DES MOINES, Iowa (AP) — Two commercial turkey farms in Iowa have been hit by the reemerging highly pathogenic bird flu, causing about 100,000 birds to be killed to prevent the disease from spreading.

The Iowa Department of Agriculture reported the infected commercial poultry flocks within weeks of a turkey farm in South Dakota and one in Utah reporting the first outbreaks in the U.S. since April, raising concerns that more would follow.

The U.S. Department of Agriculture shows 12 commercial flocks in South Dakota, Utah and Minnesota have been affected in October, totaling more than 500,000 birds.

Bird flu last year cost U.S. poultry producers nearly 59 million birds across 47 states, including egg-laying chickens and turkeys and chickens raised for meat, making it the country’s deadliest outbreak ever, according to USDA figures. The outbreak caused spikes in egg and turkey prices for consumers and cost the government over $660 million.

Iowa was the hardest-hit state last year, with nearly 16 million birds lost, but there hadn’t been a case reported in the state since March.

Iowa’s department reported Friday that one commercial turkey facility of about 50,000 birds in Buena Vista County was affected. Another facility of about 47,500 turkeys in neighboring Pocahontas County was confirmed Monday.

In Guthrie County, about 50 backyard birds were also infected, the department said.

Before last week, the only reports of bird flu in recent months in the U.S. in recent months were sporadic appearances in backyard flocks or among wild birds such as ducks, geese and eagles. While wild birds often show no symptoms of avian influenza, infections in them are a concern to the poultry industry as migration season gets underway. Migrating birds can spread the disease to vulnerable commercial flocks.

Bird flu infections are relatively rare in humans and aren’t considered a food safety risk. But as it hits other species, including some mammals, scientists fear the virus could evolve to spread more easily among people. Cambodia this week reported its third human death from bird flu this year.