Mad cow disease, or bovine spongiform encephalopathy (BSE), is a type of transmissible spongiform encephalopathy (TSE) that causes brain deterioration and only affects cattle. When food from infected cattle is consumed by humans, it is believed to cause another type of TSE that only affects humans, called variant Creutzfeldt-Jakob disease (vCJD). Like other types of TSEs, BSE and vCJD are characterized by long incubation periods and progressive nerve and brain damage and are always fatal. BSE and vCJD are most common in the United Kingdom but have also occurred in several other countries, including the United States. While BSE in cattle has reached crisis levels in some areas, vCJD as a human infection has remained relatively rare, even where BSE cattle infection is more common.

Scientists believe that BSE arose from the practice of supplementing cattle feed with meat and byproducts from animals infected with BSE or another type of TSE. All types of TSEs are related to infectious prions, which are otherwise healthy proteins that have folded into abnormal shapes and become infectious. It is believed that when a person consumes contaminated beef, the infectious prions are absorbed into the person’s body, where they may create more infectious prions. This process ultimately causes symptoms of vCJD to appear.

Although the prions may be transmitted from cattle to humans, the transmission may not produce infection. Cattle and humans are two different species and infectious prions from one species are less likely to create infectious prions in another species. In addition, not all parts of BSE-infected cattle are equally risky to consume. High-risk tissues include the intestines and areas that contact nervous tissue (e.g., brain, spinal cord, eyes, tonsils). Infectious prions do not appear to be present in milk or muscle meat. However, certain cuts of meat (e.g., t-bone steaks) may have a greater risk of being contaminated by nervous tissue.

When vCJD develops in a person, the first symptoms are psychiatric problems (e.g., depression, anxiety, insomnia). Eventually, neurologic signs (e.g., unpleasant sensations, problems walking, lack of coordination, vision problems) develop. Patients also begin to feel confused, forgetful, and have difficulty thinking and speaking. In later courses of the diseases, patients become unable to speak or move and enter a coma. Like all TSEs, vCJD is ultimately fatal.

The only ways to positively diagnose vCJD is by means of a brain biopsy (an invasive and risky procedure) while a patient is alive or examination of brain tissue during an autopsy. However, a probable diagnosis can be made from the patient’s medical history, signs and symptoms, magnetic resonance imaging (MRI) of the brain and an electroencephalogram (EEG).

There are no known methods to cure BSE or vCJD. Treatment of vCJD is aimed at making the patient feel as comfortable as possible. No methods have been developed to detect the infectious agents of BSE in food. Because contaminated food cannot be made safe, prevention relies on avoiding contaminated meat and meat byproducts. This includes halting the spread of BSE among cattle. The United States, United Kingdom and many other countries have put several strict regulations in place for the purpose of stopping the spread of BSE in cattle and preventing vCJD in humans.

Mad cow disease is the common name for bovine spongiform encephalopathy (BSE), a type of transmissible spongiform encephalopathy (TSE) that only affects cattle. It is characterized by a long incubation period (three to eight years) and progressive nerve and brain damage and is always fatal. According to the U.S. Centers for Disease Control and Prevention (CDC), the first probable infections of BSE occurred in cattle during the 1970s.

Another type of TSE that only affects humans, called variant Creutzfeldt-Jakob disease (vCJD), has been linked to eating meat and meat byproducts from cattle infected with BSE. These two diseases appear to have the same infectious agents. The agent that causes BSE in cattle appears to remain in the animal tissue even after the animal has been slaughtered and processed as food. When people consume contaminated beef, they may become infected with vCJD. Although the infection spreads quickly and easily among cattle, it is not as easily transferred to or spread by humans. Infectious agents from one species may be less likely to create additional infectious agents in another species, a complication known as the “species barrier.” Some experts believe that the BSE infectious agents may be 10 to 100,000 times less infectious in humans as it is in cattle.  

BSE, vCJD and other forms of TSE are associated with certain types of proteins. Proteins are long strings of amino acids that are folded into particular shapes. These shapes allow the proteins to perform their functions in the body. Prions, which are also called proteinaceous infectious particles, are a certain type of harmless protein – they are not viruses, bacteria or other cellular organisms. In their normal state, prions are noninfectious.

