Climate / environment and Vibrio diseases

Climate change and weather variability pose threats for water-borne diseases.The incidence of Vibrios species depends on the contents of salts and nutrients and on the water temperature…

Vibrios and the environment

Climate change and weather variability pose threats for water-borne diseases, some food-borne diseases, and marine and coastal issues, including harmful algal blooms and ecological disruption. It has been demonstrated that changes in precipitation, temperature, humidity, salinity, and wind have a measurable effect on the quality of water used for drinking, recreation, and commerce, while heavy rainfall has been associated with water-borne disease outbreaks throughout the world. Temperature also influences the occurrence of bacterial agents, toxic algal blooms (red tides), and survival of viral pathogens that cause shellfish poisoning.

In general, pathogenic vibrios species are normally present in low numbers when compared with the more abundant saprophytes, but their presence in a certain environment always means a risk of transmission to higher organisms including man, especially if they become concentrated by filter-feeding organisms living in the same habitat. Climate-related increases in sea surface temperature can lead to higher incidence of water-borne cholera and shellfish poisoning. The incidence of Vibrios species depends on the contents of salts and nutrients and on the water temperature. The highest incidence is thus found in those areas where the water temperature has been above 20° C for a long period. Cholera is well recognized as a “water-borne” disease, and the population dynamics of the causative agent, Vibrio cholerae, demonstrates a close linkage with selected physical, chemical, and biological parameters of natural waters. Climatic factors have also been shown to be significant in cholera epidemics: a linkage has been proposed between the most recent epidemic of cholera in Peru and the El Niño-derived climatic and environmental changes. Vibrio cholera has been found to be associated with marine zooplankton, and blooms from warmer sea surface temperatures could expand this important reservoir from which cholera epidemics may arise. Environmental factors, such as warm water and moderate salinity, can increase the number of V. parahaemolyticus and V. vulnificus organisms in shellfish.

Environmental reservoirs for V. cholerae make eradication of this disease almost impossible because the bacterium has been associated with blue crabs, shellfish, copepods, and aquatic vegetation. There is compelling evidence that V. cholerae may proliferate in copepod egg sacks, which can then be ingested in untreated drinking water. These associations mean that spread of these aquatic organisms, as in a copepod bloom, could potentially cause spread of the disease. Researchers have implicated seasonal outbreaks of cholera in Bangladesh with blooms of aquatic organisms and plankton blooms may also have accelerated spread of cholera in Peru in 1991, although direct evidence is lacking. The association of pathogens such as cholera with plankton has important implications for increased risk of disease through stimulation of plankton blooms. It has been suggested that nutrient enrichment through anthropogenic activity and even climate change (in particular, warming trends) may be important factors in the spread of waterborne disease.

Epidemiology of vibrios diseases: more recent data. _ Vibrio infections are becoming increasingly common in Europe and United States. The CDC estimates that 8028 Vibrio infections and 57 deaths occur annually in the United States. Vibrios infections were reported among bathers from several European countries in the summer of 2006, apparently related to an increase in water temperature, which is favorable to the growth of Vibrio species. Three people in the Netherlands developed infections caused by Vibrio alginolyticus in July 2006 after swimming in the Oosterschelde, a large inlet on the North Sea, at separate but nearby locations. Health authorities in the state of Mecklenburg-Vorpommern, Germany have reported three cases of wound infections with the bacterium Vibrio vulnificus so far last summer. Three people in Blekinge County in southeast Sweden were reported to have developed mild to severe wound infections caused by non-agglutinating (not O1 or O139) and non-toxin-producing Vibrio cholerae bacteria after outdoor water contact (Baltic Sea and possibly an irrigating pond); all 3 people had skin breakages, and two had other underlying diseases. Two cases of septicaemia caused by Vibrio cholerae non-O1, non-O139 were reported in different regions of Poland during one month in summer 2006.

Studying the ecology of vibrios and the environmental parameters influencing their presence in the aquatic environment.

Cholera behaves ecologically like a three-factor complex. There is growing evidence that a reservoir for this disease exists in bays and estuaries. Once an epidemic starts, transmission is by fecal-oral spread from carriers recovered from the disease and from asymptomatic, infected persons. So far, no aquatic animal reservoir has been found, although persistence in shellfish for several weeks has been demonstrated. A better understanding of the ecology would help us predict the effect of global climate change and prepare us to react.
Although environmental parameters have routinely been measured by using water samples collected aboard research ships, the available data sets are sparse and infrequent. Furthermore, shipboard data acquisition is both expensive and time-consuming. Interpolation to regional scales can also be problematic. Moreover, available data are mainly referred to V. cholerae but few have been obtained from the other pathogenic vibrios.
In some studies conducted in cholera-endemic areas in the world, satellite data were used to monitor the timing and spread of cholera. For example, public domain remote sensing data for the Bay of Bengal were compared directly with cholera case data collected in Bangladesh from 1992-1995. The remote sensing data included sea surface temperature and sea surface height. It was discovered that sea surface temperature shows an annual cycle similar to the cholera case data. Sea surface height may be an indicator of incursion of plankton-laden water inland, e.g., tidal rivers, because it was also found to be correlated with cholera outbreaks.

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