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Prion Airborne And Milk
Transmission - More Evidence

From Patricia Doyle
2-12-11
 
 
Airborne Prion Transmission (mice)
Date: 14 Jan 2011
Source: Science Daily 
http://www.sciencedaily.com/releases/2011/01/110113213056.htm
New findings suggest airborne pathogens can induce mad cow disease
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Airborne prions are also infectious and can induce mad cow disease or Creutzfeldt-Jakob disorder, new findings suggest. This is the surprising conclusion of researchers at the University of Zurich, the University Hospital Zurich, and the University of Tuebingen. They recommend precautionary measures for scientific labs, slaughterhouses, and animal feed plants. The prion is the infectious agent that caused the epidemic of mad cow disease, also termed bovine spongiform encephalopathy (BSE), and claimed the life of over 280 000 cows in the past decades. Transmission of BSE to humans, such as, by ingesting food derived from BSE-infected cows, causes variant Creutzfeldt-Jakob disease, which is characterized by a progressive and invariably lethal break-down of brain cells.
 
It is known that prions can be transmitted through contaminated surgical instruments and, more rarely, through blood transfusions. The consumption of food products made from BSE-infected cows can also induce the disease that is responsible for the death of almost 300 people. However, prions are not generally considered to be airborne -- in contrast to many viruses including influenza and chicken pox.
 
Prof Adriano Aguzzi's team of scientists at the universities of Zurich and Tuebingen and the University Hospital Zurich have now challenged the notion that airborne prions are innocuous. In a study, mice were housed in special inhalation chambers and exposed to aerosols containing prions. Unexpectedly, it was found that inhalation of prion-tainted aerosols induced disease with frightening efficiency. Just a single minute of exposure to the aerosols was sufficient to infect 100 per cent of the mice, according to Prof Aguzzi who published the findings in the Open-Access-Journal "PLoS Pathogens." The longer exposure lasted, the shorter the time of incubation in the recipient mice and the sooner clinical signs of a prion disease occurred. Prof Aguzzi says the findings are entirely unexpected and appear to contradict the widely held view that prions are not airborne. The prions appear to transfer from the airways and colonize the brain directly because immune system defects -- known to prevent the passage of prions from the digestive tract to the brain -- did not prevent infection.
 
Precautionary measures against prion infections in scientific laboratories, slaughterhouses, and animal feed plants do not typically include stringent protection against aerosols. The new findings suggest that it may be advisable to reconsider regulations in light of a possible airborne transmission of prions. Prof Aguzzi recommends precautionary measures to minimize the risk of a prion infection in humans and animals. He does, however, emphasize that the findings stem from the production of aerosols in laboratory conditions and that Creutzfeldt-Jakob patients do not exhale prions.
 
Reference --------- Haybaeck J, Heikenwalder M, Klevenz B, et al: Aerosols Transmit Prions to Immunocompetent and Immunodeficient Mice. PLoS Pathog. 2011; 7(1): e1001257. DOI:10.1371/journal.ppat.1001257; <http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1001257>
 
Abstract: Prions, the agents causing transmissible spongiform encephalopathies, colonize the brain of hosts after oral, parenteral, intralingual, or even transdermal uptake. However, prions are not generally considered to be airborne. Here we report that inbred and crossbred wild type mice, as well as tga20 transgenic mice overexpressing PrPC, efficiently develop scrapie upon exposure to aerosolized prions. NSE-PrP transgenic mice, which express PrPC selectively in neurons, were also susceptible to airborne prions. Aerogenic infection occurred also in mice lacking B- and T-lymphocytes, NK-cells, follicular dendritic cells, or complement components. Brains of diseased mice contained PrPSc and transmitted scrapie when inoculated into further mice. We conclude that aerogenic exposure to prions is very efficacious and can lead to direct invasion of neural pathways without an obligatory replicative phase in lymphoid organs. This previously unappreciated risk for airborne prion transmission may warrant re-thinking on prion biosafety guidelines in research and diagnostic laboratories.
 
Author summary: Prions, which are the cause of fatal neurodegenerative disorders termed transmissible spongiform encephalopathies (TSEs), can be experimentally or naturally transmitted via prion-contaminated food, blood, milk, saliva, feces, and urine. Here we demonstrate that prions can be transmitted through aerosols in mice. This also occurs in the absence of immune cells as demonstrated by experiments with mice lacking B-, T-, follicular dendritic cells (FDCs), lymphotoxin signaling, or with complement-deficient mice. Therefore, a functionally intact immune system is not strictly needed for aerogenic prion infection. These results suggest that current biosafety guidelines applied in diagnostic and scientific laboratories ought to include prion aerosols as a potential vector for prion infection.
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communicated by:
Terry S Singeltary Sr
flounder9@verizon.net
Despite the perceived risk revealed by these experiments with laboratory mice there has been no evidence to date linking prion disease to employees in slaughterhouses, animal feed plants, or research laboratories. - Mod.CP
 
