An evaluation of transmission routes for low pathogenicity avian influenza virus among chickens sold in live bird markets

Many theories about the modes of avian influenza virus (AIV) transmission have been proposed, but few have been quantified, and none within a flock or live bird market (LBM) setting where birds are often kept in stacked cages. We describe a novel experimental design and the results collected for the purpose of estimating transmission rates specific to the potential modes of AIV transmission within an LBM. Chickens of the strains and ages found in California LBMs were inoculated with low pathogenicity AIV H6N2. Aerosol exposure was found to be the most important route of transmission for this H6N2 AIV. The handling of infectious chickens resulted in the transmission of H6N2 AIV, though the virus was not detectible by rRT-PCR. Chickens with fecal exposure to infected birds (median = 8.0 DPI) had detectable virus earlier than in those with aerosol exposure only (median = 10.0 DPI). Changes in the hemagglutinin sequence were not found to be associated with oropharyngeal or cloacal shedding in this study.