Mad Cow Disease
Bovine Spongiform Encephalopathy, commonly known as mad cow disease, is a degenerative, slowly progressive and fatal disease affecting the central nervous system of adult cattle. An abnormal version of a protein normally found on cell surfaces called a prion is the infectious agent causing the disease. This alters the protein and destroys nervous system tissue, the brain and spinal cord.
Mad cow disease and humans
While humans cannot get mad cow disease, in rare cases they may get a human form of mad cow disease called variant Creutzfeldt Jakob Disease or CJD which is fatal. This is caused by eating beef products contaminated with central nervous system tissue such as brain and spinal cord from cattle infected with mad cow disease. The United States Department of Agriculture (USDA) believes that any cow products from high risk cattle, older cattle, animals that are unable to walk, and any animal that shows any signs of neurological problem should not enter the US food supply and therefore believes that this practice can effectively safeguard US public health from vCJD.
The disease can affect all age groups. It is hard to diagnose until it has nearly run its course. In the early stages, vCJD has symptoms related to nervous system such as depression, loss of coordination, dementia, illness and brain abnormalities. Tingling, burning, or prickling in the face, hands, feet and legs are other symptoms. Psychotic behavior, inability to walk and finally coma are other signs. If a person eats nerve tissue from an infected cow, he or she may not feel sick right away but usually within thirteen months of the onset of symptoms it can be fatal.
The leading theory is that vCJD is caused by infectious proteins called prions which are found in infected cows. There is no proof that prions are found in muscle meat such as steak. However, milk and milk products are not believed to pose any risk for causing mad cow disease in humans. When a cow is slaughtered and parts of it are used for human consumption, it affects the people if they eat the brain or spinal cord of infected cattle.
The first case of vCJD was reported in 1996 and since then there has been few cases of vCJD reported in the world. Most cases have been from parts of the United Kingdom. In 2003 mad cow disease was discovered in one cow in the US. In 2004 three more cows in the US have been found with mad cow disease. The most recent was found in April 2012 in a cow in California.
There is no single test to diagnose vCJD. Doctors base their assumptions upon where the person has lived and the person's symptoms and past health. Imaging tests such as MRI are done to check for brain changes caused by vCJD. As of now no blood test is available although researchers are trying to develop a blood test. A brain biopsy is the only way to confirm diagnosis of vCJD.
There is no cure for vCJD. Treatment includes managing the symptoms that occur as the disease gets worse. Researchers at New York University School of Medicine have taken a key step in developing an effective treatment. They found four compounds that significantly delayed the disease onset in mice. As prion diseases are extremely slow to develop, any treatment that can delay initial symptoms for a longer duration can be significantly life saving. Clinical trials of some anti-prion compounds are in progress. While presently little is known about prion diseases, they might probably prove simpler to treat than bacterial infections. Researchers are hopeful that tests of trimipramine and fluphenazine in people with CJD will begin soon.
Striking facts about mad cow disease
Humans cannot get the disease by simply eating regular cow meat. If someone is infected with CJD, they will probably will not know until years later.
Latest case of mad cow disease is attributed to random mutation. The cow did not contract the disease by consuming infected cattle feed since the deceased cow showed little symptoms of the disease when tests were performed randomly on dead cows.
Mad cow destroys the brain and spine in cattle as the disease attacks and destroys the brain and spinal cord in cattle. Thoroughly cooking meat will not help as prions are not affected by heat or other methods used to kill food-borne pathogens. Prions can survive in extremes up to 1800 degrees of heat to be neutralized so much so that even sterilization process used in hospitals is largely ineffective.
The mad cow disease is on the decline and is far less common than it was about a decade ago. There is at least a 99 percent decline worldwide since the disease peaked in 1992 with 37,311 cases.
This is a rare degenerative disease, a fatal brain disorder. One in every million worldwide is affected by Creutzfeldt Jakob disease which occurs about age 60, and about 90 percent of patients die within a year. Since first described in 1920, less than 1 percent of cases have acquired CJD.
Signs and symptoms
During the early stages of the disease failing memory, behavioral changes, lack of coordination and visual disturbances are exhibited. Impaired memory, judgment and thinking and insomnia, depression or unusual sensations are other symptoms. CJD may also cause fever or other flu-like symptoms. As the illness progresses, mental deterioration becomes severe. Involuntary movements, blindness and weakness of extremities are other symptoms.
Rapidly the disease progresses into dementia. Patients eventually lose the ability to move and speak and then enter a coma. Pneumonia and other infections may occur in these individuals and can lead to death. Some symptoms of CJD can be similar to Alzheimers or Huntington disease. CJD causes unique changes in brain tissue which can be seen at autopsy and the deterioration is more rapid than Alzheimer's disease or other types of dementia.
Major categories of CJD
Sporadic CJD: Here the disease appears even though the person may not exhibit any known risk factors. This is by far the most common type of CJD and 85 percent cases come under this category.
Variant CJD is caused by consuming meat from a cow that had Bovine Spongiform Encephalopathy (BSE) or mad cow disease, a prion disease similar to CJD. Strict controls have proved very effective since its discovery in 1996.
