How the bubonic plague spread?

The bubonic plague, caused by the bacterium *Yersinia pestis*, is spread primarily by fleas that have fed on infected rodents. The typical transmission scenario is as follows:

1. Transmission from Rodents to Fleas: Rats and other rodents serve as natural reservoirs for *Yersinia pestis*. When fleas feed on an infected rodent, they ingest the bacteria along with the blood meal.

2. Transmission from Fleas to Humans: After feeding on an infected rodent, the fleas become infected themselves. When they subsequently feed on a human host, they can transmit the bacteria through their bites.

3. Human-to-Fleas Transmission: Infected humans may develop buboes, which are swollen lymph nodes. Fleas that feed on these buboes can acquire the bacteria and transmit it to other people they feed on.

4. Transmission through Respiratory Droplets: In some cases, particularly in the pneumonic form of the plague, transmission can occur through respiratory droplets. This occurs when an infected person coughs or sneezes, releasing respiratory droplets containing *Yersinia pestis* into the air, which can be inhaled by others.

5. Direct Contact with Infected Fluids or Tissues: Transmission can also occur through direct contact with infected bodily fluids or tissues, such as through bites or scratches from infected animals or handling contaminated carcasses.

The bubonic plague spreads primarily through the bite of infected fleas, but other modes of transmission can also occur. Once established within a human population, the disease can rapidly spread due to the efficient transmission by flea vectors and the high mortality rate associated with untreated plague infections.