The spongiform encephalopathies: prion diseases.
Prions are unusual infectious particles. Unlike viruses, bacteria, fungi and parasites, they contain no deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). Instead, they are a type of protein normally found within cells in humans and other organisms. In some cases, however, the the prions can change into a disease-causing form. These prions in turn appear to convert other, normal proteins to the abnormal shape. Many scientists now believe this process leads to several dementing diseases in humans, including Creutzfeldt-Jakob disease (CJD). Similar diseases in animals include bovine spongiform encephalopathy or "mad cow disease" in cattle and scrapie in sheep. This article discusses prion diseases, their devastating effects on patients and families and infection control concerns.
Mrs. Smith, a 63 year-old female, was in her usual state of good health until she had a sudden onset of tremors during sleep which woke her. In addition, Mrs. Smith and her family had been noticing she was forgetful and had slurred speech. These mild symptoms continued until the day of hospital admission one week later, when the patient reported another episode of tremulousness, incontinence and nausea without vomiting. She specifically denied any headache, fevers or neck stiffness, previous neurologic complaints or changes in strength in any of her extremities. However, she did report some unusual visual and tactile hallucinations in which colors didn't seem right and familiar objects felt unusual. Her medical or family history was not significant. Nonetheless, she was admitted for a diagnostic workup for acute encephalopathy. A computed tomography (CT) scan, magnetic resonance imaging (MRI) scan and electroencephalogram (EEG) were essentially negative. She was discharged home on an antiepileptic medication to control the tremulousness.
Unfortunately, Mrs. Smith's condition continued to rapidly fail and within weeks she became unable to walk or care for herself. She became increasingly confused and the day before the second admission, did not recognize one of her daughters. Nursing staff members found her cheerful and cooperative but her face seemed frozen in a lopsided smile. She would stop talking mid-sentence and stare into space. She had multiple twitches of her hands, legs and feet. She held herself in a very stiff kind of position with her left hand in what could be seen as a possible decerebrate position. Unable to feed herself, she needed to be reminded to chew and swallow. At times she was incontinent. Total care was required at this time.
As part of further diagnostic screening, a heavy metal and toxicology screen were done which were negative. Only the EEG was abnormal with diffuse slowing; the CT and MRI scans again were normal. An environmental and occupational history search were negative.
Within three weeks, Mrs. Smith had deteriorated with rigid extremities and myoclonic jerks. Her dementia rapidly progressed to unresponsiveness. She underwent a right frontal craniotomy with brain biopsy which was positive for CJD. She was transferred to a long-term care facility where she expired within a year, never regaining consciousness.
In 1970, the transmissible spongiform encephalopathies, so named because they frequently cause the brain to become riddled with holes, were thought to be caused by infectious agents called slow viruses. (19,26) Distinguished as noninflammatory degenerative diseases with long incubation periods, they produced characteristic spongiform changes associated with neuronal loss in the brain. (30) In 1982, Stanley Prusiner, a neurologist researcher, proposed the prion theory. He theorized that the infectious agent is a neurotropic rogue protein, and named it "prion," a proteinaceous infectious particle. Seemingly, these agents attack the brain but are invisible to the immune system, eliciting no immune response. Theoretically, prions may highjack production of normal proteins in the brain and increase amyloid protein. (30)
Unlike any infectious agent known, prions may multiply in an incredible way by inducing normal protein molecules to change shape and purpose. In support of this theory, mutations in the human PrP gene on chromosome 20 have been found in familial prion diseases. (34) Worldwide research is occurring as there is no vaccine and no known treatment. The hallmark common to all of the prion diseases, whether sporadic, dominantly inherited, or acquired by infection, is that they involve the aberrant metabolism of the prion protein. (28)
Some scientists still consider Prusiner's prion theory unproven because purified prions have not been shown to cause disease. There are other unanswered questions and some researchers still suspect that a slow-acting virus plays a hidden role in the infectious process.
