How Now Mad Cow and Other Prion Diseases

California Association
for
Medical Laboratory Technology

Distance Learning Program

How Now Mad Cow
and other Prion Diseases
Course #: DL-951

1.0 CE/Contact Hour
Level of Difficulty: Intermediate

Author:
Rebecca Rosser
Education and Development Consultant
SCPMG Strategic Business Initiatives
Reseda, CA

© California Association for Medical Laboratory Technology.
Permission to reprint any part of these materials, other than for credit from CAMLT, must be obtained in writing from the CAMLT Executive Office.

CAMLT is approved by the California Department of Health Services
as a CA CLS Accrediting Agency (#0021)
and this course is is approved by ASCLS for the P.A.C.E.® Program (#519)

1895 Mowry Ave, Suite 112
Fremont, CA 94538-1766

Phone: 510-792-4441
FAX: 510-792-3045

Notification of Distance Learning Deadline
DON'T PUT YOUR LICENSE IN JEOPARDY!

This is a reminder that all the continuing education units required to renew your license must be earned no later than the expiration date printed on your license. If some of your units are made up of Distance Learning courses, please allow yourself enough time to retake the test in the event you do not pass on the first attempt. CAMLT urges you to earn your CE units early!

The headlines in Britain shouted messages like “Bring Back the Beef,” and “Scientists baffled by mystery of new BSE cases”. In 1985, an epidemic of Mad Cow Disease caused devastation in the beef industry, in the United Kingdom, that jolted the world. A disease among the cows was diagnosed as being caused by transmissible spongiform encephalopathies (TSE), also known as a prion disease. TSE’s are responsible for a number of animal and human conditions that were first thought to be caused by a virus. Research has indicated that the causative infectious agent does not contain a nucleic acid genome, therefore cannot be a virus. Others speculate that the agent is a virino, which is a small non-coding regulatory nucleic acid coated with a host-derived protective protein. Still others believe the agent is a prion. In both humans and animals this agent causes progressive brain damage and ultimately death. Animal TSE can effect cows in the form of Bovine Spongiform Encephalopathy (BSE), also known as, “Mad Cow Disease.” BSE is most prevalent in the United Kingdom and has caused the government to dispose of thousands of infected cattle, causing a crisis in the beef industry. Feline Spongiform Encephalopathy (FSE) is present in cats. In sheep and goats the disease is called Scrapie. The presence of Scrapie in sheep and goats has worldwide consequences, as only Australia and New Zealand are recognized as being Scrapie free. In mink, the disease is Transmissible Mink Encephalopathy (TME). In mule deer and elk, the disease is called Chronic Wasting Disease (CWD). Human disease can be classified as Creutzfeldt-Jakob Disease (CJD), variant Creutzfeldt-Jakob Disease (vCJD), Gerstmann-Sträussler-Scheinker Disease (GSS), Kuru, Fatal Familial Insomnia (FFI) or, in infants, Alpers Syndrome. Kuru was first identified in the early 1900’s, CJD in 1920, BSE in 1985 and most recently vCJD in 1996. While these diseases, in humans, are rare, they are always fatal.

TSE’s are also known as prion diseases. The prion (proteinaceous infectious particle) is a normal protein that has a change in its three dimensional configuration. As the prion attacks the brain it causes large vacuoles in the cortex and cerebellum, thus the spongiform appearance. The normal protein (PrPc), is a glycoprotein with secondary structures dominated by alpha helices, easily soluble and easily digested by proteases. The abnormal, disease-producing prion (PrPSc), is a glycoprotein with secondary structures dominated by beta helices, insoluble in all but strong solvents, and resistant to digestion by proteases. When PrPSc molecules come in contact with PrPc molecules, the PrPc molecule is converted into the PrPSc molecule. As this process occurs, the molecules form aggregates that might be the cause of the cell damage that results in vacuole formation. Prion disease may be acquired through one of three routes. First, when the disease has no known apparent cause the route is called sporadic. Second, the disease may be inherited through an autosomal dominant trait, and third, the disease may be acquired through infected food or medical equipment. Prions appear to be resistant to enzymes, chemicals and heat that break down other proteins. Normal disinfection procedures do not eliminate prions either.

