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Mad cow disease, also known as bovine spongiform encephalopathy (BSE), is a neurological disorder that affects cows. It is caused by abnormal proteins, or prions, that damage the brain and nervous system. Humans can also contract a variant form of the disease, called variant Creutzfeldt-Jakob disease (vCJD), by consuming contaminated beef products. Symptoms of mad cow disease in cows include behavioral changes, lack of coordination, and weight loss. There is no cure for mad cow disease, and infected cows must be euthanized to prevent the spread of the disease. Strict regulations and testing methods have been implemented to prevent the spread of BSE in the food supply.
Animal Facts
Mad cow disease, also known as bovine spongiform encephalopathy (BSE), is a fatal brain disorder that affects cattle. This disease infected 180,000 livestock in Europe during the 1980s and ’90s, and resulted in the death of dozens of humans. The British cattle industry was hit hard, and since then, strict measures have been implemented worldwide to control and prevent the disease from reoccurring. In this article, we will discuss what mad cow disease is, how it works, and what is being done to control and prevent its occurrence.
What is Mad Cow Disease?
Mad cow disease is a fatal brain disorder that occurs in cattle and is caused by an unknown agent. This agent causes the cow’s brain cells to die, leaving behind sponge-like holes in the brain. The cow behaves abnormally and eventually dies. The connection between BSE and humans was discovered in Great Britain in the 1990s, when several young people died from a new variant of Creutzfeldt-Jakob disease (CJD), a rare brain disorder that typically affects the elderly. The new variant was called new variant Creutzfeldt-Jakob Disease (nvCJD) and was found to be similar to BSE. The connection was based on the following findings:
- The nvCJD victims had lived in areas where BSE outbreaks had occurred in cattle years earlier. No victims were found in areas without BSE outbreaks.
- The brains of nvCJD victims had prions (pree-ahnz) that were similar to those found in the brains of BSE-infected cows, but different from those found in victims of classic CJD.
- The time between the BSE outbreaks and the deaths of the victims was similar to the time it takes for Creutzfeldt-Jakob disease to develop.
- Brain tissue from BSE-infected cows caused experimental animals to develop symptoms and brain tissue disorders similar to those of nvCJD victims.
The British government concluded that BSE was likely the cause of nvCJD, and that victims contracted the disease by eating meat from BSE-infected cows.
BSE is more commonly referred to as mad cow disease. It is believed to have originated from a similar disease in sheep called scrapie. During the 1980s, cattle feed producers changed the way they processed feed, allowing the scrapie disease agent to survive the production process. Cattle were then fed contaminated food and developed BSE. At the time, neither scrapie nor BSE were thought to affect humans. Meat from BSE-infected cows then entered the food supply, and humans who ate the infected meat (often hamburger or other processed meats) contracted the BSE-causing agent and developed nvCJD.
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Understanding BSE
BSE is a disease that spreads when an individual comes into contact with brain or nervous-system tissue from an infected animal. This can happen by consuming contaminated food or using instruments that have come in contact with diseased nervous tissue. Once the infectious agent enters the brain, it can remain inactive for several years before causing damage to brain cells and leaving behind spongy holes. The disease runs its course in less than a year and ultimately leads to death.
The agent that causes BSE is still unknown, but we do know that it must be small and resistant to heat, disinfectants, and freezing. The lack of genetic information in the agent has also been questioned.
Identifying the Cause
Research into diseases like BSE, nvCJD, CJD, and scrapie has led to three theories about the cause of BSE. These theories suggest that the agent could be an unidentified virus or virus-like particle, a mobile bacterium (Spiroplasma), or an abnormal protein (prion). The prion hypothesis is the most widely accepted theory, but it goes against many established theories of biology.
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The Prion Hypothesis
Prions are proteins found in the nerve cells of all mammals. While the function of prion proteins is still unknown, abnormally-shaped prions have been discovered in the brains of BSE-infected cows and humans with nvCJD or CJD. The prion hypothesis suggests that these abnormal proteins are responsible for causing BSE.
The process of how abnormal prions cause mad cow disease and nvCJD in humans is as follows: first, a person ingests an abnormally-shaped prion from contaminated food. The prion then enters the bloodstream and crosses into the nervous system. Once there, it touches a normal prion and changes its shape, destroying its original function. The abnormal prion then goes on to change the shapes of other normal prions in the nerve cell, causing the cell to clump them together in small sacs that merge with its “stomach.” However, the nerve cells cannot digest the abnormal prions, causing them to accumulate in the lysosomes and eventually causing the cell to die. When the cell dies, the abnormal prions are released to infect other cells, leading to loss of brain function and ultimately, death.
