Plague The germ that causes bubonic plague is Yersinia pestis. This one almost wiped out everyone in Europe during the Dark and Middle Ages. The natural carriers are fleas that reside on rats. When the rats get into people's homes, the infected fleas jump over to humans and cause blood and lymphatic infections. Since rat control has become a public health priority, this disease rarely occurs today. But in the hands of the new wave of twenty-first century terrorists, plague bacteria make a formidable weapon. Bioweapon scientists have been able to aerosolize this bug as well and have thereby modified it to an airborne disease. Thus they can artificially produce a pneumonic plague from bubonic plague bacteria. Once this occurs, infected people spread the disease through the air by breathing, talking, sneezing, and coughing. Therefore, one attack would be far reaching because the epidemic would take on a life of its own and literally spread with the wind.   The clinical problems arising from this disease include the following: fever cough chest pain coughing up blood cough productive of thick purulent or watery sputum fluid in the lungs (confirmed on x-ray)