The 2003-2004 H5N1 highly pathogenic avian influenza (HPAI) outbreaks in Japan were the first such outbreaks in 79 years in Japan. Epidemic outbreaks have been occurring in Southeast Asia, with the most recent in 2010. Knowledge of the transmission route responsible for the HPAI outbreaks in these countries remains elusive. Our studies strongly suggested that field and laboratory studies focusing on mechanical transmission by blow flies should be considered to control H5N1 avian influenza outbreaks, in particular in epidemic areas, where there are high densities of different fly species throughout the year. In this paper, we review these field and laboratory entomological studies and discuss the possibility of blow flies transmitting H5N1 viruses. 1. Avian Influenza Outbreaks in Japan The H5N1 subtype of highly pathogenic avian influenza (HPAI) A virus has frequently infected wild and domestic ducks in Asia, causing huge economic damage to both poultry farms and governments in the affected countries. Most avian influenza viruses do not infect humans, but the 1997 outbreak of the H5N1 virus in Hong Kong [1, 2] alerted the medical community that some subtypes of avian influenza viruses include highly pathogenic strains that can affect humans. In this influenza virus outbreak, there were 6 deaths in the 18 human cases caused by the H5N1 subtype [3]. As of August 2, 2010, WHO has identified 502 human cases of H5N1 influenza around the world, and 298 of these were fatal [4]. In particular, H5N1 outbreaks have occurred recently in Egypt, Indonesia, and Vietnam. Therefore, H5N1 influenza virus can cause serious public health problems in birds and humans and is one of the most infectious avian diseases transmissible to humans. From January 2004 to March 2004, there were outbreaks of acute, highly transmissible, lethal diseases in chickens at four poultry farms in Japan: one in Oita, one in Yamaguchi, and two in Kyoto Prefecture (Figure 1). Virus isolates from infected chickens were all identified as influenza A virus of the H5N1 subtype [5]. Such highly pathogenic avian influenza (HPAI) epidemics had not been reported in Japan for 79 years. Two avian influenza outbreaks at poultry farms in Tamba Town, Kyoto Prefecture, were the last two outbreaks of the 2004 avian epidemics in Japan. Since then, there were outbreaks of H5N1 avian influenza in Okayama and Miyazaki Prefectures in 2007. The H5N1 virus was also isolated from dead Whooper swans, Cygnus cygnus, in 2008 in Towada Lake, Akita Prefecture [6]. In addition, outbreaks of other subtypes of avian influenza
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