Yersinia pestis is a Gram-negative bacillus, or rod, form bacteria. There are three main forms relevant to human illnesses, all of which have great medical significance. One of the attributes of this bacteria that allow it to cause such illnesses is its ability to essentially move through the body without detection by the immune system. Because of this, Yersinia pestis has a very high virulence rating, or ability to cause disease in its host. One example of the bacteria’s main forms of transmission is through skin penetrating flea bites.
One of the most notorious instances of Yersinia pestis outbreak occurred in Europe in the mid 1300s. This period is widely known as the Black Plague because the infection resulted in the death of between a third and half of Europe’s entire population at the time. During this time, the bacteria were most likely spread through flea-carrying rat populations. During this time the infection had such a high mortality rate that most afflicted individuals died within a week of contracting the illness.
Another well-known illness caused by the bacteria is pneumonic plague, and although it is rarer, is significantly more virulent than the bubonic plague described above. Symptoms include fever, shortness of breath, chest pain, and even bloody saliva. Administering antibiotics generally clears up infection rather quickly; however untreated infection almost always results in death.
The third main illness caused by Yersinia pestis is called septicemic plague, an infection of the blood. This form of the plague is the most uncommon, although possibly the most devastating. Cases have been reported where individuals that contracted the disease died on the same day. Just like the previous two forms, septicemic plague is almost certainly fatal without rapid treatment. Symptoms include vomiting, fever, diarrhea, and abdominal pain, followed by rapid organ failure and death.
In more recent times, Yersinia pestis has been used in biological warfare. In World War II several Japanese planes carrying infected mice and fleas dropped their cargo over areas in China. The plague immediately broke out, ravaging the communities it infected. After the outbreak subsided, it was determined that 121 people had died as a result of the attack. In addition, this bacteria is classified as a Category A Pathogen by the CDC, meaning it has the means to be used in biological terrorist attacks against the United States, much like anthrax and tularemia. Two of its most deadly characteristics are the fact that it can persist in a rodent population for an extended period of time and can also easily be spread by airborne means.