In hereditary CJD, the person has a family history of the disease and tests positive for a genetic mutation associated with CJD. About 5 to 10 percent of cases in the US are hereditary and the symptoms usually develop in early 50s.
In latrogenic CJD, the infection spreads from someone through medical or surgical treatment. A common instance of this is spread of CJD from someone with growth hormone treatment using human pituitary growth hormones extracted from deceased individuals who might have had CJD infection.
CJD is not contagious through casual contact with a CJD patient.
Researchers believe that an unusual slow virus or any other organism causes CJD. But they have never been able to isolate a virus or any organism in people with the disease. As the agent causing CJD has several characteristics other than known organisms such as bacteria and virus, it is difficult to destroy as it does not contain any genetic information in the form of nucleic acids. For example, prions are not destroyed by the extremes of heat and radiation used to kill bacteria and viruses, and antibiotics or antiviral medicines have no effect on them. It also incubates for a long period of time before the symptoms appear, as long as even 50 years. The leading scientific theory maintains that CJD is caused by a type of protein called as a prion. Also 5 to 10 percent of CJD cases are inherited. These cases arise from a mutation, or change in the gene that controls formation of the normal prion protein.
Diagnosis of CJD
There is no single diagnostic test for CJD. First, all treatable forms of dementia are ruled out. A neurological examination is performed and consultation with other physicians is sought. Spinal tap, electroencephalogram, CT and MRI and brain scans can reveal characteristic patterns of brain degeneration that can help diagnose CJD.
For a confirmed diagnosis of CJD, brain autopsy is the only way. A neurosurgeon removes a small piece of tissue from the patient's brain and it is examined by a neuropathologist. The procedure may be dangerous as it does not always obtain tissue from the affected part of the brain. Brain biopsy is discouraged unless it is needed to rule out a treatable disorder. In autopsy, the whole brain is examined after death. Special surgical and disinfection procedures can minimize the risk. Scientists are working to develop laboratory tests for CJD.
As such there is no treatment or cure to control CJD. Studies are on to try a variety of drugs but none of the treatments have shown consistent benefits in humans. Treatment aims at alleviating symptoms and making the patient as comfortable as possible. Opiate drugs can help relieve pain. During later stages of the disease, changing person's position frequently can keep them comfortable and help prevent bed sores. A catheter is used to drain urine if bladder control is lost. Intravenous fluids and artificial feeding are also used.
Avoid spreading CJD
To reduce the very low risk of CJD transmission from one person to another, it is better not to donate blood, tissues or organs if suspected or confirmed with CJD because of family history of the disease. As normal sterilization procedures such as cooking, washing and boiling do not destroy prions, the following precautions are suggested by the World Health Organization while dealing with patients contacted with CJD.
Prion diseases are Transmissible Spongiform Encephalopathies or TSE that affect humans and animals. In humans, they cause neurological disorders that are progressively degenerative. A prion is an abnormal pathogen that affects proteins found in the brain causing them to fold and clump unnaturally. This then leads to brain damage that is progressive. Prion diseases may occur spontaneously, may be inherited or may be acquired from contaminated material.
The most common form of prion disease is Creutzfeldt Jakob Disease or CJD. A variant of CJD is the 'mad cow disease'. The infection passes on to humans through contaminated meat. The most common pathologic feature of CJD is the formation of vacuoles (fluid filled spaces) in the brain giving rise to sponge-like appearance. CJD is one of several spongiform encephalopathies. Others include Kuru and Gerstmann Straussler Scheinker Syndrome.
Typical symptoms of prion disease include muscle stiffness, dementia, hallucinations, ataxia and fatigue. There is a change in the personality and behavior of the person. Diagnostic tests such as brain MRI, Spinal tap, EEG and blood tests are done to understand the condition. Brain tissue biopsy helps to confirm the disease. With rapid progression of the disease, the patient needs help in taking care of himself and might need to be moved to assisted care.
Kuru is another degenerative human spongiform encephalopathy disease that afflicted the Fore people from Papua, New Guinea due to ritual cannibalism.
GSS or Gerstmann Straussler Scheinker Syndrome is a rare neurological disorder due to brain degeneration. It is mostly inherited and sets in middle age. Initially the patient suffers cerebellar ataxia (lack of muscular coordination) and gradually deteriorates to dementia. There might be Nystagmus (rapid involuntary eye movements) and visual problems. There is a possibility of developing Parkinsons disease too. With rapid progression of the disease, the patient needs help in taking care of himself and might need to be moved to assisted care.
FFI or Fatal Familial Insomnia is a type of prion disease where the patient has difficulty in walking and falling asleep. There might be weight loss and excessive tears in the eye. It rapidly deteriorates to loss of consciousness and death. Initially the patient suffers insomnia that later worsens to include panic attacks, phobia and hallucinations. There might be weight loss and incontinence. After this, the patient might suffer dementia and sudden death.
Bibliography / Reference
Collection of Pages - Last revised Date: February 18, 2018