However, prions can misfold, or fold into abnormal shapes and become infectious. When these infectious prions come into contact with other proteins, they cause those proteins to misfold and become infectious as well. Eventually, enough abnormal prions are present to produce symptoms of disease. It is believed that these abnormal prions kill nerve tissues (e.g., brain cells) with which they come into contact.

The theory that prions alone are responsible for TSE is widely accepted, but it has not been proven. One alternate theory claims that a slow-acting virus is the infectious agent responsible for TSE, and that the abnormal prions are a result of the infection, not the cause. However, no actual virus, bacteria or other cellular organism that may have caused the disease has been identified.

BSE and vCJD are most common in the United Kingdom, but have also occurred in several other European countries, Japan, Saudi Arabia, Canada and the United States.

According to the U.S. Food and Drug Administration (FDA), there have been more than 180,000 cases of BSE in the United Kingdom. Most of these cases have occurred in dairy cattle. While BSE in cattle has reached crisis levels, vCJD in humans has remained relatively rare, even in areas where BSE is common. Since vCJD was first identified in 1996, there have been fewer than 200 patients reported with the disease, from 11 different countries. According to the CDC, more than 80 percent of these cases occurred in the United Kingdom. Only two cases have occurred in the United States as of 2006.

A widespread outbreak, or epizootic, of BSE struck cattle in the United Kingdom in 1986 and reached its peak in January 1993. According to the FDA, almost 1,000 new cases per week occurred at this time. BSE epizootics have also been reported in Ireland, Switzerland, France, Liechtenstein, Luxembourg, the Netherlands, Portugal and Denmark.

In December 2003, BSE was confirmed in a cow in the state of Washington (but originally from Canada). After the cow died following complications of pregnancy, it was slaughtered for food, but when BSE was discovered in a sample of the cow’s brain tissue, the meat was recalled. The FDA and the U.S. Department of Agriculture (USDA) responded to this incident by implementing additional security measures against the disease. In June 2005, the first case of BSE in a cow born in the United States was confirmed in Texas. In March 2006, BSE was confirmed in a cow in Alabama. Investigators were not able to identify where the cow, which had no tags or distinctive marks, was born.

There has been some concern that even though the occurrence of BSE has decreased dramatically, more cases of vCJD may occur in the near future. Fears are that the condition may be more widespread than realized, with many current cases still in the incubation period.

Mad cow disease, or bovine spongiform encephalopathy (BSE) only affects cattle, not humans.

Scientists believe that BSE arose from the practice of feeding rendered animal byproducts to cattle, often in the form of meat-and-bone meal (a ground-up preparation) as protein supplements. Some of these byproducts may have been infected with BSE or some other transmissible spongiform encephalopathy (TSE), such as scrapie, which affects sheep. Furthermore, in the late 1970s, a change occurred in the rendering process of these animal byproducts that may have made the infectious agent in these byproducts even more sturdy and more easily spread. However, this theory for the origin of BSE has been debated. Still, the practice of feeding cattle and other ruminants (animals that chew their cud) animal byproducts is now prohibited in the United States.

BSE-contaminated meat and meat byproducts have been linked to variant Creutzfeldt-Jakob disease (vCJD). It is generally accepted that this infection occurs when such contaminated food is consumed. In theory, when the infectious prion responsible for BSE is consumed, it is absorbed into the person’s body, where it may create many more infectious prions, ultimately causing disease and death. However, because cattle and human are different species, this process is less efficient than if the prion had come from another human. Therefore, the potential for vCJD to develop in a person exposed to the BSE prion is reduced. In fact, some experts believe that this prion may be 10 to 100,000 times less infectious in humans as it is in cattle.

In addition, not all parts of cattle infected with BSE are equally risky to consume. High-risk tissues include certain intestinal tissues (e.g., the lower end of the small intestine), nerve tissues (e.g., brain, spinal cord), and tissues likely to be contaminated by nerve tissues (e.g., eyes, tonsils). The infectious prions do not appear to be present in milk or muscle meat. However, certain cuts of meat (e.g., t-bone steaks) may have a higher risk of contamination by nervous tissue. Although gelatin is derived from the hides and bones of cattle, the risk that infection can be transferred through eating gelatin appears to be very low. This appears to be due to techniques used to make the gelatin.

