Alexander Fugger
Zareef Ahmed
Adam Kalamchi
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 nonhealth 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.”1
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
1
www.pbs.org/wgbh/nova/madcow/hindsight.html.
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:
Size of cattle
Number of
Number of ill / dead
population
contagious cows
people form CJD
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.
www.m-ww.de /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.