Cows infected with BSE experience weight loss, abnormal behavior, paralysis, and eventually death. Humans with nvCJD experience psychiatric and sensory problems, followed by muscle coordination issues, muscle spasms, sensory problems, and memory loss. Ultimately, they may lapse into a coma and die.
To control and prevent the spread of BSE, the UK government banned using ruminant or ruminant by-products in animal feed, banned exports of cattle, destroyed infected cattle, and monitored herds for signs of BSE. The medical community has also monitored the general population for cases of nvCJD. These measures have contributed to a decline in BSE since 1992. The US government has also implemented policies regarding BSE.
The U.S. Department of Agriculture (USDA) has banned the import of live ruminants or ruminant products, including meat, feed, and by-products, from Europe. The USDA tests any cattle exhibiting abnormal behavior for BSE and inspects all cattle used for food for signs of neurological diseases. Cattle with unidentified neurological disorders are not accepted. The U.S. Food & Drug Administration (FDA) has prohibited the use of mammalian proteins in animal feed for ruminants and recommended that pharmaceutical companies should not use animal tissues from countries with BSE in making vaccines. Blood centers have been asked by the FDA to exclude potential donors who have spent six or more consecutive months in the UK between 1980 and 1986. The Centers for Disease Control (CDC) regularly monitor the U.S. population for signs of nvCJD and have issued guidelines for travelers visiting Europe. The National Institutes of Health (NIH) conduct research on BSE, CJD, nvCJD, and other nervous system diseases. The meat supply in the United States, as well as imports from other countries, is monitored by several U.S. government agencies (FDA, USDA, CDC), and European countries have implemented similar guidelines. To test for BSE, brain tissue from a suspected animal is injected into an experimental animal, and scientists observe the experimental animal for signs of BSE. Diagnostic tests for BSE are being developed to detect abnormal prions in suspected animals. Numerous links for additional information on BSE and related topics are provided on the next page.
FAQ
1. What is Mad Cow Disease?
Mad Cow Disease, also known as Bovine Spongiform Encephalopathy (BSE), is a fatal neurodegenerative disease that affects cattle. It is caused by an abnormal protein called a prion, which is able to spread and cause damage to the brain. The disease is characterized by different symptoms such as loss of coordination, difficulty in standing up, and aggression. In humans, exposure to infected meat can cause a similar disease called variant Creutzfeldt-Jakob disease (vCJD).
2. How is Mad Cow Disease transmitted?
Mad Cow Disease is usually transmitted through the consumption of meat that has been contaminated with prions. The prions can also be found in other animal products such as bones and organs. In rare cases, the disease can be transmitted through blood transfusions or organ transplants from infected donors.
3. How is Mad Cow Disease diagnosed?
The diagnosis of Mad Cow Disease can be difficult since it does not have specific symptoms that can be distinguished from other neurological diseases. However, veterinarians can perform a test called the rapid test, which detects the presence of abnormal prions in the brain tissue of infected cattle. In humans, the diagnosis is made through a combination of symptoms, medical history, and laboratory tests.
4. Is there a treatment for Mad Cow Disease?
Unfortunately, there is no known cure for Mad Cow Disease. The disease is fatal and most infected animals are euthanized to prevent the spread of the disease. In humans, treatment is usually focused on managing symptoms and providing support to affected individuals and their families.
5. How can Mad Cow Disease be prevented?
The best way to prevent Mad Cow Disease is to avoid consuming meat from infected animals. Governments around the world have implemented measures to ensure the safety of the food supply, including bans on the use of animal byproducts in cattle feed and strict regulations on the testing and monitoring of cattle. Additionally, people should be aware of the risks associated with consuming raw or undercooked meat.
6. Is it safe to eat beef?
Yes, it is generally safe to eat beef if it has been properly cooked and comes from a reputable source. The risk of contracting Mad Cow Disease from beef is low, especially in countries that have implemented strict regulations on the meat industry. However, it is important to be aware of the risks associated with consuming raw or undercooked beef, as well as the potential risks associated with consuming meat from sick or diseased animals.
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