Virus Microscopic Image of Mad Cow Disease Bovine Spongiform Encephalitis (BSE)

Mad Cow Disease Bovine Spongiform Encephalitis (BSE)

Mad Cow Disease (Mad Cow Disease), also known as Bovine Spongiform Encephali-tis (BSE), is a type of animal infectious spongiform encephalopathy (Transmissible Spongiform Encephalitis, TSE). Mad cow disease is a subacute progressive neurological disease caused by prions. Usually brain cells and tissues have vacuoles and astrocytes hyperplasia. Amyloid protein fibers are found in brain anatomy, accompanied by systemic symptoms, with long incubation period and death It is characterized by high rate and strong infectivity. Since the disease was first discovered in the UK in 1985, it has gradually spread throughout the world, posing a huge threat to the cattle industry, the catering industry and the safety of human life. From the mid-1980s to the mid-1990s, the outbreak was the epidemic period.

As of 2004, there were 179,000 head of cattle diagnosed in the United Kingdom alone, involving 35,181 farms. More than 11 million head of cattle were slaughtered and burned. Tens of billions of pounds. For more than 20 years, BSE has spread to 31 countries in Europe, America and Asia, and more than 100 countries have been affected by BSE, causing huge economic losses and social panic.


Nickname:    Bovine spongiform encephalopathy

Traditional Medicine disease name:    Mad Cow Disease

English name:    Bovine Spongiform Encephali-tis (BSE

Is it contagious:    Infectious

Incentive:    Infected with prion

Pathogen:    Prions


Table of Content

    1 Introduction to BSE

    2 Symptoms

    3 Pathogen

    ▪ Diagnosis of Prion

    ▪ Testing method

    4 Diagnosis of Mad Cow Disease

    ▪ Clinical diagnosis

    ▪ Pathological diagnosis

    5 BSE Prevention

    ▪ Cattle prevention and control

    ▪ Feed prevention and control

    ▪ Prevention and control of slaughter products

    6 Preventive measures

    ▪ Security management in the EU

    ▪ Canadian safety management

    ▪ American security management

    ▪ Dutch security system


Introduction to Mad Cow Disease

BSE is a subacute progressive neurological disease that mainly occurs in adult cows. It is characterized by a long incubation period, aggravation of the condition, deterioration of the central nervous system, and eventual death.

BSE was first discovered in the UK in 1985, and then spread to many countries and regions in Europe and the world, causing huge losses to the cattle industry worldwide and affecting industries related to cattle-derived materials.

Especially with the prevalence of mad cow disease, the emergence of a new type of Creutzfeldt-Jakob disease (commonly known as human mad cow disease) caused by the same pathogenic factor has caused panic about mad cow disease in the world, giving animals and human health and international political and economic fields. Bring global impact.


What are the Symptoms of BSE?

BSE can manifest as neurological symptoms and systemic symptoms, which often appear earlier than systemic symptoms. Common neurological symptoms include abnormal behavior, ataxia, and hyperalgesia.

Abnormal behavior mainly manifests as outliers, anxiety, fear, violent or depression, trance, involuntary movements (such as molars, muscle twitching, tremors and cramps, etc.), reluctance to pass through the concrete floor, turning, entering the corral, crossing the door or milking etc.

Sick animals often show aggressive behavior when someone approaches or chases them, which is also an important reason for its commonly known as mad cow disease.


The ataxia of BSE is mainly manifested as hindlimb movement disorder, especially in sharp turns.

The cow suffers from abnormal gait when walking fast, and the front and rear limbs start at the same time, and then develops the hindquarters shaking, short stride, difficulty in turning, easy to fall when walking, or even difficult to stand up or cannot stand and lie on the ground all day long.

Sensitive allergy often manifests as excessive sensitivity to touch, light and sound.

When you touch or use a blunt instrument to press the neck and ribs of a cow, the sick cow will be very nervous and tremble. When you touch the hind limbs with a broom, you will also feel nervous.


