Variant CJD / Creutzfeldt-Jakob Diseas
Before the mad cow disease epidemic in the mid-1990s, few people had heard of Creutzfeldt-Jakob disease (CJD). That's because Creutzfeldt-Jakob disease, an invariably fatal, degenerative brain disorder, has always been considered rare. Worldwide, doctors typically diagnose one case of Creutzfeldt-Jakob disease per million people each year, most commonly in older adults.
That changed a decade ago when an unusually large number of people in Great Britain developed what appeared to be CJD. Most were relatively young, and all had eaten meat from cattle suspected of having bovine spongiform encephalopathy (BSE), the medical term for mad cow disease.
Scientists eventually concluded that the new ailment — named variant Creutzfeldt-Jakob disease (vCJD) — was a form of Creutzfeldt-Jakob disease resulting from exposure to BSE. Since then, a number of cases of vCJD have been linked to contaminated beef in Great Britain and in other countries, including Spain, Portugal, France and Germany.
Although "classic" Creutzeldt-Jakob disease hasn't been linked to infected beef, it's similar to vCJD in many respects. No treatment exists for either type of CJD, and nothing can slow the progression of the disease.
Both classic and variant CJD belong to a broad group of human and animal diseases known as transmissible spongiform encephalopathies (TSEs). The name derives from the spongy holes, visible under a microscope, that develop in affected brain tissue.
TSEs in humans
One of the oldest known human TSEs is kuru. Found only in a remote New Guinea tribe, kuru reached epidemic proportions in the 1950s and 1960s. How the disease originated isn't clear, but scientists know that it spread when tribe members ritualistically consumed the brains of dead relatives.
Other human TSEs include Gerstmann-Straussler-Scheinker disease and fatal familial insomnia — hereditary diseases so rare they occur in just a few families.
TSEs in animals
The most widespread TSE in animals is scrapie, a disease that has affected sheep and goats since the mid-18th century. Infected animals become agitated, attempt to rub off their wool by scraping against trees and posts, and usually die a few months after symptoms appear. Many experts believe that British cattle developed mad cow disease after being fed the remains of scrapie-infected sheep.
Other animals affected by TSEs include domestic and exotic cats (feline spongiform encephalopathy); mule deer, white-tailed deer, black-tailed deer and elk (chronic wasting disease); and mink (transmissible mink encephalopathy).
The origin of TSEs
The cause of TSEs eluded scientists for centuries. But in the early 1980s, Stanley Prusiner, a researcher at the University of California at San Francisco, suggested that the infective agent in TSEs wasn't a virus or any other known pathogen. Instead, he blamed an infectious protein, which he called a prion — short for proteinaceous infectious particle. This was a daring leap because proteins don't contain RNA, the genetic material that allows viruses and bacteria to reproduce. But today, the link between prions and TSEs is widely accepted.
The nature of prions
Prions are proteins that occur naturally in the brains of animals and people. Normally, these proteins are harmless, but when they're misshapen they can cause devastating illnesses. The difference lies in the way the proteins are folded.
All proteins start out as loose strings of amino acids. But proteins can't perform their intended function until the amino acids fold into a specific three-dimensional shape. The shape a particular protein assumes is determined by the sequence of its amino acids. Most proteins fold spontaneously during or just after they're synthesized inside cells, the entire process lasting only a few tenths of a millisecond.
Protein folding isn't foolproof, however, and many proteins made by the body aren't usable. The rejects are sent to a kind of recycling center, where the amino acid chains are disassembled and the amino acids prepared for reuse. Normally, this system works well. But as people age, the recycling process may stop working efficiently. As a result, misfolded proteins begin to accumulate in deposits that can cause serious problems. This seems to be what happens in Alzheimer's disease, for example.
But prions go one step further. Not only do they misfold, they also enter brain cells and force normal proteins to misfold as well. When the infected cells die, prions are released into normal tissue and go on to infect more cells. Eventually, large clusters of cells die, leaving the brain riddled with holes.
Unlike any other known protein, prions are infectious. When misfolded proteins are transmitted to people or animals, they begin to transform healthy brain cells into abnormal ones, although signs and symptoms of disease may not appear for years.