In humans, the prion diseases include CJD, Kuru, familial fatal insomnia (FFI) and Gerstmann-Straussler-Scheinker syndrome (GSS). In animals, prion diseases include scrapie in sheep, bovine spongiform encephalopathy (BSE) (mad cow disease) in cows, transmissible mink encephalopathy in mink and chronic wasting disease in deer and elk. Some of these diseases have been caused by feeding cows offal (animal tissue discarded by slaughterhouses) that is rendered by a process that permits the melted fat to be collected as tallow and leaves the residual solids to be pulverized into meat and bone meal. In humans, the species barrier may have been breached with the new variant Creutzfeldt-Jakob disease cases in England. It is surmised that the outbreak started when cattle were fed with meat and bone meal from scrapie-infected sheep and somehow the infectious agent was then transmitted for the first time to humans. Prior to this time, humans did not contract the disease from animals. (29)
In 1957, Gajdusek studied among the Fore people of remote New Guinea. There he found many people with cerebellar dysfunction, ataxia, lack of coordination, profound tremor, hyperreflexia and dementia. Death usually occurred with in one year. The disease was not transmitted by casual contact; nursing mothers didn't infect their babies. At the National Institutes of Health, Gajdusek was able to transmit the disease to monkeys proving it to be infectious. It was found that cannibalism, especially with brain consumption, was the source of infection. The disease has nearly been eliminated by outlawing the practice of cannibalism. (19)
Familial Fatal Insomnia
First reported in 1986, familial fatal insomnia (FFI) is a hereditary prion disease. There is a mutation at codon 178 of the prion protein gene. At onset there is sleep loss, then hallucinations, tachycardia, hyperthermia and deterioration to coma. In one Italian family, 29 out of 288 persons covering six studied generations had the disease. (24) Very rare thus far, the world total is only nine families including one in Chicago. (30)
This is an autosomal dominant, also very rare, prion protein gene codon 102 mutation. There are thirty known families with this disease around the world. Onset occurs around forty years of age. Findings include cerebellar ataxia, pyramidal signs, loss of knee and ankle jerks and progressive dementia leading to death in 2-10 years. (30) Pathological spongiform changes and amyloid plaque depositions are found in the cerebellum, cerebrum and brain stem. The EEG usually does not show periodicity, only diffuse slowing. Diagnosis can be achieved by prion gene analysis. (10)
In 1920, Creutzfeldt described a progressive, dementing illness and in 1921 Jakob, described four patients with similar signs. The disease is very rare, occurring at a rate of one per one million worldwide. It is not spread by casual contact; conjugal cases are rare. There is some clustering of cases in Tunisia/Libyan Jews, and natives of Slovakia and Chile. (19) Questionable food practices have been described for these groups, such as lightly cooked scrapie-infected sheep brain and eyes; however, these cases have proven to be hereditary. Other cases may have a genetic predisposition. Familial cases of CJD have a mutation on the prion protein gene at codon 200 and account for 15% of all CJD disease. (24)
Symptoms of CJD start with changes in mental status, progressing to dementia and particularly characteristic, myoclonus. There is often a typical EEG with paroxysmal bursts of high-voltage slow waves. (19) Changes in white blood cell counts, cerebrospinal fluid (CSF), sedimentation rates and fever are noticeably absent. Subtypes include: (35)
* subacute- this is the type most common, with rapid deterioration.
* chronic- accounting for 8% of cases has a longer duration of 4-16 years
* amyotrophic- accounting for 5% of cases, with slower progression ending also with dementia
Recently, the detection of 14-3-3 protein in cerebrospinal fluid has shown a high sensitivity and specificity in patients suspected of having CJD. (21) However the test is positive only when the patient is symptomatic and is not a predictive test. The diagnosis is confirmed only by brain biopsy or by autopsy. Typical brain changes found include spongiform degeneration, gliosis and neuronal loss in the absence of an inflammatory reaction. When present, amyloid plaques that stain with PrP antibodies are diagnostic. (28,29)
New Variant Creutzfeldt-Jakob Disease
Mad cow disease, or bovine spongiform encephalopathy (BSE), first appeared in Britain's herds about 10 years ago. Scientists think cattle got the disease by eating feed contaminated with scrapie-infected sheep tissue added as a protein supplement. It is believed that BSE has spread to humans with 21 or more new variant Creutzfeldt-Jakob disease (nvCJD) cases in England primarily among the young. (6,12)
Atypical clinical features are seen including prominent behavior changes at the time of clinical presentation with subsequent onset of neurologic abnormalities, including ataxia within weeks or months, dementia and myoclonus late in the illness. Duration of illness is at least 6 months; nondiagnostic EEG changes are seen. (36) Testing biopsied tonsil tissue for the prion protein (PrP) marker may be used to confirm diagnosis. (23)
Iatrogenic Creutzfeldt Jakob Disease
