The H9N2-subtype viruses were primarily isolated from chickens. In contrast, all but 1 of the H1, H3, H4, and H10 subtypes were recovered from ducks; a single H1N2-subtype virus was isolated from a water trough in a chicken cage. The ducks could have obtained these infections at the market, but it is more likely that the birds were infected prior to arrival at the market and are contributing to the diversity of subtypes that exist in these locations [19] . This diversity increases the probability that reassortment could occur between influenza subtypes and produce a novel pathogenic strain. Of particular importance was the isolation of several H5N1-subtype viruses (clade 2.2), 2 of which were isolated from chickens in the same bird market in January 2009 and the remaining 2 were from fecal samples of ducks in a different poultry market in January 2010. These H5N1-subtype isolates exhibit a polybasic cleavage site (-PQGERRRKKR-GLFG-) that is characteristic of highly pathogenic viruses. Moreover, one isolate (A/Chicken/Bangladesh/828/2009 [H5N1]) is also classified as highly pathogenic because of its IVPI. The isolation of H5N1-subtype viruses in the poultry markets could be related to outbreaks that were reported in commercial farms at approximately the same time. Specifically, an outbreak at a poultry farm in Mirpur, Dhaka, was reported on January 7, 2009 (http://www.oie.int/eng/info_ev/en_AI_avianinfluenza.htm), and HP H5N1-subtype viruses were isolated 2 days later from chickens at a poultry market in Dhaka. Although no outbreaks were reported at commercial poultry operations in the Dhaka district in Janurary 2010, an H5N1-subtype outbreak was reported at a farm in the Sirajgonji district, and another was reported in the Jaipurhat district (http://www.oie.int/eng/in-fo_ev/en_AI_avianinfluenza.htm). Infected birds could have been transported to the market, but it is unknown if the infected birds were from commercial farms or from backyard flocks. Thus, the source of HP H5N1-subtype viruses in the bird markets cannot be determined. Interestingly, the chickens that were shedding the HP H5N1-subtype virus and the ducks from which the H5N1-infected fecal samples were collected were apparently healthy at the time of sampling, and H9N2-subtype viruses were isolated from other birds at the same markets. This raises an important question regarding the epidemiology of viruses of the H5N1 and H9N2 subtypes in the bird markets: are the H9N2-subtype viruses contributing to highly pathogenic H5N1-subtype virus outbreaks? Before the H5N1-subtype outbreak in Hong Kong, no chickens and very few ducks tested positive for H5N1-subtype viruses, and H9N2-subtype viruses were only isolated from ducks in those markets [8] . Extensive surveillance during the outbreak in 1997 revealed high prevalence of the HP H5N1 subtype in apparently healthy chickens. This also corresponded with the surprising find of the H9N2 subtype in chickens, which had been reported only in ducks in the markets of Southeast Asia prior to the 1990's [8] . The prevalence of the H9N2 subtype in the Hong Kong markets in 1997 (4.4%) [8] was lower than its estimated prevalence in the Bangladesh retail markets (16.5%). Interestingly, a single retail market in Hong Kong in 1997 had an isolation rate of 36.6% for the H9N2 subtype, and the HP H5N1 subtype was isolated at the same market [8] . Later studies demonstrated that the H9N2 subtype might have allowed the HP H5N1 subtype to persist and circulate in poultry. Specifically, a previous H9N2-subtype infection could confer protection against an HP H5N1-subtype challenge [11, 12] . This may explain why the HP H5N1-infected chickens in the market were asymptomatic at the time of sample collection even though the virus killed all SPF chickens in the IVPI experiment by day 2 post-infection. Given that the primary influenza A subtype in poultry markets that we have been sampling in Bangladesh is H9N2, that HP H5N1-subtype outbreaks were reported in poultry in 2007 and continue today [22] , and that HP H5N1-subtype viruses were isolated in the markets, Bangladesh could experience an outbreak similar to the Hong Kong 1997 outbreak.