Complete info about Prions and related diseases in animals/Humans

2. Proteins are fundamental components of
all living cells:
The hemoglobin
Hormones
Antibodies
Enzymes
Actin and myosin,Keratin
Collagen ……………
“All are proteins”

3. Proteins
 Primary structures
 Secondary structure
 The most common shapes are the alpha helix
and the beta conformation.
Secondary Structure
α helix β sheet
+ +
variable
loops =
Tertiary Structure

4. Secondary structure of a protein
Examples of alpha helices
and beta sheets

5.  Only one of these many ways allows the protein
to function properly.
 Too much of a misfolded protein could be worse
than too little of a normally folded one.
 This is because a misfolded protein can actually
poison the cells around it.
Why do proteins fold ?

6. To cary out their function a protein should fold
and attain stability

7. Transmissibility in 1943 when a population of
Scottish sheep was inoculated against a
common virus with a formalin extract of
lymphoid tissue unknowingly derieved from
an animal with scrapie after two years nearly
10 of flock developed Scrapie.
GORDON 1946
History of Prions

8.  Sometimes a scientific discovery shakes
the confidence of scientists, making them
question whether they truly understand
nature's "ground rules."
 That's exactly what prions have done to
scientists, understanding of the ground
rules for infectious diseases.
Confusion created by Prions
Contd…

9.  After some years a clinically and pathologically
Similar human disease KURU meaning “trembling”.
 Lead to hypotheses that the nature
of infectious agent ranging from a Replicating
polysaccharide to Nucleo protein complex
 Filterable, formalin treatment didn’t completely
abolish infectivity.

10. Kuru victims- lose the ability to walk, talk, and
see
Gajdusek

11. Scrapie
 The prototype (18th
century in England)
 Causes intense itching to make the sheep
scrape off their wool
 A natural progressive brain disease
 Evidence of transmissibility during
vaccination

12. Dr Stanely Prusiner
The Prion Hypothesis
“ a replicating protein”

13.  The molecular nature was a mystery till 15 years
 Stanley Prusiner showed its assosciation with a
specific Protein.
 Activity of prion was inactivated by
proteinase K, Diethylpyrocarbonate, Urea,
Phenol and SDS.
 Activity not lost by nuclease treatments
or UV irrradiation.
Nature of prions
Contd..

14.  PrP is a 250 amino-acid residue glycosylated protein
connected to GPI-anchor.
 The primary structure of PrP encoded by the gene of a
normal was found to be identical to that encoded by a
c DNA from a scrapie infected animal
 Ab against prP 27-30 identified the prp protein
in the brain of uninfected animals and in many
tissues as a 33-35KDa glycosylated
species,termed PrPC.

15. The normal protein is called
 PrPC-alpha helices.
 PrPSc- forscrapie
 Beta helices
Nomenclature of Prion Protein
 PrPSc
has the ability to convert
PrPc
to Itself

16. Conformational Differences between PrPc and PrPsc
PrPc PrPsc
Monomeric Multimeric
Soluble Insoluble
Protease sensitive Protease resistant
Predominantly alpha helices Beta helices

18. A protein of identical size was also observed in scrapie-infected
brain extracts.
Limited proteinase k digestion
Prpc completely degraded.
Prpsc a protein in infected
Brain was only partially
cleaved
66 aa on –NH2 terminus
Yields PrP 27-30

19.  Proteinaceous infectious particles
 Abnormal proteins that have an affinity for the
CNS
 Very highly resistant to heating (survive
routine autoclaving)
 Not sensitive to irradiation
 Not destroyed by enzymes that damage DNA
or
RNA
 Sensitive to protein denaturing agents
Characteristic features of Prions
Contd…

20.  Abnormal prions contact and change the
shapes of other normal prions in the nerve cell.
 The nerve cell tries to get rid of them
 When the cell dies, the abnormal prions are
released to infect other cells.
 Large, sponge-like holes are left where many cells
die.

