BSE Virus is a Prion. Mad Cow Disease
BSE virus is a prion. It is an infectious pathogenic factor
without nucleic acid, it exists in two forms in cells, namely cell type and
abnormal type. The cell type is contained in normal cells and is not
infectious. The abnormal type is an isomer and is infectious. Infectious
spongiform encephalopathy that causes fatal infections in animals and humans.
The virus was first discovered in 1936. Stanley Bruchner won the Nobel
Prize in Physiology or Medicine in 1997 for the discovery of prions and the
study of new patterns of infection.
Disease name: Mad
Cow Disease Virus
English name: Prion
Alias: Prion, prion
protein infectious factor
Attributes:
Non-immune hydrophobic protein
Incubation period: 2
- 5 years
Disease course: 14 -
180 days
Table of Content
- Prion properties
- Pathogenesis
- Pathological changes
- Epidemiological characteristics
- Prevention
- Introduction to Mad Cow Disease
What are the Properties of Prion?
Prions are highly resistant to high temperatures, acids and
bases, and common disinfectants. Prions in brain tissue can survive for more
than 1h after being subjected to high temperature of 138 ℃.
In 20% formalin can also survive for more than
2 years. It has strong
tolerance to sodium hydroxide, phenol and sodium hypochlorite. The method of
killing prions is incineration.
The normally structured prion protein (PrPC) is encoded by
the host chromosome PrnP and is an important component of normal mammalian
cells. It consists of 254 amino acid residues with a molecular weight of about
33 to 35 kDa, and in turn includes a signal peptide sequence composed of 22
amino acid residues at the amino terminus.
An octapeptide repeat sequence
composed of amino acid residues rich in glycine at positions 51 to 59 ). It can be
combined with metal ions, then connect a section of adenine-rich region and the
C-terminal transmembrane region.
After synthesis by ribosomes, prion protein is
transported to the Golgi apparatus along the cell secretory pathway to complete
the post-translational modification process, that is, to remove the hydrophobic
sequence at the carboxyl end (231 - 254), and at the same time install the
glycosylphosphatidylinositol (GPI) at Ser231.
The receptor binding site forms disulfide bonds and glycosylation at the Asn (181, 197) site. PrPC has a tendency to shift to the conformation of PrpSc during its conformation formation, but the N-terminal sugar group can effectively prevent this transition.
The receptor binding site forms disulfide bonds and glycosylation at the Asn (181, 197) site. PrPC has a tendency to shift to the conformation of PrpSc during its conformation formation, but the N-terminal sugar group can effectively prevent this transition.
Pathogenesis
Nucleic acids that encode genetic information are not
detected in sufficient quantities or long enough in prion. The main component
of prion is protein polymer, which may contain a small amount of lipids or sugars.
Prion infection mainly causes the death of central nervous cells. The necessary
condition for infection is that central nervous cells express prion protein,
which is a protein PrPC that has the same amino acid sequence as prion PrPSc
but different secondary structures.
Prions are insoluble in water and partially
resistant to proteinase K. Studies have found that methods of damaging nucleic
acids cannot eliminate the infectivity of prions, while prion proteins are
soluble in water and easily digested by proteinase K. This is to distinguish
prion from prion Important biochemical means.
What is the Prion replication model?
The prion of pathogenic factor is only composed of PrPSc with
abnormal configuration mainly β-sheet.
These misfolded PrPSc proteins can
self-replicate although they are not expressed by nucleic acid encoding.
Prusiner was equivalent to the prion replication model proposed in 1999. This
model theoretically explains the pathogenesis of prion.
According to this model,
the random change of PrPC during the folding process may produce a partially
unfolded monomer form (PrP *), which is a protein monomer in an intermediate
state, which can be converted into PrPC or further form PrPSc .
The
concentration of PrP * is generally low, so the amount of PrPSc formed is
negligible. However, in the case of prion infection, exogenous PrPSc will be
used as a template to promote the transformation of PrP * to PrPSc.
The
insolubility of PrpSc makes this process irreversible and further accelerates
the production of PrPSc.
