In pneumonic plague, transmission occurs from human to human by

Pneumonic plague is spread by droplet infection. The bacilli spread through the lungs producing hemmorhagic pneumonia. Cyanosis is very prominent. The bloody mucoid sputum that is coughed out contains bacilli in numerous numbers. Pneumonic plague is highly infectious and in untreated patients almost invariably fatal. Ref: Textbook of microbiology; Ananthanarayan and paniker's; 10th edition; Pg: 328