If the sick cow hears the sound of striking a metal instrument, it will react with shock and tremor. The sick cow will startle and tremble in the dark environment when the light is suddenly turned on. This is a very important clinical diagnostic feature of mad cow disease.

50% of sick cows kick and kick when milking. In a quiet environment, the sick cow feels allergic symptoms significantly reduced, and other neurological symptoms can also be alleviated.

The systemic symptoms of 70% to 73% of sick cows are weight loss and reduced milk production. Most sick cows have slow heart rate (average 50 beats / min) in the later period, rapid respiratory rate, tonic spasm, and hard stools. Both ears are symmetrical and sexual activity is difficult.

From the initial symptoms to the death or emergency slaughter of cattle, the course of disease can last from a few weeks to 12 months

The pathological anatomy is not obvious to the naked eye, and the liver and other parenchymal organs are normal.

Histopathological changes are mainly limited to the central nervous system, and its characteristics are:

  • Symmetrical lesions on both sides of the brainstem gray matter
  • Vacuolar degeneration of the brain gray matter
  • Disappearance of neurons and hypertrophy of proglia cells, and a moderate number of nerve fiber network
  • Discontinuous oval and spherical hollows
  • Nerve cells swell into a balloon
  • The cytoplasm narrows


In addition, there are obvious degeneration and necrosis of nerve cells. Apoptosis of nerve cells and formation of vacuole-like structure, which can cause disturbance of relevant signal transduction, so that animals exhibit neurological symptoms such as dysregulation of autonomous movement, fear, disturbance of circadian clock, etc.



Earlier studies did not successfully isolate the causative agents of mad cow disease and other related diseases, nor did they detect immune responses related to infection.

Although hypotheses such as pesticides and autoimmunity have been proposed, none of these theories can explain the characteristics of the mad cow disease pathogen.

In the 1980s, the American biologist Prusaine discovered in a study of mad cow disease that the infection of mad cow disease was completely prion (also known as prion protein), a peculiar nucleic acid-free protein infecting particles, and no other based on The role of RNA or DNA.



It is mainly distributed in the central nervous system such as the brain, neck spinal cord, and end of the spinal cord of the sick cow. It is rarely found in the spleen, lymph nodes, muscles and blood.

In addition, it is difficult to detect in more than 40 tissues including peripheral nerves and their distribution.

Studies have shown that oral intake of 1g of mad cow disease brain tissue can cause cattle disease, while 1g of pure prion extract can infect 10 million cattle.

Prions can be inactivated by 2% to 5% sodium hypochlorite or 90% carbolic acid after 24 hours of treatment, while ultraviolet, ionizing radiation, ultrasonic waves, non-ionic detergents, proteases and other physical and chemical factors that can inactivate common viruses have Strong resistance.


How to Diagnose Prion?

Diagnosis of Prion: Depending on the area where the brain is damaged, the symptoms of Kuru disease and Creutzfeldt-Jakob syndrome caused by prions in humans are also different. If the cerebellum is infected, it will cause damage to the motor function; if it is infected with the cerebral cortex, it will Causes memory decline and eventually progressive death.

Pathological changes mostly occur in the central nervous system, with diffuse neuronal degeneration and sponge-like changes in the cerebral cortex or ganglia.

The diagnosis of prion depends on the diagnosis of the laboratory in addition to the specific clinical features and pathological diagnosis.



What are the ways to detect Prions?

Prions Detection Method: There are many ways to detect prions in the laboratory. Animal transmission experiments are a method to determine whether prions are infected at an early stage.

In addition to judging whether humans or animals are infected with prions, they can also determine the titer and toxicity of infection.

However, because animal experiments are time-consuming, expensive, and have large errors, they have been gradually replaced by other methods that are faster and more accurate.

Tissue blotting technology that combines protein detection technology and anatomical preservation technology can be used to detect trace prions with high sensitivity and accuracy.

However, it requires tissue specimens in the clinic and is not suitable for rapid detection.

The dot blot method also requires tissue samples and has low sensitivity, but the operation is simple and the equipment requirements are not high, which is suitable for screening a large number of samples.

Immunoblotting can identify specific components in specimens and display electrophoretic patterns.

