Francesca Tomasi received her B.A. from the University of Chicago and is now a microbiologist.
Vibrio cholerae is a comma-shaped, gram-negative bacterium and the etiologic agent of cholera. Cholera is a serious illness that causes severe dehydration and death if untreated, due to loss of fluids through horrible diarrhea. It causes disease in humans via the cholera toxin, which is released into host target cells by ingested bacteria and causes the opening of cellular ion channels that result in a surge of watery diarrhea out of the victim. Even though the infectious dose of cholera is relatively low (several thousand bacteria need to be ingested through water, or several hundred to a thousand through food), especially in regions with poor sanitation, untreated food/water, and poor sewerage the pathogen typically remains endemic until public health measures are taken to eliminate it. Cholera is therefore able to spread to individuals from the environment through their consumption of infected food and water. It also spreads between people through fecal-oral spread, which is exacerbated in areas with poor sanitation and/or in households, where people frequently come into contact with each other’s bodily fluids. Additional interactions between V. cholerae and the environment facilitate its ability to infect people, spread, and persist in human populations. The bacterium’s natural reservoir is chitinous organisms (such as planktons) living in water. Studies have shown that the bacteria actually biochemically interact with chitin, which promotes their evolution and proliferation, ultimately helping them survive in a dynamic environment. As a result, V. cholerae are able to live in an external environment as well as within human hosts. When individuals go to a contaminated river, for instance, and ingest water (cook with it, wash their food with it, drink it, you name it), they may consume the appropriate dose to wreak havoc on their gastrointestinal system. Furthermore, the proportion of asymptomatic to symptomatic cases is quite high with cholera: about 80 or 90 percent of infected individuals who have it do not actually get sick, whereas the other 10-20 percent become incredibly ill. Regardless of symptoms or lack thereof, infected individuals shed the bacterium for months or years after the initial entry of V. cholerae into their bodies, and can therefore unknowingly spread the disease to others. Cholera is essentially eradicated in developed nations with solid infrastructure including well-designed sewerage, which prevents the leaking of potentially infected fecal remnants around the environment, and treated water. However, in places like Haiti where a terrible cholera outbreak is currently underway, the environmental persistence of V. cholerae is a recipe for disaster in a country that lacks the public health infrastructure to treat its water and further prevent illness.