21.  Sheep - Scrapie Spongiform Encephalopathy.
 Chronic Wasting Disease -Elk, Deer
 Cow - Bovine spongiform encephalopaty
 Human - Creutzfeldt-Jakobs Disease
Kind of Disease they cause in Different animals

22. Cerebral cortex : loss of memory and mental acuity,visual impairment (CJD)
Thalamus : Damage to the thalamus may result in insomnia (FFI)
Cerebellum : problems to coordinate body movements and difficulties to walk
(kuru, GSS)
Brain stem : In the mad cow disease (BSE), the brain stem is affected

23. Prion replication theories
2) Splitting theory
1) The nucleated polymerization theory
Jarret and Lansbury, (Cell 1993)

24. PrPC
PrPSC
PrPC

26. PrPsc
fibrils

27. Plaque

28. How are these abnormal proteins acquired?
 Spontaneous conversion
 A mutation in the prion gene in a brain
cell
 Inherit the abnormal gene from your
parents
 Ingestion of the protein
 Humans could be accidentally infected
with the protein (iatrogenic) Needles,
Tissue, Pituitary extracts

29. How are Prion Diseses Usually Diagnosed ?
 There is no blood test to detect the presence of
prions
 Currently there are two laboratory methods to
confirm a diagnosis:
– Microscopic examination of the brain tissue
– Special staining and microscopic techniques to
detect the partially-proteinase resistant form of
the prion (PrP) protein. SDS PAGE

30. Bovine Spongiform Encephalopathy
First noted in UK in early 1985
Animals fed rendered sheep meal
Prevalence peaked at about 35,000
animals
2 to 4 year incubation time (longer?)
Loss of motor control, other neural
control

31.  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.
How Does it Progress?

32. 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:

33. Cattle affected by BSE
experience progressive
degeneration of the
nervous system.

34. Affected animals may display changes
in temperament, nervousness or
aggression,abnormal posture……….

35. How to identify the affected
Cattle

37.  Prions in cattle are mainly from the carcasses
of scrapie-infected sheep
 Infected sheep brains and other sheep
byproducts infected with scrapie is used to
feed cattle with the meat and bone meal
 The prions are concentrated in the brain, and
spinal cord of these animals
How Prions transmitted from Sheep to Cattle?

38.  UK still had about 200 BSE cases in 2005.
Portugal and Spain are still increasing in
numbers of BSE cases.

39. Cattle on the way to
Grave yard

40. Impact of mad cow disease on economy

41.  The shock wave ripples across the world.
 Import bans imposed by many other nations have cut deeply into
the US beef industry
 Direct and indirect economic activity from the industry adds up to
$188 billion annually, making it the largest portion of the nation's
food and fiber industry in US
 Japan which had been the largest importer of US beef - continues
to demand that all US cattle scheduled for export be tested for
BSE
 One challenge is that the animals have to be killed in order to test
for BSE.

43. 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 Creutzfeldt-Jakob Disease

44. 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

45. Creutzfeldt-Jakob disease (CJD)
 Identified by Creutzfeldt and Jakob (1920)
 A progressive fatal neurodegenerative disease of
unknown cause
 Characterized by seizures, massive
incoordination, dementia
 Incidence about 1/1,000,000

46. CJD is classified into 2 forms:
 Classic CJD & Variant CJD
 Classic CJD can be transmitted to other species,
however other animals cannot carry it. Variant Creutzfeldtt-Jakob Disease (vCJD), is
caused by the consumption of BSE infected
meat products
 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

47. New Treatment for vCJD?
 A 19-year-old male from Belfast has been
treated with pentosan polysulphate by injection
into the brain

48. There is no Cure for
Mad Cow Disease
&
Creutzfeldt-Jakob Disease
Prevention is the
only available
option

49. What is the risk?

50. Mad cow disease in india
Epidemic that struck Europe had its
roots in India
Lancet

51. “thank you”