For combating cholera, rice is nice

Japanese researchers say they have used a staple of their nation’s diet–rice–to develop what could become an effective, safe, and inexpensive vaccine against cholera. The new vaccine, which would be taken as a pill and does not require refrigeration, could pave the way for similar vaccines for diseases that also affect the body’s mucous tissues, such as influenza, botulism, and even anthrax. Cholera, a disease of the intestinal lining, continues to ravage populations in the developing world–even though it is easily treated with fluids and antibiotics. Caused by consuming water or food contaminated with Vibrio cholerae bacteria, the disease unleashes severe diarrhea and accompanying dehydration. Researchers at the University of Tokyo engineered two strains of domestic rice to carry the gene for CTB, one of the primary cholera proteins, to help the body develop immunity to infection. Tests with laboratory mice fed varying doses of the genetically-altered rice showed that the new vaccine, called MucoRice, immediately protected them from cholera, whereas the control group became infected, the team reports online this week in the Proceedings of the National Academy of Sciences.

The team selected rice as the vaccine vector because the grain survives digestion in the stomach, which breaks down most other foods. That allows the CTB protein to travel to the intestinal mucous, where it activates the body’s immune system, says microbiologist and team member Hiroshi Kiyono. Ground up as a powder and delivered in tablet or capsule form, the rice-based vaccine could easily be taken orally to eliminate the need for syringes–which can cause secondary infections and create disposal problems. People cannot eat the rice directly, however, Kiyono says, because they would overdose on the vaccine. “We do not have any plans to deliver the vaccine as a form of steamed rice,” he jokes. Other advantages of the vaccine are that it can be stored without refrigeration for at least a year and a half, and rice is easily grown in areas where cholera is rampant.

The research follows other efforts over the past decade to develop oral vaccines that can bypass the stomach to treat diseases attacking the intestinal lining, says plant biotechnologist Hugh Mason of Arizona State University in Tempe. He thinks using engineered rice offers promise against cholera and similar pathogens for two reasons. First, Mason says, rice is edible, so the vaccine requires little purification, and second, proteins like CTB are fairly resistant to the body’s digestive actions, whereas others are less effective in the harsh environment of the stomach.

June 26, 2007

Original web page at ScienceNow