Prions also seem capable of crossing species' barriers, jumping, for example, from sheep to cows to humans. Although infection may occur more readily when proteins have the same amino acid sequence and exist within a single species, evidence is strong that prions can move from one species to another.
To make matters worse, prions are nearly indestructible. They're impervious to radiation, washing, boiling and the intense heat of autoclaves used to sterilize surgical instruments. Unlike many harmful bacteria, prions aren't destroyed by cooking or by the strong juices produced in your stomach.
How CJD is transmitted
Most people with classic CJD develop the disease for no apparent reason. CJD that occurs without explanation is termed spontaneous or sporadic CJD and accounts for the great majority of all cases.
Researchers have been able to identify some causes of CJD, however, including:
How vCJD is transmitted
- Heredity. In the United States, about 5 percent to 10 percent of people with CJD have a family history of the disease or test positive for a genetic mutation associated with CJD.
- Certain medical procedures. So far, classic CJD hasn't been linked to tainted beef. But a small number of people have developed the disease after being exposed to infected human tissue as a result of medical procedures (iatrogenic CJD), such as cornea and skin transplants and grafts of dura mater, the membrane that covers the brain. Some adults have developed CJD decades after receiving injections of human growth hormone (HGH). Traditionally, HGH has been used to treat children who fail to grow normally, but in recent years it also has become popular as an anti-aging therapy. Before the 1980s, when a genetically engineered version of the hormone became available, HGH was derived from human pituitary glands.
- Exposure to contaminated medical instruments. Because rogue prions aren't affected by standard sterilization methods including heat, radiation, alcohol, benzene and formaldehyde, instruments used in some types of brain surgery can harbor small bits of infected tissue, even after undergoing stringent cleaning procedures.
To date, vCJD has been linked primarily to the consumption of beef infected with mad cow disease. The parts of meat most likely to harbor infection include:
Hot dogs, ground meat and sausages are especially likely to contain contaminated tissues, whereas milk and other dairy products haven't been implicated in vCJD.
- Bone marrow
- Spinal cord
- Nerves attached to the brain, eyes, tonsils and spinal cord
- Small intestine
Studies have also shown that vCJD can spread through blood transfusions, even if the infected donor has no signs or symptoms of the disease.
TSEs in animals appear to spread through close contact; one study suggests infected prions may spread through animal urine. But current evidence doesn't suggest that either CJD or vCJD can be transmitted from one person to another through social or sexual contact.
The true risk of developing either CJD or vCJD is largely unknown. But certain factors may increase your risk. They include:
- A family or genetic history of CJD. A few people have a genetic mutation that increases their likelihood of developing CJD.
- Human growth hormone injections. You're at increased risk of CJD if you have received HGH from human sources. This is most likely to have occurred before a genetically engineered form of the hormone became available in the mid-1980s.
- Certain medical procedures. Worldwide, a small number of people have developed CJD from infected tissue used in cornea and skin transplants and from dura mater grafts used during brain or spinal cord surgery.
- Contaminated surgical instruments. A few people have contracted CJD from contaminated instruments used during brain surgery.
- Some blood transfusions. You also may be at risk if you received a blood transfusion or used bovine-derived insulin after 1980 in a country with a high incidence of mad cow disease, such as Great Britain, Portugal, Spain, France and Germany.
- Eating beef from certain countries. If you eat beef from countries with a relatively high incidence of BSE — such as the United Kingdom, Portugal, France, Spain and Germany — you increase your chances of contracting vCJD. The risk is highest if you eat meat products that are more likely to contain prions, such as hamburgers, hot dogs, sausages and luncheon meats. Even so, in the U. K. the current risk of acquiring vCJD from beef and beef products appears to be very low — about one case per 10 billion servings. The risk from beef in other high-incidence countries is equally small. On the other hand, it's difficult to assess the true risk of contracting vCJD from infected beef because so much about the disease is still unknown, including the exact length of its incubation period and the ultimate effectiveness of public health control measures. People believed to be at greatest risk are those who ate British beef between 1980 and 1996, before measures to prevent the spread of mad cow disease were implemented. The risk in other countries where BSE is endemic remains unclear.
