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Overview of transmissible spongiform encephalopathies (TSEs)

Understanding transmissible spongiform encephalopathies (TSEs)

Transmissible spongiform encephalopathies (TSEs) are diseases that occur when abnormal proteins (prions) accumulate in the tissue of affected animals, particularly brain tissue. The protein causes a spongy degeneration of the brain and spinal cord, producing symptoms such as staggering and tremors, before eventually killing the animal.

TSEs have a very long incubation period. After infection, it takes years for symptoms to develop but, once they do, animals usually deteriorate and die within weeks to months.

The most significant TSEs in animals are:

  • bovine spongiform encephalopathy (BSE) in cattle ('mad cow disease')
  • scrapie in sheep and goats.

Other TSEs occur in wild and captive animals such as mink, deer and cats.

There is no treatment or vaccine for TSEs.

TSE in cattle (bovine spongiform encephalopathy)

BSE is a fatal chronic disease of adult cattle. It is known as 'mad cow disease' because of the erratic behaviour of affected cattle.

The main signs of BSE are:

  • increased apprehension and nervousness
  • staggery gait
  • increased sensitivity to touch and sound
  • muscle tremors.

BSE was first described in the United Kingdom in 1987. It spread when cattle were fed manufactured animal feed that included meat meal and bonemeal containing the BSE protein. Bans on feeding meat meal and bonemeal to ruminants have now controlled the disease.

TSE in sheep and goats (scrapie)

Scrapie is a fatal chronic disease of adult sheep and goats. It is called 'scrapie' because infected animals will often scrape against hard surfaces to relieve itching caused by the disease.

The main signs of scrapie are:

  • severe persistent itchiness
  • staggery gait
  • wasting.

Scrapie can be transmitted from mothers to young animals after they are born, and from infected adult animals to other adults by direct contact and environmental contamination.

Geographic distribution

BSE first emerged in the United Kingdom and other parts of Europe in 1987. Small numbers of cases have also been identified in the USA, Canada and some other countries. It is not known to occur in Australia.

Classical scrapie has occurred in Europe for more than 200 years. It is also seen in the USA, Canada, and a few other countries. It is not known to occur in Australia.

TSEs in humans

Several TSEs occur rarely in humans in countries other than Australia. Variant Creutzfeldt-Jakob disease (vCJD) in humans is thought to be caused by the same agent as BSE in cattle.

There is no evidence that scrapie can be transmitted to humans.

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