Virus
A virus is a submicroscopic particle that contains either RNA (ribonucleic acid)or DNA (deoxyribonucleic acid). Viruses are not capable of performing metabolic functions outside of a host cell upon which the virus depends for replication. Viruses are found in the environment in a wide range of sizes, chemical composition, shape, and host cell specificity. Viruses can cause disease or genetic damage to host cells and can infect many living things, including plants, animals, bacteria, and fungi.
Bacteriophages are viruses which use bacteria as hosts. Of particular interest in the aquatic environment are coliphages, viruses that infect Escherichia coli, a bacteria that commonly grows in the colons of mammals. E. coli is an important bacterial indicator of fecal pollution of water. However, coliphages tend to survive much longer in the environment than E. coli, and their detection in water in the absence of E. coli tends to be a more sensitive indicator of former fecal contamination than coliform bacteria.
Human intestinal viruses are the most commonly encountered viruses in wastewater and water supplies since they are shed in large numbers by humans (109 viruses per gram of feces from infected individuals) and are largely unaffected by wastewater treatment before discharge to the environment. Viruses cannot replicate in the environment, but can survive for long periods of time in surface water and groundwater. Viruses are difficult to isolate from the environment and, once collected, are difficult to culture and identify because of their small size, numerous types, low concentrations in water, association with suspended particles, and the limitations in viral identification methods.
There are more than 100 types of known enteric viruses, and there are many others yet to be found. Enteric viruses include polio viruses, coxackieviruses A and B, echoviruses, and probably hepatitis A virus. Waterborne transmission of the polio virus in developed countries is rare. Of more consequence are the coxackieviruses and hepatitis A virus, with hepatitis A virus being a leading etiological agent in waterborne disease. Other viruses of concern include the gastroenteritis virus group, a poorly understood family of viruses which are probably a subset of the enteric viruses. The important members of this group include the Norwalk agent, rotaviruses, coronaviruses, caliciviruses, the W agent, and the cockle virus.
Preventing the transmission of viruses through water supplies depends upon adequate chemical disinfection of the water. Resistance of viruses to disinfectants is due largely to their biological simplicity, their tendency to clump together or aggregate, and protection afforded by association with other forms or organic material present. Proper chlorination of water is usually sufficient for inactivation of viruses. Ozone has been used for inactivation of viruses in drinking water because of its superior virucidal properties. France has been a leader in the use of ozone for inactivation of waterborne viruses.
Resources
Books
Feachem, R. G., et al. Sanitation and Disease. Health Aspects of Excreta and Wastewater Management. New York: Wiley, 1983.
Greenberg, A. E., L. S. Clesceri, and A. D. Eaton, eds. Standard Methods for the Examination of Water and Wastewater. 18th ed. Washington, DC: American Public Health Association, American Water Works Association, Water Environment Federation, 1982.
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.
This is the complete article, containing 534 words
(approx. 2 pages at 300 words per page).
