http://www-micro.msb.le.ac.uk/3035/prions.html
Prions do not have a nucleic acid genome. It seems that a protein alone is the infectious agent. The infectious agent has been called a prion. A prion has been defined as "small proteinaceous infectious particles which resist inactivation by procedures that modify nucleic acids". The discovery that proteins alone can transmit an infectious disease has come as a considerable surprise to the scientific community.
Prion diseases are often called spongiform encephalopathies because of the post mortem appearance of the brain with large vacuoles in the cortex and cerebellum. Probably most mammalian species develop these diseases. Specific examples include:
* Scrapie: sheep
* TME (transmissible mink encephalopathy): mink
* CWD (chronic wasting disease): muledeer, elk
* BSE (bovine spongiform encephalopathy): cows
Humans are also susceptible to several prion diseases:
* CJD: Creutzfeld-Jacob Disease
* GSS: Gerstmann-Straussler-Scheinker syndrome
* FFI: Fatal familial Insomnia
* Kuru
* Alpers Syndrome
Humans might be infected by prions in 2 ways:
1. Acquired infection (diet and following medical procedures such as surgery, growth hormone injections, corneal transplants) i.e. infectious agent implicated.
2. Apparent hereditary mendelian transmission where it is an autosomal and dominant trait. This is not prima facie consistent with an infectious agent.
Empasis:
>>>Kuru is the condition which first brought prion diseases to prominence in the 1950s. Found in geographically isolated tribes in the Fore highlands of New Guinea. Established that ingesting brain tissue of dead relatives for religious reasons was likely to be the route of transmission. They ground up the brain into a pale grey soup, heated it and ate it. Clinically, the disease resembles CJD. Other tribes in the vicinity with same religious habit did not develop the disease. It is speculated that at some point in the past a tribe member developed CJD, and as brain tissue is highly infectious this allowed the disease to spread. Afflicted tribes were encouraged not to ingest brain tissue and the incidence of disease rapidly declined and is now almost unknown.<<<
>>>Is it in phosphorous based fertilizers?
I couldn't find too much on that one. This article talks about that though.
Mad Cows in the Garden
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Hundreds of thousands of cows infected with mad cow disease (BSE) have been destroyed in England, and the British government believes that 10 people have succumbed to a human form of the disease as a result of eating infected beef. Last year, researchers concluded that it was possible for mad cow disease to be passed through beef bone and marrow, and the government subsequently banned the sale of most cuts of beef on the bone.
Bone meal is commonly used as a fertilizer in agriculture, especially in organic gardening. Is it possible that people could become infected with mad cow disease through contact with bone meal, either as they apply it to their gardens, or through ingesting residues on vegetables? Could the infective agents, called prions, be absorbed by plants and transferred to humans who consume them? No one knows for sure, but the British government has already banned the use of bone meal as a fertilizer in commercial agriculture.
The U.S. Department of Agriculture (USDA) contends that there is no need to worry about mad cow disease in this country, since no cases have turned up in U.S. cattle. Yet, some experts believe that a variant of the disease, perhaps just as deadly, may already be widespread. Also, infected bone meal may be imported from other countries with the disease.
To be on the safe side, experts recommend that gardeners handling bone meal wear masks and gloves, and take care not to become exposed to the substance through an accidental cut or splinter. Many high-phosphorous alternatives can substitute for bone meal, such as rock phosphate and soft rock phosphate.
[Editor: In a recent PBS special on mad cow disease, researchers found that prions were not harmed when buried in the ground for three years. In a recent conversation I had with a university plant scientist, he said that it was theoretically possible for prions from contaminated fertilizers to be absorbed by plants. Given these facts, it might be prudent to avoid vegetables grown with bone meal until more is known.]
In related news: Microbiologists at the Environmental Protection Agency (EPA) believe that the processed sewage sludge commonly sold as fertilizer for home gardening may contain disease-causing organisms such as Salmonella. Apparently, bacteria are able to hide in clumps of sludge, going undetected by standard tests for contamination. People who accidentally ingest small bits of sludge clinging to unwashed hands or improperly cleaned vegetables may become ill. Based on information in: Organic Gardening, Mar 1997; Science News, 2-28-98