The risk of acquiring vCJD by eating beef and beef products is small, even in areas with high numbers of BSE cases. According to the U.S. Centers for Disease Control and Prevention (CDC), this risk in the United Kingdom is only about 1 in 10 billion servings. This low risk is largely due to public health control measures that have been put in place to stop the spread of BSE.

The transmission of TSEs through blood may have occurred in the United Kingdom. In response to this potential risk, the Food and Drug Administration (FDA) and the American Red Cross have increased donor requirements to safeguard the American blood supply. For example, people who have lived for more than three months in a country or countries where BSE is common cannot donate blood in the United States.

Some concern exists about the transmission of vCJD through medical products that use cattle components (e.g., blood, enzymes, amino acids). The FDA has concluded that risk of transmission through vaccines with bovine products is remote and theoretical. No cases of this type of transmission have been reported, and no vaccines are known to contain the infectious prion that causes BSE. Still, manufacturers of vaccines containing cattle components from countries that have or may have BSE have agreed to change their source of these components. This is being done in an effort to avoid potentially harmful health consequences, such as a rise in disease due to people refusing vaccines based on a misconception that vaccines are dangerous.

In addition, the prion that causes vCJD is not transmitted through insulin available in the United States because it is not made from cattle. However, purchasing beef insulin from other countries may increase the risk of transmission. 

It appears that susceptibility to vCJD varies. In fact, a susceptibility to the disease may be inherited. According to the FDA, all known cases of vCJD have occurred in patients with a particular set of genes. About 40 percent of all people in the world have this particular genetic profile.

Most TSEs affect older patients. Unlike other TSEs, vCJD in the United Kingdom tends to affect younger people. According to the CDC, the average age of death for people with this disease is about 29 years.

Like other transmissible spongiform encephalopathies (TSEs), variant Creutzfeldt-Jakob disease (vCJD), the human form of mad cow disease, has a long incubation period before irreversible brain and nerve damage occurs. These diseases always result in progressive dementia and death. There are no signs or symptoms in the early course of the diseases and the first signs or symptoms may not appear for years or even decades after the infection occurred.

After symptoms appear, the diseases tend to progress very quickly, often leading to death within a single year. According to the Food and Drug Administration, vCJD patients only live for an average of 13 months after symptoms appear.

The first symptoms of vCJD are psychiatric problems (e.g., depression, anxiety, insomnia). Personality changes may also occur. Eventually, neurologic signs develop. Patients may experience unpleasant sensations, problems walking and a lack of muscle coordination. They may have involuntary jerking motions (myoclonus). Vision problems, which may lead to blindness, are also common. Patients may feel confused, forgetful, or have difficulty thinking and speaking.

In later courses of vCJD, patients may become unable to speak or move, and enter a coma. Infections (e.g., pneumonia) are common and may be the cause of death for many patients. The presence of many tiny holes in the brain (giving it a spongy appearance) at autopsy indicates TSEs such as vCJD. Flower-shaped areas of damage (clumps of prions called plaques) are also generally present.

Mad cow disease, or bovine spongiform encephalopathy (BSE), only affects cattle and can only be accurately detected by microscopic examination of brain tissue after the animal’s death.

Consumption of BSE-contaminated meat and meat byproducts has been linked to variant Creutzfeldt-Jakob disease (vCJD) in humans. Like other transmissible spongiform encephalopathies (TSE), vCJD is difficult to positively diagnose.

When vCJD is suspected, treatable forms of dementia (e.g., encephalitis, chronic meningitis) must first be ruled out. This may involve a spinal tap or computerized tomography (CAT scan) of the brain. After other forms of dementia have been ruled out, a probable diagnosis of vCJD (or another TSE) can be made by a physician’s evaluation of the patient’s medical history (including whether any potentially contaminated beef products were consumed), the presentation of signs and symptoms, magnetic resonance imaging (MRI) of the brain and an electroencephalogram (EEG). In patients with vCJD, an EEG or brain MRI may reveal unique abnormalities.

vCJD can be positively diagnosed using a brain biopsy. This is an invasive and risky procedure that removes a small amount of brain tissue for laboratory examination. However, if the tissue is taken from a part of the brain that is not affected by the disease, it may produce a false negative result. The disease can be positively diagnosed with the greatest degree of reliability through a microscopic examination of brain tissue during an autopsy. However, this is only possible after death.

Research on new diagnostic tests for TSEs, including vCJD is ongoing.

