Last month, Mike Weber got the news every poultry farmer fears: His chickens tested positive for avian flu.

Following government rules, Weber’s company, Sunrise Farms, had to slaughter its entire flock of egg-laying hens — 550,000 birds — to prevent the disease from infecting other farms in Sonoma County north of San Francisco.

“It’s a trauma. We’re all going through grief as a result of it,” said Weber, standing in an empty hen house. “Petaluma is known as the Egg Basket of the World. It’s devastating to see that egg basket go up in flames.”

A year after the bird flu led to record egg prices and widespread shortages, the disease known as highly pathogenic avian influenza is wreaking havoc in California, which escaped the earlier wave of outbreaks that devastated poultry farms in the Midwest.