The first confirmed case of human-to-human transmission of avian influenza (or bird flu) is an Indonesian man who died after catching the avian influenza virus from his 10-year-old son, according to a report issued by the World Health Organization (WHO) on June 23, 2006.

The confirmation of human-to-human transmission of the bird flu virus raises deeper concerns about the possibility of an approaching pandemic that could result in millions of deaths worldwide.

Scientists have said consistently that the bird flu virus does not spread easily to humans, and the general belief has been that all human infection has resulted from close contact with poultry or wild birds who carry the virus.

Some observers had suspected that human-to-human transmission was occurring, in part because of the pattern of infection in certain areas, but there was never any way to prove it. In the Indonesian case, the virus mutated slightly in the body of the 10-year-old boy, so it was easy to track when it moved to his father.

Scientists at WHO and the Centers for Disease Control said mutation did not cause the human-to-human transmission, nor did it make it easier for the virus to spread to humans.

"Yes, it is slightly altered, but in a way that viruses commonly mutate," said Dick Thompson, a spokesman for WHO in Geneva told The New York Times. "But that didn't make it more transmissible or cause more severe disease."

Approximately 200 people have died from the A(H5N1) virus, and the disease has killed or led to the extermination of hundreds of millions of birds around the world.

More information:

Human-to-Human Infection by Bird Flu Virus Is Confirmed (The New York Times)
Lab confirms transmission of bird flu between people (Baltimore Sun)
Avian Influenza (World Health Organization)
New Bird Flu Vaccine is 100 Percent Effective in Tests