Molecular detection and characterization of gastroenteritis viruses occurring naturally in the stream waters of Manaus, central Amazonia, Brazil

To assess the presence of the four main viruses responsible for human acute gastroenteritis in a hydrographic network impacted by a disordered urbanization process, a 1-year study was performed involving water sample collection from streams in the hydrographic basin surrounding the city of Manaus, Amazonas, Brazil. Thirteen surface water sample collection sites, including different areas of human settlement characterized as urban, rural, and primary forest, located in the Tarumã-Açu, São Raimundo, Educandos, and Puraquequara microbasins, were defined with a global positioning system. At least one virus was detected in 59.6% (31/52) of the water samples analyzed, and rotavirus was the most frequent (44.2%), followed by human adenovirus (30.8%), human astrovirus (15.4%), and norovirus (5.8%). The viral contamination observed mainly in the urban streams reflected the presence of a local high-density population and indicated the gastroenteritis burden from pathogenic viruses in the water, principally due to recreational activities such as bathing. The presence of viral genomes in areas where fecal contamination was not demonstrated by bacterial indicators suggests prolonged virus persistence in aquatic environments and emphasizes the enteric virus group as the most reliable for environmental monitoring.Although water is recognized as the most precious natural resource on our planet, human activities disregard this fact by continually polluting freshwater bodies. Increasing worldwide awareness of the poor quality of potable water has occurred mainly due to the significant increase in human morbidity and mortality. More than 2.2 million people die every year from diseases associated with poor quality water and sanitary conditions, mostly in developing countries. The presence of pathogenic enteric microorganisms in aquatic environments reveals how human health can be affected by contamination from sewage discharge into surface waters. It is estimated that nearly a quarter of all hospital beds in the world are occupied by patients presenting complications arising from infections caused by enteric microorganisms (53, 56).Water sanitary quality is usually determined by the concentration of fecal indicator bacteria and occasionally by bacteriophages (8, 17). However, numerous investigations have shown that achieving minimum fecal coliform standards does not predict viral contamination (8, 47). Enteric viruses are highly stable in the environment, maintaining their infectivity even after exposure to treatment processes, and are often the most diluted pathogens in water, thus requiring concentration methods for their detection (2, 8, 42, 53).After replication in the gastrointestinal tract, human enteric pathogenic viruses are excreted in high concentrations in the feces (10⁵ to 10¹¹/g feces) and can enter the environment through the discharge of waste materials from symptomatic or asymptomatic carriers and therefore may be dispersed in environmental waters (2). Difficulties in obtaining viruses from environmental samples have been overcome through the association of virus concentration methods with the use of molecular techniques, such as PCR, which provide rapid, sensitive, and specific detection (2, 15, 16, 32, 35, 46, 48, 54).Although the presence of viruses in water is underestimated, mainly due to the difficulties associated with the detection of such agents in different matrices, enteric viruses have been implicated in waterborne outbreaks in different countries every year (2, 36, 38, 53). Among these, rotaviruses (RV), noroviruses (NoV), human astroviruses (HAstV), and human adenoviruses (HAdV) are recognized as the most important etiologic agents of acute gastroenteritis and have been considered for environmental monitoring (11, 29, 55).Diarrhea, a water-related disease, is a global public health problem and is ranked third among the causes of death affecting children under 5 years old, accounting for 17% of all deaths. It is estimated that 1.5 billion episodes occur each year, mostly in developing countries. It is recognized that a significant proportion of diarrhea cases caused by waterborne transmission in such countries is related to water quality. Levels of diarrhea disease differ between communities due to socioeconomic factors such as water availability and hygienic behavior (9, 45).Despite a significant decrease in diarrhea-related mortality in developed and some developing countries, such as Brazil, diarrhea is still an important cause of morbidity in these countries (37). In the Northern region of Brazil, the city of Manaus reported an increase of 90.5% in the number of diarrhea cases between 1998 and 2000, from 8,878 cases to 16,914 (4).The goal of this study was to assess viral contamination by the four main viruses responsible for acute gastroenteritis (RV, HAdV, HAstV, and NoV) in the hydrographic network that surrounds Manaus. Investigation and determination of the viruses that are dumped into streams from domestic sewage without prior treatment, as occurs in Manaus, could reveal how rapid population growth associated with a disordered urbanization process represents a threat to human health caused by the increased risk of disease transmission.