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[5] Milkborne Prion Transmission (sheep)
Date Thu 20 Jan 2011
Source: Science Daily [edited]
http://www.sciencedaily.com/releases/2011/01/110119191350.htm
Prion disease spreads in sheep via mother's milk
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Transmission of prion brain diseases such as bovine spongiform encephalopathy (BSE) -- also known as mad cow disease -- and human variant Creutzfeldt-Jakob disease (vCJD) is generally attributed to the consumption of the brain or organ meat of infected animals but new research demonstrates lambs exposed to milk from prion-infected sheep with inflamed mammary glands can develop prion disease as well. The research, which is published in the January 2011 issue of the Journal of Virology, has major implications for human and livestock health.
 
"Prions cause devastating, ultimately fatal infections in humans," says corresponding author Christina Sigurdson of the University of California, San Diego School of Medicine. "This study is the 1st demonstration of prions from an inflamed organ being secreted, and causing clinical symptoms in a natural host for prion disease."
 
Recent research had suggested that human-to-human transmission of prions has occurred via blood transfusions, "underscoring the importance of understanding possible transmission routes," the researchers write. The misfolded prions that cause vCJD in humans, and BSE in cattle -- which can be transmitted to humans -- commonly accumulate in lymphoid tissues before invading the central nervous system, where they wreak their deadly effects. Inflammation can cause lymphoid follicles to form in other organs, such as liver and kidney, which leads prions to invade organs that normally do not harbor infection. In recent research, this team, led by Ciriaco Ligios of the Istituto Zooprofilattico Sperimentale in Sardinia, Italy and Adriano Agguzi at the University of Zurich, Switzerland, reported sheep with misfolded prions in inflamed mammary glands, also known as mastitis, raising concerns that prions could be secreted into milk.
 
In the new research, the team infected sheep with a common retrovirus that causes mastitis, and misfolded prions. They bred the sheep, in order to stimulate the females to produce milk, which they then collected and fed to lambs that had never been exposed to prions. The lambs developed prion disease after only 2 years, a speed which surprised the researchers, and "suggested that there was a high level of prion infectivity in milk," says Sigurdson.
 
The research raises several disturbing possibilities. - A common virus in a sheep with prion disease can lead to prion contamination of the milk pool and may lead to prion infection of other animals. - The same virus in a prion-infected sheep could efficiently propagate prion infection within a flock, through transmission of prions to the lambs, via milk. This might be particularly likely on factory farms, where mastitis may be common, and could occur in goats as well as sheep. - Humans with variant Creutzfeldt-Jakob disease might accumulate prions in inflamed organs, and could also secrete prions.
 
However, "this work cannot be directly extrapolated to cattle," says Sigurdson. She says that BSE prions do not accumulate to detectible levels in lymphoid organs, and thus would not be expected to accumulate with inflammation. "Nonetheless," she says, "it would be worth testing milk from cattle with mastitis for prions as there may be other cellular sources for prions entry into milk."
Reference
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Ligios C, Cancedda MG, Carta A, et al: Sheep with Scrapie and Mastitis Transmit Infectious Prions through the Milk. J Virol. 2011 Jan; 85(2):1136-9. Epub 2010 Nov 17. DOI:10.1128/JVI.02022-10; http://jvi.asm.org/cgi/content/abstract/85/2/1136.
 
Abstract: Prions are misfolded proteins that are infectious and naturally transmitted, causing a fatal neurological disease in humans and animals. Prion shedding routes have been shown to be modified by inflammation in excretory organs, such as the kidney. Here, we show that sheep with scrapie and lentiviral mastitis secrete prions into the milk and infect nearly 90 per cent of naive suckling lambs. Thus, lentiviruses may enhance prion transmission, conceivably sustaining prion infections in flocks for generations. This study also indicates a risk of prion spread to sheep and potentially to other animals through dietary exposure to pooled sheep milk or milk products.
 
--
communicated by:
Terry S Singeltary Sr
flounder9@verizon.net
These research confirms experimentally previous observations by others (such as, Lacroux C et al: Prions in Milk from Ewes Incubating Natural Scrapie. PLoS Pathog 4(12): e1000238. doi:10.1371/journal.ppat.1000238;
 
 
http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1000238 
 
 
Despite the potential risk of prion spread to other animals through dietary exposure to pooled sheep milk or milk products none has been observed so far.
 
Perhaps of greater interest is the comment that humans with variant Creutzfeldt-Jakob disease might accumulate prions in inflamed organs, and could also secrete prions.- Mod.CP]
 
Patricia A. Doyle DVM, PhD Bus Admin, Tropical Agricultural Economics Univ of West Indies Please visit my "Emerging Diseases" message board at:http://www.emergingdisease.org/phpbb/index.php Also my new website: http://drpdoyle.tripod.com/ Zhan le Devlesa tai sastimasa Go with God and in Good Health
 
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