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,
Members of the enteric viruses infect the gastrointestinal
tract of humans and animals, and are excreted in feces. If
the feces enter a surface water system, there is potential
for the spread of waterborne disease. Enteric viruses of
particular concern in water are hepatitis A, Norwalk-type
viruses, rotaviruses, adenoviruses, enteroviruses, and
Hepatitis A virus (HAV): HAV is readily
transmitted through water. HAV causes infectious
hepatitis, an illness characterized by inflammation
and necrosis of the liver. HAV can be removed from
drinking water through coagulation, flocculation, and
filtration (AWWA, 1990).
Norwalk-type viruses: Norwalk-type viruses
cause acute epidemic gastroenteritis. No information
is available on their occurrence in water (AWWA,
Rotaviruses: Rotaviruses cause acute
gastroenteritis, especially in children. Like HAV,
rotaviruses can be removed from drinking water
through coagulation, flocculation, and filtration
Adenoviruses: Adenoviruses can infect both the
intestine and the upper respiratory tract.
Adenoviruses have been detected in wastewater and
contaminated surface water, but not in drinking water
Enteroviruses: Enteroviruses can infect both
the intestine and the upper respiratory tract.
Enteroviruses have been detected in wastewater,
natural water, and finished drinking water. No
incidents of waterborne disease have been documented,
so the importance of this virus as a disease- causing
agent is uncertain (AWWA, 1990).
Reoviruses: Reoviruses can infect both the
intestine and the upper respiratory tract. Reoviruses
have been detected in wastewater, natural water, and
finished drinking water. No incidents of waterborne
disease have been documented, so the importance of
this virus as a disease-causing agent is uncertain
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.,
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.,
Agriculture: Viruses may be found in livestock
excrement from barnyards, pastures, rangelands,
feedlots, and uncontrolled manure storage areas; and
areas of land application of manure and sewage
Residential and Urban: Failed on-site wastewater
disposal systems can contribute viruses to a water
body. Urban runoff may convey viruses from litter and
domestic pet excreta.
Other: Viruses in ground water may originate from
landfill oxidation ponds and deep well injection of
sewage. Other surface water sources include boats
that discharge raw sewage overboard; excreta from
wild animals in surrounding watersheds; and excreta
from wildfowl that congregate on the water body.
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
Waterborne diseases may be transmitted to humans through:
Drinking water: municipal, domestic, industrial, and
Primary contact recreation: bathing, water skiing.
Secondary contact: boating, fishing.
Ingestion of shellfish.
The Big Picture Book of Viruses
to the Viruses
(APHA, 1992) Three-step process:
Collect a representative sample.
Concentrate viruses in sample. Methods include:
Adsorption to and elution from microporous
Aluminum hydroxide adsorption-precipitation.
(Involves electrostatic interactions between virus
and aluminum hydroxide.)
Polyethylene glycol (PEG)
Identify and estimate the number of viruses
present. Methods include:
Viral assay, usually employing mice or primate