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Evolution of the Mad Cow
Disease in the United States
Denish Moorthy, Eugene Shubnikov,
Ron LaPorte
The Supercourse Network of the Global
Health University
www.pitt.edu/~super1/
Outline of Presentation
1. The Mad Cow Disease – What is It?
2. What Causes it?
3. How is it Diagnosed?
4. How Does it Spread?
5. Should Humans Be Worried?
6. What is Creutzfeld-Jakob Disease (CJD)?
7. What Happens in CJD?
8. Is there a Cure?
9. Epidemiology
10. Implication for World Trade
11. The UK Story
12. We are faced with a potential problem
Mad Cow Disease: What is it?
 The Mad Cow Disease in Cows, Scrapie
in Sheep, the Creutzfeldt-Jakob Disease
in human beings belong to a class of
disease called Transmissible Spongiform
Encephalopathy (TSEs)
 Initially thought to be due to “slow
viruses”, due to the long incubation period
between time of infection and appearance
of disease, these are now known to be
caused by agents called prions.
Transmissible Spongiform
Encephalopathy (TSE) What Are They?
 Transmissible Spongiform Encephalopathy
(TSEs) are rare forms of progressive
neurodegenerative disorders that affect both
humans & animals
 They are caused by similar agents (prions)
 They are called so because they produce
spongiform changes in the brain
 Also, the agent causing the disease is found
at the highest titre in the brain
Mad Cow Disease
Scientific Name: Bovine Spongiform
Encepalopathy
It is found on any type of cloven hoofed
animals such as: pigs, sheep, and cattle
Sheep: Scrapie Spongiform Encepalopathy.
There is a human form called CreutzfeldtJakobs Disease
• Bovine Spongiform
Encephalopathy
(BSE) is so named
because of the spongy
appearance of the
brain tissue of
infected cattle (and
also in the human
beings) when sections
are examined under a
microscope
How Does it Progress?
The incubation period (the time from when an
animal becomes infected until it first shows
disease signs) varies from 2 to 8 years.
Following the onset of clinical signs, the
animals condition deteriorates until it either
dies or is destroyed.
This process usually takes from 2 weeks to 6
months.
Most cases in Great Britain (where it was first
detected) have occurred in dairy cows between
3 to 6 years of age.
There are three phases of BSE in cattle:
 The first phase:
Low infectivity rate, and the cow does not pose
a large threat to humans at this level
 The second phase:
Symptoms are not evident, but the infectivity
level is very high
The prion agent is abundant in both the spinal
chord and the brain – the cow is a risk to
public health
 The third phase:
Clinical symptoms, & then death follows shortly
What Causes
Mad Cow Disease?
Initially thought to have been
caused by a “slow” viruses, these
were classified as “slow Viral
Diseases
Now there is evidence to point
out Prions as the causative factor
Prions
- Shortened form of Proteinaceous infectious
particles
- Prions are single molecules containing about
250 amino acids
- They are abnormal variants of proteins
which normally occur in cells
- Prions have the ability
to convert the normal
forms that they come
into contact with into
abnormal forms
Prion Hypothesis
 PrP is a normal cellular protein referred to as PrPc
 Diseased brain contains aberrant PrP which is
referred to as PrPSc
 PrPSc has the ability to convert PrPc to itself
 A chain reaction follows, resulting in a cluster of
tangled, nonfunctional proteins called plaques,
which are aggregates of PrPSc in the brain
 The body defences remove these PrPSc aggregates
leaving behind holes
 This causes degeneration of the brain cells leading
to mental changes and ultimately, death
Variant CJD in humans: section of cerebral
cortex stained to show aggregates of PrPSc
within plaques and more finely distributed
throughout the grey matter (PrP stains brown)
Prion Characteristics
 No antibiotics can cure disease caused by prions
 They are not typical of a prokaryotic organism or
a eukaryotic organism
 All that is present in this pathogen is the protein
PrPSc, the mutation of PrPC
 PrPSc is resistant to any form of digestion
 Prions are non immunogens and do not induce
an immune response
 Prions are not easy to decompose biologically
 They are resistant to high temperatures &
disinfectants
How is it Diagnosed
in Cattle?
Clinical Signs - 1
Cattle affected by
BSE experience
progressive
degeneration of the
nervous system.
 Affected animals may display changes in
temperament, such as nervousness or
aggression, abnormal posture, inco-ordination
and difficulty in rising, decreased milk
production, or loss of body weight despite
continued appetite
Clinical Signs - 2
 The clinical signs are:
 Apprehension
 Hyperaesthesia
 Frequent licking with progressive
paresis, & ataxia
 No blindness or circling is seen
(At the London Zoo it was first noticed
by the public when a Puma became
ataxic).
Diagnosis
Currently, there is no
test to detect the
disease in a live animal
or in humans
Veterinary pathologists
confirm BSE by
postmortem
microscopic
examination of brain
tissue or by the
detection of the
abnormal form of the
prion protein
Histological Findings on Post Mortem
 Histological findings include
Vacuolation of the neurones and
neuronal ground substance in
cerebella/cortex
Perivascular fibrils of amyloid in
which PrPsc can be demonstrated by
immunostaining and congo red
bifringence
Astrocyte infiltration.
How Does it Spread?
The Source of Prion
Prion in cattle is mainly
are from the carcasses of
scrapie-infected sheep.
