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1. Introduction
Viral gastroenteritis outbreaks are associated with water contamination due to wastewater containing the viral particles, which is discharged in surface waters and rivers. Infectious agents can be spread in this way, particularly during periods of low flow [1,2]. Although the number of viral particles in the surface water is very low, ten viral particles are sufficient for a healthy individual to be infected [3,4].
Bassaseachic Falls National Park is located in the western side of the state of Chihuahua, Mexico, in the Sierra Madre Occidental. Basaseachi Waterfall is the main flowing part of the Basaseachi and Durazno micro-basins. This park is a natural, protected area that is considered a unique ecosystem, with endemic flora and wildlife species. Environmental conditions favor the development of a forest ecosystem in the highest areas, whereas in lower areas, such as “Barranca de Candameña”, the ecosystem is that of jungle vegetation. Bassaseachic Falls National park has peculiar climatic characteristics as a result of the latitude and altitude, with temperatures ranging from 26 °C to 16 °C. There is frosty weather from October to May, while there is snowy weather from November to March [5].
It is usually difficult to detect viruses in water samples because of their very low concentration and the presence of inhibitors, such as humic and fulvic acid, polysaccharides, bacterial debris, nucleases and metal ions that make it difficult to extract RNA. For this reason, the detection of viruses in water requires specific methods involving viral particle concentration, such as ultrafiltration. Large water volumes (100-1000 L) usually need to be processed. Ultrafiltration techniques with electropositive commercial membranes, coupled with a SYBR Green reverse transcription-real time polymerase chain reaction (RT-qPCR) assay are inexpensive and useful to amplify genes for detecting low virus concentrations [6,7,8]. Using this method, in recent years, more than 100 types of viruses that can be transmitted to humans have been reported in contaminated waters, such as adenovirus (AdV), rotavirus (RV), norovirus (NV) and hepatitis virus (HepV) [9]. RV and NV are the major etiological agents responsible for the known cases of viral gastroenteritis worldwide [10]. The aim of the present study was to detect RV and NV as well as their concentration variations in the surface water of Bassaseachic Falls National Park...