New Oral Vaccine May Protect Against Bubonic Plague

They report their findings in the August 2008 issue of the journal Infection and Immunity.

Transmitted by infected fleas, Yersinia pestis is the causative agent responsible for bubonic and pneumonic plague. Both highly contagious, the bubonic form of the disease is the most common in the world and can be treated; however, pneumonic plague is almost always fatal within 3 days of infection. Pneumonic plague can also be generated into aerosols and transmitted from human to human placing it at serious risk for use as weapon of bioterrorism.

Yersinia pseudotuberculosis shares a genetic identity rate of 95% with Y. pestis, but is much less virulent and rarely attributed to disease-related fatalities. In the study 41 strains of Y. pseudotuberculosis were screened for low pathogenicity. Researchers identified one strain (IP32680) which was then tested and found to persist in the mouse intestine for 2 months following intragastric and subcutaneous inoculation without any clinical signs of disease. The previously inoculated mice were then challenged intravenously with Y. pestis following which low levels of the bacteria were found in the organs and blood. Finally, IP32680 was administered orally and results showed that one dose protected 75% of mice, while two doses protected 88%.

"We report that oral inoculation with a Y. pseudotuberculosis strain, selected for its very low virulence, induces an efficient immunity against bubonic plague without causing adverse reactions," say the researchers. "This demonstrates that a live attenuated Y. pseudotuberculosis can be a promising vaccine against bubonic plague."