Q: What is bovine spongiform encephalopathy
(BSE), or "mad cow disease," and how is it
thought to infect cattle?
Dr Lurie: BSE is a progressive neurologic disorder of cattle
that is currently understood to be an infectious disease--
but not in the customary sense. It does not appear
to be caused by a virus, a parasite, a bacterium, or a fungus.
Instead, a misfolded protein, or prion, is believed
to be the infectious particle that is transmitted between
animals, or from an animal to a person. These misfolded
proteins occur in high concentration in the diseased
areas of the brain of animals with BSE and are highly resistant
to heat, chemicals, irradiation, and other methods
Q: What's the chief mode
Dr Lurie: It is not thought to be transmitted horizontally--
that is, from one cow to another through a mechanism
such as sneezing. The chief mode of transmission appears
to be ingestion of those parts of an infected animal that
contain prions. The epidemic of BSE in Great Britain that
peaked in the late 1980s has been linked to changes in the
way cattle feed was produced in that country in the early
1980s. One of these changes led to an increase in the use
of cattle parts in cattle feed.
One theory of how that epidemic started is that parts
of sheep infected with scrapie were included in cattle feed.
Scrapie is another type of transmissible spongiform encephalopathy
that for hundreds of years has been present
at relatively low levels in the British sheep population. Alternatively,
there might have been a spontaneous mutation
among cattle. Either way, infected cattle were slaughtered,
ground up, and included in the feed of a large number of
other cattle. Some of these animals became infected and
were then ground up and "recycled" yet again. This ongoing
cycle of cannibalism eventually caused an epidemic of
some 183,000 cases of BSE in the British cattle herd.
Q: So humans contract the disease in the same
way, through consumption of infected meat?
Dr Lurie: When the British BSE epidemic first received
public attention in the mid-1980s, scientists and public
health officials worried whether the disease might cross
the species barrier and become a problem for humans.
Because it typically takes several years after infection
for the symptoms and detectable brain changes of the
disease to appear, there was no way to know at first.
Then, in 1996, the first case of what is now called variant
Creutzfeldt-Jakob disease (vCJD)--the human counterpart
of BSE--was detected. As of December 1, 2003, a
total of 153 cases of vCJD had been reported worldwide.
The great majority of human cases have occurred in
Britain. But there have been a modest number in France,
and others have occurred in places to which people who
lived for extensive periods in Britain have subsequently
moved (including Florida, where vCJD in a young woman
was attributed to her prior residence in Britain). It is assumed
that all contracted the illness by eating parts of infected
Q: What has been done to prevent the spread
of BSE to American cattle?
Dr Lurie: The major barriers against BSE were erected
in 2 phases in this country. In 1989, a ban was placed on
the import of ruminants and ruminant products (such as
feed made from cattle parts) from any country that had
reported a case of BSE. (Ruminants are animals with
multi-chambered stomachs, which include goats, sheep,
cows, and so forth.) Then, in 1997, a ban was instituted on
the feeding of ruminants to other ruminants. This "feed
ban" is probably as important as any safeguard we have in
this country--probably more important than any testing
Q: The fact that BSE was diagnosed in an American
cow in December seems to indicate that these
measures have not been sufficient to ensure the safety
of American beef. So, where are the loopholes?
Dr Lurie: The first problem is that the ban on foreign
animals and feed products is far from airtight. Even if you
ban animals from each country in which a case of BSE
crops up, infected animals may have been imported before
the detection of BSE. An example is the American
cow in which BSE was diagnosed; it was brought in from
Canada before the disease was detected there. Also, real
questions exist about the extent to which foreign feed
products can be excluded when the rate of inspection at
our borders is very, very low--probably under 1%.
Q: So, if it's still possible that infected foreign
cattle are being imported into this country,
can the ban on feeding ruminants to other ruminants
at least prevent BSE from spreading?
Dr Lurie: It is very helpful, but there have been worrisome
exceptions to the ban. For example, you could feed cows
to pigs and chickens. And then, any feed that chickens
did not totally consume--so-called chicken litter--was allowed
in turn to be fed to cattle.
Another permitted practice was the feeding of "plate
waste" to cattle. Plate waste is food and even packaging that is left over at the end of a meal. These leftovers
were collected from large institutional eating places,
treated in various ways, and pressed into pellets for use
as cattle feed. These could easily have contained leftover
The FDA has indicated that it will eliminate the foregoing
2 exceptions to the ruminant feed ban. However, an
even more serious concern than these obvious loopholes
is lack of proper enforcement of the current feed ban.
