Vibrio is a genus of ubiquitous bacteria found in a wide variety of aquatic and marine habitats; of the >100 described Vibrio spp., ~12 cause infections in humans. Vibrio cholerae can cause cholera, a severe diarrhoeal disease that can be quickly fatal if untreated and is typically transmitted via contaminated water and person-to-person contact. Non-cholera Vibrio spp. (for example, Vibrio parahaemolyticus, Vibrio alginolyticus and Vibrio vulnificus) cause vibriosis - infections normally acquired through exposure to sea water or through consumption of raw or undercooked contaminated seafood. Non-cholera bacteria can lead to several clinical manifestations, most commonly mild, self-limiting gastroenteritis, with the exception of V. vulnificus, an opportunistic pathogen with a high mortality that causes wound infections that can rapidly lead to septicaemia. Treatment for Vibrio spp. infection largely depends on the causative pathogen: for example, rehydration therapy for V. cholerae infection and debridement of infected tissues for V. vulnificus-associated wound infections, with antibiotic therapy for severe cholera and systemic infections. Although cholera is preventable and effective oral cholera vaccines are available, outbreaks can be triggered by natural or man-made events that contaminate drinking water or compromise access to safe water and sanitation. The incidence of vibriosis is rising, perhaps owing in part to the spread of Vibrio spp. favoured by climate change and rising sea water temperature.

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Cholera has historically occurred in periodic epidemics, with the most severe epidemics limited to a few countries, namely Bangladesh, India, and countries in Africa and South America. During the past three decades, however, this disease has occurred in geographical areas from which it had seemingly disappeared almost a century ago (35). Including these new appearances, epidemics have been reported in over 75 countries in South America, Africa, and Asia during the past decade (38). In addition, each year sporadic cases are reported in other countries around the world (38).Interestingly, cholera is one of the few bacterial diseases known for its pandemicity, and until 1992, all epidemics of cholera were caused by Vibrio cholerae serogroup O1. In the latter part of 1992, a newly recognized O139 serogroup was isolated in areas surrounding the Bay of Bengal and was linked to major epidemics, first in Madras on the eastern coast of India and then in the southern part of Bangladesh. Later it was detected in neighboring countries and has continued to persist in that geographic region (6, 28).In 1992 in Bangladesh during a 12-week period, there were approximately 220,000 cases of cholera caused by serotype O139, with over 8,000 deaths, more deaths than in all of Latin America that same year (31,35). Cholera is known to be a disease with a high mortality (Ϸ60% if untreated); with adequate treatment (intravenous and oral rehydration therapy, supplemented with appropriate antibiotics) the mortality drops to Ͻ1.0% (5, 26). The large numbers of deaths indicate that adequate therapy was not available to the many persons who died (6,35).In the recent history of cholera, most major epidemics originated in coastal regions, including both the South American epidemic that began in the coastal regions of Peru, spreading to 21 countries, including Mexico, and the new O139 outbreak in India and Bangladesh. In Dhaka City and a rural area of Bangladesh, Matlab, cholera occurs year-round, with a distinct pattern of two peaks of disease, one in the spring and the other in the fall (16,30).The presence of V. cholerae O1 year-round via its commensal association with plankton was established by Colwell and coworkers using direct detection methods (17). It is still not certain what triggers the continuing seasonal epidemics of cholera in Bangladesh and what determines the persistence and multiplication of V. cholerae O1 and O139 in the choleraendemic regions of the world. However, coexistence of V. cholerae O1 and O139 serogroups in association with plankton has

Toxigenic Vibrio cholerae, rarely isolated from the aquatic environment between cholera epidemics, can be detected in what is now understood to be a dormant stage, i.e., viable but nonculturable when standard bacteriological methods are used. In the research reported here, biofilms have proved to be a source of culturable V. cholerae, even in nonepidemic periods. Biweekly environmental surveillance for V. cholerae was carried out in Mathbaria, an area of cholera endemicity adjacent to the Bay of Bengal, with the focus on V. cholerae O1 and O139 Bengal. A total of 297 samples of water, phytoplankton, and zooplankton were collected between March and December 2004, yielding eight V. cholerae O1 and four O139 Bengal isolates. A combination of culture methods, multiplex-PCR, and direct fluorescent antibody (DFA) counting revealed the Mathbaria aquatic environment to be a reservoir for V. cholerae O1 and O139 Bengal. DFA results showed significant clumping of the bacteria during the interepidemic period for cholera, and the fluorescent micrographs revealed large numbers of V. cholerae O1 in thin films of exopolysaccharides (biofilm). A similar clumping of V. cholerae O1 was also observed in samples collected from Matlab, Bangladesh, where cholera also is endemic. Thus, the results of the study provided in situ evidence for V. cholerae O1 and O139 in the aquatic environment, predominantly as viable but nonculturable cells and culturable cells in biofilm consortia. The biofilm community is concluded to be an additional reservoir of cholera bacteria in the aquatic environment between seasonal epidemics of cholera in Bangladesh.Toxigenic Vibrio cholerae O1 and O139 are causative agents of cholera (38), an acute dehydrating diarrhea, which occurs in epidemic (13, 31) and pandemic (23) forms. Since the first pandemic was recorded in 1817, as many as seven cholera pandemics have occurred (35). The most recent, the seventh pandemic, began in Indonesia (14), but cholera pandemics have usually begun in the Gangetic delta of the Indian subcontinent and then in other continents (10,40). Of the 206 O serogroups of V. cholerae, serovar O1 was the only recognized cause of cholera until late 1992. At that time an outbreak of acute watery diarrhea clinically resembling cholera erupted in India and southern Bangladesh (1, 10). The bacterium causing cholera-like diarrhea failed to agglutinate with any of the then existing 138 V. cholerae O antisera (1) and was thus designated O139 with the synonym "Bengal" to commemorate its emergence in the coast of the Bay of Bengal. Since then, O1 and O139 remain the two recognized serogroups causing epidemics of cholera.Epidemiological studies of V. cholerae O139, including its emergence, prevalence, and coexistence with O1 El Tor V. cholerae, have been conducted primarily in Bangladesh and India via systematic surveillance (19). In the Ganges delta region, cholera outbreaks occur seasonally (13,14), but variations in prevalence of the two epidemic serogroups O1 and O139 of V. cholerae are distinct ...

How Vibrio cholerae spreads around the world and what determines its seasonal peaks in endemic areas are not known. These features of cholera have been hypothesized to be primarily the result of environmental factors associated with aquatic habitats that can now be identified. Since 1997, fortnightly surveillance in 4 widely separated geographic locations in Bangladesh has been performed to identify patients with cholera and to collect environmental data. A total of 5670 patients (53% <5 years of age) have been studied; 14.3% had cholera (10.4% due to V. cholerae O1 El Tor, 3.8% due to O139). Both serogroups were found in all locations; outbreaks were seasonal and often occurred simultaneously. Water-use patterns showed that bathing and washing clothes in tube-well water was significantly protective in two of the sites. These data will be correlated with environmental factors, to develop a model for prediction of cholera outbreaks.