Cases Per Year: 3,000 to 5,000
Fatality Rate: 20% to 60%
First Discovered: the plague first appeared in ancient China and Medieval Europe; Alexandre Yersin isolated the bacteria causing it in 1894 in Hong Kong
Plague has been responsible for widespread pandemics throughout history, including the Black Death that caused 50 million deaths in Europe during the 14th century. Now, it can be easily treated with antibiotics.
The bacteria causing plague is usually found in small mammals and their fleas. Humans can be contaminated by the bite of infected fleas, through direct contact with infected materials, or by inhalation. Plague is found on all continents except Oceania, but most human cases since the 1990s have occurred in Africa and Peru.
The incubation period lasts 1 to 7 days. Symptoms include fever, chills, head and body aches, weakness, nausea, and vomiting. Bubonic plague is the more common form of plague. It is an infection caused by circulating bacteria in the bloodstream and affects the lymphatic system, inflaming lymph nodes and turning them into open sores filled with pus. Bubonic plague can advance and spread into the lungs, causing the pneumonic plague. Pneumonic plague is the most virulent and severe type of the plague. If pneumonic plague is not treated early, it can be fatal, but recovery rates are high if treated within 24 hours of developing symptoms.
Photo: Yersinia pestis – Electron micrograph.