Historically, the ban has not been carefully enforced. It
took the FDA many years to finally inspect all the registered
feed mills for the first time. Yet some have not been
reinspected in years--and there are thousands of feed
mills that are not registered.
Q: Can you tell me about some of the things
that are being done to minimize the risk of
transmission to humans?
Dr Lurie: For years there have been regulations to prevent
animals with a high possibility of infection, such as those
with neurologic disease, from entering the human food
supply. Since January, the United States Department of
Agriculture (USDA) has also excluded all cows that are unable
to ambulate ("downer" cows); these are thought to be
at higher risk for BSE than healthy animals. The Canadian
cow in which BSE was diagnosed last year was reported
to have been a downer cow. However, because downer cattle
are much less common than cattle that appear normal,
most of the risk of BSE is actually among "non-downers."
Thus, the elimination of downers was a good move, but
its impact is limited.
Q: Wouldn't testing of cattle be a simpler and more
effective way to keep infected animals out of the
Dr Lurie: I think one has to have modest expectations
about what testing can accomplish. There is no blood or
cerebrospinal fluid test, either for animals or humans.
The only way to diagnose BSE is by brain biopsy, which
in cows is done at slaughter. Also, evidence suggests that
while animals (and humans) are infected at a fairly young
age, symptoms of the disease and detectable brain changes
develop only as they get older. Thus, younger animals
will test negative for the prion even if they have already
been infected. Worldwide, only a small number of the cattle
known to have been infected have been younger than
Last year, about 20,000 cows were tested. This represents
a tiny fraction of the 40 million or so cattle that are
slaughtered in this country each year.
Q: Are there parts of a cow that are more risky to
eat than others?
Dr Lurie: Fortunately, the infectious prions are primarily
confined to neurologic tissue. Thus, to the extent that you
can avoid eating neurologic tissue, you can dramatically--
if not wholly--eliminate your risk of contracting the disease.
USDA regulations now prohibit the use, in food for
humans, of skull, brain, trigeminal ganglia, eyes, vertebral
column, spinal cord, and dorsal root ganglia of cattle aged
30 months or older, as well as the tonsils and small intestines
of all cattle.
It may also be wise to avoid cuts of meat that have
bone on them, such as T-bone steak, because they are
more likely to contain neurologic tissue. Even ribs could
be risky, because ribs attach to the vertebrae. However,
most authorities feel that consumption of a cut of beef that
is pure muscle meat represents minimal risk--if any.
Although infectious material has recently been detected
even in skeletal muscle, this was only with a highly sensitive
Q: What about
Dr Lurie: This can be somewhat worrisome, because of
the use of a process called "advanced meat recovery."
When an animal is slaughtered, the meat is trimmed from
the bones with a circular saw. Still, little scraps adhere to
the bone. Advanced meat recovery is the process by
which these bones are either crushed in powerful machines
or exposed to belts that shave off the last scraps
of muscle. The material that results can be called "meat,"
according to US regulations, and can then be processed
and used in hamburger, pizza toppings, or hot dogs.
However, a number of tests have demonstrated that
small amounts of neurologic tissue do get into the advanced
meat recovery end product. The government has
now banned advanced meat recovery for animals older
than 30 months. We think it should just be banned entirely.
More fundamental, the new regulations do not actually
ban the inclusion of spinal cord in advanced meat recovery
product; they only prevent any such product from
being labeled as "meat." But it can still be labeled as "beef"
and used in beef extract, beef flavoring, and beef stock.
Q: Does it matter how well
the meat is cooked?
Dr Lurie: No, that's irrelevant. You can inactivate the infectious
agent only at extremely high temperatures and pressures.
Exposure to a very strong base is also effective. But all of these things will make any cut of meat inedible.
Thus, normal cooking procedures are not going to
inactivate the agent.
Q: So when a patient says, "I ate beef last night.
Do I need to be worried?" how do you respond?
Dr Lurie: You need to find out exactly what the patient ate
so that you can educate him or her about the riskiest
types of beef. However, in general, I would assure the patient
that there is very little need to worry. The risk at the
public health level is different from the risk for an individual.
As much as I may be personally concerned about the
overall risk of vCJD occurring in the United States, and as
critical as I am of the public health job being done, I still
think the risk to individual Americans posed by BSE so
far is small.
Q: Are cattle parts used in any other products that
could pose a risk?
