BSE Virus is a Prion. Is it? | Mad Cow Disease

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

1.      Prion properties
2.      Pathogenesis
3.      Pathological changes
4.      Epidemiological characteristics
5.      Prevention
6.      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.

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

Dr. Shawna Reason

Name: 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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