‘Ocean current hypothesis’ and Vasco da Gamas of the microbial world

At the end of the 15^th century, Vasco da Gama, the Portugese explorer, led an expedition that opened a sea route from Europe to India via the Cape of Good Hope at the southern tip of Africa. Not only humans, but, bacteria such as Vibrio cholerae, the causative organism of cholera, are also good explorers (as per some published research findings)

The seventh pandemic cholera that originated in Indonesia in 1961 reached Peru in 1991 and later spread to many countries of Latin America. Since Latin America was free of cholera for nearly a century, there were many speculations on how the organism might have reached Peru. One of the speculations was that the ocean currents carried toxigenic V. cholerae from endemic areas to Peruvian coasts.

Munro and Colwell (1996), Colwell (1996) and Mourino-Perez (1998) suggest that V. cholerae can remain in seawater for a relatively long time, i.e. sufficiently long to be carried by ocean currents to widely distant geographical locations. So, if the hypothesis is correct and if the source of origin of cholera in Peru is Indonesia or other South-east Asian countries, the organism should have crossed the entire Pacific to reach Peru, after travelling thousands of miles. However, later findings suggested a possible origin in Africa (Lam et al. 2010). Even if this is the case, it can still be argued that there are two routes for the organism to reach Peru via sea. One to cross both the Indian and Pacific Ocean to reach Peru and the second to cross the Atlantic, reach the Southern cone and then move north to reach Peru.

In any case, Vasco da Gama will be envious of the organism!!

Next, I will discuss the article by Munro and Colwell (1996) that have ‘demonstrated’ the long distant carriage of the organism.

Munro, P. M. and Colwell, R. R. (1996). Fate of Vibrio cholerae O1 in seawater microcosms. Wat. Res. 30(1): 47-50

Colwell, R. R. (1996). Global climate and infectious disease: The cholera paradigm. Science 274 (5295): 2025-2031

Mourino-Perez, R. R. (1998). Oceanography and the seventh cholera pandemic. Epidemiology 9(3): 355-357