Mad Cow Disease (Variant Creutzfeldt-Jakob)

Mad cow disease in humans can be fatal.

• "Mad cow" disease is an infectious disease caused by prions that affect the brains of cattle. The actual name of the disease is bovine spongiform encephalopathy (BSE), a name that refers to the changes seen in the brain tissue of affected cows.
• Abnormal proteins called prions are found in the brain tissue of diseased cattle and appear to be the particle that transmits the infection. Characteristic changes are seen in the brain of infected cattle.
• The infection leads to tiny holes in parts of the brain, giving the tissue a sponge-like appearance when viewed with a microscope. These so-called spongy holes cause slow deterioration within the cow's brain and eventually other symptoms develop affecting the whole body. Death follows.
• If humans eat diseased tissue from cattle, they may develop the human form of mad cow disease known as variant Creutzfeldt-Jakob disease (vCJD) or a new variant Creutzfeldt-Jakob disease (nvCJD).
• The disease was named after the researchers who first identified the classic condition. Creutzfeldt-Jakob disease in its classic form usually occurs in older people either through an inherited tendency of the brain to change or the disease occurs spontaneously for no apparent reason.
• The type identified as occurring from eating diseased cattle occurs in younger people and has atypical clinical features, with prominent psychiatric or sensory symptoms at the time of clinical presentation and delayed onset of neurologic abnormalities. These neurologic abnormalities include
  • ataxia within weeks or months,
  • dementia (loss of memory and confusion) and
  • myoclonus late in the illness,
  • duration of illness of at least six months, and
  • a diffusely abnormal nondiagnostic electroencephalogram.
• The transmissible agents that cause the disease in both cattle and humans are abnormal protein particles called "prions." Prions are not like bacteria or viruses that cause other infectious diseases; rather, they are considered infectious abnormal proteins that can "induce abnormal folding of specific normal cellular proteins" according to the CDC. The CDC further states that the abnormal folding of proteins, especially in brain tissue, is responsible for the signs and symptoms of the disease.
• The abnormal prions are found in the brain, spinal cord, eye (in the retina), and other tissues of the nervous system of affected animals or humans. In addition, prions can be found outside the nervous system in locations including bone marrow, spleen, and lymph nodes. Low levels of prions may also be found in the blood.
• Prions are highly resistant to heat, ultraviolet light, radiation, and disinfectants that normally kill viruses and bacteria. Prions may infect humans who eat meat from infected cattle. Even cooking meat infected with BSE does not eliminate the prions or the risk.
• Once infection occurs, there is a long incubation period that typically lasts several years. When prions reach a critical level in the brain, symptoms such as depression, difficulty walking, and dementia occurs and progress rapidly.
• Scientists believe that BSE is transmitted from animals to humans when humans eat meat from infected animals. The content of infected brain tissue may be higher in some food products than others, and it may also depend on the way the animal was slaughtered.
• BSE can be transmitted from one human to another through cannibalism or transplantation of infected tissue. Consequently, certain human blood products and blood donations are not accepted from people who have lived in areas of the world where BSE outbreaks have occurred in cattle. BSE is transmissible by blood transfusion in an experimental model using sheep. The U.K. surveillance unit for vCJD has also reported three cases of vCJD that occurred as a result of blood transfusion.

Prions are diseases that cause a variety of infectious diseases. Prions are abnormally folded proteins that lack DNA. Prions replicate by causing other normally folded proteins to rearrange themselves into a misfolded form. The misfolded proteins accumulate in the brain, which eventually leads to tissue damage and results in neurological signs and deficiencies.

Primarily prions concentrate in the:

• Brain
• Spinal column
• Lymph nodes of infected animals. 

Prions have also been found in much lower concentrations in various other tissues and fluids in the body.

In December 2003, the first case of BSE in the United States was detected in a dairy cow in the state of Washington. Two further cases were reported in 2005 and 2006. Before that, a devastating major outbreak occurred in the United Kingdom (England and Ireland) in the 1980s, peaking in 1993. Because the suspected cause was a prion transmitted in meat and bone meal products fed to cattle there, the government banned the practice of feeding such products that may contain diseased tissue to animals in 1988. By then, however, infected cattle had already entered the human food supply. At the peak of this outbreak in 1993, almost 1,000 cases per week of infected cattle were reported; the numbers have dropped dramatically since then, and currently, there are only about 10 infected cattle identified each year in the U.K. The BSE-related condition vCJD was first described in the U.K. in 1996. By 1996, several people in the U.K. and others who had lived there were identified with a variant form of CJD (vCJD), and the cause was linked to eating meat from cattle infected with mad cow disease. In June 2014, over 4,000 pounds of beef were recalled by the U.S. Department of Agriculture due to improper processing that allowed cattle brain material (dorsal root ganglia) to be mixed with processed beef.

