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Creutzfeldt-Jakob ("Mad Cow") Disease a Grim Reality

Fatal Brain-Wasting Disease May Result from Eating Infected Beef

June 11, 2005
While the name "mad cow disease" conjures up images of an angry Bessie, the reality behind bovine spongiform encephalopathy (BSE) is quite a bit grimmer. BSE is a degenerative brain disease that is thought to be spread through infected meat. Cattle can be infected by eating protein supplements made with the ground-up remains of other animals, a practice now outlawed in most countries.

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The human variant of BSE is Creutzfeldt-Jakob disease (CJD), which the National Institutes of Health describes as a rare, degenerative, invariably fatal brain disorder. There are three major categories of CJD: sporadic CJD, hereditary CJD, and acquired CJD.

CJD is characterized by rapidly progressive dementia. Initially, patients experience problems with muscular coordination; personality changes, including impaired memory, judgment, and thinking; and impaired vision. People with the disease also may experience insomnia, depression, or unusual sensations. CJD does not cause a fever or other flu-like symptoms.

As the illness progresses, the patients’ mental impairment becomes severe. They often develop involuntary muscle jerks called myoclonus, and they may go blind. They eventually lose the ability to move and speak and enter a coma. Pneumonia and other infections often occur in these patients and can lead to death.

In the case of hereditary CJD, onset of symptoms occurs at about age 60. For other forms, there can be an incubation period of many years.

How Is It Contracted?

CJD cannot be transmitted through the air or through touching or most other forms of casual contact. Spouses and other household members of sporadic CJD patients have no higher risk of contracting the disease than the general population. However, exposure to brain tissue and spinal cord fluid from infected patients should be avoided to prevent transmission of the disease through these materials.

In some cases, CJD has spread to other people from grafts of dura mater (a tissue that covers the brain), transplanted corneas, implantation of inadequately sterilized electrodes in the brain, and injections of contaminated pituitary growth hormone derived from human pituitary glands taken from cadavers.

Since 1985, all human growth hormone used in the United States has been synthesized by recombinant DNA procedures, which eliminates the risk of transmitting CJD by this route.

The appearance of a new variant of CJD in several younger than average people in Great Britain and France has led to concern that BSE may be transmitted to humans through consumption of contaminated beef. Although laboratory tests have shown a strong similarity between the prions causing BSE and the new variant of CJD, there is no direct proof to support this theory.

However, the World Health Organization has stated that the new variant (vCJD) is "strongly linked to exposure, probably through food, to a TSE of cattle called Bovine Spongiform Encephalopathy (BSE)."

"In contrast to the traditional forms of CJD, vCJD has affected younger patients (average age 29 years, as opposed to 65 years), has a relatively longer duration of illness (median of 14 months as opposed to 4.5 months)," according to the WHO.

"The most recent and powerful evidence comes from studies showing that the transmission characteristics of BSE and vCJD in laboratory mice are almost identical, strongly indicating that they are due to the same causative agent," the WHO said.

Many people are concerned that it may be possible to transmit CJD through blood and related blood products such as plasma. Some animal studies suggest that contaminated blood and related products may transmit the disease, although this has never been shown in humans. If there are infectious agents in these fluids, they are probably in very low concentrations. Scientists do not know how many abnormal prions a person must receive before he or she develops CJD, so they do not know whether these fluids are potentially infectious or not.

Normal sterilization procedures such as cooking, washing, and boiling do not destroy the prions thought to be responsible for CJD.

Diagnosis

There is currently no single diagnostic test for CJD. The first concern is to rule out treatable forms of dementia such as encephalitis or chronic meningitis. The only way to confirm a diagnosis of CJD is by brain biopsy or autopsy, the NIH said.

In a brain biopsy, a neurosurgeon removes a small piece of tissue from the patient's brain so that is can be examined by a neurologist. Because a correct diagnosis of CJD does not help the patient, a brain biopsy is discouraged unless it is need to rule out a treatable disorder. While CJD can be transmitted to other people, the risk of this happening is extremely small.

No Treatment

There is no treatment that can cure or control CJD. Current treatment is aimed at alleviating symptoms and making the patient as comfortable as possible. Opiate drugs can help relieve pain, and the drugs clonazepam and sodium valproate may help relieve involuntary muscle jerks.

About 90 percent of patients die within one year, NIH said. In the early stages of disease, patients may have failing memory, behavioral changes, lack of coordination and visual disturbances. As the illness progresses, mental deterioration becomes pronounced and involuntary movements, blindness, weakness of extremities, and coma may occur.

The leading scientific theory at this time maintains that CJD is caused by a type of protein called a prion. The harmless and the infectious forms of the prion protein are nearly identical, but the infectious form takes a different folded shape than the normal protein. Researchers are examining whether the transmissible agent is, in fact, a prion and trying to discover factors that influence prion infectivity and how the disorder damages the brain.

Using rodent models of the disease and brain tissue from autopsies, they are also trying to identify factors that influence the susceptibility to the disease and that govern when in life the disease appears.

CJD belongs to a family of human and animal diseases known as the transmissible spongiform encephalopathies (TSEs). Spongiform refers to the characteristic appearance of infected brains, which become filled with holes until they resemble sponges under a microscope. Other TSEs are found in specific kinds of animals. These include bovine spongiform encephalopathy (BSE), which is found in cows and is often referred to as “mad cow” disease; scrapie, which affects sheep and goats; mink encephalopathy; and feline encephalopathy. Similar diseases have occurred in elk, deer, and exotic zoo animals.

More Information

To learn more, see:

• National Institutes of Health CJD Page
• CDC's CJD Page
• World Health Organization
• CJD Foundation

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