BACKGROUND: The bubonic plague is caused by Yersinia pestis, a bacterium that is spread by infected fleas that live on rodents. During plague outbreaks, infected fleas that have lost their normal hosts to death, look for other blood sources to feed on. This increases human's and other animal's risk of exposure. Today, plague epidemics still occur in developing countries, especially in rural locations. According to the Centers for Disease Control (CDC), every year 1,000 to 2,000 cases are reported throughout the world. In the United States, human cases of the plague are intermittent with an average of 13 cases reported each year. Most incidents occur in the western states. The last rat-borne epidemic in the country occurred in Los Angeles in 1925.

The main symptom of the plague is developing buboes, or enlarged lymph nodes that are often hot-to-the touch and painful. If no therapy is given to a victim, the result is often a progressive and fatal illness. As the disease advances, it leads to blood infection followed by lung infection or plague pneumonia, which more than half the time results in death. Plague victims should be isolated and cases should be reported to local and state health departments. Currently, the only way to treat the plague is with antibiotics. The preferred ones are streptomycin or gentamycin, but others are used as well.

PREVENTING THE NEXT OUTBREAK: Although not many cases of the plague exist today, creating a vaccine for it has been put on the fast track. The CDC lists the plague as one of the top-ranked bioterrorism threats, just second to anthrax. Currently, there is no vaccine commercially available to the public, but researchers at the University of Central Florida have developed one that has shown a tremendous ability to halt the illness.

Henry Daniell, Ph.D., a molecular biologist at the University of Central Florida in Orlando, Fla., and his research team, created an oral vaccine that may be available to the public in just a few years. The vaccine was studied on rats that were vaccinated at UCF and then transported to the U.S. Army Medical Research Institute of Infectious Diseases in Maryland, where they were exposed to a massive dose of the plague -- 50 billion spores. Within three days, the rats that were unvaccinated died. Twenty-five percent of those give the injectable version of the vaccine survived, but incredibly, 100 percent of the rats given the oral vaccine lived with no traces of the plague remaining. The vaccine is made by genetically engineered plant cells with a protein from Yersinia pestis. Therefore, developing immunity to the plague does not require being exposed to the bacteria itself. Dr. Daniell's lab has also developed an injectable vaccine for anthrax and oral vaccines for cholera and malaria.