There are many strains of avian influenza virus that can cause varying degrees of clinical
illness in poultry. These viruses can infect chickens, turkeys, pheasants, quail, ducks,
geese and guinea fowl, as well as a wide variety of other birds.
The viruses can be classified as highly pathogenic or low pathogenic strains based on the
severity of the illness they cause. Highly pathogenic avian influenza is an extremely infectious
and fatal form of the disease that, once established, can spread rapidly from flock to flock
and has also been known to affect humans. At this time, there has been no report of a spread
to humans within the United States.