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A river intensively used along its entire course for extracting potable water and for discharging domestic and industrial effluents permanently carries a high load of viruses, including hepatitis A and rotaviruses. In the areas supplied with potable water from this river hepatitis A is endemic. The river has been investigated four times at 16 or more sampling points throughout its course in the years 1981, 1982 and 1983. Coincident with the virological investigation, biological, microbiological and chemical examinations were conducted with the same water sample. At some representatively distributed sampling points along the river course, tests for heavy metals (Cd, Ni, Cu, Cr, Pb) and selected chemical compounds were also performed. The virological quality of the river water largely depends on the virus input via domestic sewage. Statistically significant correlations have been found between virus level, pH, NH4+ and NO3−. Amoebae species are likely to counteract viruses. Knowing the dynamics of river water exploitation above the extraction sites, a model for the estimation of virus content in the raw water could be developed.

Summary:The investigation was performed inMarch 1988 a t 24 stations from the delta (km 16) up to Vienna (km 1,940) and yielded positive findings at 13 stations with 0.135 t o 1.24 MPN/I (5 0.599 MPN/I). Of the 37 strains detected, 12 Coxsackie-B and 11 ECHO serotypes were identified. Other 14 strains were electron-optically classified as picorna viruses (5), adeno viruses (7) and isometric viruses (2). Rotaviruses were detected by means of the indirect immunofluorescence in 15 of 17 samples, whereas Hepatitis-A viruses could not be detected (gene-probe technique). In the longitudinal section of the river, two stretches with a high virus load were found: in the Bulgarian-Yugoslavian reach of the Danube with the maximum a t the river-kilometre 1,078 and in the Hungarian-Czechoslovakian reach with the maximum a t the river-kilometre 1,819. The virus load in these reaches was 6 -1011 and 2 * 1011 MPN/d, respectively. Rotaviruses were found above all in the Delta region as well as downstream of Belgrade. The results show pronounced virological risks, especially for the obtaining of drinking water. Future research is required mainly into the behaviour of viruses in existing and planned barrages of the Danube as well as in the infiltrat.ion from the river into the groundwater.

The construction of the Marchfeldkanalsystem (Austria) creates irreversible environmental changes which could have an impact on environmental health. Virological investigations of the river Danube have been carried out as a part of the environmental impact assessment procedure. The repeated detection of viruses in 61% of all water samples with a mean level of 0.762 MPN/l suggests that a permanent viral contamination of Danube is occurring and that the self-purifying capacity of the river is relatively inefficient. Strains of some virus families not hitherto detected in water (toga-(bunya) viridae) could be found. Provided the proposed treatment facilities are as effective as to remove the virus load to an extent of 99.99% the Marchfeldkanalsystem project will not endanger public health.