A number of subtypes of CJD exist, many with slight variations in signs and symptoms. Yet the various forms of the disease are more alike than they are different, and everyone affected by CJD must eventually contend with grave mental and physical problems.
Classic CJD and variant CJD share the characteristics listed below, but the characteristics manifest somewhat differently in each form of the disease.
Long incubation period
The incubation period is the time it takes you to become sick after you've contracted a disease. Cold symptoms usually start a day or two after you're exposed to a cold virus, for example, whereas the time frame for CJD is considerably longer.
- Classic CJD. It often takes years or even decades after infection before someone with classic CJD develops signs and symptoms of the disease.
- Variant CJD. Although it's too early to know for certain, scientists suspect that the same is true of vCJD. That's why some experts predict that an epidemic of vCJD is still to come.
Both classic and variant CJD begin with personality changes such as anxiety, depression, memory loss and impaired thinking. As the diseases progress, mental symptoms become more severe. Ultimately, people with both forms of CJD develop dementia — a mental disorder that robs them of the ability to speak, think, reason, remember and move. Although the symptoms of CJD sometimes resemble those of other neurological disorders such as Alzheimer's and Huntington's disease, CJD usually progresses much more rapidly than do other diseases associated with dementia.
Problems with balance and coordination
- Classic CJD. The progression from initial personality changes to complete dementia occurs very quickly, usually within a few months of the onset of symptoms.
- Variant CJD. Psychiatric symptoms are the most prominent feature early in vCJD, but dementia develops later in the course of the disease than it does in classic CJD.
Both types of CJD affect balance and coordination, leading to stumbling, falls and difficulty walking, but these problems occur sooner in vCJD than they do in classic CJD.
Coma and death
Most people lapse into coma before succumbing to these invariably fatal diseases.
Other signs and symptoms of classic CJD include:
- Classic CJD. People with classic CJD generally live less than 12 months after signs and symptoms appear, although some people may live as long as two years. Death is usually not a result of the disease itself, but rather of complications such as heart failure, respiratory failure and pneumonia.
- Variant CJD. People with vCJD tend to live slightly longer — about 12 to 14 months after signs and symptoms appear.
Other signs and symptoms of vCJD include:
- Blurred vision and, often, eventual blindness
- Involuntary muscle contractions (myoclonus)
- Difficulty speaking, which may lead to mumbling or speech that's hard to understand
- Difficulty swallowing
- A sense that the skin feels sticky
- Sensations of cold or pain
- Muscle paralysis
Only a brain biopsy or an examination of brain tissue after death (autopsy) can definitively confirm the presence of CJD or vCJD. But doctors often can make an accurate diagnosis based on your medical and personal history, a neurological exam, and certain diagnostic tests.
The exam is likely to reveal such characteristic symptoms as muscle twitching and spasms, abnormal reflexes, and coordination problems. People with CJD also may have areas of blindness and changes in visual-spatial perception.
In addition doctors commonly use these tests to help detect CJD:
- Electroencephalogram (EEG). Using electrodes placed on your scalp, this test measures your brain's electrical activity. People with CJD and vCJD show a characteristically abnormal pattern.
- Magnetic resonance imaging (MRI). This technique uses radio waves and a magnetic field to create cross-sectional images of your head and body. It's especially useful in diagnosing brain disorders because of its high-resolution images of the brain's white matter and gray matter.
- Spinal fluid tests. Cerebral spinal fluid surrounds and cushions your brain and spinal cord. In a test called a lumbar puncture — popularly known as a spinal tap — doctors use a needle to withdraw a small amount of this fluid for testing. The presence of a particular protein in spinal fluid is often an indication of CJD or vCJD.
What makes CJD and vCJD particularly devastating is that both diseases destroy personalities as well as bodies. Physical complications include infection, heart failure and respiratory failure — a serious condition in which the body doesn't receive enough oxygen to carry out its metabolic processes. But as deadly as these can be, the psychosocial complications are equally cruel.
