The avian virus has been around for decades without turning into a monster.
But little is known about how quickly an avian virus can develop the ability to pass easily from person to person.
It is also a dangerous one when an avian virus is loose.
Find out more about the avian influenza virus, including how it's spread, symptoms, and prevention.
But scientists say that although the threat from the current avian virus is real, it is probably not immediate.
H6N2 is an avian influenza virus with two forms: one has a low and the other a high pathogenicity.
The current avian virus, known as H5N1, does not; about 100 people have caught it from infected birds, one way or another.
Leavitt has described the avian influenza virus as the most serious threat to American security.
The reason is that the outbreaks are caused by two different strains of avian influenza virus.
The avian influenza virus has killed more than 330 people around the world, with Indonesia the worst-hit country.