Vaccine Could Fight Chronic Wasting Disease in Deer
MILWAUKEE, Wis. _ An experimental oral vaccine designed to prevent prion disease warded off symptoms in mice, raising the prospect that a similar approach someday could be used to stop the spread of chronic wasting disease in wild deer.
Already the same researchers are working on a deer and elk version of the vaccine, which uses a weakened, genetically engineered strain of salmonella.
In theory, if the deer vaccine were found to work, it could be put into feed and spread in areas where chronic wasting disease is endemic.
“It was pretty impressive, the degree of protection they got,” said G. Richard Olds, an infectious-disease expert and professor and chairman of the department of medicine at the Medical College of Wisconsin.
Such a vaccine also could be used in cattle in the event that mad cow disease became widespread, said Olds, who was not part of the study.
“Obviously, the much more immediate market is in deer and elk because the approaches we are taking aren’t working,” he said.
The study involved about 100 mice that were inoculated with a vaccine using a salmonella strain that had been engineered to express, or produce, mouse prion protein, which normally is present in the brains of the animals. The normal prion protein is virtually identical to the rogue prion that is believed to cause the family of fatal brain disorders known as transmissible spongiform encephalopathy diseases, such as mad cow disease, chronic wasting disease, sheep scrapie and Creutzfeldt-Jakob disease in humans.
The mice were then infected orally with a form of scrapie that had been manipulated to be infectious in mice.
After the mice were vaccinated, researchers checked if they had high or low levels of antibodies to the vaccine.
Those that had high levels of antibodies, about 20 percent of the mice, remained symptom-free after 400 days.
When the brains of those mice were examined, no evidence of prion disease was found, said lead researcher Thomas Wisniewski, a professor of neurology, pathology and psychiatry at New York University School of Medicine.
“So they had protection,” Wisniewski said.
Essentially, the vaccine had activated the immune systems of the mice to recognize the scrapie prion as an invader and attack it.
All the other mice, those with low levels of antibodies to the vaccine, developed symptoms and died within 160 days, although they showed a delay in symptoms of about 40 days.
By boosting the strength of the vaccine or revaccinating the mice, higher levels of antibodies could be achieved, Wisniewski said.
He said that for the vaccine to work against chronic wasting disease in deer, a different strain of salmonella would have to be used. And that strain would have to be genetically engineered to express normal deer prion protein.
He said he now is testing a similar vaccine in mice that have been genetically engineered to express deer prion protein in their brains.
Although such a vaccine might not be 100 percent effective in protecting deer from chronic wasting disease, it could provide a high level of resistance, he said.
“It would interrupt the vicious cycle of infection,” he said.
“It would be an easy thing to do. You could just spread it on deer and elk feed in pellets they might like to eat.”
The research was presented Thursday at the annual meeting of the American Academy of Neurology in Boston.
The research looks promising, said Suzette Priola, a senior scientist with the National Institute of Allergy and Infectious Disease.
However, she said the researchers should have waited longer to look for symptoms and to check the brains of the mice for signs of prion disease. She said mice such as those used in the experiment can live 500 to 600 days in optimal conditions.
Still, it appeared that the vaccine provided some level of protection, she said.
“At the very least, you are slowing things down significantly,” said Priola, who was not involved in the study.
She said putting such a vaccine in feed to protect deer in the endemic areas of chronic wasting disease might work, but “it would be a mammoth undertaking.”
And before that can be done, the vaccine would have to prove effective in mice that express deer prion protein in their brains and then in captive deer, she said.
The National Institutes of Health funded the study.
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