Eight million chickens have so far been slaughtered in Mexico and 66 million more were vaccinated in a bid to contain a bird flu outbreak in the west of the country, authorities said Tuesday.

The agriculture ministry said in a statement that during the vaccination process in the Los Altos region of Jalisco state, diseased chickens were identified, leading to the destruction of the flu-carrying fowl.

Food safety officials say the outbreak, which was first detected on June 20, is confined to Los Altos, which is an egg-producing area. Inspections in other parts of the country have not turned up any signs of the disease.

A national animal health emergency was declared at the beginning of July, and the prices of both eggs and chickens have skyrocketed.

Mexican authorities hope to vaccinate 80 million fowl in the first phase of its program, and then analyze the results before proceeding to phase two.

The virus responsible for the outbreak, H7N3, has occasionally caused human disease in various parts of the world, according to the United Nations, but has not shown itself to be easily transmittable between humans.

Some bird flu strains, such as H5N1, have caused serious infections in people. The World Health Organization has documented 607 human cases of bird flu since 2003, 358 of which were fatal, according to July data.

Authorities in Guatemala have stepped up safety checks on its border with Mexico to keep bird flu from spreading into the country.