A shocking new study has found that mad cow disease can be transmitted through the air. Prior to the study, it was believed that humans could only be infected through consumption of food products from infected cows or through contaminated surgical instruments blood transfusions. The new findings raise serious questions about airborne transmission risks, particularly among people who work in science labs and meat and animal feed facilities.

Mad cow disease is the popular term for “bovine spongiform encephalopathy” (BSE), a fatal neurodegenerative disease in cattle that causes a spongy degeneration in the brain and spinal cord. The disease is transmitted by tiny micro-organisms known as prions. Five known human prion diseases exist, including Creutzfeldt-Jakob disease, as well as six non-human diseases, including scrapie, chronic wasting disease and mad cow disease (which sometimes jumps to humans through contaminated meat).

Almost 300 people have died from mad cow disease to date. In addition, over half a million cattle have died from the diseases and several million more have been killed from extermination efforts. Although thus far prions have only been found to infect one to two people per million in the United States each year, as much as 15 percent of deer in some Colorado populations carry chronic wasting disease.

The new study was conducted by a team of scientists at the universities of Zurich and Tübingen and the University Hospital Zurich and was led by Professor Adriano Aguzzi. To see if airborne prions could cause infection in mammals, Aguzzi and his team exposed several small groups of mice to different concentrations and exposure times of aerosolized prions that cause scrapie.

All mice except one group, which was exposed to a very light concentration of prions, got infected and died about 150 to 200 days after exposure. Other forms of prion exposure typically require very high concentrations to do anything, thus Aguzzi was surprised by the lethality of the mad cow prions.

“Common knowledge is that prions aren’t airborne, and can’t cause infection that way,” said Aguzzi. “We were totally surprised and also a bit frightened at how efficient [airborne infections] were.”

Most infectious diseases are spread by bacteria or viruses, which use genes to copy themselves. But prions are a third form of disease discovered in 1982, and they’re made only of misfolded proteins. The misfolded proteins convert healthy proteins into long fibrils, which in turn create more prions until the host dies from destroyed brain and nervous tissue. Prion symptoms appear suddenly months or years after infection and are 100 percent fatal.

The prions appear to transfer from the airways and colonize the brain directly because the immune system which prevents the passage of prions from the digestive tract to the brain does not recognize airborne prion infection.

“Prions are like an enemy within, the alien in some B-movie that transforms people to an evil version,” said prion biologist Edward Hoover of Colorado State University, who was not involved in the study. “The immune system doesn’t see them coming.”

Due to the disease’s long incubation period, the number of human and animal deaths is expected to rise. Almost half a million BSE-infected animals had entered the human food chain before controls on high-risk offal were introduced in 1989.

Strict precautionary measures against airborne prion infections do not exist in most scientific laboratories, slaughterhouses and animal feed. Given the new findings, Professor Aguzzi recommends precautions be taken to minimize the risks prion infection in humans and animals.

Aguzzi emphasized, however, that the findings stemmed from the production of aerosols in laboratory conditions and that Creutzfeldt-Jakob patients do not exhale prions.

Sources included:

http://www.sciencedaily.com/releases/2011/01/110113213056.htm
http://www.wired.com/wiredscience/2011/01/airborne-prions-disease/
http://en.wikipedia.org/wiki/Bovine_spongiform_encephalopathy