What is Mad Cow Disease Bovine Spongiform Encephalitis (BSE)?
BSE is also known as
bovine spongiform encephalopathy (BSE). Its pathogen is neither bacteria nor
virus in the traditional sense, and it does not even contain genetic
material-nucleic acid. At present, most of the pathogens are called prion, and
the symptoms are similar to pruritus of sheep, commonly known as mad cow
disease.
The brain tissue of the diseased cow is spongy, with symptoms of
unstable gait, imbalance, itchiness, restlessness, etc. It usually dies within
14 to 90 days. Due to different types, the incubation period of mad cow disease
is different, generally between 2 and 30 years.
The disease was first
discovered in the United Kingdom in April 1985 and was named BSE in November
1986. BSE is not only widespread in the UK, but cases have also been reported
in many other countries and regions. The disease is now spreading globally.
Thematic content on BSE
Incidence
BSE was first
discovered in the UK in April 1985 and was diagnosed as BSE by pathology in
1986. Since then, the number of BSE cases has been increasing.
In 1989, Mad Cow
Disease first appeared in a country outside of England (Iceland). Since then,
cases of BSE have been reported in Northern Ireland, Ireland, Portugal,
Switzerland, France, Belgium, Denmark, Germany, Luxembourg, Netherlands, Spain,
Liechtenstein, Italy and other countries.
In 2001, Japan discovered the first
mad cow disease in Asia.
In 2002, Israel discovered the first mad cow disease
in the country.
In 2003, Canada discovered the first mad cow disease in North
America.
Since 1985, mad cow disease has occurred in 26 countries around the
world. Among them, 490 cases of mad cow disease occurred in 19 countries around
the world in 2005.
377 cases of mad cow disease occurred in 12 countries around
the world in 2006.
Fortunately, in Asia there are negligible chances and China
has not yet discovered BSE.
Pathogen
Prions are abnormal
proteins formed by certain glycoproteins (PrPc, which can be hydrolyzed by
proteases) on the surface of normal host nerve cells (PrPsc, which cannot be
hydrolyzed by proteases after translation). Different secondary structure).
Prions can cause bovine spongiform encephalopathy, with a mortality rate of up
to 100%, and can also cause human Kuru, Creutzfeldt-Jakob disease (CJD),
Gehr-Sherman syndrome (GSS) and lethal families eye loss, sheep pruritus in
animals, infectious encephalopathy in mink, chronic atrophy of deer, etc.
The pathogen is
highly resistant to physicochemical factors such as ultraviolet rays, ionizing
radiation, ultrasonic waves, non-ionic detergents, proteases, etc.
It cannot be
completely inactivated by high temperature, and ethanol, formalin, hydrogen
peroxide, phenol, etc. Inactivate it.
However, it can be inactivated by
treatment with 2% to 5% sodium hypochlorite or 90% carbolic acid for 24 hours,
and protein denaturants such as SDS, urea, and phenol can inactivate it.
CSF is
non-immunogenic, does not cause fever, no inflammatory reaction, and no immune
response after infection.
The cause of the disease is the infectivity of the
brain, cervical spinal cord, spinal cord end and retina and other tissues, less
in the spleen, lymph nodes, muscles and blood, and feces and urine are almost
infectious.
Popular features of Mad Cow Disease
What is the source of BSE infection?
At present, it is
generally believed that the main reason for the large-scale outbreak of BSE is
due to the consumption of meat and bone meal (MBM) containing cattle scrapie
prions, which is a large amount of sheep on stock.
Imported animals and animal
products contaminated with pruritus pruritus.
Processing methods for meat and
bone meal failed to inactivate prions.
Feeding cattle with meat and bone
meal for ruminants.
However, some scholars believe that the cause of BSE is
related to mites living in hay.
After injection of chemicals extracted from
mites, mice can develop itch.
What is the way for spreading of Mad Cow Disease?
The pathogen of mad
cow disease is mainly generated from the carcasses of sick cattle and sick
sheep, and is transmitted through the food chain; recent studies have found
that BSE can be transmitted by maternal sources, but the probability is lower.
This method alone does not seem to be sufficient to continue the epidemic of
BSE.
At present, there has not been any mutual infection of mad cow disease
among individuals in the herd, that is, no horizontal transmission has been
found.
What is the BSE Incubation period and age of onset?
BSE incubation
period is 2-8 years, with an average of 4-5 years. The age of onset cattle is
mostly 4-6 years old, rare under 2 years old.
Beginning in October 2000, the EU
bans the sale of bone-in meat for cattle aged 12 months and older
Susceptible animals
Domestic cattle,
dairy cows, bison, antelope, etc. are susceptible. Feline animals such as
domestic cats, tigers, leopards, mink, lions and other carnivores also have
certain susceptibility.
