Plague transmission generally occurs in one of three ways: bites from infected fleas, direct contact with infected tissue or bodily fluids, or inhaling infected droplets. The most common method is through the bites of infected rodent fleas. Plague transmission from person to person is uncommon, but when it does occur, it usually results in dangerous epidemics that can spread quickly.
Yersinia pestis (the bacteria that cause plague) is found in animals throughout certain parts of the world, most commonly in rats, but occasionally in other wild animals, such as prairie dogs. Plague transmission from these infected animals generally occurs in one of three ways:
- Bites from infected rodent fleas
- Direct contact with infected tissue or bodily fluids
- Inhaling infected droplets.
Plague transmission to humans or animals is usually through the bites of infected rodent fleas (see Plague and Animals for other animals that can transmit plague). During rodent plague outbreaks, many animals die, and their hungry fleas seek other sources of blood to survive. People and animals that visit places where rodents have recently died from plague risk getting plague from flea bites.
This method of plague transmission accounts for about 85 percent of the human cases of plague.
Plague transmission can also occur through direct contact with infected tissue or bodily fluids. For example, people can become directly infected with plague by handling infected rodents, rabbits, or wild carnivores that prey on these animals when plague bacteria enter through the person's skin.
House cats also are susceptible to plague. Infected cats may become sick and directly transmit plague to people who handle or care for them. Also, dogs and cats may bring plague-infected fleas into the home.