Transmission of H6N2 wild bird-origin influenza A virus among multiple bird species in a stacked-cage setting.

Live bird markets are common in certain regions of the U.S. and in other regions of the world. We experimentally tested the ability of a wild bird influenza A virus to transmit from index animals to naïve animals at varying animal densities in stacked cages in a simulated live bird market. Two and six mallards, five and twelve quail, and six and nine pheasants were used in the low-density and high-density stacks of cages, respectively. Transmission did not occur in the high-density stack of cages likely due to the short duration and relatively low levels of shedding, a dominance of oral shedding, and the lack of transmission to other mallards in the index cage. In the low-density stack of cages, transmission occurred among all species tested, but not among all birds present. Oral and cloacal shedding was detected in waterfowl but only oral shedding was identified in the gallinaceous birds tested. Overall, transmission was patchy among the stacked cages, thereby suggesting that chance was involved in the deposition of shed virus in key locations (e.g., food or water bowls), which facilitated transmission to some birds.