Pig waste contamination is considered a major environmental concern. Improper or poor swine waste disposal can lead to excessive nutrients, organics, metals and antimicrobial residuals in water and soils. Furthermore, since swine are known to harbor human pathogens such as
Salmonella spp. and pathogenic
E. coli, proper monitoring and remediation of this form of
fecal contamination is essential for maintaining viable water systems.
Detection of swine viruses in water samples can serve as an indicator of swine contamination. Of particular concern are teschoviruses. These viruses infect the gastrointestinal tract of pigs, and are excreted in feces in detectable amounts. Although originally thought to be the causative agent of
Teshen-Talfan disease, teschoviruses are generally non-pathogenic and infections with swine largely unapparent. As such, they are endemic to swine. Additionally, teschoviruses are found worldwide and they are highly stable in water.
One of the advantages of the
Pig Fecal Virus ID™ service is that the entire water is sampled and filtered for teschoviruses. As such, this method avoids the randomness effect of culturing and selecting bacterial isolates off a petri dish. This is a particular advantage for highly contaminated water systems with potential multiple sources of
fecal contamination.
Teschoviruses 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 two 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.
To strengthen the validity of the results, the
Pig Fecal Virus ID™ service should be combined with the
Pig E. coli ID™ service. The
Pig E. coli ID™ service is designed around the principle that certain strains of
E. coli are specifically pathogenic in swine. As such, this service targets the heat stable toxin II (STII) gene from enterotoxigenic
E. coli as an indicator of swine
fecal contamination.
