El Tor

El Tor is the name given to a particular strain of the bacterium Vibrio cholerae, the causative agent of cholera. Also known as V. cholera biotype eltor, 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 serogroup O1 and both contain Inaba, Ogawa and Hikojima serotypes. It is also distinguished from classic biotypes by the production of hemolysins.

It was first identified in 1905 at a quarantine camp on the Sinai Peninsula in El-Tor, Egypt by a German physician, E. Gotschlich. The vibrios were found in the guts of six pilgrims returning from Mecca. Though the pilgrims failed to show ante or post mortem evidence of cholera, the vibrios isolated from the guts were agglutinable within the anti-cholera serum. Later in 1905, Kraus and Pribram found that the bacteria, which produced soluble hemolysin, were more related to non-cholera vibrios; therefore, referred to all hemolytic vibrios as El Tor vibrios. In the early 1930s, A. Shousha, A. Gardner and K. Venkatraman, all researchers, suggested that only hemolytic vibrios agglutinated with anti-cholera serum should be referred to as El Tor vibrios. In 1959, R. Pollitzer designated El Tor as its own species V. eltor separate from V. cholera, but six years later, in 1965, R. Hugh discovered that V. cholerae and V. eltor were similar in 30 positive and 20 negative characteristics. Thus, they were classified as a single species V. cholera: however, Hugh believed the differing features between the two could be of epidemiological importance, so El Tor vibrios were further classified as V. cholerae biotype eltor (serogroup O1).

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. 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. The outbreaks during this time frame are believed to be due to the rapid development of transportation and communication on an international level, as well as decreased sanitation levels in areas with increasing populations. In the late 1970s there were small outbreaks in Japan and in the South Pacific.

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