Iatrogenic transmission of CJD has been reported from corneal transplantation, implantation of dura mater or electrodes in the brain and use of contaminated surgical instruments. (6,7,8) More recently, new cases have been reported after blood transfusion but CJD transmissibility through the transfusion of blood or blood products is controversial. (16) Still, revision of policies and procedures worldwide affecting all facets of blood product manufacturing from blood collection to transfusion are transpiring. (31) Transmission after liver transplantation has also been reported. (13) Also, Defebvre reports CJD in a patient who, during a thoracic surgery procedure, had embolization of intercostal arteries with lyophilized cadaveric dura mater. (4) Fewer than 20 cases of CJD linked to dura mater allografts had been reported world-wide until recently. Now Japan has acknowledged 43 cases over the past ten years. (33)
Pituitary hormones, derived from cadaver donors, were administered between 1963 and 1985 as pituitary gonadotropins (hPG) to infertile women and as growth hormone (hGH) to children with pituitary insufficiency. This source of pituitary hormones was abandoned in most countries in 1985 when two hGH recipients died in the USA from CJD. (17) TO date, there have been 16 deaths from CJD among approximately 8,000 hGH recipients in the United States for whom the National Hormone and Pituitary Program (NHPP) provided growth hormone. The rate of occurrence of new cases has averaged between one and two per year since the risk of CJD was recognized in 1985. (27) There is a potential for more cases due to the long incubation period. Five women treated for infertility in Australia have died from CJD contracted via hPG as a source of follicle-stimulating hormone, given to promote fertility. (17) Around the world, there are a total of approximately 100 deaths from contaminated pituitary hormones that have caused CJD.
Health Care Workers
Determining relevant antecedent events for an infectious illness with a very long incubation period is fraught with difficulty. Nevertheless, there have been at least 24 health care workers reported with CJD. These include six physicians, a pathologist, three dentists, a dental surgeon, nine nurses, three nursing assistants and two histopathology technicians. (3) Risk appears to be particularly associated with contact with cerebrospinal fluid or central nervous system tissue. (5) Guidelines have been established for the handling of blood and tissue specimen collection, surgical procedures and the performance of autopsies (Table 1). (15,8,32)
Nurses in the operating room are at particular risk of exposure to brain or spinal cord tissue or blood. It is best to use as many disposable items as possible. As a result of the extreme resistance of prions to normal sterilization procedures, current recommendations from England are to destroy neurosurgical instruments used in patients with CJD. (23,18) Although the disease is not spread by casual contact, stringently following universal precautions is required by nursing personnel (Table 2). Any patient must be considered infectious until proven otherwise.
Practical experience with these patients in the end stages of disease have shown many possibilities for the spread of infection. Usually they have to be suctioned frequently, need frequent mouth care, have tube feedings and diarrhea and other attendant difficulties of terminal patient care. (25) Consistently practicing universal precautions with every patient may help prevent disease transmission.
Families ask many questions. In the words of a family member, "To watch a loved family member go through such a horrific experience is total torture and to feel as though I know nothing is so frustrating." At the very least, nursing staff members should explain new tests and procedures in simple terms, share knowledge about the prion diseases and explain infection control concerns. The family's need for information is great and any explanations will help to decrease their anxiety.
In addition, the family must be supported through the grieving process. If the family asks about organ donation, it should be explained it is not an option because of the risk that the disease will be transmitted. (9) It's likely that the family will need help with end-of-life decisions which have been thrust upon them so abruptly. (4) Involving support services such as clergy and social services help create a larger base of support. (2)
With the diagnoses of any prion disease, there is little information to give. Often the cause is not known, no effective treatment has been found and even the diagnosis is unproven until after the patient has died. (2) There are resources available for additional information if desired (Table 3).
Prions, once dismissed as an impossibility, have now gained wide recognition as extraordinary agents that cause a number of infectious, genetic and spontaneous disorders. (30) Prions have apparently crossed the species barrier between animals and humans creating new variant CJD and endangering food supplies. Iatrogenic cases continue to be troublesome. Blood supplies must be screened for CJD. Nurses are challenged to meet the needs of patients and families with these devastating, hopeless illnesses; patient/family education become a top priority. It behooves nurses to be aware of the latest research on these prion diseases, transmissible spongiform encephalopathies, so resistant to disinfectants and thus difficult to eradicate and control.
