Knowledge of the transmission route responsible for the HPAI outbreaks in Southeast and East Asian countries still remains elusive [5, 9] . Four hypotheses have been suggested for transmission of H5N1 in the HPAI outbreaks in Japan [6] : (1) H5N1-virus-infected chickens may have been imported from other countries, (2) materials (e.g., vehicles and egg containers) from infected area may have been used, (3) viruses may have been carried on clothes, boots, hands, and so forth, and (4) infected wild birds may have carried H5N1 virus into poultry farms to infect chickens. In particular, it has been suggested that migratory birds carried the viruses and subsequently infected domestic and/or wild ducks [9] . HPAI outbreaks in Japan. Therefore, it is very likely that the 2004 epidemics H5N1 virus was transmitted to Japan from East Asian countries. The important question is how could the H5N1 virus be transmitted from virus-positive migratory wild birds to domestic poultry in Japan? We have noted that it is unlikely that wild birds directly transmitted influenza viruses to poultry in Japan, because all of the Japanese poultry farms, where H5N1 virus outbreaks occurred, had fowling nets in place to prevent entry of wild birds. However, flying insects (e.g., flies) can easily get through the nets and invade a poultry farm. We have shown that a chicken can eat all 31 blow flies put inside its cage in just 7 min [10] . A chicken can catch and break down the body of a fly and even catch and swallow a fly in flight. Therefore, we have been interested in whether, if a chicken eats blow flies carrying H5N1 virus, the chickens might become infected and develop symptoms of H5N1 influenza.