Pathological changes
The autopsy of the sick cow shows that the most typical
change is in the brain, showing spongy edema of the gray matter of the brain.
By making brain lesion tissue into sections for examination, it can be seen
that cavitation occurs in the gray matter of the brain stem. In the central
nervous system, bilateral neuronal cells showed a large number of vacuolar
degeneration. The number of neurons is greatly reduced, and can even be reduced
to 50% of the original. The brain shows amyloidosis.
What are the Epidemiological Characteristics of BSE?
Susceptible hosts are wide. In addition to bovines, wild
animals such as domestic cats, tigers, leopards, and lions are also
susceptible, and people are also infected. Sources of infection are pruritus
sheep, bovine spongiform encephalopathy breeding cattle and poisoned cattle.
Animals are mainly infected through ingestion of contaminated feed in the
digestive tract. There is no evidence of vertical transmission.
Prions can
persist and spread in body fluids and excreta, plants, water environment, soil,
dust and wild animals, and infect animals.
Generally, it has nothing to do with
the animal's sex, breed and genetic factors, but the survey shows that the
number of cows is higher, and black and white cows are the most.
The age of
onset of cattle is mostly 3 to 11 years old, of which 4 to 6 years old cattle
are more, and the incidence is less than 2 years old and above 10 years old.
Beef cattle around 2 years old in the incubation period are likely to enter the
food chain, causing public health issues.
What is the Prevention Method against Prions causing BSE?
After the occurrence of BSE, there are no specific
therapeutic drugs and no corresponding vaccines are available.
At present, no
sick cattle with bovine spongiform encephalopathy have been found in China, but
they may spread from abroad at any time. Therefore, it is necessary to
strengthen the monitoring of cattle, especially the monitoring of imported
breeds from abroad.
The main measures taken to prevent this disease are to
restrict imports, and to strengthen the quarantine of imported cattle and their
meat products and semen.
In particular, care should be taken to avoid importing
these products from affected countries. Severely crack down on the smuggling of
various animals and animal products. Strengthen the management of ruminants
after entry.
Due to the relatively long incubation period of this disease, a
longer period of isolation observation is required. The feed of these animals
must be strictly managed.
If sick cattle are found, they should be quarantined
and reported to the epidemic in time. The brain tissue of sick cows is usually
checked.
After the diagnosis is made, the sick cows and all cows that have been
in contact with the sick cows must be treated, and the carcasses of the sick
cows must be burned and buried deeply.
The suspicious diseased cattle must also
be culled and destroyed. The slaughtering and sale of the diseased cattle are
strictly prohibited. The meat products of the suspected diseased cattle must
also be destroyed. They cannot be used for food manufacturing and animal feed
production.
Introduction to Mad Cow Disease
Mad cow disease (mad cow disease) is scientifically known as
bovine spongiform encephalopathy (BSE).
It is a progressive and fatal central
nervous system disease that occurs in cattle. The symptoms are similar to sheep
pruritus.
It is one of the infectious spongiform encephalopathy (TSEs).
It
has the characteristics of long incubation period, latent onset, and slow
course of disease.
The clinical symptoms are characterized by abnormal
behavior, ataxia, paralysis, and weight loss, and are accompanied by typical
cerebral gray matter spongy edema and neuronal vacuolization. Mainly infected
bovine animals, such as cattle and buffalo. The fatality rate of infected
cattle is 100%.
The disease infects people and causes variant Creutzfeldt-Jakob
disease. The disease was first discovered in England, and then occurred in some
countries. In the UK it is most prevalent. It has been recognized that cattle
infections mainly come from bone meal polluted by sheep scrapie or bovine
spongiform encephalopathy.
Human infection may be ingestion disease. Cow's meat
and milk products.
At present, more than 30 countries have stopped importing
British cattle and their products. Therefore, effective control of the disease
is of great significance.
In 2014, China was recognized by the OIE as a country
with a negligible risk of mad cow disease.
Author's Bio
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Dr. Shawna Reason |
Education: MBBS, MD
Occupation: Medical Doctor / Virologist
Specialization: Medical Science, Micro Biology / Virology, Natural Treatment
Experience: 15 Years as a Medical Practitioner
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