It is simple and fast, and does not require high equipment. It has early diagnostic value, so it is widely used. Immunohistochemistry is a mature method that has been repeatedly improved by researchers.

It has many advantages and has become the gold standard for the diagnosis of TSE disease.


The basis of prion laboratory diagnosis is mainly the detection of PrPSc protein in brain tissue. The most commonly used methods at present are immunohistochemistry and immunoblotting.

Immunological methods are currently widely used as the main methods for detecting prions because of their high sensitivity, specificity, and diverse methods.

Among them, enzyme-linked immunosorbent assay uses indirect method and double antibody sandwich method to detect antigen.

The method is fast, specific, sensitive, quantifiable, and automated. It is very suitable for screening large numbers of samples.

In addition, the current method that has high sensitivity in blood samples and can detect viruses is PCR nucleic acid detection technology, which has a high sensitivity for whole blood and is the most likely to detect whether the blood is virus. A technology is therefore widely used in blood donation testing, but because the main component of prion is protein, some methods of nucleic acid detection are difficult to detect prion.

Therefore, for a long period of time, how to quickly detect prion from the blood has become a problem in the medical community.

After all, according to the protein-only hypothesis, prions are composed of proteins, and the main component is PrPSc, which is also one of the subtypes of prion protein.

In the current research on prions, it is found that PrP (prionprotein) is an important factor affecting prion infection.

PrP (prionprotein) is required to cause infectious spongiform encephalopathy. 

PrPSc will promote the conversion of PrPC to PrPSc, thus laying the foundation for prion detection.

Although the nucleic acid detection method cannot be used to determine the type of virus, it can be detected by the wrong folding method of protein.

A “PCR” -like high-sensitivity detection method for prion detection. This method is called protein misfolding cycle amplification technology (PMCA). This technology provides a basis for clinical detection of prion infection.


What is the Diagnosis of Mad Cow Disease?

There are Clinical and Pathological Diagnosis:

i. What is Clinical Diagnosis for BSE?

The average incubation period of mad cow disease is 4 to 6 years. Once onset, the sick cow has subacute or chronic progressive dysfunction, the initial appetite and body temperature are close to normal.

With the progressive increase of the central nervous system, the typical neurological symptoms appear, and Systemic symptoms appear.

Common neurological symptoms are abnormal behavior, ataxia and sensory abnormalities.

Some people think that if the sick cow shows the above three symptoms at the same time and the symptoms exceed 1 month, it can be considered that the cow has mad cow disease.

Abnormal behavior mainly manifests as outliers, anxiety, fear, violent or depression, trance, involuntary movements (such as molars, muscle twitching, tremors and cramps, etc.), reluctance to pass through the concrete floor, turning, entering the corral, crossing the door or milking etc.

Sick animals often show aggressive behavior when someone approaches or chases them.

Ataxia is mainly manifested by abnormal posture and movement, accounting for about 3% of cases. The maladjustment of the hind legs of the sick cattle is especially obvious when turning sharply.


The cow suffers from abnormal gait when walking fast, and the front and rear limbs start at the same time, and then develops the hindquarters shaking, short stride, difficulty in turning, easy to fall when walking, or even difficult to stand up or cannot stand and lie on the ground all day long.


Sensory abnormalities account for about 90% of cases, with diverse manifestations.

One type shows excessive sensitivity to touch, light and sound. When the hand touches or touches the neck and ribs of the cow with a blunt object, the sick cow will be very nervous and tremble. Kick reaction.

Sick cows will be shocked and trembling when they hear the sound of striking metal equipment.

Sick cows will have panic and trembling reactions in the dark environment when the lights are turned on suddenly.

50% of the sick cows are chaotic during milking kick and kick. The other category is the loss of tactile and hearing senses of sick cows, which are manifested as unresponsiveness.

The above three clinical symptoms account for about 87% of mad cow disease cattle, which is consistent with the diffuse lesions of the central nervous system.

Put the sick cow in a quiet and familiar environment, some symptoms can be reduced, especially the feeling of decline.

