An outbreak of the H7N3 bird flu virus in western Mexico has infected about 2.5 million chickens and led authorities to destroy or dispose of almost a million birds.

The country's Agriculture Department says that 129 farms in the western state of Jalisco have been inspected. Flu was confirmed in birds at 24 of the sites, and tests continued on most of the rest.

The farms in question have been placed under quarantine, the department said in a Tuesday press statement.

The outbreak has caused price increases in chicken and egg products in Mexico.