Cholera

Cholera is one of the most severe and contagious diseases transmitted by water. It is marked by severe diarrhea, resulting in fluid loss and dehydration, sometimes followed by shock and death. If not treated, mortality occurs in over 60% of cases. The Latin American cholera epidemic claimed 4,002 lives in 1991, and resulted in 391,742 reported cases that year, mostly in Peru and Ecuador. Cholera is caused by the bacillus Vibrio cholerae, a member of the family Vibrionaceae, which are described as Gram negative, non-sporulating rods that are slightly curved, motile, and have a fermentative metabolism .

The natural habitat of V. cholerae is human feces, but some studies have indicated that natural waters may also be a habitat of the organism. Fecal contamination of water is the most common means by which V. cholerae is spread, however, food, insects, soiled clothing, or person-to-person contact may also transmit sufficient numbers of the pathogen to cause cholera.

The ability of V. cholerae to survive in water is dependent upon the temperature and water type. V. cholerae reportedly survive longer at low temperatures, and in seawater, sterilized water, and nutrient rich waters. Also, the particular strain of V. cholerae affects the survival of the organism in water, since some strains or types are hardier than others. Most methods to isolate V. cholerae from water include concentration of the sample, by filtration , exposure to high pH and selective media. Identification of pathogenic strains of V. cholerae is dependent upon agglutination tests. Final confirmation of the strain or type must be done in a specialized laboratory.

Persons infected with V. cholerae produce 10⁷ to 10⁹ organisms per milliliter in the stool at the height of the disease, but the number of excreted organisms drops off quickly as the disease progresses. Asymptomatic carriers of V. cholerae excrete 10² to 10⁵ organisms per gram of feces. The mild form of the illness lasts for five to seven days. Hydration therapy is the treatment of choice for cholera. It is suggested that antibiotics not be used, following the emergence of multiple antibiotic resistant strains in many areas. Vaccines exist to prevent cholera, however, they do not prevent the acquisition of the bacteria in the gastrointestinal tract, do not diminish symptoms in persons already infected, and are effective for well less than a year. Proper water treatment should eliminate V. cholerae from drinking water, however, the most effective control of this pathogen is dependent upon good sanitary practices.

[E. K. Black and Gordon R. Finch ]

RESOURCES

BOOKS

Christie, A. B. Infectious Diseases: Epidemiology and Clinical Practice. 4th ed. Edinburgh, Scotland: Churchill Livingstone, 1987.

Feachem, R. G., et al. Sanitation and Disease: Health Aspects of Excreta and Wastewater Management. New York: Wiley, 1983.

Mitchell, R., ed. Environmental Microbiology. New York: Wiley-Liss, 1992.

PERIODICALS

Foliguet, J. M., P. Hartemann, and J. Vial. "Microbial Pathogens Transmitted by Water." Journal of Environmental Pathology, Toxicology, and Oncology 7 (1987): 39-114.