Researchers who support the ‘autochthonous V. cholerae theory’ propose that the bacteria present in endemic areas can reach most of the world through ocean currents. As per their theory, the organism are present in the coastal and estuarine environment around the world in dormant forms and are mostly attached to phytoplanktons, zooplanktons, crustaceans and other marine organisms. During favorable climatic conditions, the dormant bacteria multiply enough to constitute an infectious dose for humans resulting in an outbreak. Thus, even though there were no reports of cholera in Latin America before 1991 for nearly a century, it was suggested that the organism was already present in the aquatic environment of Peru before the outbreak. It was argued that, in 1991, due to the effect of El Nino, the surface temperature of the sea increased which helped in ‘phytoplankton blooms’ resulting in the multiplication of dormant bacteria leading to cholera outbreak. Similarly, it was argued that, the effect of La Nina, along with a decrease in water and sanitation quality following an earthquake in Haiti in January 2010, was responsible for the cholera outbreak in October 2010. Thus, these researchers claim that, it is the climatic and environmental factors that initiate the outbreak of cholera and that the cholera outbreak can be predicted by studying the macro-environmental factors using remote sensing data.
Even though the researchers claim that the bacteria were present in Peru before 1991 or in Haiti before 2010, there have been no reports on the isolation of toxigenic V. cholerae before the outbreaks. But, on the other hand, there are a few reports of isolation of non-toxigenic O1 V. cholerae (Batchelor and Wignall 1988; Levine et al. 1982) and non-O1 V. cholerae (Kay et al. 1984; Finch et al. 1987) from Peru and other regions of Latin America and also from Caribbean (Moore and Mathison 1994) before the outbreak. If non-toxigenic V. cholerae could be isolated before the outbreak, why toxigenic V. cholerae were not reported if they were already present in the environment?
On the other hand, there are a number of research articles that have reported the transport of V. cholerae to distant places with the help of human carriers. Below are a few….
1. Cholera among Belgian travelers who visited Turkey (De Schrijver et al. 2007. Travel Med Infect Dis. 5:236-8)
2. Cholera imported from Senegal to Rimini, Italy (Ciofi degli Atti et al. 2005. Euro Surveill. 10(6):E050630.6.)
3. V. cholerae non-O1, Non-O139 in Slovenia, imported from Tunisia (Strumbelj et al. 2005. Euro Surveill. 10(10):E051020.6)
4. Cholera in a traveler from Haiti to Canada (Bekal et al. 2011. Emerg Infect Dis.)
5. Cholera in U.S. through travelers to Haiti (http://www.medscape.com/viewarticle/734778)
6. Two cases of imported cholera from India in Austrian travelers (Strauss et al. 2004. Euro Surveill. 8(30)
Similarly, it has been reported that the organism can also be imported through food products
1. An outbreak of cholera in Maryland, U. S. associated with imported coconut milk from Thailand (Taylor et al. 1993. J Infect Dis. 167:1330-5)
2. Cholera in Sydney linked to imported whitebait from Indonesia (Forssman et al. 2007. Med J Aust. 187: 345-347)
3. Outbreak of cholera in New Jersey associated with the import of crab from Ecuador (Finelli et al. 1992. J Infect Dis. 166(6):1433-5)
Import of the organism to a developed nation may not result in the outbreak of cholera due to high levels of sanitation conditions and excellent health facilities. On the other hand, when the organism is imported to a region with poor levels of sanitation and hygiene, lack of clean drinking water, poor infrastructure and health facilities, the disease can spread quickly, resulting in an outbreak.
Given the fact that the organism can be carried from one place to another with ease, why El Nino, La Nina or other climatic factors should take the blame for the outbreak of cholera in Peru and Haiti? It is true that, once introduced into a geographical region, the multiplication and the spread of the disease may be facilitated by favorable climatic conditions. However, the theory that climatic factors can initiate cholera outbreaks in non-endemic areas by activating autochthonous V. cholerae remains scientifically questionable.
Next- VBNC hypothesis- the foundation on which the ‘autochthonous V. cholerae theory’ is built
Kay et al. 1984. Vibrio cholerae non-O1 isolated from five people with diarrhoea in Lima. Lancet 1: 218.
Finch et al. 1987. Non-O1 Vibrio cholerae infections in Cancun, Mexico. Am J Trop Med Hyg 36: 393–397.
Levine et al. 1982. The pathogenicity of non-enterotoxigenic Vibrio cholerae serogoroup O1 biotype El Tor isolated from sewage water in Brazil. J Infect Dis 145: 296- -299.
Batchelor RA, Wignall FS, 1988. Nontoxigenic 01 Vibrio cholerae in Peru: a report of two cases associated with diarrhea. Diagn Microbiol Infect Dis 10: 135–138.
Moore, R. and Mathison, GE. 1994. The occurrence of non-O1 V. cholerae in non-potable water samples in Barbados. West Indian Med J. 43: 7-8
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