More than 250 years ago Scrapie was recognized as a disease in sheep and goats in Western Europe. In 1947, the first case was identified in the United States. Since then more than 1000 flocks have been diagnosed with Scrapie. As with the other prion caused diseases, Scrapie is a fatal, degenerative disease affecting the central nervous system. In the United States it has been reported in the Suffolk breed, along with over a dozen other breeds and some crossbreeds. As of August 2001, 1,600 cases in sheep and 7 cases in goat have been diagnosed. Transmission is mainly from the ewe to her offspring through contact with the placenta and placental fluids. The incubation period is two to five years with the sheep living one to six months after symptoms appear. There is no evidence that Scrapie is transmittable to humans. Early signs of Scrapie include slight changes in behavior or temperament, followed by scratching or rubbing against fixed objects. This rubbing phenomenon is how the disease was named Scrapie. Other symptoms include loss of coordination, weight loss, hopping like a rabbit and swaying of the rear end. Diagnosis is made based on the animals physical symptoms, the animals history and finally by exam of brain tissue. A diagnostic test is undergoing evaluation by USDA’s Animal and Plant Health Inspection Service for the detection of Scrapie in live animals. Increased concern over this disease has caused packers and producers to have difficulty in disposing of sheep offal and dead sheep, causing increases in disposal costs. In addition, other countries are hesitant to purchase sheep products. Control programs are focusing on developing a diagnostic test, investigating transmissibility, and providing effective cleanup strategies that are economic for packers and producers.

North American deer and elk are the target of this TSE. It was first discovered in Colorado in the mule deer population and manifested itself as a “wasting” syndrome, resulting in severe weight loss and consequently death. CWD is limited to an endemic area that includes the southwest corner of Nebraska, northern Colorado, southern Wyoming and southwestern Nebraska. These areas have populations of free ranging deer and elk that have not been moved from this area. The disease has also been diagnosed in farmed elk herds in South Dakota, Nebraska, Oklahoma, Montana, Kansas, and Colorado. These herds have undergone quarantine and no further disease has been identified. CWD has infected Rocky Mountain elk, mule deer, white-tailed deer and black-tailed deer. There is no evidence that this disease has been passed to other ruminant animals, such as cattle, sheep and goats. CWD occurs mostly in adults. Symptoms include, not only weight loss over time, but decreased interaction with other animals, listlessness, and repetitive walking in a set pattern. Nervousness may also be exhibited in elk. A decreased appetite for hay and increased drinking are also symptoms. Transmission of the disease is thought to be from animal to animal but may occur through birth. Currently researchers are in the process of developing a live-animal diagnostic test. As in other spongiform diseases, brain lesions occur and current diagnosis is made after the animal has died. Prevention of CWD is by elimination of infected animals and limiting the distribution of the disease to the endemic area for free-range animals and surveillance of farm-raised animals.

Kuru is a prion disease that was discovered in the early 1900’s in the people of New Guiena. The disease manifests itself as a neurodegenerative disorder starting with unsteadiness, deterioration of speech and tremor. It then moves on to cause more severe tremors, shock-like muscle jerks and uncontrolled bursts of laughter. In the final stage, all the symptoms become severe and include the presence of deep ulcerations. The incubation period, for Kuru, was determined to be from 2 years to 23 years after exposure. The disease reached epidemic proportions in the 1960’s after five decades of neurological disease and death, mostly in the female population. So, how did this group of natives acquire this devastating disease? In this
part of New Guinea there was a ritual of mortuary cannibalism. The females would remove organs of the dead, which were then used as food sources especially for children and the elderly. Fortunately for these natives of New Guinea, this practice has been eliminated from the culture. With the elimination of this practice, the disease in New Guinea has disappeared.

GSS Disease is an inherited neurodegenerative disorder caused by an accumulation of a mutated prion protein amyloid. It is inherited as an autosomal dominant disease, which means that both sexes are affected and there are no carriers of the mutant gene. GSS slowly progresses with symptoms beginning between the ages of 30 and 70. Patient’s experience lack of muscle coordination and have difficulty walking. As the disease progresses, symptoms include slurring of speech, involuntary movements of the eyes, rigid muscle tone and eventually dementia, which is less common than in Creutzfeldt-Jakcob Disease (CJD). In some cases the disease progresses rapidly and consequently cannot be distinguished from CJD. In GSS, spongiform changes in the brain tissue may or may not occur. GSS can live from 2 to 10 years with treatment aimed at alleviating symptoms. Currently there is no cure for this rarely inherited disease. Current research is focused on the prion that causes the disease, attempting to characterize, clarify the disease mechanism and then developing ways to prevent, treat and cure GSS disease.

