Validity of serological methods (ELISA) for detecting infectious viruses in water

Detection of cultivable enteric viruses in environmental water samples in tissue culture is time consuming and expensive. Moreover, some important enteric viruses grow very slowly (Hepatitis A virus) or do not grow as yet (Norwalk) in tissue culture. Therefore, sensitive serological and molecular methods have been developed to simplify and speed the detection of viruses in environmental samples. This study was conducted to test the reliability of serological methods to monitor the presence of viable viruses in natural waters. The study was performed with poliovirus purified in CsCl gradients and impure virus. Poliovirus 1 either purified or impure was seeded in raw wastewater, groundwater and phosphate buffered saline (PBS) and incubated for 20 days at 4°C, 20°C and 30°C. Virus survival was monitored by a nylon filter A-ELISA and plaque-assay in BGM cells. In all water samples at 4°C, no die-off was observed neither by A-ELISA nor by plaque-assay. In wastewater and groundwater at 20°C and 30°C, greater die-off was observed with A-ELISA than with plaque-assay. Purified poliovirus was undetectable by the A-ELISA after two days of incubation at 20°C in wastewater and groundwater, whereas under the same conditions, only 2log₁₀ reduction were observed in the titer of poliovirus 1. The data of this study have shown that in all cases, a positive test by A-ELISA was also positive by the plaque-assay. Therefore, a positive result of A-ELISA indicates the presence of viable virus in natural waters.