Bubonic plague may be next threat

In the mid-fourteenth century, the bubonic plague tore through Asia, India and Europe, killing a quarter of the world's population.

"I just kind of look back on history and things happen and you just kind of move on from it. I don't want to live my life worrying about it all the time," said mother, Andrea Reyes.

But the plague may not be history. The Centers for Disease Control lists the bubonic plague as one of the top bioterrorism threats.

"We could take out all the bioterrorism weapons one by one by immunizing the population," said molecular biologist, Henry Daniell, Ph.D.

Henry Daniell created a vaccine by injecting genes from Yersinia pestis -- the bacterium that causes the bubonic plague -- into plant cells, which are then put into capsules. The hope -- the body will develop immunity to the plague.

"So this is a very sophisticated way of delivering a vaccine, where you could never get the disease," said Daniell.

The vaccine was tested in rats exposed to 50 billion spores of the plague -- an enormous amount Daniell says humans would never face.

Within three days, all of the unvaccinated rats and three-quarters of those given the injectable vaccine died. But every rat given the oral vaccine survived -- with no traces of the plague left in their bodies.

Because it doesn't require an injection, the vaccine could be easily distributed to the public.

"Plague epidemics can happen anytime," said Daniell.

But now, researchers hope they can keep history from repeating.

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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.

In the event of a bioterror attack, the oral form of the vaccine is much more practical than the injected version, because no special skills or sterile equipment are needed.

Dr. Daniell expects the capsules for the plague vaccine will be available in a few years.


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.

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