Plague is caused by the bacteria Yersinia pestis. Rodents such as rats carry the disease. It is spread by their fleas.
People can get plague when they are bitten by a flea that carries the plague bacteria from an infected rodent. In rare cases, people get the disease when handling an infected animal.
Plague lung infection is called pneumonic plague. It can be spread from person to person. When someone with pneumonic plague coughs, tiny droplets carrying the bacteria move through the air. Anyone who breathes in these particles may catch the disease. An epidemic can be started this way.
In the Middle Ages in Europe, massive plague epidemics killed millions of people. Plague has not been eliminated. It can still be found in Africa, Asia, and South America.
Today, plague is rare in the United States. But it has been known to occur in parts of California, Arizona, Colorado, and New Mexico.
The three most common forms of plague are:
- Bubonic plague, an infection of the lymph nodes
- Pneumonic plague, an infection of the lungs
- Septicemic plague, an infection of the blood
The time between being infected and developing symptoms is typically 2 to 8 days. But the time can be as short as 1 day for pneumonic plague.
Risk factors for plague include a recent flea bite and exposure to rodents, especially rabbits, squirrels, or prairie dogs, or scratches or bites from infected domestic cats.