Some agricultural supply chains are cracking under the weight of the worst avian-influenza outbreak in U.S. history. The Wall Street Journal reports the bird flu has devastated poultry flocks across the country over the past year. The relentless nature of the outbreak has frustrated efforts to keep the virus from affecting U.S. egg prices and supply.

Deaths of hens and turkeys are being counted in the millions across a swath of the country and the virus has been spreading even as farms have replaced entire flocks. The impact is straining consumer markets. Wholesale prices of Midwest large eggs surged to a record $5.46 a dozen in December before retreating this month.

Egg supplies are strained, with an industry group estimating there are about 6% fewer hens laying eggs than normal nationwide.

Buyers are seeking other sources, but experts say the problem won’t be solved until the virus runs its course.