Cholera remains a public health problem in countries without access to safe drinking water and adequate sanitation. Researchers are trying to come up with theoretical models for cholera that allow them to understand how an outbreak happens, how it can best be contained, and how it might be prevented. Until now, the existing cholera models have not been able to describe and explain actual outbreaks very well. Taking new experimental data into account, David Hartley and colleagues (of the University of Maryland) now report a major advance in cholera modelling in the international open-access medical journal PLoS Medicine.
Caption: Scanning electron micropgaph of Vibrio cholerae. (Photo: Hartley et al.)
Transmission electron micrograph of Vibrio cholerae. (Photo: Hartley et al.)
In 2002, Andrew Camilli and colleagues reported that cholera bacteria isolated from the stools of sick patients were much more infectious than those found in contaminated water. (They compared the two by exposing mice to a mix and determining which bacteria made the mice sick.) Those researchers proposed that the infection of a human patient (i.e., the exposure to an environment that is quite different from their regular freshwater ponds) changes the cholera bacteria. As a result, for a short period of time, the bacteria become more infectious.
The study caught the attention of David Hartley and colleagues, who saw a chance to improve the modeling of cholera epidemics. Hartley was interested because Camillis results shed new light on a fundamental question in cholera epidemiology: what is the relative importance of human-to-human infection(i.e. fecal to oral) versus environment-to-human infection (through contaminated food or water)? If the infective dose of bacteria that have become hyperinfectious because of recent passage through a human host is much lower than that of bacteria from the environment, this would support a crucial role of human-to-human transmission in cholera epidemics.
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