Pneumonic plague, a severe type of lung infection, is one of three main forms of plague, all of which are caused by the bacterium Yersinia pestis. It is more virulent and rarer than bubonic plague. The difference between the versions of plague is simply the location of the infection in the body; the bubonic plague is an infection of the lymphatic system, the pneumonic plague is an infection of the respiratory system, and the septicemic plague is an infection in the blood stream.
Typically, pneumonic form is due to a secondary spread from advanced infection of an initial bubonic form. Primary pneumonic plague results from inhalation of fine infective droplets and can be transmitted from human to human without involvement of fleas or animals. Untreated pneumonic plague has a very high fatality rate.
Since 2002, the World Health Organization (WHO) has reported six plague outbreaks, though some may go unreported because they often happen in remote areas. Between 1998 and 2009, nearly 24,000 cases have been reported, including about 2,000 deaths, in Africa, Asia, the Americas and Eastern Europe. The vast majority of the world's cases (98%) are in Africa.
Pathology and transmission
Pneumonic plague can be caused in two ways: primary, which results from the inhalation of aerosolised plague bacteria, or secondary, when septicemic plague spreads into lung tissue from the bloodstream. Pneumonic plague is not exclusively vector-borne like bubonic plague; instead it can be spread from person to person. There have been cases of pneumonic plague resulting from the dissection or handling of contaminated animal tissue. This is one type of the formerly known Black Death. It could kill 90%–95% of a population if the victims coughed and passed on the bacteria.
The most apparent symptom of pneumonic plague is coughing, often with hemoptysis (coughing up blood). With pneumonic plague, the first signs of illness are fever, headache, weakness, and rapidly developing pneumonia with shortness of breath, chest pain, cough, and sometimes bloody or watery sputum. The pneumonia progresses for two to four days and may cause respiratory failure and shock. Without early treatment, patients will die, some within 24 hours.
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