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Science

Mad cow disease prions can be transmitted by air, scientists say

In the wake of a BSE-related death, German, Swiss researchers alter conventional wisdom on prions. The scientific team notes, however, that there is 'no evidence' infected animals can transmit prions by breathing.

A black and white cow

BSE has killed almost 300,000 cows

According to a new study published Thursday, Swiss and German scientists have now discovered that the infectious agents known as prions, are also transmissible by air.

In the paper, which was published in the journal PLoS Pathogens, the researchers showed that these misfolded proteins are potentially much more infectious than had been previously thought.

Prions are the main method through which cows are infected and then contract bovine spongiform encephalopathy (BSE), which is more commonly known as mad cow disease.

The disease's human variant, Creutzfeld-Jakob disease, still remains rare.

According to the Centers for Disease Control and Prevention, an American government health authority, the disease is quite rare, affecting only one in a million people per year. To date, hundreds of people have died worldwide because of Creutzfeld-Jakob disease.

Earlier this month, a woman in Livorno, Italy, became the most recent known victim of Creutzfeld-Jakob disease, after having contracted the neurodegenerative brain malady in July 2010.

Humans typically acquire the disease by eating beef tainted with BSE, who in turn, get it from also eating diseased, processed meat. However, BSE's true origins remain a mystery.

Prions are 'alarmingly effective' at infection

In the study, the researchers tested aerosol sprays containing protein prions on laboratory mice, where they were surprised to find a complete, 100 percent infection rate.

A hand holding a white mouse

Mice fell ill after just one minute of exposure to the prions

"What we saw is that one minute was enough to get the animals sick," said Lothar Stitz, a virologist at the Federal Research Institute for Animal Health in Tuebingen.

He explained that higher prion concentrations led to a shorter incubation period, while shorter periods of exposure meant it took them longer to become diseased.

"But in all cases, they got sick," the scientist told Deutsche Welle.

He says the most interesting discovery was that the immune system was not triggered to prevent infection, but allowed the prions entering through the nostrils to colonize the brain directly.

"The results were both surprising and shocking," said Adriano Aguzzi, a professor of neuropathology at the University Hospital of Zurich, who was also part of the research team.

"It was a bit much for me," he told Deutsche Welle. "We handle this stuff, so to see how efficiently it can work was frightening."

No immediate danger

But Aguzzi stressed that he can see no implications for everyday people, and that the laboratory discovery does not mean it is possible to become infected with prions by traveling in public spaces, like on a subway.

People getting off the train

Not a worry for the public at large

"There is no evidence that people or animals would release prions into their environment," he said. "But if prions are airborne and aerosols are produced then breathing that air is a very efficient way of catching the infection."

Although he said it would be inappropriate to call a national emergency, he underlined the potential dangers to people who are exposed to aerosols, such as laboratory or slaughter house workers.

"Any handling of biological fluids will create aerosols," he said. "So it is imperative to put measures in place to protect against them."

For laboratories, he suggests introducing negative air pressure, so that no air can exit the room unless it has been filtered first.

In the case of slaughter houses, he urges regulators to examine working conditions and see what can be done to improve them.

Precautions already underway

Lothar Stitz from Tuebingen added that while this finding is new, both laboratories and abattoirs have been taking precautions against that eventuality for a long time already.

Man in a slaughter house, meat carcasses in the background

Scientists say slaughter house workers should take care

"In labs you have high security cabins and people use masks and glasses, and in a slaughter houses they use visors," he said, adding that just because something has never been proven, it cannot be ruled out.

"Life is dangerous," the scientist stated. "If you take precautions it is still dangerous, but less so than before."

The researchers are planning to continue their research into prion transmitability of prions, and to explore why prions are so toxic to humans.

"We want to understand what it is that these little proteins, which should be harmless, do to nerve cells in the brain that kills them off so efficiently," Aguzzi said.

Author: Tamsin Walker
Editor: Cyrus Farivar

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