Bovine spongiform encephalopathy in the context of Meat-and-bone meal

A prion (/ˈpriːɒn/ ) is a misfolded protein that induces misfolding in normal variants of the same protein, leading to cellular death. Prions are responsible for prion diseases, known as transmissible spongiform encephalopathy (TSEs), which are fatal and transmissible neurodegenerative diseases affecting both humans and animals. These proteins can misfold sporadically, due to genetic mutations, or by exposure to an already misfolded protein, leading to an abnormal three-dimensional structure that can propagate misfolding in other proteins.

The term prion comes from "proteinaceous infectious particle". Unlike other infectious agents such as viruses, bacteria, and fungi, prions do not contain nucleic acids (DNA or RNA). Prions are mainly twisted isoforms of the major prion protein (PrP), a naturally occurring protein with an uncertain function. They are the hypothesized cause of various TSEs, including scrapie in sheep, chronic wasting disease (CWD) in deer, bovine spongiform encephalopathy (BSE) in cattle (mad cow disease), and Creutzfeldt–Jakob disease (CJD) in humans.

The major prion protein (PrP) is encoded in the human body by the PRNP gene also known as CD230 (cluster of differentiation 230). Expression of the protein is most prominent in the nervous system but occurs in many other tissues throughout the body.

The protein can exist in multiple isoforms: the normal PrP form, and the protease-resistant form designated PrP such as the disease-causing PrP (scrapie) and an isoform located in mitochondria. The misfolded version PrP is associated with a variety of uniformly fatal neurodegenerative diseases in humans and nonhuman species. In nonhuman species these include ovine scrapie, bovine spongiform encephalopathy (BSE, mad cow disease), feline spongiform encephalopathy, transmissible mink encephalopathy (TME), exotic ungulate encephalopathy, chronic wasting disease (CWD) which affects deer; human prion diseases include Creutzfeldt–Jakob disease (CJD), fatal familial insomnia (FFI), Gerstmann–Sträussler–Scheinker syndrome (GSS), kuru, and variant Creutzfeldt–Jakob disease (vCJD). Similarities exist between kuru, thought to be due to human ingestion of diseased individuals, and vCJD, thought to be due to human ingestion of BSE-tainted cattle products.

Chronic wasting disease (CWD), sometimes called zombie deer disease, is a transmissible spongiform encephalopathy (TSE) naturally affecting members of the deer family. TSEs are a family of diseases caused by misfolded proteins called prions and include similar diseases such as mad cow disease in cattle, Creutzfeldt–Jakob disease in humans, and scrapie in sheep. In the United States, CWD affects mule deer, white-tailed deer, red deer, sika deer, elk, antelope, caribou, and moose. The transmission of CWD to other species such as squirrel monkeys and humanized mice has been observed in experimental settings.

In 1967, CWD was first identified in mule deer at a government research facility in northern Colorado, United States. It was initially recognized as a clinical "wasting" syndrome and then in 1978, it was identified more specifically as a TSE disease. Since then, CWD has been found in free-ranging and captive animal populations in 33 US states and five Canadian provinces. In addition, CWD has been found in one Minnesota red deer farm, one wild reindeer herd in Norway (March 2016) as well as in wild moose. Single cases of CWD in moose have been found in Finland (March 2018) and in Sweden (March and May 2019, September 2020). CWD was found in South Korea in some deer imported from Canada. CWD is typified by chronic weight loss and clinical signs compatible with brain lesions, aggravated over time, always leading to death.

Agriculture in Chile encompasses a wide range of different activities due to its particular geography, climate, geology and human factors. Historically agriculture is one of the bases of Chile's economy, now agriculture and allied sectors—like forestry, logging and fishing—account only for 4.9% of the GDP as of 2007 and employed 13.6% of the country's labor force. Some major agricultural products of Chile include grapes, apples, onions, wheat, corn, oats, peaches, garlic, asparagus, beans, beef, poultry, wool, fish and timber. Due to its geographical isolation and strict customs policies, Chile is free from diseases such as Mad Cow, fruit fly and Phylloxera, this plus being located in the southern hemisphere (having quite different harvesting times compared to the Northern Hemisphere) and its wide range of agriculture conditions are considered Chile's main comparative advantages. However, the mountainous landscape of Chile limits the extent and intensity of agriculture so that arable land corresponds only to 2.62% of the total territory.

Chile's principal growing region and agricultural heartland is the Central Valley, bounded by the Chilean Coast Range to the west, the Andes to the east, Aconcagua River to the north, and Bío-Bío River to the south. In the northern half of Chile, cultivation is highly dependent on irrigation. South of the Central Valley, cultivation is gradually replaced by aquaculture, silviculture, sheep and cattle farming.