Several viruses of different pathogenic category are continuously excreted with feces of infected persons and discharged in wastewaters. From here, they reach surface waters and, in special circumstances, percolate through the soil thus reaching drinking water systems. Assay and identification of viruses in drinking water is very difficult, and conventional investigation procedures as cell cultures are often inadequate. Special equipment, as electron microscope or molecular research procedures, is required to this purpose. For this reason, testing for viruses in surface and drinking waters is beyond the capability of the majority of microbiology laboratories and does not fall within the competence of most Public Supervisory Boards. On the contrary, it should be done only by specially equipped laboratory facilities. In spite of this, however, the presence of viruses in water is reported quite often. As for the type of identified viruses, the most common are: a) Surface waters: Enterovirus; HAV; Rotavirus; Astrovirus and Norovirus b) Mineral waters: Norovirus and Enterovirus (Echovirus and Coxsackievirus) The major properties of the a.m. viruses are shortly described in the following.
Viruses and their characteristics
Enteroviruses, belonging to the Picornaviridae family, are transmitted by the oral route or by inhalation. Their name results from the fact that they are generally found in the intestinal tract of man and animals; however, some of them may involve the central nervous system, the liver and heart. Enteroviruses, hence, are widely present in case of poor personal and domestic hygiene. They may cause a wide range of illnesses – some of which very serious – including poliomyelitis, infectious hepatitis, myocarditis, and meningitis. Most infections with Enteroviruses, however, are asymptomatic. Enteroviruses include a number of different serological types, as: Poliovirus, Coxsackievirus and Echovirus, whose major characteristics are described in Table 1. The hepatitis A virus, HAV, originally classified as Enterovirus 72, and now called Heparnavirus, belongs to the Picornaviridae family; it has a diameter of 27 μm, lacks an envelope, and has a genome consisting of a single strand of RNA of approx. 7,500 nucleotides, protected by a protein coat. The hepatitis A virus is widespread, and widely present where personal and domestic hygiene are poor; furthermore, it is highly persistent in the environment, which favours its diffusion. Its presence in surface waters is frequently reported even in Italy. More infrequent, however documented, is its presence in drinking waters for human consumption. Rotaviruses belong to the Reoviridae family; they measure 70 μm in diameter and contain a double RNA strain surrounded by a protein capsid. These viruses are widely present in the environment, and their transmission in uncontrollable, and for this reason they easily contaminate surface waters. Rotaviruses cause acute gastroenteritis; six serologic types have been identified, three of which (groups A, B and C) infect humans. Their major characteristics are listed in Table 2. Astroviruses belong to the recently identified family of Astroviridae. The name is derived from their distinctive appearance in electron microscopy showing a 5 or 6 pointed star-shaped core. They are defined as “Small Round Structured Viruses” (SRSVs), and possess well-defined surface structures, unlike the group designated “Small Round Viruses” (SRV) characterised by a smooth edge and no discernible structure. They are responsible for viral gastroenteritis, diseases spread by person-to-person contact or ingestion of contaminated foods and water. Astroviruses mainly infect children and elderly persons. Noroviruses (Norwalk/Norwalk-like viruses) are a group of “Small Round Structured Viruses” within the family of Caliciviridae. The genus Norwalk-like virus is divided into three distinct genogroups:
- genogroup I : gg I – NV-like
- genogroup II : gg II – Snow-Mountain – like or SMA-like
- genogroup III : gg III – Sapporo-like Noroviruses are single-stranded RNA viruses without envelope.