Detection of human viruses in water samples can serve as an indicator of human contamination. Of particular concern are human enteric viruses. These viruses infect the gastrointestinal tract of humans and animals, and are excreted in feces.1 More than one hundred different enteric viruses may be excreted in human fecal material and as many as 1,000,000 plaque-forming units (pfu) of enteroviruses (a subgroup of enteric viruses) per gram may be present in the feces of a sick individual.
can serve as a good indicator of human fecal and viral contamination. Enteroviruses
account for an estimated 10 to 15 million symptomatic infections in the United States each year. At present, 66 serotypes of enteroviruses
are recognized, including three poliovirus serotypes. Enteroviruses
are a major cause of gastrointestinal symptoms and they are recognized as an important factor in acute infections especially of the central nervous system, i.e., encephalitis and meningitis and in chronic infections of the cardiovascular system, i.e., myocarditis, pericarditis, and cardiomyopathy. They can also lead to post viral fatigue syndrome.
are found worldwide. Infections occur by the fecal-oral route, and in most cases, treated surface water acts as the carrier of these pathogens. Enteroviruses
are highly stable in water and are not completely eliminated by sewage treatment plants. Thus, the increasing use of treated surface water for drinking purposes harbors a potential source of pathogens, which are often not screened in a satisfactory manner.
are RNA viruses; therefore, a PCR (polymerase chain reaction) method called reverse transcriptase PCR (RT-PCR) must be used to transcribe the detected RNA back into DNA. PCR allows quantities of DNA to be amplified into large number of small copies of DNA sequences. This is accomplished with small pieces of DNA called primers that are complementary and specific to the viruses to be detected.
Through a heating process called thermal cycling, the double stranded DNA is denatured and inserted with complementary primers to create exact copies of the DNA fragment desired. This process is repeated rapidly many times ensuring an exponential progression in the number of copied DNA. If the primers are successful in finding a site on the DNA fragment that is specific to the virus or genome to be studied, then billions of copies of the DNA fragment will be available for detection by gel electrophoresis.
The gel electrophoresis apparatus uses an electrical field to distinguish different DNA fragments according to their molecular weights. Lighter DNA fragments will move farther along the gel than their heavier counterparts. At the end of the procedure different bands of accumulated DNA fragments will aggregate at different parts of the gel. It is this accumulation of DNA fragments that creates a band on the gel. Researchers use these bands to confirm and distinguish viral genomes.
Viruses cannot replicate themselves. They need a host organism to transcribe and replicate their genetic code. Viruses come in 2 genetic forms, either RNA or DNA based. Their genetic material is protected with a protein coat. Detection of virus RNA or DNA strongly indicates the presence of intact, encapsulated viruses, as free RNA or DNA quickly degrades in the environment.
It is not known whether detected enteroviruses
by RT-PCR are in an infectious stage. Nonetheless, it has been shown that infections with enteroviruses
can occur with as few as 1 virus particle. Therefore positive findings by RT-PCR could suggest a serious health risk. A cultivable enterovirus
detection test should nonetheless be done to provide conclusive evidence of infectivity of the enteroviruses
in the water source.
Human viral contamination is potentially the most serious health concern effecting water systems, yet it is also the least monitored. Enteric viruses
that are spread through water such as Norwalk-type viruses, rotaviruses, enteroviruses, reoviruses
, Hepatitis A viruses and adenoviruses are of a particular concern. Furthermore, certain viruses have been known to survive for months, and even years in water systems. Viability is maintained when high levels of suspended sediment in water provide substrates to which viruses can absorb. Sorbed viruses may remain nearly 100% viable for extended periods of time.
For the time being, no proven methods have been demonstrated that remove viable viruses entirely from water systems. Consequently, proper monitoring of viruses can at least prevent additional illnesses and possible deaths of immunocompromised individuals, such as HIV/AIDS or cancer patients. Should potentially hazardous viruses be confirmed in specific water systems, then more rigorous remediation steps can be undertaken to remove, or at least diminish the viral loads.
To strengthen the validity of the results, the Human Fecal Virus ID™
service should be combined with other DNA analytical services such as the Human Bacteroidetes ID™
and Human Enterococcus ID™
services. Negative results should be analyzed further for the presence of other human enteric viruses such as adenoviruses, rotaviruses, Norwalk viruses, reoviruses and Hepatitis A viruses