What is the Difference Between Bubonic and Pneumonic Plague?

With the latest news on pneumonic plague in China that has killed three as of this writing, and a town of 10,000 people is sealed off to try to prevent the spread of the infection, I thought it would be instructive to differentiate the different forms of plague.

The term “plague” has struck fear into the hearts of people for centuries and for good reason. Historically, plague has destroyed entire civilizations. Probably the most noteworthy, the “Black Death” of the 1300s, that killed approximately one-third of Europe’s population.

Plague is an infectious disease caused by the bacterium, Yersinia pestis. It is found in animals throughout the world, most commonly rats but other rodents like ground squirrels, prairie dogs, chipmunks, rabbits and voles. Fleas typically serve as the vector of plague. Human cases have been linked to the domestic cats and dogs that brought infected fleas into the house.

People can also get infected through direct contact with an infected animal, through inhalation and in the case of pneumonic plague, person to person.

Yersinia pestis is treatable with antibiotics if started early enough.

There are three forms of human plague; bubonic, septicemic and pneumonic.

o Bubonic plague

This is the most common form. In this form the bacteria enter the body through the bite of an infected flea or rodent. Here the bacteria infect the lymphatic system. After a few days to week, the person will experience fever, chills, weakness, and swollen lymph glands. These are called buboes.

In the U.S., bubonic plague is sporadic, primarily in the West. Typically there are around 10 cases annually here. Just a couple months ago, there was at least one death and several exposures in New Mexico.

Untreated bubonic plague is fatal about half the time.

o Septicemic plague

This form is also contracted from a flea or rodent bite. Sometimes it appears subsequent to untreated bubonic or pneumonic plague. It involves bloodstream dissemination to all areas of the body. Buboes do not occur. Symptoms are endotoxic shock and disseminated intravascular coagulation. Untreated septicemic plague is nearly always fatal.

o Pneumonic plague

Probably the most serious form of plague and it’s when the bacteria infect the lungs and cause pneumonia. It is contracted when the bacteria is inhaled (primary) or develops when bubonic or septicemic plague spreads to the lungs.

Pneumonic plague is contagious and can be transmitted person to person. It is highly communicable under appropriate climate conditions, overcrowding and cool temperatures. This is the form that is of concern in China today. Untreated pneumonic plague is frequently fatal.

In the U.S., there has not been a case of person to person transmitted plague since 1924.

Due to antibiotics, improved sanitation and better living conditions, in 2007 there was just over 2000 cases of plague worldwide with approximately 150 deaths.