BSE, also known as mad cow disease, stands for Bovine Spongiform Encephalopathy. This cattle disease also causes a variant of Creutzfeldt-Jakob disease, a deadly human brain disease. BSE resulted in disaster for cattle farmers in the United Kingdom: more than 180,000 cattle infected with BSE had to be destroyed.
What is BSE and what causes the disease?
BSE is an infectious disease belonging to the group of "transmissible spongiform encephalopathies" (TSEs). BSE and other TSEs are caused by prions. Prions are proteins that can deform the normal proteins in the brain. Prion diseases can be caused by infection, but also by small changes in the genes that produce these proteins. Prions are very resistant to heating and disinfection, and are also resistant to protein-splitting enzymes.
How does mad cow disease spread?
Epidemiological data have clearly shown that BSE spreads primarily through the reuse of animal proteins (cattle proteins) in animal feed. This results in a circular flow of animal material in which pathogens can multiply. This problem was recognised long ago. As a result, sterilisation has become an important part of processing animal cadavers.
Other transmission routes may also be possible, including transmission from mother cow to calf at birth and transmission via the environment, but none of these transmission routes have been proven conclusively. If the infection can be transmitted via these other routes, the role of these routes is very limited.
It is assumed that the outbreak of BSE was caused by feed concentrates that included insufficiently sterilised meat and bone meal originating from carcasses of sheep or cows that were infected with prion disease. In Great Britain, the processing method for carcasses was changed in the early 1980s, and a second heat treatment with steam was discontinued. Because BSE prions are resistant to high temperatures, they were no longer eliminated during processing, and it became possible for them to contaminate meat and bone meal. This possibly contaminated meat and bone meal was included in feed concentrate for cattle.
Animals contracting BSE became infected especially during their first year of life by eating contaminated concentrate. It is also likely that calves can be infected in the uterus by direct transmission from the mother to the calf.
Which animals are susceptible to BSE?
The disease is seen in adult cattle, mainly at the age of three years and older (in the Netherlands the average age is 6.5 years). There are concerns that it may also occur in other small ruminants. Until now, however, only one case of the disease has been detected under natural circumstances in a French goat.
What are the symptoms of mad cow disease?
The central nervous system of the animals is affected by BSE. Microscopically small cavities develop in the brains of the animals, which cause behavioural changes (startling, hypersensitivity to light, sound, touch) and movement disorders. The animal will eventually die of the disease. The period between the infection and the first symptoms is usually several years.
Can people become infected?
In humans, BSE causes a variant of Creutzfeldt-Jakob Disease. The disease was first observed in 1996 in Great Britain. In the Netherlands it has been diagnosed in three patients (until 2011), all of whom died. Worldwide more than 220 patients have been diagnosed with this variant of CJD. This variant of the disease could be caused by eating contaminated organs from cattle (particularly brains) that are infected with BSE.
Is BSE still present in Europe?
In 2018, a case of BSE was discovered on a farm in Scotland. This discovery is not unique. For example, two cases have been reported on the continent of Europe in 2016 and four in 2017.
Is the Netherlands BSE free?
Since 1987, a total of 88 cattle from the Netherlands have been diagnosed with a BSE infection. Since the last case, in September 2011, no new cases have been reported in the Netherlands.
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