Bovine spongiform encephalopathy is also commonly known as mad cow disease which causes spongy neurodegeneration in the brain and spinal cord of adult cattle. The main causative agent of bovine spongiform encephalopathy is prion, which is a misfolded protein.
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Mad cow disease or bovine spongiform encephalopathy BSE

Image: “Section of brain from a cow infected with bovine spongiform encephalopathy. The brown staining indicates the presence of the agent causing the disease.” by CSIRO. License: CC BY 3.0

Etiology of Bovine Spongiform Encephalopathy

The postulated cause of mad cow disease is MBM (meat and bone meal) which is a concentrated protein rich supplement feed given to the dairy cows. Due to this reason, dairy cows are more prone to develop the disease as compared to beef cattle.

cow with bse

Image: “Cow with BSE.” License: Public Domain

The infectious agent, which is the prion protein, can survive in temperatures of more than 600 degrees Celsius. Some theories also state that the disease is caused by a virus. The animals carry an allele which converts the normal alpha helical arrangement of protein into beta pleated sheets. This leads to the formation and accumulation of plaques which causes degeneration and holes in the brain, leading to mental impairment of the animal.

Healthy animals can become infected by coming in contact with infected animals. Two leading hypotheses suggest that the disease might have come from other species of sheep or it may have happened before as well in the past centuries.

Incubation period varies from 2.5 to 5 years with the peak age of onset of 5 years.

Transmission to Humans

In humans, the disease variant is known as Creutzfeldt-Jakob disease (vCJD or nvCJD). It is said that the infectious agent is found in the brain and spinal cord but still it is present in every tissue of the body of the infected cattle. The disease is likely to occur if a person consumes food that has been contaminated with the brain and spinal cord of the infected animal.

The disease is not curable and eventually fatal.

The signs and symptoms include memory loss, hallucinations, personality changes, psychosis, speech impairment, loss of balance, seizures and rigid posture. Usually, the victims die within six months after the development of disease due to pneumonia caused by defective cough reflexes.

tonsil biopsy in variant CJD

Image: “Tonsil biopsy in variant CJD. Prion protein immunostaining.” by Sbrandner – Own work. License: GFDL

The diagnosis of the disease can be done by:

  • Electroencephalography demonstrates sharp wave pattern.
  • Cerebrospinal fluid analysis shows misfolded proteins.
  • Magnetic resonance imaging of the brain shows damage in the caudate nucleus and putamen.
  • Neuron specific enolase: this tumor marker is mostly raised in patients with Creutzfeldt-Jakob disease.

Signs and Symptoms of Bovine Spongiform Encephalopathy

As the disease has a very long incubation period the symptoms and signs of the disease occur very late. The infected animal usually has an abnormal gait and when muscles are affected, the animal loses the ability to stand. The animal might have changes in behavior, anxiety, aggression, persistent rubbing or teeth grinding due to pain. The disease eventually leads to coma and death.

Diagnosis of Bovine Spongiform Encephalopathy

As the disease has a very long incubation period of months to years, it is very difficult to diagnose the disease at an early stage. So, presumptive diagnosis can only be made by the developing signs and symptoms. At the time of development of signs and symptoms the disease has virtually progressed into every body tissue and fluid.

Definitive diagnosis can only be made by examining the postmortem brain and body tissues by using neuropathological and immune-histochemical stains. The toxic prion protein is also present in the blood and urine of the infected animal but the amount of the protein is very low and scientists are still developing methods to diagnose the disease in blood and urine.

Pathogenesis of Bovine Spongiform Encephalopathy

Pathogenesis of bovine encephalopathy is still not well understood and research is still under process. Although the disease affects the brain and spinal cord, pathogenesis occurs in other body parts as well.

One theory strongly suggests the presence of prion protein in peyer’s patches of the ileum. The infectious protein was demonstrable in the macrophages of the peyer’s patches of the ileum. Months after inoculation, the protein was only found in the peyer’s patches which led the researches to think that the organism only replicates in the peyer’s patches.

Prevention of Bovine Spongiform Encephalopathy

Prevention can only be done by regulating the constituents of the feed which is being given to dairy cows. In the UK and US, body parts like brain, spinal cord and eyes are considered to be high risk and proper methods are proposed for their disposal.

Treatment of Bovine Spongiform Encephalopathy

There is no treatment of mad cow disease till date.

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