Type 1 – Bubonic Plague
The most common form. This disease is characterised by an extremely high fever, chills, and ultimately delirium and death. The bacilli collect in the lymph nodes, particularly those in the armpits and groin. The nodes swell and become extremely painful. These swellings are called buboes, hence the name bubonic plague. Death from bubonic plague usually comes within a week.
Type 2 – Septicemic Plague
When an individual suffers an overwhelming invasion of plague bacilli, the germs may go directly into the bloodstream. Such an infection is known as septicemic plague. This form of plague kills more quickly, commonly within three days. There are even stories of a person going to bed healthy and being dead of plague the following morning. The victim may die before the swellings and other characteristic signs of plague appear. In some cases purplish or blackish spots appear on the victim’s skin. This symptom may account for the name Black Plague often used to describe the disease.
Type 3 – Pneumonic Plague
In this case the bacilli invade the lungs, which are called pneumons in Greek. Pneumonic plague can appear as a complication of bubonic plague, just as pneumonia can sometimes be a complication of influenza or even a common cold. Pneumonic plague can also be the original infection. Death from this form of plague comes with a few days.
Not everyone who contracted the plague died, but the chances of recovery in the fourteenth century was slight. Sometimes the buboes would burst and drain, and then the victim may have recovered. Medical authorities estimate that ninety percent of untreated cases of plague resulted in death. With modern medical treatment, particularly antibiotics, the mortality rate can be reduced to five percent.
Usually in a plague epidemic, all three different forms of the infection are present.
Bubonic plague is spread by the bite of a flea that has previously bitten an infected rat. In this form of plague, there are not enough plague bacilli in the bloodstream of a human victim to cause infection in another human being.
In the septicemic form of plague, however, there is a high concentration of bacilli in the bloodstream. Some medical authorities believe that in this form the disease may be carried from one human victim to another by Pulex irritans, a flea that uses man as its primary host. Human fleas were common pests in medieval Europe.
Plague bacilli can also enter the bloodstream of a person who handles an infected rat or human through a break in the skin. This method of infection, however, is rare.
Pneumonic plague is the only form of plague which can be spread easily from one human being to another. During the disease the victim commonly coughs up blood and mucus. The tiny droplets of mucus coughed or sneezed into the air contain plague bacilli. These bacilli are breathed in by others. Once in the lungs of a new victim, the bacilli multiply and produce another case of pneumonic plague.