marsh RF, Bessen RA. Epidemiologic and experimental studies on transmissible mink encephalopathy. Dev Biol Stand. 1993;80:111-118.
11. United States Department of Agriculture, National Agricultural Statistics Service.Fact sheet: U.S. dairy and beef cattle facts. April 25, 2012. Available at
http://www.nass.usda.gov/Newsroom/Notices/Fact%20Sheet%20-%20U.S.
%20Dairy%20and%20Beef%20Cattle%20Facts%2004.25.12.pdf
. Accessed May 3, 2012.
12. Holman RC, Belay ED, Christensen KY, et al. Human prion diseases in the United States. PLoS ONE. 2010;5:e8521.
13. Foster PR. Prions and blood products. Ann Med. 2000;32:501-513.



 
 

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