Mad cow disease, or bovine spongiform encephalopathy (BSE), only affects cattle, but has been linked to variant Creutzfeldt-Jakob disease (vCJD) in humans. There are no known methods to cure vCJD or any other transmissible spongiform encephalopathies (TSE), although research is ongoing to find potential treatments.

Current treatments for vCJD are entirely palliative (pain-relief related). The goal of this treatment is to make the patient as comfortable as possible. Pain medications are used as necessary. Bed-bound patients may be fed artificially (e.g., feeding tubes) and may receive intravenous fluids. Catheters may be used to drain urine and healthcare workers regularly shift the patient’s position to prevent bedsores.

No methods have been developed to detect the infectious agents of BSE in food. When present, the infectious agents (prions) are very difficult to destroy. Standard cooking or irradiation techniques, which can kill most viruses and bacteria, are not effective. Because contaminated food cannot be made safe, prevention relies on avoiding contaminated meat and meat byproducts. This includes halting the spread of BSE among cattle.

The Animal and Plant Health Inspection Service (APHIS) of the U.S. Department of Agriculture (USDA) has instituted and enforced many restrictions on the American cattle industry in an attempt to keep BSE out of the United States. For example, APHIS has prohibited the import of live cattle and other ruminants (animals that chew the cud) and most ruminant products and byproducts from countries where BSE is common, including the entirety of Europe. APHIS also conducts surveillance for BSE, such as the testing of “downer” animals (animals that, due to weakness or illness, are not able to stand on their own).

The Food and Drug Administration (FDA) has prohibited the feeding of meat and meat byproducts of other mammals to all ruminants, including cattle. Air-injection stunning has also been prohibited. This is a humane method of slaughter, but may contaminate parts of cattle used for food with potentially contaminated brain tissue.

The FDA has also prohibited many cattle products from being used in human cosmetics and foods, including dietary supplements. Prohibited cattle products include:

• Material from organs of cattle 30 months of age or older
  
  
• Small intestine and tonsils of all cattle, regardless of age
  
  
• All materials from “downer” cattle
  
  
• All materials not inspected and passed for human consumption
  
  
• Mechanically separated beef (which may spread contamination)

To lessen the risk of exposure to BSE-contaminated meat, consumers may choose low-risk beef products such as cuts of beef muscle or whole muscle meats. In addition, consumers may wish to confirm that the beef they are purchasing comes from cattle not fed any animal byproducts, in accordance with FDA standards.

Some stores may even ensure the beef they sell comes from cattle slaughtered before the age of 30 months. This is just below the shortest incubation time required for infectious prions to develop in infected cattle. According to the FDA, the incubation period for BSE to develop in cattle is between three and eight years. Thus, cattle slaughtered before they are three years of age are not likely to have developed BSE.

Casual contact with a person with vCJD does not spread vCJD, but contact with certain infected body tissues (e.g., brain tissues, spinal fluids) can. Contact with these materials from an infected person should be avoided. For example, direct superficial contact (e.g., kissing or touching the face) with the body of an autopsied vCJD patient is not advised. The same risk of infection is not present if the body has not been autopsied.

One woman in the United Kingdom may have become infected with vCJD via a contaminated blood transfusion. In response to this incident, the FDA and American Red Cross have also instituted restrictions on donating blood to help prevent the spread of vCJD. For example, people who have lived for more than three months in a country or countries where BSE is common cannot donate blood in the United States.

Preparing questions in advance can help patients have more meaningful discussions with healthcare professionals regarding their conditions. Patients may wish to ask their doctor the following questions related to mad cow disease and variant Creutzfeldt-Jakob disease (vCJD):

1. Is mad cow disease common in the areas of the world where I have lived?
   
   
2. Do you recommend that I avoid beef when traveling internationally?
   
   
3. I think I may have eaten contaminated beef. What can I do?
   
   
4. Why do you think I may have vCJD?
   
   
5. How may I have been infected?
   
   
6. For how long have I probably been infected?
   
   
7. How advanced does my disease seem to be?
   
   
8. What treatments may help alleviate symptoms and make my life more comfortable?
   
   
9. How might I tell my friends and loved ones about my condition?
   
   
10. What symptoms or signs should I immediately report to you?
    
    
11. Will I require the assistance of a specialized medical worker?