Itching symptoms that occur in sheep pruritus also occur in sick cows, but they are not the main symptoms.

The symptoms of bovines in the zoo are similar to domestic cattle, but some cases have a sudden onset and a rapid course of disease.

The most common systemic symptoms of sick cattle are physical decline (78%), weight loss (73%) and decreased milk production. Most sick cattle have good appetite.

At some stage during the clinic period, approximately 79% of the sick cattle appear-a systemic symptom and a neurological symptom.

From the initial symptoms to the death or emergency slaughter of the cattle, the course of disease can last from a few weeks to 12 months. Eventually, the sick cattle are inactive and die due to increased symptoms.


ii. What is Pathological Diagnosis of BSE?

When a suspected BSE case is slaughtered, the primary diagnostic method is histopathological examination, which is the standard for evaluating the effectiveness of other methods.

The pathological changes of the deceased cattle carcasses were not obvious, and the liver and other parenchymal organs were normal.

Histopathological changes are mainly limited to the central nervous system.

Microscopic examination of brain tissue showed that the number of neurons in the brain tissue of the sick cow was reduced, the protoglial hypertrophy, the symmetrical cavernous lesions of the gray matter plexus on both sides of the brain, and the vacuolation of neurons in the brain thousand nucleus, amyloid in brain tissue.

There are “petals” formed by spongy degeneration around the core, which can be diagnosed as BSE when they constitute the characteristic lesions of daisy-like pathological spots.

The characteristic pathological changes of neurons occur more frequently in the medulla oblongata, the medulla oblongata at the ventral corner of the cerebellum, the pons and the midbrain, and the changes are more consistent.

Especially in the bulbar nucleus of the medulla oblongata and the trigeminal nerve spinal nucleus nucleus occur very frequently.

Therefore, the examination of degenerative changes such as vacuole degeneration of neurons in the transverse section of the brain is a routine method for diagnosing the early stage of BSE.

Data show that 80% of suspected BSE diseased cattle can be diagnosed by examining only the medulla oblonga section, and the detection rate of this section is equivalent to 99.6% of cases diagnosed by more complicated methods.


What is BSE infection prevention?

The infection path of mad cow disease is mainly caused by the digestive tract, and due to the specificity of prion protein, it is not possible to use antibody vaccines for effective prevention and treatment at this stage. Therefore, the current prevention and control measures for mad cow disease are mainly to cut off the transmission route and eliminate the source of infection.

Most countries have adopted prevention and control of herds, feed, slaughter products, etc., to avoid the potential hidden dangers of prion protein to cause the spread of mad cow disease.


What is the process for Preventing Mad Cow Disease?

i. Cattle Prevention and Control

In order to prevent mad cow disease from causing harm to humans again, the European Union has formulated very strict control measures for mad cow disease.

The European Union has established many professional mad cow disease detection institutions. These institutions can carry out rapid and accurate detection and analysis of parts of cattle organs.

The samples to be tested come from cattle circulating in the market, sudden slaughter cattle, cattle slaughtered for more than 24 months due to special reasons, etc.

In order to better prevent and control mad cow disease, the US agricultural department has strictly implemented the requirements of the “BSE monitoring and access system” for many year.

The US agricultural department recommends the implementation of a national certification system for all circulating livestock and poultry products in the international market. Tracking detection.

Since 2001, according to the relevant standards formulated by the OIE (World Organisation for Animal Health), the agricultural department of our country has launched a mad cow testing program to the whole country, and actively and passively tested mad cow disease in China.

Focus on the full-scale follow-up investigation of imported herds, even embryos and their offspring, this type of herds must be monitored for a long time.


Feed prevention and Control

Feed generally refers to all foods for animals raised by humans. Generally speaking, feed refers to foods for animals raised in agriculture or animal husbandry.

Therefore, its safety issues are directly related to the safety of animal products.

Therefore, it is particularly urgent to pay attention to the issue of feed safety. To do a good job in the prevention and control of feed safety from the roots, we must first clearly understand the role and status of feed in the entire livestock production, and the multiple aspects of feed safety.

