Freshman Seminar 93
Wednesday May 8, 2002
Mad Cow Disease: A Risk to Public Health in America?
Bovine spongiform encephalopathy (BSE), more commonly known as Mad Cow Disease, is a fatal virus that triggers progressive neurological deterioration in cattle. First reported in the U.K. in November of 1986, BSE was thought to have arisen from the feeding of cattle with meat and bone powders as dietary supplements. These modern agricultural practices of recycling animal proteins effectively turned cows into partial carnivores (if not cannibals) and thereby opened new barriers for host-parasite relationships. Though it was known how the disease spread, it was not know until 1997 what the biological causes were within the cattle’s body. Stanley Prusiner, who won the Nobel Prize in that same year, pinned the problem to the warping of proteins into prions, which brings about the progressive degeneration of the nervous system and brain. Since the symptoms of BSE had been around for years and seemed similar to those of the non-health threatening Scrapie, Sir Richard Southwood of Oxford University made the claim in 1989 that it was “most unlikely that BSE will have any implication for human health.” Unfortunately as we saw in 1996 in the United Kingdom, the assumption that the species barrier between ruminant animals (cud chewers) and humans would protect us form the disease was sadly mistaken. Along with the obvious danger BSE poses for cattle, it has been shown to be harmful to humans also. Scientific studies have shown that consuming cattle products infected with BSE can lead to a variant of Creutzfeldt-Jakob disease (vCJD), a humanoid disease similar to BSE which degenerates the neurological system. BSE and vCJD are especially dangerous because neither has any visible signs of infection and since there are still no cures for either disease, they are ultimately fatal.
The outbreak of “Mad Cow Disease” in Great Britain drew significant attention and provided a scare to Britain’s European neighbors as well as trade partners like the United States. Could a similar outbreak of Mad Cow Disease happen elsewhere? It is no surprise that officials were extremely concerned with preventing BSE from spreading to cattle stocks of other countries. Not only would this pose a serious risk to human populations, it would decimate the cattle industries in infected countries. As of March 2002, the statistics show that there is a high localized risk of BSE in Europe, yet that in the larger picture, the relative percentage of infected cattle can remain small if the disease is contained:
Germany / 14.5 mil / 161 / 0
Switzerland / 1.6 mil / 370 / 0
Great Britain / 11 mil / 180900 / 107
Ireland / 6.7 mil / 625 / 1
France / 20 mil / 426 / 3
WORLD / 1.3 billion / ~182500 / 111 out of 6 billion
Data from: Medezin Weltweit – Prionenkrankheiten. /krankheiten/prionenkrankheiten/bse.html
As we can see from the statistical output, there is a strong, positive correlation between cases BSE in cattle and instances of vCJD in humans. Luckily, BSE has only spread to .00014 percent of the world population of cattle, which, except for suspicions in Argentina, has for the most part been isolated on the continent of Europe. In a recent study concluded in November of 2001, the Harvard Center for Risk Analysis (HCRA) deemed that the safety measures now in place in the United States would prevent an outbreak of BSE in the human food supply.
In this study, the researchers first compared the meat industries in the United States and Great Britain. There are three main factors influencing the spread of Mad Cow Disease: (1) the degree of compliance with restrictions on feed practices that restrict using rendered animal proteins in cattle feed; (2) the quantity of transmissible disease in tissue, depending on the time since infection; and (3) slaughtering and processing techniques. In order to help prevent the spread of the disease to the United States, cattle imports from Great Britain were banned in 1989. After the sudden out break in 1996, the Food and Drug Administration (FDA) went one step further and banned the use of rendered protein from ruminant species imported from all European countries as fortification for cattle feed. The purpose of this new ban was to help prevent the spread of BSE from sick animals to other cattle through recycled feed. Also, the FDA instituted stricter measures in meat packaging plants to reduce the chance of human food being contaminated by infectious tissues. Furthermore, the FDA recommended that animal tissues used in drug products should not come from a country with a history of BSE problems. The FDA went as far as issuing guidelines asking blood centers to exclude potential donors who have spent six or more cumulative months in the U.K between 1980 and 1996 from donating. Similarly, the USDA has also continued to prohibit the importation of live ruminant animals and most ruminant products from all of Europe.
The Harvard Center for Risk Analysis created a model with the intention of quantifying all variables in an effort to better predict the possibility for an outbreak in the United States. As a test for accuracy, the HCRA was able to compare their model to a small breakout of Mad Cow Disease in Switzerland. Their model replicated the time scale and magnitude of this real outbreak fairly well. The study found that the system currently in place in the United States is highly resistant to an outbreak of Mad Cow Disease. With the FDA ban on imported proteins, even if a large number of infected cattle were introduced, the disease would not take hold in the United States. The source of the problem in Great Britain was most likely the feed – infected animal tissues (especially the spinal chord and brain) were repeatedly fed to healthy cattle. The model that the HCRA used integrated a less than full compliance with the FDA feed ban which is likely the case in the United States and even then, the study found that the BSE would disappear after roughly 20 years, most likely having not affected the human population.