BSE and resulting cases of vCJD in humans have been diagnosed in other European countries such as Bosnia-Herzegovina, Liechtenstein, Macedonia, Norway, Sweden, and Yugoslavia. According to the World Health Organization (WHO), over 220 cases of vCJD have been reported worldwide, with the majority occurring in the UK (177 cases) and in France (27 cases). Only four cases have been reported in the U.S., and in all four of these cases, there is evidence that indicates that the infection was acquired while abroad in Europe or the Middle East.

Because there is no way to detect BSE in blood, people who have lived for long periods in areas where mad cow disease has been found are not allowed to donate blood in the U.S.

Prion diseases are also known as transmissible spongiform encephalopathies (TSEs). Overall, prion diseases are a large group of related conditions affecting the nervous system, which affect both animals and humans. Included are Creutzfeldt-Jakob disease (CJD) and variant CJD discussed in detail herein in relation to bovine spongiform encephalopathy (BSE, mad cow disease). Another human prion disease is Gerstmann-Sträussler-Scheinker (GSS) disease (see causes below). In animals, chronic wasting disease (CWD) is found in mule deer and elk in the U.S., and scrapie is a similar condition found in sheep. Cases have been reported in the U.S. These diseases all take a long time to develop but are typically rapidly progressive once symptoms begin.

All prion diseases are fatal. Animals and humans who develop a prion disease will die of it. There is no effective treatment. It is important to understand how these diseases are transmitted in order to prevent their spread.

Infected adult cattle may develop signs of the disease slowly. It may take from two to eight years from the time an animal becomes infected until it first shows signs of disease.

Symptoms in the animal include

• a change in attitude and behavior,
• gradual uncoordinated movements,
• trouble standing and walking,
• weight loss despite having an appetite, and
• decreased milk production.
• Eventually, the animal dies.

From the onset of symptoms, the animal deteriorates until it either dies or is destroyed (cattle who cannot stand are called "downers"). This disease process may take from two weeks to six months.

Similar symptoms may develop in humans:

• muscle spasms,
• lack of muscle control,
• worsening problems with memory.

Researchers looked at the first 100 people to develop vCJD in the United Kingdom and found psychiatric symptoms in the early stages of the disease include:

• Depression
• Withdrawal
• Anxiety
• Trouble sleeping
• Within four months of the disease onset, those affected developed poor memory and an unsteady gait.

Mad cow disease has been experimentally transmitted among cattle and from cattle to monkeys who eat infected tissue (particularly brain tissue) in lab tests.

But the question remains: How do cattle develop BSE? Feed is the major route for transmission among cattle, according to veterinary medicine experts. When ranchers and farmers feed cattle with products made from other cattle or sheep, such as ruminant feed, they are recycling diseased animal protein in feed containing meat and bone meal, thus causing the disease in cattle. This practice has since been outlawed after the association of BSE with vCJD.

Prions may be transmitted among laboratory animals also through broken skin, suggesting the possibility of similar transmission to humans who contact infected tissue or products and who have broken skin.

Prion diseases are unique and can be transmitted in a variety of ways:

• Some forms can be inherited such as familial CJD, Gerstmann-Sträussler-Scheinker disease (GSS), and fatal familial insomnia (FFI). The disease is caused by a mutation in the gene that codes for prions. Other inherited prion diseases are rarer.
  • Prion disease may develop sporadically, for no apparent reason, and with no pattern, such as sporadic CJD. Cases can occur in men and women of all ages, but the average age is 62 years. The prevalence of sporadic CJD is about one case per million people each year throughout the world, even among vegetarians. Sporadic CJD is the most common type of human prion disease.
  • Sporadic prion disease may be introduced into a human through infected surgical instruments or transplant tissues.
• Infectious prion disease such as variant CJD (vCJD or nvCJD) is likely caused by eating BSE-infected meat from cattle.
• A few seemingly sporadic cases in young men in Michigan may point to transmission to hunters from deer or elk with chronic wasting disease (CWD), a form of animal prion disease. CWD is becoming common in this animal population in the U.S. Because hunters eat the meat of these animals, there is a potential for the prion disease to cross from hunted to hunter.

One additional form of human prion disease is called kuru. It was found among native peoples of New Guinea who practiced ritualistic cannibalism (eating of humans, and their brains, specifically). Probably the illness began when a person with sporadic CJD was eaten. Death from kuru takes about one year following the onset of symptoms; however, the average incubation period was about 12 years and can be as long as 40 years. With the end of such rituals, this disease has nearly disappeared in New Guinea.

People or their caregivers should seek medical care if a person is experiencing any of the signs and symptoms of BSE or vCJD such as

• memory problems or muscle control, especially in younger individuals.

