A total of 480,000 birds affected by an outbreak of avian influenza at 12 farms in the central Mexican state of Guanajuato have been destroyed, the National Food Health, Safety and Quality Service, or Senasica, said.

Some 189,500 birds have been immunized to contain the outbreak of "avian influenza of highly pathogenic AH7N" in four cities in Guanajuato, the Agriculture Secretariat agency said.

Health specialists have taken 2,543 samples at 22 farms and are analyzing them, the Senasica said.

"Distribution and application of vaccines will continue in neighboring areas with no presence of the virus in an effort to prevent the spread of the disease," the Senasica said.

Officials in states that have poultry farms, including Michoacan, Aguascalientes, Queretaro, Nuevo Leon and Yucatan, are monitoring the entry of poultry to prevent infected birds from spreading the disease to farms within their territories.

Egg and chicken prices have started to rise ahead of possible shortages caused by bird flu, media reports said. EFE