Vaccine Prevents Prion Disease in Laboratory Mice

An oral vaccine can prevent mice from developing a brain disease similar to mad cow disease, according to investigators.

Prion diseases, which include scrapies, mad cow disease, and chronic wasting disease, are fatal and currently there is no treatment or cure. The disease spreads when an animal eats the body parts of other animals contaminated with prions. The disease causes dementia and abnormal limb movements.

Prion is a protein that is also an infectious agent. The proteins are so similar to proteins found normally so that the immune system does not fight them off. To devise a vaccine that would stimulate the mice's immune system, researchers attached prion proteins to a genetically engineered strain of Salmonella.

For the study, the mice were orally vaccinated with a safe, attenuated Salmonella strain, which expressed the prion protein. The mice were then divided into two groups--those who had high levels of antibodies in their blood and therefore responded well to the vaccine, and those with low levels of antibodies.

The mice with high levels of antibodies had no symptoms of the disease after 400 days. The mice with low levels of antibodies also had a considerable delay in the onset of the disease. It typically takes 120 days for mice that have not been vaccinated to develop the disease.

"These are promising findings,” said study author Thomas Wisniewski, M.D., from the New York University (NYU) School of Medicine (New York, NY, USA) and a member of the American Academy of Neurology. "We are now in the process of redesigning the vaccine so it can be used on deer and cattle.”

Dr. Wisniewski reported that much more research is still needed before the vaccine could be considered for humans. "The human version of prion disease usually occurs spontaneously and only rarely because of eating contaminated meat. But if, for example, a more significant outbreak of chronic wasting disease in deer and elk occurs and if it were transmissible to humans, then we would need a vaccine like this to protect people in hunting areas.”

Dr. Wisniewski also noted that a vaccine that decreases the spread of prion disease in animals also decreases the possibility that the disease could infect humans. These findings were presented at the American Academy of Neurology's 59th annual meeting in Boston, MA, USA, April 28-May 5, 2007.


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