Mad cow disease and vCJD

ALTHOUGH RARE, Creutzfeldt-Jakob disease (CJD) is the most common type of human transmissible spongiform encephalopathy. A rapidly progressive neurodegenerative disorder, it's characterized by dementia, memory loss, rapid physical and mental deterioration, and death. Most cases occur randomly, for unknown reasons, in people ages 50 to 75. Equally deadly, variant Creutzfeldt-Jakob disease (vCJD) was identified in 1996. Because of its link to a similar disease in cattle called bovine spongiform encephalopathy (BSE), vCJD has been popularly but incorrectly termed mad cow disease. It's believed to be transmitted to people when they eat meat from BSE-infected cattle or possibly when they receive blood transfusions from infected donors. Some suspect it can be transferred from contaminated surgical instruments. After an incubation period that may last many years, infected people experience progressive impairment leading inevitably to death. Of 156 confirmed or probable cases of vCJD reported worldwide as of April 2004, 146 patients lived in Great Britain, 6 in France, and 1 each in Italy, Ireland, the United States, and Canada. Although the chance of contracting vCJD is extremely small, fear of contracting the disease is widespread. Renegade protein The infectious agents believed to be responsible for CJD, vCJD, BSE, and related diseases are called prions. Identified in 1992, prions aren't living pathogens, but rather a renegade form of normal protein. For unknown reasons, the normal protein changes shape and becomes infectious, converting adjacent normal protein into the infectious form. This starts a cascade of damage causing the characteristic spongiform appearance of an infected brain. Unlike the typical patient with CJD, usually an older adult, the typical patient with vCJD is between ages 18 and 41. The initial symptoms are psychiatric, including depression, mood swings, anxiety, withdrawal, behavioral changes, and possibly hallucinations and delusions. Next, the patient may develop neurologic symptoms, such as paresthesia (“pins and needles”) in her arms and legs, bad headaches, cold extremities, painful sensory symptoms, and problems with gait and coordination. Most patients develop muscle spasms called myoclonus. Memory and concentration problems seen in the early stages give way to severe cognitive impairment and akinetic mutism, the inability to talk or move. The patient dies after 7 to 24 months of illness, with the average being 14 months. Diagnosing vCJD can be difficult, especially early in the disease. One clue is a history of living in or traveling to BSE-infected countries, especially the United Kingdom, since 1980. The patient's electroencephalogram may be normal. On magnetic resonance imaging, abnormalities in the brain suggest vCJD. A tonsil biopsy may be positive for prion protein. But definitive diagnosis is possible only after the patient's death, when brain tissue can be examined for characteristic spongiform abnormalities. To date, the Centers for Disease Control and Prevention doesn't have evidence of vCJD that's been transmitted from direct person-to-person contact, but transmission can occur during blood transfusions or medical procedures. Transmission of the CJD agent has been linked to dura mater and corneal transplants, contaminated neurosurgical instruments, and contaminated human growth hormones. Since 1976, when current sterilization procedures began to be used, no iatrogenic transmission has occurred. Prions are difficult to destroy, so any instruments that may have touched infected tissue must be decontaminated according to special protocols or discarded. Follow recommendations from the World Health Organization. Nursing considerations Although chlorpromazine and quinacrine have been used experimentally to treat patients with vCJD, no treatment provides lasting effects. Nursing care is supportive and palliative, with these goals. Safety. As the patient's mobility and cognitive function deteriorate, she'll need assistive devices such as a walker, a wheelchair, a commode, and a hospital bed. Skin and mouth care. Provide meticulous skin care, regularly assessing for skin breakdown. Provide good oral hygiene. Nutrition. Obtain a swallowing evaluation and nutritional consult if the patient has difficulty swallowing. Comfort. Administer medications as indicated to keep her comfortable. Keep her room calm and quiet or consider playing music. Continue touching and talking to her as if she's aware of what's happening. Provide emotional support to her family and information about hospice care when needed. Patient education Tell patients that the risk of contracting vCJD is extremely small. In England, the country with the highest incidence, the risk of acquiring the disease may be 1 case per 1 billion meat servings. In 1989, the United States banned the import of cattle and most cattle-derived products from countries where BSE had been found. In 1997, the Food and Drug Administration (FDA) banned the use of mammalian protein in feed for cattle, thus eliminating the most probable route of disease transmission in cattle. Additional restrictions were enacted to safeguard the U.S. beef supply in 2003, after one cow imported from Canada tested positive for BSE. The FDA is considering whether to require that only certified BSE-free cattle herds be used to produce cattle-derived medical products, including drugs and vaccines. Milk and milk products are believed to be safe. To reduce the risk of acquiring vCJD when traveling to Europe or other areas with indigenous cases of BSE, patients may want to avoid eating beef or to eat only beef from solid muscle (no brains or ground beef). SELECTED WEB SITES Centers for Disease Control http://www.cdc.gov/ncidod/diseases/cjd/cjd_fact_sheet.htm World Health Organization infection control guidelines for transmissible spongiform encephalopathies http://www.who.int/emc=documents/tse/whocdscsraph2003c.html Last accessed January 3, 2005. Barbara Sheff is a microbiology consultant in Boston, Mass.

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