Here's a quick primer on the bird flu — when it started, how it spreads and what you can do to protect against it.

Two domestic cats in Washington state have been infected with bird flu after eating raw pet food. The state Department of Agriculture confirmed the virus in both animals based on test results received on Tuesday.

The outbreak has sickened and killed millions of animals, caused alarm among farmers, and, perhaps most notably to the public, raised the price of eggs.