Spatial transmission of avian influenza (type H5) in birds.

Highly pathogenic avian influenza (HPAI) H5N1 continues to threaten domestic and wild birds, as well as human health. However, the mechanism of spatial transmission of HPAI is still unclear. We analyzed the current distribution of HPAI occurrences based on World Organization for Animal Health reported data from 3049 sites in the world from December 2003 to June 2006, and found that these sites were spaced at distances with a frequency peak of 100-200 km. We built a cellular automata model to simulate the spatial transmission process of HPAI as a function of transmission distance, variance of the transmission distance, infection rate, and transmission times (how many times HPAI transmits from one host to another before suppression). We determined that the transmission distance between HPAI occurrences is approximately 100 km on the basis of historical HPAI occurrences from 2003 to 2006 in both wild and domestic birds. To effectively reduce the long-distance spreading of HPAI, preventing close contact between domestic birds and waterfowl within a radius of 100 km around HPAI occurrence sites is essential.