Feed: The laws and regulations, supervision system and advanced technology have an important impact on the safety of animal products.

Safeguarding feed safety is very difficult, careful and requires long-term persistence. Not only must we establish sound laws and regulations, but we must also explore advanced feed new technologies and improve feed processing technology in order to solve safety problems from the root causes.

To realize the sustainable development of animal husbandry safety and human food safety, we must explore and develop new feed technologies and products.


Slaughter product prevention and control

At this stage, there are still certain deficiencies in the safety risk control of beef cattle slaughtering in China, and there is an urgent need to establish and improve relevant laws and regulations on slaughter product safety management.

It can draw on the relevant systems specified by countries around the world in order to reduce the risk of BSE and strengthen the monitoring of BSE, such as Canada ’s cattle waste management regulations, which effectively improves the supervision of BSE.

The series of measures promulgated and implemented by the US agricultural department include, adding any cattle scraps in the food production process to isolate the highly infectious organs of cattle over 30 months of age.

Japan has begun to carry out all slaughter cattle one by one after the detection of the first BSE in 2001 BSE detection, so as not to leak.


What are Preventive Measures against Mad Cow Disease?

Preventive measures against BSE are:

EU Security Management

In 2001, the European Union established a comprehensive quality control management agency-the European Food Safety Authority, which is mainly responsible for monitoring the entire food chain.

The EU has issued a series of regulations on BSE control and feed safety, which can be summarized to include the following four aspects:

(1) BSE passive monitoring and active detection plan and killing policy.

(2) Removal of designated risk substances (SRM).

(3 ) Safely destroy risky materials.

(4) Animal-derived feed ban.

The EU has strengthened the quality and safety control standards for livestock products and implemented a strict and unified quality and safety system.

The European Union began implementing the HACCP system in 1996, and made provisions in the EU Food Sanitation Law, requiring animal production and processing companies to recognize that all aspects of production should pay attention to quality and safety, and ensure that the HACCP system is established, implemented, and maintained And revise appropriate animal product safety measures.

In order to deal with the problem of mad cow disease, the European Union has gradually established a food information traceability system in 1997 as an important means of animal product quality and safety control.

According to the provisions of the EU Food Law, food, feed, livestock for food manufacturing, and articles related to food and feed manufacturing must have a food information traceability system at all stages of production, processing, and distribution.


Canadian Safety Management

Canada passed the “Canadian Food Inspection Agency Act” in 1997, and formed the Canadian Food Inspection Agency to uniformly exercise food safety supervision and enforcement powers including feed and animal products, the Food Safety Accreditation Program of the Brigade Farm and the BSE Prevention Program.


American Security Management

The main safety measures in the United States include:

  • Sound animal product quality safety laws, regulations, and standard systems.
  • Full control of animal product production, processing, storage, transportation and sales processes.
  • Strict animal product quality and safety management organization system.
  • Strengthening production sources Control and import and export quarantine.

The US Congress has passed laws to ensure food quality and safety, and establishing a quality standard system is an important measure to ensure the quality and safety of animal products.


Dutch Security System

The main measures for the implementation of cow health and health records in the Netherlands are: each cow must have a health certificate (mandatory), regular disease control and quarantine, and monitoring cow registration (mandatory).

There are specific regulations and requirements for feed Dutch Power.

Only companies that meet IS09002 quality management standards and HACCP technical standards and have obtained good manufacturing practice certificates are allowed to provide mixed feed to the pasture.

The Animal Feed Commodity Committee is responsible for issuing certificates of good manufacturing practice, and the Animal Feed Quality Service Agency and the National Livestock Meat Testing Service Agency are responsible for product inspection and supervision of the implementation of quality regulations.

The quality assurance of the feed manufacturing process is achieved by implementing the following standards:

  • Quality management standards, material ingredient detection standards to monitor harmful ingredients)
  • Technical standards for feed manufacturing equipment
  • Hygiene standards for manufacturing and storage
  • Final inspection standards for feed products (components and quality).
  • The standard for transportation and storage of final products and materials.




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