After these infected
sheep having died , their
brains and other sheep
byproducts infected with
scrapie is used to feed
cattle with the meat and
bone mill (MBM)
How does it spread
from animal to animal?
• Feeding cattle animal bi-products such as
meat-n-bone mill that has an infected prion
causes the infection in the cattle
• The prions are concentrated in the brain,
and spinal cord of these animals
• There is no evidence that it is concentrated
in the muscle mass of cattle, and they are
considered safe as long as they are not in
contact with the brain and spinal cord
during the slaughter process
How did BSE Transfer to Humans
Sheep with Scrapie used in Meat
and Bone Meal (MBM) – known as
“Offal”
MBM fed to cattle
Infected Beef eaten by humans
Not affected by cooking
Should Humans
be Worried?
Mad Cow Disease in Humans
When cattle brains
and other cattle
byproducts
infected with BSE
are ingested by
humans, there is a
risk of developing
the CreutzfeldtJakob Disease
What is
Creutzfeldt-Jakob
Disease (CJD)?
Origins of CJD
 Bovine Spongiform Encephalopathy (BSE)
was first described in the UK in 1985 as a
prion-based disease that affected cattle.
 In 1996 it was first detected in a human being
 It was suspected at that time (which turned
out to be correct) that humans were
contracting the disease from eating cows that
had been infected with BSE
 In humans, it is has been named the
Creutzfeldt-Jakob Disease (CJD)
Types of CJD
CJD is classified into 2 forms: Classic CJD & Variant CJD
 Classic CJD can be transmitted to other species,
however other animals cannot carry it.
 Sub classified into: Sporadic CJD and Iatrogenic CJD
 Sporadic CJD - >85% of Classic CJD cases
 Most common between 50 – 75 years
 Characterized by rapidly increasing dementia
 Iatrogenic CJD - < 5% Classic CJD cases
 Transmission of prion via medications & surgical
equipment
What is vCJD
Variant Creutzfeldtt-Jakob
Disease (vCJD), is caused by
the consumption of BSE
infected meat products
The first 10 cases of variant
CJD were observed in 1996,
ten years after the outbreak of
BSE in the UK
Variant CJD seems to affect
mostly young patients
Clinical Symptoms
CJD causes fatal degradation of brain tissue &
the nervous system
The symptoms include loss of expressiveness,
muscular tremble, spasm, impaired muscle
coordination, loss of memory & dementia
vCJD patients also display unusual psychiatric
problems
There is no cure for CJD
The condition of the patient deteriorates,
finally resulting in death
Is there a Cure?
At Present, there is no Cure for
the Mad Cow Disease
(Bovine Spongiform Encephalitis)
and for the
Creutzfeldt-Jakob Disease
Prevention is the only
available option
Prevention
Don’t feed cattle
animal bi-products
Watch to make sure
you are feeding your
animals safe feeds
Always vaccinate
cattle properly
Prevention
USDA requires all
imported meat to be
inspected
US will not import
cattle from Britian
Animals suspected of
the disease are
quarantined
Epidemiology
Mad Cow Disease in the world
Mad cow disease was first
identified in Britian in 1985
The outbreak infected more
than 100,000 cows across
Europe in the mid-1990s
The recent resurgence of the
disease comes despite
widespread beef import
restrictions and other
measures intended to protect
the food supply
Mad Cow Disease in Europe
Cases of BSE have now been
identified in 10 of the 15
European Union (EU)
countries, as well as
Switzerland and
Liechtenstein
Although the incidence is
low, the discovery of the
disease across the continent
has had a dramatic effect on
beef consumption
Beef consumption has has
fallen by 27% across the EU
vCJD in Europe
The number of people who
have died from variant
Creutzfeldt Jacobs Disease
(vCJD), is also growing
By the end of 2000, nearly
90 people had either died or
were dying from the disease
in the UK
Deaths from vCJD have
also been reported in
France & Italy
vCJD in Europe
France
160 cases of BSE were diagnosed in 2000
Beef sales dropped by > 25%
Germany
Confirmed 20 cases of BSE in 2001
Beef sales dropped by 50 percent
United Kingdom
Single largest source of BSE
1,277 cases confirmed in 2000
Implications for
World Trade
Consumer Perception of BSE
Beef Consumption
UK and EU decreased by 30%
US – Steady Overall
World – slight increase
Fast Food Chains
Demand BSE Free
Implications for World Trade
Increased Demand for Grass Fed and
Grain Fed Beef due to low possibility of
BSE
Reduced trade in products made from
Beef by-products
Make up
Diet Supplements
Health Products
The United Kingdom (UK)
Story
BSE First Discovered in the UK
 BSE was discovered in ataxic cows by
the Central Veterinary Laboratory in
November 1986 by observing
vacuolation of brains by histopathology
 BSE considered to be caused by a single
strain of scrapie
Confirmed cases of BSE plotted
by month and year of clinical onset
Feed ban introduced
First
histopathological
confirmation
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
BSE in the UK
 A further 750,000 cases of subclinical BSE
may have occurred and been culled before
the peak age for clincal disease of 5.5yr
 Brains and spinal cords from 440,000 of
these could have contributed to the human
food chain before the offal regulations of
1989
 The disease should be almost extinct in the
year 2001 when no animals fed on Meal
and Bone Mill (or MBM) are left
Effects on the U.S.
Caused great worries for many beef consumers
Caused cattle ranchers to take many
precautionary steps
“This disease has not been known to be in the
US…”
“…And chances are, it never will because the
US has so many safety standards”