Figure 2
The illustration of adaptation and transmission of Human AIVs. An adaptation from AIVs to human AIVs includes two circulations, the aquatic habitat circulation and the land habitat circulation. In the aquatic habitat circulation, AIVs are transmitting, mutating, and adapting between aquatic birds and minks (as well as other semiaquatic mammals). This adaptation may or may not change their infectivity to avian, but can significantly increase the infectivity to human and terrestrial mammals. Poultries such as duck, goose can be infected through contacting with epidemic water. In a free stall barn system, usually in some areas of South Asia, Southeast Asia, Southern and Eastern China, it will inevitably lead to a land habitat circulation including human beings. The blue pathway is transmitted by faecal-oral route, while the red one is transmitted by intra-tracheal inoculation. The conception for this scene is partly based on the observation of daily lives; e.g., in rural areas of South Asia, Southeast Asia, Southern and Eastern China, pigs and poultries, in particular chick, are often observed to eat each other’s feces. Pigs also eat duck feces, but ducks seldom eat pig feces; and partly based on the available reports, e.g., human infected by a human-adapted AIV from the live poultry market was often reported in China.
