Final answer:
Human-to-human transmission of plague is usually through the respiratory route. It is caused by the bacterium Yersinia pestis and can be transmitted from mammal reservoirs to humans through flea vectors or consumption of infected animals. The primary mode of transmission between humans is respiratory aerosols, typically in the form of pneumonic plague.
Step-by-step explanation:
Human-to-human transmission of plague is usually through respiratory route. Plague is a zoonotic infection caused by the bacterium Yersinia pestis. It can be transmitted from mammal reservoirs to humans through flea vectors or consumption of infected animal. However, the primary mode of transmission between humans is through respiratory aerosols, mainly in the form of pneumonic plague.