Research Article: FRNA Bacteriophages as Viral Indicators of Faecal Contamination in Mexican Tropical Aquatic Systems

Date Published: January 23, 2017

Publisher: Public Library of Science

Author(s): Luis Jose Rene Arredondo-Hernandez, Carlos Diaz-Avalos, Yolanda Lopez-Vidal, Gonzalo Castillo-Rojas, Marisa Mazari-Hiriart, Andrew C Singer.


A particular challenge to water safety in populous intertropical regions is the lack of reliable faecal indicators to detect microbiological contamination of water, while the numerical relationships of specific viral indicators remain largely unexplored. The aim of this study was to investigate the numerical relationships of FRNA-bacteriophage genotypes, adenovirus 41, and human adenoviruses (HADV) in Mexican surface water systems to assess sewage contamination. We studied the presence of HADV, HADV41 and FRNA bacteriophage genotypes in water samples and quantified by qPCR and RT-qPCR. Virus and water quality indicator variances, as analyzed by principal component analysis and partial least squared regression, followed along the major percentiles of water faecal enterococci. FRNA bacteriophages adequately deciphered viral and point source water contamination. The strongest correlation for HADV was with FRNA bacteriophage type II, in water samples higher than the 50th percentiles of faecal enterococci, thus indicating urban pollution. FRNA bacteriophage genotypes I and III virus indicator performances were assisted by their associations with electrical conductivity and faecal enterococci. In combination, our methods are useful for inferring water quality degradation caused by sewage contamination. The methods used have potential for determining source contamination in water and, specifically, the presence of enteric viruses where clean and contaminated water have mixed.

Partial Text

Waterborne enteric viruses inflict a heavy disease burden on developing countries. Enteric viruses negatively impact the quality of life for people and reduce their productivity and the number of days spent working. Enteric virus emissions to water bodies and the low infectious doses required represent a major obstacle to further mortality reductions in children younger than five years of age. The incidence of enteric viruses in children can be very high, as revealed by the presence of one viral agent in 43% of the children living in developing countries where most diarrhea attributable deaths occur, being rotavirus the most common pathogen in children, followed by norovirus in all countries [1]. Indeed, a relationship was found between the number of hepatitis cases and monsoons in India [2], thus highlighting the prominence of the waterborne route for enteric viruses. In addition, a relationship was found between the number of gastroenteritis outbreaks, and heavy rainfall and runoff events in the USA [3] and across the world [4]. Nevertheless, at least 50% of the gastroenteritis cases in the USA have an unknown causal agent [5].

Molecular tools for accurate quantification of the biological indicators of contamination with waterborne enteric viruses are urgently needed for timely alerts of water safety breaches in populated areas of tropical countries [37]. Incidental transmission of enteric viruses via recreational bathing water and contaminated drinking water poses a real threat to public health because of the large number of enteric viruses emitted, wastewater usage in agriculture, inadequate wastewater treatment, infrastructure maintenance, and operational deficiencies [38,39,40]. Consistently, urban rivers are receiving higher loads of faecal contamination [41,42], becoming part of sewer system. In wastewater, a highly variable amount of bacterial indicators has been reported [43]; as for suspended particle size, concentrations reaching as high as 108/100 mL have been reported at Mezquital Valley [44]. Differentiating non-point contamination to which enteric viruses don’t correlate at all has been a major challenge [45,46]. Incoming from animal sources, and indicator habituation to water environment may exert a different risk than CSO effluent discharge. Similarly, unpredictable heavy rainfall can also increase virus emissions into water sources, but only up to 20% of bacterial indicators are from wastewater [47]. Therefore, where practicable, corrective measures should be employed to avoid the unintentional mixing of recreational water and source water used for potable water supply with virus-contaminated sewer overflows, sewage, or effluent from wastewater treatment plants. However, ensuring that these waters remain separate requires indicator monitoring systems that overcome the specific limitations of monitoring bacteria, particularly in tropical middle-income and developing countries. Accurate and reliable identification of point and diffuse contamination in a water system requires an indicator that can provide information on the contamination point in time and space, be sensitive enough to identify trace amounts of wastewater, and be fast enough to quantify the bacterial indicator to avoid a service safety failure, thereby limiting the risk of enteric virus spread to the population to an acceptable threshold.




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