Dr Lurie: One that bears mentioning is dietary supplements.
The supplement industry is hardly regulated at all
in the United States. It is theoretically possible to take a
piece of cow brain, crush it up, put it into a dietary supplement,
and import it into this country with very little chance
of its being detected. There is no requirement that such
supplements be clearly labeled as to their contents or the
country of origin of their ingredients.
The supplements that pose the greatest risk are
those that contain ground-up organs--so-called glandular
supplements. I would stress to patients that it is foolish to
take a dietary supplement that contains something like
bovine brain or testis. The FDA has said it will ban parts
of cattle older than 30 months from use in dietary supplements;
however, since there is no evidence that beef products
are medically effective for anything, there is no reason
not to ban them entirely.
Q: Aren't animal materials also used in the
manufacture of some standard medications
and biologics--such as various kinds of gel caps and
vaccines? Is there any danger from these?
Dr Lurie: In the early 1990s, the FDA banned the use in
vaccines of bovine material from countries with BSE.
However, the manufacturers ignored the ruling and the
FDA failed to enforce it. In 2000, several companies admitted
that they had used fetal calf serum and other
bovine materials from British cattle in the preparation of
some vaccines. There was great concern that millions of
doses of many different vaccines might be dangerous. However, the consensus of those who studied the matter
was that, because of the processing that vaccines undergo,
the risk to patients was very, very small. So far, no one
is known to have contracted vCJD from a vaccine. The
risk cannot be conclusively eliminated, because the incubation
for the disease is 10 years on average. Still, it is
small enough that no patient should forego a necessary
vaccination as a result.
The gelatin used in medical products such as gel
caps and depo injections has also been somewhat of an
issue, because gelatin is made from cow hooves and hide.
Much of the gelatin in this country is imported from
Germany, which has had a modest BSE epidemic.
Although the risk from imported gelatin is most likely
minimal, because of the extensive processing it undergoes
during manufacture, it would be safer to require that
only domestic gelatin be used in medical products.
Q: What advice would you give patients who hunt
and eat the game they kill?
Dr Lurie: A type of transmissible spongiform encephalopathy--
chronic wasting disease--is seen in deer and elk.
Chronic wasting disease appears to be much more infectious
than BSE. However, there has never been a case of
vCJD attributed to consumption of a deer or elk with
chronic wasting disease.
Even so, we suggest that anyone who hunts his or
her own meat either have someone else dress it, or else
acquire the necessary expertise to ensure that he or she
will not contaminate the meat with fragments of brain or
Q: Has there been any evidence that vCJD can
be transmitted from human to human, for
example, through blood transfusion?
Dr Lurie: There is now a case of vCJD in Britain which
very likely resulted from transmission by blood transfusion.
Even before this case, the United States placed restrictions
on blood donation by people who had resided
for a length of time in Britain (3 months or longer, between
1980 and 1996) or in Europe (5 years or longer,
between 1980 and the present). The risk of contracting
vCJD from a blood transfusion is very, very low. Physicians
should reassure patients that fear of vCJD is no
reason not to receive a transmission that is medically
Q: Although it seems clear that the chances of a
physician in this country seeing a patient with
vCJD are minimal, it is always best to be prepared.
What are the symptoms that suggest vCJD?
Dr Lurie: Psychiatric manifestations, such as depression,
are very often the presenting symptom in patients with
vCJD. This helps distinguish vCJD from ordinary CJD, in
which gait difficulties, jerky movements, and rapidly progressing
dementia are more commonly seen early on.
Also, vCJD tends to develop in patients who are much
younger (average age, 29 years) than those in whom CJD
is seen (average age, 65 years), and it has a slower progression
(median duration of illness, 14 months) than CJD
(median duration of illness, 4.5 months).
Q: What should you do if you suspect that a
patient has vCJD?
Dr Lurie: The most important thing, as always, is to exclude
other potential causes of the condition that you are
evaluating--by the usual means. Get a good history of
travel and nutritional habits and a medical, surgical, and
transfusion history from the patient and his or her family.
Pay particular attention to patients with a history of neurosurgery;
cadaveric dura mater grafts have been a source
of numerous cases of CJD, approaching in number the
well-known epidemic of CJD caused by human growth
At this point, vCJD can only be diagnosed by identification
of the characteristic spongiform brain changes in
a biopsy specimen. A specialized laboratory at Case Western
Reserve University in Cleveland accepts specimens
for diagnosis and study.