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Table 1. Guidelines for Decontamination, Sterilization, Handling of Equipment and Materials Used for CJD Patients 1. Use as many disposable items as possible. Disposable drapes for procedures or in surgery should have excellent barrier qualities to prevent strike through. 2. Wear protective eye wear and gloves when coming in close contact with body fluids and blood, especially central nervous system tissue. Wear goggles when suctioning. 3. Wash hands thoroughly with soap and water or detergent after any contact with the patient even when the contact does not involve handling blood, percutaneous fluid or body tissues. 4. Irrigate any percutaneous exposure to blood, CSF and tissue (particularly brain tissue) immediately with 0.5% sodium hypochlorite (household bleach diluted 1: 10) and water. Keep in mind bleach is destructive to human tissue, instruments and fabrics. 5. Label all specimens sent to the laboratory from CJD patients as "Biohazardous." 6. Sterilize all potentially contaminated materials in a gravity displacement autoclave at 132 degrees C for a least one hour before discarding, cleaning, or resterilizing. It is preferred that contaminated materials be autoclaved in a prevacuum autoclave at 134-138 degrees for 1 hour. 7. Immerse all reusable equipment that came in direct contact with the patient in 1 N sodium hydroxide for one hour at room temperature. An alternate method is to immerse all reusable equipment coming in contact with the patient in 5% sodium hypochlorite (full-strength household bleach) for two hours. Full-strength solution will damage instruments. This extended contact time ensures deactivation of agents. 8. If possible destroy instruments and incinerate. Otherwise, autoclave all instruments before they are washed. After sterilization, instruments can be cleaned following the usual process and resterilized. 9. Disinfect all surfaces of the operating room with 5% sodium hypochlorite, then clean routinely. 10. Bag and label all linens and disposable materials with "Biohazard" labels so that they can be handled safely by housekeeping and laundry personnel. 11. Organ or tissue donation is not acceptable for the patient with Creutzfeldt-Jakob disease. 12. Request visitors to wash hands well. Source: Adapted from Bailes B: Ceutzfeldt-Jakob disease: A fatal neurodegenerative transmissible disorder. AORN Journal 1990:52:976-985. Committee on Health Care Issues, American Neurological Association: Precautions in handling tissue, fluids and other contaminated materials from patients with suspected Creutzfeldt-Jakob Disease. Ann Neurol 1986; 19:75-77. Used with permission. Table 2. Sterilization Procedures for Creutzfeldt-Jakob Disease Tissues and Contaminated Materials Fully Effective (Recommended) Procedures Steam autoclaving at 132[degrees]C for 1 hour Immersion in 1N sodium hydroxide for 1 hour at room temperature Partially Effective Procedures Steam autoclaving at either 121[degrees]C or 132[degrees] for 15-30 minutes Immersion in 1N sodium hydroxide for 15 minutes, or lower concentrations (less than 0.5N) for 1 hour Immersion in undiluted bleach, or up to 1:10 dilution for 1 hour Ineffective Procedures Boiling, ultraviolet irradiation, ethylene oxide, sterilization, ethanol, formalin, beta-propiolactone, detergents, quaternary ammonium compounds, Lysol, alcoholic iodine, acetone, potassium permanganate Used with permission from: Rosenberg RN, White CL, Brown P et al: Precautions in handling tissues, fluids and other contaminated materials from patients with documented or suspected Cruetzfeldt-Jakob Disease. Ann Neurol 1986; 19(1):75-77 Table 3. Resources for Families/Patients Creutzfeldt-Jakob Disease Foundation PO Box 611625 North Miami, Florida 33261-1625 Internet: http://members.aol.com/crjakob http://www.medicinenet.com/ http://www.mad-cow.org/ http://www.healthfinder.gov
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Questions or comments about this article may be directed to Noreen Mocsny, RN, MEd, 707 Park Avenue, Cincinnati, Ohio 45246. Now retired, she was a staff nurse for med/surg, neurology and outpatient clinics at the Veterans Affair Medical Center in Cincinnati, Ohio.
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|Publication:||Journal of Neuroscience Nursing|
|Date:||Oct 1, 1998|
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