Routes of avian influenza virus (AIV) dispersal among aquatic birds involve direct (bird-to-bird) and
indirect (waterborne) transmission. The environmental persistence of H5N1 virus in natural water reservoirs
can be assessed by isolation of virus in embryonated chicken eggs. Here we describe development and
evaluation of a real-time quantitative reverse transcription (RT)-PCR (qRT-PCR) method for detection of
H5N1 AIV in environmental water. This method is based on adsorption of virus particles to formalin-fixed
erythrocytes, followed by qRT-PCR detection. The numbers of hemagglutinin RNA copies from H5N1 highly
pathogenic AIV particles adsorbed to erythrocytes detected correlated highly with the infectious doses of the
virus that were determined for three different types of artificially inoculated environmental water over a 17-day
incubation period. The advantages of this method include detection and quantification of infectious H5N1 AIVs
with a high level of sensitivity, a wide dynamic range, and reproducibility, as well as increased biosecurity. The
lowest concentration of H5N1 virus that could be reproducibly detected was 0.91 50% egg infective dose per ml.
In addition, a virus with high virion stability (Tobacco mosaic virus) was used as an internal control to
accurately monitor the efficiency of RNA purification, cDNA synthesis, and PCR amplification for each
individual sample. This detection system could be useful for rapid high-throughput monitoring for the
presence of H5N1 AIVs in environmental water and in studies designed to explore the viability and epidemiology
of these viruses in different waterfowl ecosystems. The proposed method may also be adapted for
detection of other AIVs and for assessment of their prevalence and distribution in environmental reservoirs.