The findings of this model can be verified by looking at actual statistics. Between 1980 and 1989, 334 animals were imported from England. The typical incubation period of BSE is four to five years and despite active surveillance, there have been no cases of BSE detected in the last 12 years. Half of the imported cattle were killed before they could have caused contamination, but the other half were tracked and most lived well beyond the incubation period. Since these particular animals were imported as breeding stock, and not to supply beef or dairy products, they were less likely to have been exposed to the high risk feeding habits in England. Also, none of the farms from which these animals came had any reported cases of BSE. Overall, there is about a one in five chance that the imported cattle introduced BSE. If they actually had BSE, it would have been apparent because a large number of the animals would have become infected and died by now. There is less than a 5% chance that the disease is present at even very low levels.
If BSE were introduced in the United States, it is important to be aware of the ways in which it is spread among cattle and to humans. The disease can be spread to cattle because of incomplete compliance with the feed ban, mislabeling of feed products intended for cattle, or by feeding cattle with feed that was intended for pigs or poultry, which can legally have rendered cattle protein. Rendering of seemingly healthy cattle that may in fact carry BSE and the use of this material in the production of cattle feed can also lead to the spread of BSE among cattle. Since the brain and spinal cord tissues carry almost all of the infectious material, consumption of these parts of the cattle (ie- T-bone steaks) can lead to the spread of vCJD in humans. Similarly, consumption of products that were processed by advanced meat recovery systems (AMR) can also lead to vCJD in humans. An AMR is a machine that cleans the meat left on the bone after butchering. In many cases, the tissue from the nervous system could contaminate this meat. The spinal cord is supposed to be removed before putting meat through an AMR but this requirement may not always be followed.
An article by David Brown, titled “Human Version of ‘Mad Cow’ on Rise” was published in The Washington Post on March 28th, 2002. He states that despite the measures to protect meat which have been in place for nearly a decade, the vCJD cases are doubling every three years. Robert Will, of Western General Hospital in Edinburgh, Scotland, describes the trend as continuing upward. Due to the lack of knowledge concerning the incubation period of vCJD, it is difficult to make clear claims about the recently occurring cases. A team of French researchers roughly predicts that there will be between 267 and 672 cases in the upcoming years. According to one survey of British vCJD patients, the victims have eaten a higher then usual amount of hamburgers, sausages, meat pies and other foods made of ground meat. Since the incubation period of the disease has been roughly estimated to be between 14 to 18 years, the most drastic consequences of vCJD might still be before us. We cannot forget that even though the chances of BSE infiltrating the US cattle industry are low, the American tourist has surely consumed a high amount of European meats over the last twenty years. The Harvard study seems optimistic about the BSE cases in America, yet vCJD that was contracted abroad might not have fully kicked in yet among the US population.
A reasonable question to ask then is what is the condition of the food supply in the United States as a whole. Surely there are more serious problems than BSE contamination in beef. In fact, according to an article publish in the May 2002 issue of National Geographic, there are indeed some major healthy risks in the food supply in the United States. Writer Jennifer Ackerman said of a conference at the Centers for Disease Control, “The stories are not those I expect to hear, of people getting sick from drinking unpasteurized milk or eating deviled eggs left too long in the hot sun at a picnic, but tales of people sickened by contaminated parsley and scallions, cantaloupes, leaf lettuce, sprouts, orange juice, and almonds.” The list goes on, but it seems that the risk for illness may be higher in more common foods than in the all-feared hamburger. According to the
CDC, over 76 million people suffer from food contracted illnesses each year. Of those, 325,000 are hospitalized and 5,000 die. This is dramatically higher than even the highest estimations for an outbreak of vCJD. It seems then that the hype over BSE was wasted, for it is a small problem and even eliminating the risk by 90% will do little for the health of the population at large. The issues that should be addressed are those causing these 5,000 deaths per year. It is generally agreed that the most dangerous hazards to the food supply today are not pesticide residue or allergens, but foodborne pathogens: bacteria, parasites, and viruses.
Again the preparation of food before it reaches your kitchen is incredibly important. When fecal matter from dead animals taints the meat, it lays a trap of bacteria that can multiply and sicken a human. Often, the cleanliness of slaughterhouses is less than perfect and this sort of contamination occurs. Carmela Velazquez said, “Simple but vital changes, like regular hand washing and use of proper toilets by field-workers, have made all the difference.” With increased globalization and demand for tropical and exotic foods year-round, our food supply is more and more coming from all over the Earth. This has potential to spread diseases more quickly from country to country, especially from less developed and wealthy produce based countries to the United States. Ms. Velazquez speaks of the improving sanitary conditions in foreign countries in Central America, which has a direct affect on the cleanliness and risk of the food we consume.