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Viruses

General Information: Viruses are a group of infectious agents ranging from 10 to 25 nanometers (nm) in diameter. A virus consists primarily of a genome that replicates itself within a host cell by using its nucleic acids to direct the host cell to synthesize more viral nucleic acids and proteins. Viruses are comprised of highly organized sequences of nucleic acids, either DNA (double-stranded) or RNA (usually single-stranded), depending on the virus. All viruses have a protein covering which encloses the nucleic acid. Some viruses also have a lipid-rich lipoprotein envelope over the protein covering. The protein or lipoprotein covering determines to what surface the virus will adhere (AWWA, 1990).

Certain environmental factors may affect the viability of viruses. Viability is maintained when high levels of suspended sediment in water provides substrates to which the viruses can adsorb. Sorbed viruses may remain nearly 100% viable. Viability decreases when high water temperatures and high sunlight intensity dessicate and inactivate viruses (Kubek et al., 1990).

Numerical Categories:

Designated Use

Human Consumption: The maximum contaminant level goal (not enforced) for viruses is zero viruses per 100 ml sample of drinking water. The maximum contaminant level (MCL) is simply whatever level the best available technology can achieve (Kubek et al., 1990).

Health Effects: Members of the enteric viruses infect the gastrointestinal tract of humans and may be spread through water. Enteric viruses of particular concern in water are hepatitis A, Norwalk-type viruses, rotaviruses, adenoviruses, enteroviruses, and reoviruses. Hepatitus A virus causes hepatitus. Rotaviruses are the primary cause of childhood gastroenteritis and adult's "traveler's diarrhea." Adenoviruses may cause eye infections and respiratory disease. Entero viruses may cause paralysis, meningitis, respiratory illness, and diarrhea. (Kubek et al., 1990; AWWA, 1990).

Environmental Effects: Members of the enteric viruses infect the gastrointestinal tract of mammals (Kubek et al., 1990).

Sources:

  1. Nonpoint:
  2. Point source: Sewered communities may not have enough capacity to treat the extremely large volume of water resulting from large rainfalls. Periodically, treatment facilities may need to bypass treatment of their wastewater. In this case, water containing viruses is discharged directly into the surface water body. Estuaries may be particularly susceptible to viral contamination from offshore sewage sludge dumping and offshore sewage pipe outfalls (Kennish, 1992).

Mode of Transport: Transport in water: Virus-laden wastewater can either leach into groundwater and eventually seep into a surface water body, or rise to the ground surface and move to a water body in overland flow. Viruses in overland flow can be transported freely and within organic particles.

Additional Information:

  1. The Big Picture Book of Viruses
  2. Introduction to the Viruses
  3. Visualization of Viruses
  4. How Viruses Work

Analytical Techniques:

(APHA, 1992) Three-step process:

  1. Collect a representative sample.
  2. Concentrate viruses in sample. Methods include:
    • Adsorption to and elution from microporous filters.
    • Aluminum hydroxide adsorption-precipitation. (Involves electrostatic interactions between virus and aluminum hydroxide.)
    • Polyethylene glycol (PEG) hydroextraction-dialysis.
  3. Identify and estimate the number of viruses present. Methods include:
    • Viral assay, usually employing mice or primate host cells.