Bovis ISSN 2398-2993

Bovine spongiform encephalopathy: the prion

Introduction

Classification

Taxonomy

• Bovine spongiform encephalopathy (BSE) is an example of a group of diseases called transmissible spongiform encephalopathies (TSEs).
• TSEs are characterized by a degeneration of brain tissue giving it a sponge-like appearance.

Etymology

• The causative agent of BSE is a proteinacious infectious particle prion, a disease-causing form of a normal protein called cellular prion protein (PrP^c). 
• Prions stimulate normal PrP^c, to refold into the disease causing form called PrP^sc.
• This leads to a progressive accumulation of the rogue protein within the brain causing the formation of amyloid plaques which leads to neurological and behavioral effects and, eventually to, death.

Active Forms

Clinical Effects

Epidemiology

Habitat

• Prion protein (PrP^c) is a native protein which is naturally present with the body, although its role is not fully understood. 
• BSE is caused when an abnormal version of the prion proten (PrP^sc) stimulates the naturally occurring PrP^c to misfold into the abnormal version.

Lifecycle

• The incubation period of prion diseases is relatively long (5 to 20 years), once symptoms appear the disease progresses rapidly, leading to brain damage and death.

Transmission

Pathological effects

• The pathogenesis is not well defined.
• Prions have been found in the ileum, CNS and retina.
• Long incubation period.
• Hind limb ataxia resulting in poor balance and coordination.
• Difficulty in rising.
• Behavioral changes including aggression, anxiety, nervousness or frenzy. Cattle Behavior
• Decreased milk production and weight loss. Approach to the cow with milk drop

Control

Control via animal

• Slaughter of infected animals.
  • In some countries the whole herd is slaughtered with the carcasses incinerated.
• Animal feed that contained animal protein thought to have spread BSE is banned. This is called the feed ban.
• Specified risk material control measures ensure that the parts of an animal most likely to contain BSE, such as brain and spinal cord, are removed when an animal is slaughtered to ensure they do not enter the food chain.
• In the UK:
  • All fallen stock or stock that is slaughtered on farm, or in transit, older than 48 months will be tested.
  • All stock older than 72 months that are brought for regular slaughter to an abattoir, where the official veterinarian suspects a health problem, will also be tested.

Control via chemotherapies

• There is no treatment for BSE.

Diagnosis