What are the Clinical Symptoms of Mad Cow Disease?
This disease mostly
occurs in adult cattle around 4 years old. Symptoms vary.
Most sick cows have
changes in the central nervous system, abnormal behavior, irritability,
excessive sensitivity to sound and touch, especially head touch, unstable gait,
frequent kicks and even falls and convulsions.
In the late period,
there was tonic spasm, hard stools, symmetrical movements in both ears, slow
heartbeat, increased respiratory rate, weight loss, extreme weight loss, and
even death.
It is not only cows
that are affected by mad cow disease. People who eat contaminated beef, bovine
spinal cord, etc. may also be infected with the new fatal Creutzfeldt-Jakob
disease.
A spongy cavity will appear in the brain of the patient, which first
shows anxiety, and then leads to memory loss, dysfunction of the body, and
eventually mental confusion or even death.
Pathological changes
Not obvious to the
naked eye. The main pathological change of histological examination is that the
brain tissue has a sponge-like appearance (cavitation of brain tissue).
The
brainstem gray matter undergoes bilateral symmetrical spongy degeneration and
contains varying amounts of vacuoles in the nerve fiber network and nerve
cells. There is no inflammation.
What is the diagnosis method of Mad Cow Disease?
According to the
characteristics of clinical symptoms and epidemiological characteristics can
make a preliminary diagnosis of mad cow disease.
Because the disease has
neither an inflammatory response nor an immune response, it has been difficult
to diagnose serology so far. Therefore, qualitative diagnosis is currently
based on brain histopathological examination.
According to Well et al. (1989),
changes in vacuoles in the brainstem region, especially in the nucleus
oblongata and trigeminal spinal nucleus, the accuracy of diagnosing BSE is as
high as 99.6%.
Vascularization of brainstem neurons and neural fiber network is
of pathogenic significance.
For laboratory
diagnosis, such as animal infection test, PrPsc immunological test and SAF
test, etc., please refer to the itch.
What is the Prevention Method against Mad Cow Disease?
The body does not
produce a protective immune response to BSE infection. Therefore, immunization
is not an ideal way to prevent BSE. There are two international transmission
routes for BSE: importing live cattle and their products or contaminated feed
in countries or regions with BSE disease; importing live sheep and their
products or contaminated feed in countries or regions with itchy disease.
The current international preventive and control measures are:
(1) Embargoed beef products in epidemic-free areas:
A comprehensive ban on live cattle, cattle
embryos, semen, milk products, by-products, etc. from countries and regions in
BSE-endemic areas.
(2) Establish an epidemic report system:
once a suspected BSE disease is found, it must be reported
to the government's competent veterinary department in time.
(3) Slaughter and safe destruction
All cattle and
other animals infected with BSE are slaughtered and safely destroyed.
(4) Forbidden for Humans
It is forbidden
for humans and animals to consume animal feeds and internal organs that may be
vectored over 6 months of age.
(5) Strict feed processing regulations
Prohibiting the use of meat and bone by-products such
as cattle and sheep and other animals as feed additives for ruminants.
What is the harm from Mad Cow Disease?
1. Harm to human economic and social development
In the
international agricultural trade, the risk status of animal epidemics such as
mad cow disease in one country has become an important means for other
countries to impose trade barriers on it.
The sending of mad cow disease has
caused a heavy blow to the world's cattle industry.
At present, although there
is no BSE outbreak in Asia, from the analysis of the pathogenesis of BSE, the
current status of animal husbandry development and the history of Asia's
animal husbandry international trade.
There is still a risk of BSE transmission
in Asia. The basic level of domestic animal husbandry production should
also strengthen the understanding of BSE, animal husbandry. And the grassroots
level of feed supervision should strengthen the effective and rapid detection
methods for mad cow disease.
2. Harm to human health
The study found
that the spread of human Creutzfeldt-Jakob disease is closely related to the
consumption of food contaminated with BSE factors. The source of the disease
first enters the local lymphatic tissue of the intestine and proliferates
therein, and finally locates in the central nervous system. Since 1995, there
have been 11 cases of human infection in the world, with a mortality rate of
about 95%.
According to statistics from British scientists, about 4,000 people
in the UK are carriers of the prion virus, and about 20 people die of mad cow
disease each year.
In addition, the disease protein of Alzheimer's disease and
the BSE virus protein are surprisingly similar.
Therefore, research on the
prevention and control of mad cow disease is conducive to the prevention and
diagnosis of human mental diseases such as Creutzfeldt-Jakob disease and
Alzheimer's disease.
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