El Tor

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El Tor is the name given to a particular strain of the bacterium Vibrio cholerae, the causative agent of cholera. Also known as O1, it has been the dominant strain in the seventh global pandemic. It is distinguished from the classic strain at a genetic level, although both are in the O1 serogroup and both contain Inaba, Ogawa and Hikojima serotypes. It was first identified in 1905 at a camp in El-Tor, Egypt.

El Tor was identified again in an outbreak in 1937 but the pandemic did not arise until 1961 in Sulawesi. El Tor spread through Asia (Bangladesh in 1963, India in 1964) and then into the Middle East, Africa and Europe. From North Africa it spread into Italy by 1973. In the late 1970s there were small outbreaks in Japan and in the South Pacific.

The extent of the pandemic has been due to the relative mildness (lower expression level) of El Tor, the disease has many more asymptomatic carriers than is usual, outnumbering active cases by up to 50:1. El Tor also remains in the body for longer and survives better than other known types. The actual infection is also relatively mild, or at least rarely fatal. Additionally El Tor is capable of host-to-host transmission, unlike the classic strain.