Enteric viruses as new indicators of human and cattle fecal contamination of irrigation waters

Enteric viruses as new indicators of human and cattle fecal contamination of irrigation waters

Jan. 1, 2015 - Dec. 31, 2016

$219,879.00

Kelly R. Bright, Ph.D
University of Arizona

Marc P. Verhougstraete, Ph.D.

Final Report

The standards used by the produce industry to detect fecal contamination (by indirectly testing for indicator organisms) in irrigation waters are based on tests developed for drinking waters (rather than surface waters) and include risk threshold levels established by the Environmental Protection Agency for recreational (bathing) waters. There is little scientific evidence that this threshold is meaningful for waters used to irrigate food crops. Thus, it may not be appropriate for determining if there is a risk of contamination of crops irrigated with waters tested in this manner. We will use “next generation” sequencing to determine the identities and relative concentrations of the entire prokaryotic (bacterial) and eukaryotic (e.g., protozoan) communities in water samples to identify microbial species which are present in the samples when the presence of foodborne pathogens has been confirmed. This work will evaluate the accuracy of this threshold and hopefully result in the identification of new species or shifts in the microbial communities which are more reliable indicators of the presence of contamination of fecal irrigation waters and the presence of foodborne pathogens. This will allow the produce industry to make risk-based assessments of water quality to determine when it is safe to irrigate fields.

Technical Abstract

The use of current recreational water standards of the safety of irrigation water is considered to be an outdated and inaccurate approach. The EPA criteria were not intended to apply to risks associated with irrigation management of edible crops. The development of novel approaches to evaluate the presence or absence of fecal contamination in irrigation waters is needed to provide relevant exposure data for risk assessments for fresh produce. Without accurate exposure data, risk based analysis
cannot be conducted and future “risk relevant” standards will be difficult to implement to improve regulatory efforts for produce safety. Recent research has shown that viral targets may provide more conservative and accurate estimates of human and animal fecal contamination. Evaluations of viruses such as pepper mild mottle virus (PMMoV), Aichivirus, the enteroviruses, and human and bovine adenoviruses have shown these viruses to be highly prevalent and abundant in waste water and human and cow fecal samples. In addition, the development of low cost and low sample volume collection methods has yielded efficient and rapid approaches for detecting viruses from environmental water samples.

The proposed study has the following specific objectives: 1) to assess the occurrence of bovine polyomavirus, bovine adenovirus , human adenovirus , Aichivirus, Pepper Mild Mottle Virus, and the enteroviruses in irrigation waters of varying quality in Arizona, California, Georgia, and Wisconsin; 2) to evaluate these enteric viruses as novel indicators of fecal contamination of water via side-by-side comparisons with the presence of Salmonella and E. coli (the currently used fecal indicator) in the same water to determine if the presence of these enteric viruses can be correlated with the presence of bacterial pathogens in irrigation waters; and 3) this information will then be used to perform a quantitative microbial risk assessment to determine what levels of fecal contamination from irrigation water pose a public health risk.

With these new advances in environmental virus detection, we hope to provide a more accurate quantitative assessment of the presence of both human and cow fecal contamination associated with irrigation water for fresh or ready to eat produce. We will
attempt to quantify the level of fecal contamination to attempt to identify the level of fecal exposure. This information will then be used in improved risk based models. This work will inform future efforts with a more scientifically accurate approach to evaluating the use of irrigation water for fresh produce to better inform industry standards and to mitigate risks.