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Comparative study of enteric viruses, coliphages and indicator bacteria for evaluating water quality in a tropical high-altitude system

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      Abstract

      BackgroundBacteria used as indicators for pathogenic microorganisms in water are not considered adequate as enteric virus indicators. Surface water from a tropical high-altitude system located in Mexico City that receives rainwater, treated and non-treated wastewater used for irrigation, and groundwater used for drinking, was studied.MethodsThe presence of enterovirus, rotavirus, astrovirus, coliphage, coliform bacteria, and enterococci was determined during annual cycles in 2001 and 2002. Enteric viruses in concentrated water samples were detected by reverse transcriptase-polymerase chain reaction (RT-PCR). Coliphages were detected using the double agar layer method. Bacteria analyses of the water samples were carried out by membrane filtration.ResultsThe presence of viruses and bacteria in the water used for irrigation showed no relationship between current bacterial indicator detection and viral presence. Coliphages showed strong association with indicator bacteria and enterovirus, but weak association with other enteric viruses. Enterovirus and rotavirus showed significant seasonal differences in water used for irrigation, although this was not clear for astrovirus.ConclusionColiphages proved to be adequate faecal pollution indicators for the irrigation water studied. Viral presence in this tropical high-altitude system showed a similar trend to data previously reported for temperate zones.

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      Most cited references 34

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      Rotavirus and Severe Childhood Diarrhea

      Studies published between 1986 and 1999 indicated that rotavirus causes ≈22% (range 17%–28%) of childhood diarrhea hospitalizations. From 2000 to 2004, this proportion increased to 39% (range 29%–45%). Application of this proportion to the recent World Health Organization estimates of diarrhea-related childhood deaths gave an estimated 611,000 (range 454,000–705,000) rotavirus-related deaths.
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        Inactivation credit of UV radiation for viruses, bacteria and protozoan (oo)cysts in water: a review.

        UV disinfection technology is of growing interest in the water industry since it was demonstrated that UV radiation is very effective against (oo)cysts of Cryptosporidium and Giardia, two pathogenic micro-organisms of major importance for the safety of drinking water. Quantitative Microbial Risk Assessment, the new concept for microbial safety of drinking water and wastewater, requires quantitative data of the inactivation or removal of pathogenic micro-organisms by water treatment processes. The objective of this study was to review the literature on UV disinfection and extract quantitative information about the relation between the inactivation of micro-organisms and the applied UV fluence. The quality of the available studies was evaluated and only high-quality studies were incorporated in the analysis of the inactivation kinetics. The results show that UV is effective against all waterborne pathogens. The inactivation of micro-organisms by UV could be described with first-order kinetics using fluence-inactivation data from laboratory studies in collimated beam tests. No inactivation at low fluences (offset) and/or no further increase of inactivation at higher fluences (tailing) was observed for some micro-organisms. Where observed, these were included in the description of the inactivation kinetics, even though the cause of tailing is still a matter of debate. The parameters that were used to describe inactivation are the inactivation rate constant k (cm(2)/mJ), the maximum inactivation demonstrated and (only for bacterial spores and Acanthamoeba) the offset value. These parameters were the basis for the calculation of the microbial inactivation credit (MIC="log-credits") that can be assigned to a certain UV fluence. The most UV-resistant organisms are viruses, specifically Adenoviruses, and bacterial spores. The protozoon Acanthamoeba is also highly UV resistant. Bacteria and (oo)cysts of Cryptosporidium and Giardia are more susceptible with a fluence requirement of <20 mJ/cm(2) for an MIC of 3 log. Several studies have reported an increased UV resistance of environmental bacteria and bacterial spores, compared to lab-grown strains. This means that higher UV fluences are required to obtain the same level of inactivation. Hence, for bacteria and spores, a correction factor of 2 and 4 was included in the MIC calculation, respectively, whereas some wastewater studies suggest that a correction of a factor of 7 is needed under these conditions. For phages and viruses this phenomenon appears to be of little significance and for protozoan (oo)cysts this aspect needs further investigation. Correction of the required fluence for DNA repair is considered unnecessary under the conditions of drinking water practice (no photo-repair, dark repair insignificant, esp. at higher (60 mJ/cm(2)) fluences) and probably also wastewater practice (photo-repair limited by light absorption). To enable accurate assessment of the effective fluence in continuous flow UV systems in water treatment practice, biodosimetry is still essential, although the use of computational fluid dynamics (CFD) improves the description of reactor hydraulics and fluence distribution. For UV systems that are primarily dedicated to inactivate the more sensitive pathogens (Cryptosporidium, Giardia, pathogenic bacteria), additional model organisms are needed to serve as biodosimeter.
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          Typing of human astroviruses from clinical isolates by enzyme immunoassay and nucleotide sequencing.

          A typing enzyme immunoassay (TYPE-EIA) was used to determine the antigenic types of 64 astrovirus-positive specimens from nine collections from seven countries. Six of the seven known astrovirus types were detected in the collections, with HAstV-1 predominating in all collections for one from the United Kingdom. Selected specimens were analyzed further by reverse transcriptase PCR and nucleotide sequencing of 348 bp within the capsid protein precursor region of the genome. The phylogenetic groupings (genotypes) determined from the sequences were entirely consistent with the antigenic groupings (serotypes) of isolates obtained by using the TYPE-EIA. The genetic variation within genotypes was small compared with the variation between genotypes, allowing unambiguous categorization of all specimens. Although some strains from widely separated geographic areas had identical sequences, in general, within a region most strains of the same type were identical. The TYPE-EIA may help further our understanding of the epidemiology of astrovirus and the possible role of serotype-specific immunity, while further knowledge of sequences could facilitate the development of simpler molecular methods of typing astrovirus strains.
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            Author and article information

            Affiliations
            [1 ]Instituto de Ecología, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Coyoacán, 04510 México, DF, México
            [2 ]Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av Universidad 2001, Col Chamilpa, 62210 Cuernavaca, Morelos, México
            [3 ]Consultoría Ambiental y Estadística, Cerrada de Cortés 43, Colonia Campestre Tlacopac, San Ángel, 01049 México, DF, México
            Contributors
            Journal
            Environ Health
            Environmental Health
            BioMed Central
            1476-069X
            2009
            27 October 2009
            : 8
            : 49
            2777857
            1476-069X-8-49
            19860917
            10.1186/1476-069X-8-49
            Copyright ©2009 Espinosa et al; licensee BioMed Central Ltd.

            This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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            Public health

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