Insomnia can be the result of a malfunctioning thalamus, which is the center of brain that controls the communication that allows a person to sleep. FFI is also an autosomal dominant hereditary disease caused by a prion that results in amyloid plaques, which in this case affects the thalamus, causing severe selective atrophy. As a result of the degradation of the thalamus, there is an interruption of the body’s circadian rhythms. Consequently, patients with FFI lose sleep, can have hallucinations and eventually go into coma. There are four stages of FFI, which causes death in about 18 months. Progressive insomnia, panic attacks, and bizarre phobias developing over a four-month period characterize the first stage. The second stage lasts about five months with symptoms including hallucinations, panic, agitation and sweating. In stage three, total insomnia is paired with weight loss and lasts about three months. The final stage, which lasts six months, includes dementia, total insomnia, loss of hearing and sudden death. New techniques such as DNA sequencing or molecular hybridization should be developed to make a diagnosis, as the disease does not begin progression until after childbearing years. Currently there is no cure for this disease, but gene therapy could be promising to prevent FFI. In this case, the correct gene could be inserted to cause the correct protein to be developed, consequently allowing for the thalamus to function, as it should, thus preventing insomnia.

Unfortunately, Alpers’ Disease affects infants and children. It is an autosomal recessive disorder that can be seen in siblings and is known also as Christensen’s disease or Christensen-Krabbe disease. Alfons Jakob first recognized it in the early 1900’s and his students, Souza, Freedom, and Alpers further described cases. It is manifested by convulsions, developmental delay, mental retardation and dementia. Only thirteen cases have been identified since 1931, but others may have been missed due to the fact that chronic liver dysfunction can be present, which may mask diagnosis of Alpers’ Disease. Final diagnosis is at autopsy when spongiform plaques are identified in the gray matter of the brain. There is no current treatment for the disease, only for the symptoms, such as anti-convulsants for the seizures. Liver failure is usually the ultimate cause of death within the first two years of life.

CJD is also referred to as subacute spongiform encephalopathy due to the formation of microscopic vacuoles or holes in the neurons that appear “sponge-like.” The disease is named for Drs. Hans Creutzfeldt and Alfons Jakob who documented the first cases in the 1920’s. This disease affects both men and women in the 50 to 75 year age range, with one case per million per year. Cases in persons less than 30 years old are extremely rare, at less than 5 cases per billion. There appears to be three ways in which a person can acquire CJD. First, the disease can appear sporadically, without any apparent cause. Second, it can be inherited as an autosomal dominant pattern. This type of transmission occurs in about 10-15 % of the cases. Third, a transmissible agent can transmit the disease through infection. Iatrogenic transmission is an unintended consequence of a medical procedure using tainted instruments, by contaminated human growth hormone (about 100 cases), by corneal grafts or by infected neural material. In 1976, sterilization procedures were put into place. Additionally recombinant DNA technology is used for producing human growth hormone. Both of these advances have contributed to there being no further documented cases of CJD from iatrogenic transmission. Symptoms begin with insomnia, depression, confusion and problems with memory, coordination and sight. As the disease progresses, patients experience progressive dementia and involuntary jerking movements. In the final stages of the disease, patients loose all mental and physical functions, lapse into coma and die, usually from pneumonia due to the unconscious state. CJD patients will succumb within one year of diagnosis. CJD is difficult to diagnose, so the first step is to rule out other diseases that might have similar symptoms. It may be mistaken for Alzheimer’s Disease, Pick’s Disease, Huntington’s disease, cerebral hematomas and vascular irregularities. An EEG can detect a characteristic abnormal brain pattern associated with the later stages of the disease, but cannot confirm a CJD diagnosis. A new test to detect a specific protein (14-3-3) in CSF has been developed, but again this does not give a definitive diagnosis. CJD can definitively be diagnosed by performing a brain biopsy or autopsy. However, brain biopsies can be a dangerous procedure, can result in a false-negative result, if the wrong area of the brain is chosen, and are quite costly. In addition, there is a risk to healthcare workers, if strict sterilization and infection control precautions are not taken. When available, the use of disposable equipment should be used in suspected cased of CJD. If equipment is reusable, then steam sterilization or cleaning with 1 N sodium hydroxide (followed by steam sterilization) can be utilized. If this cannot be accomplished, then the equipment must be disposed of by incineration. Contaminated skin surfaces are to be washed with 1 N sodium hydroxide or 10% bleach followed by rinsing with copious amounts of water. Splashes to the eyes should be treated using copious amounts of water or saline. Contaminated dry waste or sharps waste should be autoclaved for 4.5 hours prior to incineration. There are no known effective treatments for CJD, so treatment focuses on easing symptoms.

