Bird flu continues to spread in the Australian state of Victoria, where more than 500,000 chickens have been euthanized. Strict quarantine zones restricting the movement of birds and equipment have also been put in place. Australian health authorities say bird flu spreads mainly among wild water birds.

The highly pathogenic H7N3 strain of avian influenza has been found on four farms, while another virus, H7N9, has been detected at a fifth property over the past seven weeks in Victoria state. The Australian farms have been put into lockdown. At least 580,000 birds have been destroyed as part of sweeping biosecurity controls.

Japan and the United States have temporarily banned imports of poultry from Victoria as a precaution.

In Australia, some supermarkets are restricting the number of eggs that consumers can buy because of disruptions to the supply chain.

Avian influenza is a viral disease found across the world. It spreads between birds or when contaminated animal feed and equipment is moved between areas.

Danyel Cucinotta is the vice president of the Victorian Farmers Federation, an industry group. She told the Australian Broadcasting Corp. Tuesday that the virus can spread quickly.

“There is very little we can do and no matter how good your biosecurity is you cannot stop wild fowl coming in. This is a particular flight path for migratory birds. There is housing orders at the moment, which means all birds get locked up. This is about protecting our birds and protecting the food supply chain,” she said.

The strains of bird flu identified in the states of Victoria and Western Australia can infect people, but experts insist that cases are rare.

The virus can also infect cows. The United States’ Department of Agriculture has said that avian flu has infected dairy cows in more than 80 herds across several states since late March.

At least three U.S. dairy workers have tested positive for bird flu after exposure to infected cattle. All three patients are recovering.

The U.S. Centers for Disease Control and Prevention said the infections do not change its assessment that bird flu is a low risk to the general community and that it has not seen evidence of human-to-human transmission.

Last month, health authorities in Mexico confirmed a fatal case of human infection with an avian flu virus that had been reported in poultry.