新的口服疫苗可预防小鼠感染疯牛病
根据一份今天提出的报告，医学界已研发出预防小鼠罹患狂牛症等严重脑部疾病的口服疫苗。这种疫苗可以防止感染致命蛋白质prion，而这种有毒蛋白质会藉由改变正常细胞的prion蛋白质，引发脑部受损。
因为这种有毒蛋白质与正常prion蛋白质过于类似，免疫系统无法消灭它们，受到感染的动物与人的脑部受到无法复原的损害，会出现痴呆与肢体异常活动症状。
研究人员将这种prion有毒蛋白质附加在一个经过基因改造的沙门氏菌菌株上，让免疫系统找出并消灭这种具有传染性的有毒蛋白。他们发现，血液内抗体量较高的小鼠，经过四百天后仍无疾病症状，抗体量低的小鼠发病时间也延后了。
小鼠通常需要一百二十天，才会罹患这种prion蛋白疾病。纽约大学医学院的Thomas Wisniewski表示，这些发现可说是大有可为的。研究人员目前正在重新设计疫苗，使疫苗可以使用在鹿与牛身上。但是要将疫苗使用在人类身上，还须经过许多研究工作。但是广泛为动物施打疫苗，可以保护人类。
（姜欣慧译）
英文原文：
Vaccine Prevents Prion Disease In Mice
biocompare，5/3/2007
Source: American Academy of Neurology
An oral vaccine can prevent mice from developing a brain disease similar to mad cow disease, according to research that will be presented at the American Academy of Neurology's 59th Annual Meeting in Boston, April 28 – May 5, 2007. Prion diseases, which include scrapie, mad cow disease, and chronic wasting disease, are fatal and 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 that the immune system does not fight them off. To develop a vaccine that would stimulate the mice's immune system, researchers attached prion proteins to a genetically modified strain of Salmonella.
For the study, the mice were orally vaccinated with a safe, attenuated Salmonella strain, which expressed the prion protein. Then they were divided into two groups – those who had high levels of antibodies in their blood and thus 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 significant delay in the onset of the disease. It normally takes 120 days for mice that have not been vaccinated to develop the disease.
"These are promising findings," said study author Thomas Wisniewski, MD, of NYU School of Medicine in New York, 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."
Wisniewski said much more work is 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," he said. "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."
He also noted that a vaccine that decreases the spread of prion disease in animals also reduces the possibility that the disease could infect humans.
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