Third Pandemic
Third Pandemic is the designation of a major plague pandemic that began in the Yunan province in China in 1855.  This episode of bubonic plague spread to all inhabited continents, and ultimately killed more than 12 million people in India and China alone.  According to the World Health Organization, the pandemic was considered active until 1959, when worldwide casualties dropped to 200 per year.
Bubonic plague is an infectious disease that is widely thought to have caused several epidemics or pandemics throughout history; including two previous pandemics commonly designated as the Plague of Justinian and the Black Death.  However, the cause of these outbreaks is now questioned by some biological scientists.
Casualty patterns indicate that waves of this late 19th century/early 20th century pandemic may have been from two different sources.  The first was primarily bubonic and was carried around the world through ocean-going trade, through transporting infected persons, rats and cargoes harboring fleas.  The second, more virulent strain, was primarily pneumonic in character with a strong person to person contagion.  This strain was largely confined to Asia, particularly Manchuria and Mongolia.

# Pattern of the pandemic
The bubonic plague was endemic in populations of infected ground rodents in central Asia, and was a known cause of death among migrant and established human populations in that region for centuries; however, an influx of new people due to political conflicts and global trade led to the distribution of this disease throughout the world.
The initial outbreak was in China's Yunnan Province in the 1850s.  The disease was stable within the province, but was spread due to a Muslim rebellion which resulted in population disruption.  Refugees from the conflict moved south, into regions of China with larger populations.  The plague went with them, producing an increasing number of casualties.  In the city of Canton, beginning in March 1894, the disease killed 60,000 people in just a few weeks.  Daily water traffic with the near by city of Hong Kong rapidly spread the plague.  Within two months, after 100,000 deaths, the death rates dropped below epidemic rates, although the disease continued to be endemic in Hong Kong until 1929.
The network of global shipping ensured the widespread distribution of the disease over the next few decades.  Recorded outbreaks include:
- Pakhoi, China  1882.
- Canton, China  1894.
- Hong Kong, China  1894.
- Formosa (Taiwan), China  1896.
- Bombay, India  1896-1898.
- Calcutta, India  1898.
- Madagascar, 1898.
- Egypt, 1899.
- Manchuria, China  1899.
- Paraguay, 1899.
- South Africa, 1899-1902.
- Hawaii, United States, 1899.
- San Francisco, United States, 1900.
- Australia, 1900-1905.
- Russia/Soviet Union, 1900-1927.
- Fukien Province, China  1901.
- Thailand, 1904.
- Burma, 1905.
- Tunisia, 1907.
- Trinidad, Venezuela, Peru and Ecuador, 1908.
- Bolivia and Brazil, 1908.
- Cuba and Puerto Rico, 1912.
Each of these areas, as well as Great Britain, France and other areas of Europe, continued to experience plague outbreaks and casualties until the 1950s.  The last significant outbreak of plague associated with the pandemic occurred in Peru and Argentina in 1945.

# Disease research
Researchers working in Asia during the "Third Pandemic" identified plague vectors and the plague bacillus.  In the 1890s, French researcher Paul-Louis Simond postulated a connection between human and rodent plague and identified the flea as a possible vector.  In 1894, in Hong Kong, bacteriologist Alexandre Yersin isolated the responsible bacterium (Yersinia pestis) and determined the common mode of transmission.  A short time later, Japanese physician and researcher Shibasaburo Kitasato independently identified the plague bacillus (after mis-identifying the bacterium at an earlier point).
The disease is caused by a bacterium usually transmitted by the bite of fleas from an infected host, often a black rat. The bacteria are transferred from the blood of infected rats to the rat flea (Xenopsylla cheopsis). The bacillus multiplies in the stomach of the flea, blocking it. When the flea next bites a mammal, the consumed blood is regurgitated along with the bacillus into the bloodstream of the bitten animal. Any serious outbreak of plague is started by other disease outbreaks in the rodent population. During these outbreaks, infected fleas that have lost their normal hosts seek other sources of blood.  The bacterium which causes this disease, Yersinia pestis, was named for Yersin.  His discoveries led in time to modern treatment methods, including insecticides, the use of antibiotics and eventually plague vaccines.