Just what circumstances lead to the transformation of bubonic plague to the pneumonic form is uncertain. However, if victims of bubonic plague develop pulmonary abscesses, their fits of coughing will release hordes of bacteria. When inhaled, the bacteria make their way through the mucous membranes to spread and multiply in their new hosts, who are classified as victims of primary pneumonic plague. The incubation period for pneumonic plague is usually only 1-3 days and the onset of symptoms is very abrupt. Pain in the chest is accompanied by violent coughing which brings up bloody sputum.
Neurological disorders progress rapidly and incapacitate the victim.
Hemorrhages under the skin produce dark purple blotches. Coughing and choking, the patient finally suffocates and dies. As if to provide unequivocal proof that plague was not a medieval disease, bubonic plague swept across Asia in the 1890s, from Canton to Hong Kong to Bombay, killing about one million people in India in 1903, while invading Java, Japan, Asia Minor, South Africa, the shores of North and South America, Portugal, Austria, and parts of Russia. Originally called Pasteurella pestis, the plague bacillus was renamed Yersinia pestis in honor of Yersin. Although he recovered, his daughter and others in his neighborhood fell ill and died.