VOA慢速英语 2007 0626a（在线收听）

This is the VOA Special English Agriculture Report.

Someday, rice plants might not only provide food but also a way to prevent cholera and other diseases.

Cholera is a bacterial infection of the intestines. Today it is found mostly in Africa, Asia and Latin America. Current vaccines to protect against cholera must be kept in cold storage. The need for refrigeration limits use in poor countries.

But research in Japan may lead to rice plants that contain a cholera vaccine that does not need to be kept cold. So far, the research has been carried out only on mice. The Proceedings of the National Academy of Sciences in the United States published the study earlier this month.

Hiroshi Kiyono of the University of Tokyo and his team experimented with genetic material from the bacterium responsible for cholera. They placed it into the Kitaake rice plant.

Mice ate the genetically changed rice seeds as a powder. The report says the vaccine was not destroyed by stomach acid; instead, the animals developed antibodies against the cholera toxin. The scientists say the vaccine remained active even after being stored at room temperature for more than a year and a half.

People would take the vaccine as a drug that contains the powder.

Cholera is usually spread through water or food, in places where conditions are dirty and drinking water supplies are unsafe. Cholera infections are often mild. But some people develop severe cases. The World Health Organization says half of them will die if they are not treated.

The researchers say the experimental cholera vaccine produced reactions in the immune system and in areas of mucosal tissue. Mucosal surfaces include the mouth, nose and reproductive organs. Cholera as well as viruses like those that cause influenza and AIDS infect these areas.

The scientists have great hopes for rice-based vaccines as a way to protect large populations against mucosal infections. There would be no need for injection, since the vaccine would be taken by mouth.

Yet scientists have tried for some time to make plant-based vaccines. Researchers in the United States have developed one for Newcastle disease in chickens, but so far there are no products for humans. At the same time, scientists have to deal with concerns about genetically engineered plants accidentally mixing with food crops.

And that's the VOA Special English Agriculture Report, written by Jerilyn Watson.