People with CJD and vCJD usually withdraw from friends and family and eventually lose the ability to recognize or relate to them in any meaningful way. They also lose the ability to care for themselves and may become aggressive, engaging in behavior that can be dangerous to themselves or to others.
No effective treatment exists for either CJD or vCJD. A number of drugs have been tested — including steroids, antibiotics and antiviral agents — with disappointing results. For that reason, doctors focus on alleviating pain and other symptoms and on making people with these diseases as comfortable as possible.
Most countries have adopted measures to prevent BSE-infected tissue from entering the food supply. Great Britain and the European Union have some of the most stringent guidelines, including a ban on animal feed containing meat-and-bone meal; strict procedures for dealing with sick animals; a registry that follows every cow throughout its life; and required screening of all cattle
|30 months and older — those most likely to harbor infection. Japan, which has the most aggressive BSE surveillance in the world, tests nearly all cattle.
The United States lags behind these countries in some important respects. The Department of Agriculture's ban on ruminant feed doesn't prohibit the use of organs that can harbor mad cow disease in products for pets or livestock other than ruminants. After a case of mad cow disease was confirmed in Texas in 2005, however, more rigorous inspection practices were put in place, including selective screening of healthy cattle. Before that, only diseased or lame cattle were tested for mad cow disease in the United States.
What you can do
To help reduce the risk of contracting CJD from infected beef, consider these options:
- Be selective when eating abroad. Meat from higher risk countries is banned in the United States, but you can still eat the meat if you travel abroad. For that reason, be selective when eating beef in other parts of the world, especially in countries without stringent safeguards. Ask questions about where the meat comes from. If you don't feel safe eating beef, choose something else on the menu.
- Choose the right cuts. In the United States and elsewhere, avoid the highest risk parts of cattle, such as the eyes, brain, spinal cord and intestine. You may feel more comfortable avoiding hot dogs, hamburger, sausages and luncheon meats. Keep in mind that natural sausage casings made from sheep intestines also may put you at risk. On the other hand, muscle meats such as steaks and roasts don't appear to harbor the prions that cause BSE.
- Go organic. Several other choices exist if you're nervous about BSE but want to continue to eat beef. Many independent farmers, natural foods stores, co-ops and some larger grocery stores sell organic beef. This meat comes from cows fed on grains and grasses rather than on feed that contains parts of other animals. If you're nervous about vCJD, you might feel better feeding your family beef from cows that have eaten only grass. Organic beef is labeled with a green circular symbol that signifies it's certified.
To help ensure the safety of the blood supply, people with a risk of exposure to CJD or vCJD aren't eligible to donate blood. This includes people who:
If you're contemplating surgery and feel uncertain about the safety of the blood supply, consider donating your own blood (autologous donation) before your surgery, especially if it involves your bones, blood vessels, urinary tract or heart — the operations most likely to require a transfusion. Blood can be stored in its liquid form for 42 days, and you can donate blood up to 72 hours before your procedure. This allows your body enough time to replenish its blood supply before the operation.
- Have a biological relative who has been diagnosed with CJD
- Have received a dura mater brain graft
- Have received human growth hormone
- Spent a total of at least three months in the U.K. from 1980 to 1996
- Spent five years or more in France from 1980 to the present
- Received a blood transfusion in the U.K. between 1980 and the present
- Have injected bovine insulin at any time since 1980
Other methods of transmission
The best way to protect yourself from products that may harbor infection is to become as well informed as possible.
- Vaccines. Some parts of cows, including blood, enzymes and amino acids, are used to grow the bacteria and viruses needed to make certain vaccines. Not all vaccines are grown in cattle parts, however, and the Food and Drug Administration (FDA) recommends that companies producing such vaccines use cattle parts only from low-risk countries. These recommendations apply to cosmetics as well. The FDA keeps a listing on its Web site of companies that use cattle from countries that aren't classified as low-risk.
- Insulin. Insulin sold in the United States isn't derived from cows, but you're allowed to import beef insulin from other countries if you follow specific guidelines. Because there's no way to guarantee the safety of imported insulin, talk to your doctor about the best way to obtain insulin from sources outside the United States.
|Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.