Remote Sensing of Cholera Outbreaks: First Year Report


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Tracking Global Epidemics: Vibrio cholerae as a Paradigm

An environmental source of cholera was hypothesized as early as the late nineteenth century by Robert Koch, but not proven because of the ability of Vibrio cholerae, the causative agent of cholera, to enter a dormant phase between epidemics. Furthermore, the association of V. cholerae with plankton was established only recently, allowing analysis of epidemic patterns of cholera, especially in those countries where it is endemic. The sporadicity and erraticity of cholera epidemics can now be related to climate and climate events, such as El Niño. Since zooplankton have been shown to harbor the bacterium and zooplankton blooms follow phytoplankton blooms, remote sensing can be employed to determine the relationship of cases of cholera with chlorophyll, as well as sea surface temperature (SST), ocean height, and turbidity. Cholera occurs seasonally in Bangladesh with two annual peaks in the number of cases occurring each year.

Data examined in this study, included CZCS data, available from 1978-1986, so these data were only retrospective. However, imagery was sparse over the Bay of Bengal and cloud cover limited data quality. Thermal channels (AVHRR) were used to derive SST. Cloud cover limited data quality, but data could be interpolated. Data from TOPEX/Poseidon yielded ocean height and sea level data derived from radar altimetry, with less of a problem from cloud cover. These data are available globally from September 1992 onward. From the data obtained and analyzed to date, we conclude that cholera cases are more numerous when the ocean is high and SST is elevated. That is, we observed that when the height of the ocean was high and sea surface temperature was also elevated, cholera cases were numerous. When the height was low and sea surface temperature also low, little or no cholera was recorded.

From examination of data for the 1992-1993 cholera epidemic in India, preliminary comparisons of cholera data for Calcutta show a similar relationship between cholera cases, ocean height, and SST. Investigation of SST, phytoplankton, and zooplankton relationship to incidence of cholera are in progress.

In conclusion, from results of studies to date, the relationship of selected climatological factors and cholera appears to be significant, bringing the potential of predicting conditions conducive to cholera outbreaks closer to reality.

Cholera Project Introduction

Last updated: Feb 2000