The circumstances under which water becomes contaminated are as varied as the ways water is taken internally. It is then conceivable that almost any virus could be transmitted through the water route. The increased use of water for recreational purposes increases the incidence of human contact with bodies of water and, consequently, with waterborne viruses and bacteria. The major waterborne viruses among pathogens, and the most likely candidates for water transmission, are the picornaviruses (from pico, meaning very small, and RNA, referring to the presence of nucleic acid). The characteristics of picornaviruses are shown in Table 1. Among the picornaviruses are the enteroviruses (polioviruses, coxsackieviruses, and echoviruses) and the rhinoviruses of human origin. Also included are enteroviruses from excrements of cattle, swine, and other domesticated animals; and rhinoviruses of nonhuman origin, viruses of foot and mouth disease, teschen disease, encephalomyocarditis, mouse encephalomyelitis, avian encephalomyelitis, and vesicular exantherm. of pigs. Additionally, certain viruses can be transported by the water route because their vectors, water molds, and nematodes live in the soil and move with the movement of water. Plant pathogenic viruses also enter the water route and contribute to the problem, though this area has been given little attention in the past. Viruses associated with industrial abattoirs, meat packing, food processing, pharmaceutical, and chemical operations are also a potential problem. All enteric viruses occur in sewage in considerable numbers, and recent detection techniques make it possible to find these viruses in almost all streams that receive sewage effluents. Enteric viruses have been isolated from surface waters around the world. Samples collected from tidal rivers in the United States contained viruses in 27 percent to 52 percent of the cases. The contamination of surface water by enteric viruses appears to be ubiquitous.
Table 1. Picornavirus Characteristics (Very Small RNA Viruses)
1. Small spheres about 20-30 It in diameter
2. RNA core, icosahedral form of cubic symmetry
3. Resistant to ether, chloroform, and bile salts, indicating lack of essential lipids
4. Heat stabilized in presence of divalent cations (Molar MgC12)
5. Enteroviruses separated from rhinoviruses by acid lability of the latter viruses (inactivated at pH 3.0-5.0)_
WHY THEY SURVIVE
A variety of factors is responsible for the survival of viruses in water bodies. Some of the more significant ones are listed for you in Figure 1. The survival of enteric viruses under laboratory conditions and in estuaries varies from a few hours to up to 200 days. Survival in winter is superior to that at summer temperatures. It is not known exactly what happens to these multitudes of viruses introduced in water bodies. The inability of rhinoviruses to withstand pH changes, temperature fluctuations, and the lack of protective covering
Sea or estuary water River water Tap water Soil
Landfill leachates Sediments
2-130 days 2->188 days
5-168 days 25-175 days
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