Use of filter carrier technique to measure the persistence of avian influenza viruses in wet environmental conditions.

A germ carrier technique was adapted for the determination of the persistence of influenza viruses in moist environments. The technique was employed with 3 low pathogenic avian influenza viruses (H4N6, H5N1, and H6N8), one human influenza virus (H1N1), and two model viruses (NDV and ECBO) in lake water at five different temperatures (30, 20, 10, 0, and -10°C). Viral quantitation was carried out at regular intervals on cell culture for a maximum duration of 16 weeks. Serial data were analyzed by linear regression model to calculate T-90 values (time required for one log reduction in the virus titer). Persistence of all of the viruses was highest at -10°C followed by 0, 10, 20, and 30°C. At -10°C, the single freeze-thaw cycle resulted in an abrupt decline in the virus titer, followed by long term persistence. Generally, influenza viruses persisted shorter than model viruses while ECBO has the highest survival time in lake water. Individual influenza viruses differed in their persistence at all temperatures. The findings of the present study suggest that AIV can remain infectious in lake water for extended periods of time at low temperatures.