A health-care professional would do initial testing similar to checking for dementia -- looking for progressive deterioration of the patient's ability to think and control movement.

• Certain lab tests may be performed to rule out other forms and causes of brain dysfunction. Individuals may have a complete blood count and liver function tests checked with a sample of their blood. The doctor may also check blood for evidence of a bacterial or other infection.
• More detailed lab tests might include blood testing of thyroid, B-12 and folate levels, and for certain types of sexually transmitted diseases such as syphilis and HIV, which may produce similar symptoms.
• Imaging such as an MRI or PET scan may be helpful.
• The doctor may perform an EEG to look at brain waves. Sporadic CJD typically is associated with some abnormalities on this test, and most cases of vCJD reveal abnormalities in the EEG, although these may not always be present.
• A brain biopsy (sample of brain tissue) may be taken. Although certain microscopic changes may be present on a brain biopsy to suggest CJD or vCJD, currently, the diagnosis of vCJD can only be confirmed with certainty following examination of the brain post mortem at the time of autopsy.

The doctor may ask about the person's eating patterns if BSE transmission is suspected.

• Do they routinely eat red meat?
• Have they traveled to countries where BSE is known to exist in the cattle?
• Have they eaten meat in those countries?
• Did they receive a blood transfusion or have surgery overseas?

There are no effective treatments available that cure mad cow disease in humans.

• Patients may be asked to stop taking any medications that could affect memory or cause confusion.
• A doctor may refer a person to specialists in neurology and infectious diseases, and the doctor will provide medications to ease symptoms.
• If patients develop seizures, for example, they may be given drugs to help control them.
• Continuing laboratory testing is looking at a number of medications to prevent the development of prion disease in animals.
• Work continues on experimental vaccines to delay or prevent the effects of prion disease.

Yes. Human prion diseases are devastating and incurable but extremely rare and they all-cause death. Progression from symptoms to diagnosis to death may be rapid (from eight months for sporadic CJD to up to 60 months for GSS).

Fears that an epidemic of the animal disease (BSE) would lead to an epidemic of the human form (vCJD) have not occurred, even in the U.K., where entire herds of diseased cattle were destroyed and over 184,000 animals were known to develop the disease.

Public-health authorities maintain that the food supply in the U.S. is extremely safe. Additionally, the number of cases in the U.K. has decreased dramatically over the past decades. Still, the only absolute way to avoid infection is to entirely eliminate the consumption of beef and other animals that may be prion-infected. Milk and milk products from sheep can transmit prions; currently, cow's milk has not been linked as a means of prion transmittal but few studies have been done.

The U.S. government has implemented a number of measures to prevent BSE from entering the U.S. and to prevent the spread of the disease, as outlined by the Food Safety and Inspection Service (FSIS). Some of these measures include the following:

• The USDA's Animal and Plant Health Inspection Service (APHIS) has prohibited the importation of live cattle and certain cattle products, including rendered protein products, from countries where BSE is known to exist. In 1997, due to concerns about widespread risk factors and inadequate surveillance for BSE in many European countries, these importation restrictions were extended to include all of the countries in Europe.
• APHIS has prohibited all imports of rendered animal protein products, regardless of species, from BSE-restricted countries because of concern that feeds intended for cattle may have been cross-contaminated with the BSE agent.
• In 1997, the FDA prohibited the use of most animal protein in the manufacture of animal feeds given to cattle and other hoofed animals (known as ruminants).
• The Centers for Disease Control and Prevention (CDC) leads a surveillance system for vCJD and performs random testing (screening) on U.S. cattle slaughtered for human consumption.
• Additional safeguards include keeping downer animals out of the human food chain because these are at the highest risk for being ill with BSE, tracking cattle from birth to slaughter in case an infected animal is found and its meat can be destroyed, and using less aggressive ways to harvest meat from carcasses to avoid brain and spinal tissues. An additional feed-control ban was implemented in the U.S. in 2009 to align U.S. practices with a similar ban enacted in Canada in 2007. These regulations prohibit the use of high-risk parts of cattle in the generation of any animal feed.

Live animal tests may provide valuable information about the level of BSE in all animals, including downer cattle and cattle aged 24 months or older (those most at risk and in whom BSE is found). However, currently, there is no sensitive and reliable live animal test for BSE and the only definitive test can be made on the brain and other tissues after slaughter.

• California Department of Food and Agriculture, Statement From CDFA Secretary Karen Ross on USDA Announcement of Detection of BSE
• Centers for Disease Control and Prevention, BSE (Bovine Spongiform Encephalopathy, or Mad Cow Disease)
• Centers for Disease Control and Prevention, Prion Diseases
• U.S. Food and Drug Administration, All About BSE
• World Health Organization, Variant Creutzfeldt-Jakob Disease