An epidemic began in 1985 and before it was under control over 170,000 cattle were stricken with BSE. “Mad Cow Disease” is aptly named due to the behavior exhibited by the cattle when they are infected. The origin of the disease appears to be cattle feed that contained brain tissue from Scrapie infected sheep. These sheep had been treated in a new way that did not destroy the infectiousness of the Scrapie prions. Yes, the sheep Scrapie had crossed over into the cattle population. In addition, waste cattle (presumably contaminated) were also ground up for feed. In 1988, such food was banned, but it took until 1992 for the epidemic to decline due to the incubation period of three to eight years. BSE has not been shown to exist in the United States. This is due to the banning of use of ruminant feed in 1997.

In 1996, a disturbing fact emerged that associated a causal relationship between BSE and a new disease called new variant Creutzfeldt-Jakcob Disease (now referred to simply as vCJD). Young adults were dying after exhibiting clinical symptoms of CJD, including dementia and muscle jerks. Cases were predominately coming from Britain, but several cases were documented from patients outside of Britain. These patients were found to have lived in the endemic British areas for at least 5 years during the epidemic (1984-1986). The incubation period for vCJD is still unknown. The current risk to travelers of acquiring vCJD from eating beef cannot be determined. However, the risk decreases by avoiding beef or beef products or selecting beef or beef products that are solid pieces (versus calf brains or burgers or sausages). Public health preventative measures have been put into place. Enhancement of BSE surveillance, culling of sick animals and using the “over thirty months scheme.” This excludes animals over 30 months old from both the human and animal food chain. At this time there is no indication that CJD or vCJD can be transmitted through the blood supply. However, there is a donor deferral program in place. Permanent deferrals are for anyone who has been diagnosed with CJD or vCJD or are relatives of anyone who has been diagnosed. An indefinite deferral is in place for anyone who has spent more than three months in the United Kingdom from 1980 to 1996, or anyone who has spent more than 5 years in Europe from 1980 to present. Indefinite deferrals also apply to anyone who received a blood transfusion in the United Kingdom from 1980 to present. There is no current treatment for vCJD.

Transmissible spongiform encephalopathies (TSE) are prevalent in both human and animal populations. Surveillance, along with advances in detection, and prevention are needed to eliminate this prion caused disease. Research into how prions are formed and transmitted may be the key to unlocking the mystery. Once there is more information about how prions work, treatment modalities may be discovered.

References *:
1. Akroush, Ann M., Fatal Familial Insomnia. 1996-1997. Available at: http://www.mic.ki.se/Diseases/c10.228.html. Accessed January 19, 2003.
2. Alpers Disease. Available at: http://www.cs.jmu.edu/common/projects/mtDNA/alpersdisease.html. Accessed April 27, 2003.
3. CDC. New Variant CJD: Fact sheet. April 18, 2002. Available at: http://www.cdc.gov/ncidod/diseases/cjd/cjd_fact_sheet.htm. Accessed January 18, 2003.
4. CDC. Questions and Answers regarding Bovine Spongiform Encephalopathy (BSE) and Creutzfeldt-Jakob Disease (CJD). January 4, 2001. Available at: http://www.cdc.gov/ncidod/diseases/cjd/bse_cjd_qa.htm. Accessed January 18, 2003.
5. CDC. Questions and Answers Regarding Creutzfeldt-Jakob Disease Infection-Control Practices. May 9, 2002. Available at: http://www.cdc.gov/ncidod/diseases/cjd/cjd_inf_ctrl_qa.htm. Accessed January 18, 2003.
6. Kuru: the Dynamics of a Prion Disease. Available at: http://www.as.ua.edu/ant/bindon/ant570/Papers/McGrath/McGrath.htm. Accessed January 18, 2003.
7. National Scrapie Education Program. Scrapie Fact Sheet. August 2001. Available at: http://www.animalagriculture.org/scrapie/Scrapie.htm. Accessed January 19, 2003
8. Orphanet. Disease: Gerstmann-Straussler-Scheinker syndrome. Available at: http://www.orpha.net/consor/cgi-bin/../../Pat/GBG.html. Accessed January 19, 2003
9. Veterinary Services. Chronic Wasting Disease. Available at: http://www.aphis.usda.gov/vs/nahps/cwd/. Accessed January 19, 2003.
* A list of additional references is available on request from the CAMLT Executive Office.