biology

Mad cow crisis

Mad cow crisis is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mad cow crisis rather than just read about it. In short: The mad cow crisis is a health and socio-economic crisis characterized by the collapse of beef consumption in the 1990s, as consumers became concerned about the transmission of bovine spongiform encephalopathy (BSE) to humans through the ingestion of this type of meat. Background BSE is a degenerative infection of the central nervous system in cattle.

Key takeaways

Mad cow crisis belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mad cow crisis to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mad cow crisis from memory before moving on to harder problems.

Reference excerpt

The mad cow crisis is a health and socio-economic crisis characterized by the collapse of beef consumption in the 1990s, as consumers became concerned about the transmission of bovine spongiform encephalopathy (BSE) to humans through the ingestion of this type of meat.

Background BSE is a degenerative infection of the central nervous system in cattle. It is a fatal disease, similar to scrapie in sheep and goats, caused by a prion. A major epizootic affected the UK, and to a lesser extent a number of other countries, between 1986 and the 2000s, infecting more than 190,000 animals, not counting those that remained undiagnosed. The epidemic is thought to have originated in the feeding of cattle with meat and bone meal, obtained from the uneaten parts of cattle and animal cadavers. The epidemic took a particular turn when scientists realized in 1996 that the disease could be transmitted to humans through the consumption of meat products. As of 24 January 2017, the disease had claimed 223 human victims worldwide (including 177 in the UK and 27 in France) affected by symptoms similar to Creutzfeldt-Jakob disease, a disease of the same nature as BSE. Communicated to the general public by the media, the crisis erupted in 1996. It involved both ethical aspects, with consumers becoming aware of certain practices that were common in livestock farming but of which they had been unaware, such as the use of meat and bone meal, and economic aspects, with the ensuing fall in beef consumption and the cost of the various measures adopted. Various measures were taken to curb the epidemic and safeguard human health, including a ban on the use of meat and bone meal in cattle feed, the withdrawal from consumption of products considered to be at risk, and even of certain animals (animals over 30 months of age in the UK), screening for the disease in slaughterhouses, and the systematic slaughter of herds where a sick animal had been observed. Nowadays, the epidemic is almost completely under control, despite 37 bovine cases still being diagnosed in the UK in 2008. On 23 March 2016, a new case of mad cow disease was detected in France in the Ardennes department. This is the third isolated case of BSE of this type detected in Europe since 2015.

Epidemiology

The disease was first identified in the United Kingdom in 1986.

Symptoms

BSE affects the brain and spinal cord of cattle. It causes brain lesions characterized by spongy changes visible under the light microscope, corresponding to vacuolated neurons. Neurons are lost to varying degrees, and astrocytes and microglia (brain cells with an immune function) multiply. Pathogens accumulate to form characteristic amyloid plaques, though these are less prevalent than in other transmissible spongiform encephalopathies. External symptoms generally appear 4 to 5 years after contamination, and always in animals over 2 years of age (generally between 3 and 7 years). Initially, they are manifested by a change in the animal's behavior (nervousness and aggressiveness), which may sometimes kick, show apprehension and hypersensitivity to external stimuli (noise, touch, dazzle), and isolate itself from the rest of the herd. Milk production and weight generally decrease, while appetite remains unchanged. Progression can last from a week to a year, with the different phases of the disease varying in duration from one animal to another. In the final stage of evolution, the animal has real locomotion problems. They frequently lose their balance, sometimes unable to stand up again. Physiologically, the animal is tachycardic and feverless. However, the appearance of these symptoms is not a sure sign of BSE. In fact, locomotor disorders such as grass tetany are common in cattle, making diagnosis of the disease difficult.

Nature of the pathogen The nature of the infectious agent remains debated. The leading theory is that a protein folds abnormally and becomes a prion, capable of causing other proteins to also fold incorrectly. A resistant form of the prion (PrPSc, also known as PrPRes, PrPD, or PrPBSE) accumulates in the brain, eventually leading to neuronal death and the formation of amyloid plaques. As a protein, the prion has no metabolism of its own, and is therefore resistant to freezing, desiccation and heat at normal cooking temperatures, even those reached for pasteurization and sterilization. To be destroyed, the prion must be heated to 133 °C for 20 minutes at 3 bars of pressure.

Origins of the epizootic The origins of the BSE pathogen are uncertain. Two hypotheses are widely supported. The first is that the disease originated through interspecific contamination from a closely related disease, scrapie, which affects sheep and goats. The possibility of interspecific transmission of scrapie has been proven experimentally, but the clinical and neuropathological disorders associated with the disease differ from those of bovine spongiform encephalopathy. This observation led to the formulation of a second hypothesis, according to which the disease is endemic to the bovine species, and very thinly spread before it was amplified in the mid-1980s. The description in an 1883 veterinary journal of a case of scrapie in a bovine is an argument used by advocates of this second theory, although this case may correspond to a completely different neurological disease. Numerous other more or less credible theories regularly enter the debate, with none really emerging.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Mad cow crisis

Start with the simplest possible case. Write down what Mad cow crisis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mad cow crisis before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mad cow crisis ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mad cow crisis

In research: Mad cow crisis appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mad cow crisis in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mad cow crisis is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1990s in the European Union, 1990s in the United Kingdom, Animal disease control, so understanding it makes those chapters shorter.
In everyday life: Look for Mad cow crisis outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mad cow crisis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mad cow crisis means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mad cow crisis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mad cow crisis in simple terms?

Why does Mad cow crisis matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mad cow crisis?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mad cow crisis.